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Territorial system and adult dispersal in a cooperative-breeding tanagerTerritory and dispersal of a tanager

Territorial system and adult dispersal in a cooperative-breeding tanagerTerritory and dispersal... Abstract Latitudinal differences in territorial behavior are considered to have great influence on differences in life-history strategies of Nearctic and Neotropical birds. Most territorial behavior of tropical birds has particularities that cannot be explained only by theories from studies of birds in temperate regions. We evaluated the territorial system of the cooperative-breeding White-banded Tanager (Neothraupis fasciata) in central Brazil's savanna and present results on stability of territory site occupation, relationship between territory size and group size, and dispersal patterns. Territories (n = 27, mean per season) were monitored for 3 yr in a protected area in the cerrado of central Brazil and were defined by the minimum convex polygon method. Territory size averaged 3.7 ± 0.6 ha, and was defended by all individuals of groups of 2–8 individuals (mean = 3.4 ± 1.2). We recorded 44 dispersal events between territories, and most individuals dispersed distances equal to one territory in length. Males tended to stay in the same territory, whereas females dispersed. Our results support hypotheses that predict year-long territory defense for tropical birds. Territory size reflected group size, corroborating the hypothesis that individuals adjust the territory size to ensure the amount of resources for survival. Resumo Diferenças latitudinais no comportamento territorial exercem influencia nas estratégias da história de vida de aves da região neártica e neotropical. O comportamento territorial de aves tropicais apresenta particularidades que não podem ser explicadas apenas com base em teorias provenientes de estudos realizados na região temperada. Nós avaliamos o sistema territorial de um traupídeo com reprodução cooperativa, cigarra-do-campo (Neothraupis fasciata), em uma área de Cerrado do Brasil central, apresentando resultados a respeito da estabilidade de ocupação do território, relação entre tamanho do território e número de indivíduos no bando, e padrões de dispersão. Os territórios (n = 27, média por estação) foram monitorados durante três anos em uma unidade de conservação do Brasil central e foram estimados pelo método do polígono convexo. O tamanho médio dos territórios foi de 3,7 (± 0.6) ha. O número de indivíduos nos bandos variou de 2 a 8 (média: 3.4 ± 1.2) indivíduos e todos participaram da defesa do território. Foram registrados 44 eventos de dispersão entre territórios, sendo que a maioria dos indivíduos dispersaram distâncias equivalentes à largura média de um território. Machos tenderam a permanecer no mesmo território e fêmeas a dispersarem. Os resultados apresentados corroboram a hipótese que prediz a defesa do território durante todo o ano para aves tropicais. O tamanho do território foi diretamente relacionado com o tamanho do grupo, corroborando a hipótese que os indivíduos ajustam o tamanho dos territórios para garantir a quantidade de recursos necessários para a sobrevivência. Palavras chave: Cerrado, cigarra-do-campo, dispersão por sexo, Neothraupis fasciata, savana Neotropical, tamanho de área de vida Introduction Latitudinal differences in territorial behavior are considered to have great influence on differences in life-history strategies of Nearctic and Neotropical birds. Most territorial behavior of tropical birds has particularities that cannot be explained only by theories from studies of birds in temperate regions. In the tropics, year-long territory defense is common and adult survival is high, so opportunities for territory acquisition may be scarce (Stutchbury and Morton 2001). For insectivorous species it is common to defend year-round territories, but this behavior is not expected for frugivorous birds (Morton 1973, Buskirk 1976). Territorial intrusions are rare among tropical birds (Gorrell et al. 2005, Duca et al. 2006, Freitas and Rodrigues 2012) but common in temperate species (Preston et al. 1998), a behavior often associated with extrapair mating behavior (Gowaty et al. 1989, Meek and Robertson 1994). Some tropical birds occupy the same territory over time, and adult turnover is low (Duca et al. 2006, Woltmann and Sherry 2011, Freitas and Rodrigues 2012), a characteristic that can maintain stability between neighboring territories. Even when owners are replaced, the new owner of a vacant territory tends to adjust its boundaries similar to those of the original territory (Greenberg and Gradwohl 1986). Eason (1992) suggested that the territory site should be determined more by the ability to defend it than by quality. An explanation for stability of territory occupancy is based on the minimum territory size necessary to obtain enough resources to supply the foraging demand and, thus, respond to fluctuating foraging conditions (Greenberg and Gradwohl 1986, 1997). According to Hixon (1980), there is an optimization of territory sizes whereby the need for foraging habitat regulates the minimum size, and intraspecific competition determines the maximum size. The main resources that birds can defend in their territories include food, breeding sites, and mates (Perrins and Birkhead 1983). The influence of food availability in territory size can be illustrated by the relationship between the area of territories and body mass of species. Studies of species with similar diet demonstrated that territory sizes were related to body mass of different species (Schoener 1968, Duca et al. 2006). This relationship is expected for species defending territories where all breeding and feeding activities occur (Perrins and Birkhead 1983). The relationship between food availability and territory size can also be expected for species living in cooperative groups, because larger groups demand more food. Territory acquisition has been carefully studied in cooperative birds in the tropical region, where juveniles often inherit their natal territory or use them as a refuge from which to compete for breeding positions on nearby territories (Stutchbury and Morton 2001). Several studies have demonstrated that individuals can use their helper status as an intermediate step for breeder status in the population (Grimes 1980, Brown and Brown 1984, Rabenold 1985). Moreover, individuals should be more reluctant to divorce or engage in breeding dispersal in a more saturated environment, where their chances of finding a new mate or territory are probably low (Doerr and Doerr 2006). Some species have sex-biased dispersal tendency (Greenwood 1980). Male Great Tits (Parus major) captured in their natal territories had lower dispersal probability than females (Dhondt 1979). This pattern was also recorded in other populations (Dhondt and Hublé 1968) and confirmed by studies of sex ratio, showing that male Great Tits have a higher tendency to stay near their natal territory, whereas females prevail among dispersing individuals (Payevsky 2006). Here, we describe the territorial system and dispersal pattern of a near-threatened bird species, the White-banded Tanager (Neothraupis fasciata). It is the only species in this genus, uncommon to locally fairly common in the Cerrado (Neotropical savanna). It is a generalist forager that takes both insects and fruits (Alves 1991) and constructs a basket-shaped nest <1 m above ground (Alves and Cavalcanti 1990, Duca and Marini 2011). It has a cooperative breeding system (Alves 1990, Manica and Marini 2012) and is frequently observed in mixed-species flocks sharing sentinel function with White-rumped Tanager (Cypsnagra hirundinacea; Ragusa-Netto 2000). Our objective was to describe the territorial system and adult dispersal pattern of White-banded Tanagers. Specifically, we assessed the following issues of territoriality: (1) stability of the territory location and size (breeding vs. nonbreeding seasons and years), (2) relation between territory size and group size, and (3) dispersal pattern by sex. Methods Study Area We studied the White-banded Tanager in a 10,547-ha protected area, Estação Ecológica de Águas Emendadas (ESECAE) (15°29–15°36′S, 47°31–47°41′W) in Distrito Federal, Brazil. There are 287 bird species in ESECAE (Bagno 1998), or 35% of the total birds known for the Cerrado biome (Silva 1995). ESECAE is an isolated protected area currently surrounded by farms, small rural properties, and a city. The local vegetation is a mosaic ranging from grassland to dense and closed woodland and gallery forest. Local climate is markedly seasonal. The rainy season is from October to April, and the remainder of the year is exceptionally dry (Nimer 1979). White-banded Tanagers were studied mostly in a 100-ha grid established in 2002 in the interior (>1 km from the border) of the reserve. The grid is a 1 × 1 km square, divided into four hundred 50 × 50 m squares. The topography is nearly flat at an altitude of ∼1,040 m. The area is covered with a mosaic of different vegetation physiognomies typical of Cerrado patches of grasslands (campo limpo), open cerrado (campo sujo), shrubby grassland (cerrado ralo), and cerrado sensu stricto (cerrado típico) (Ribeiro and Walter 1998). Territory Size The territory was defined as the area used for living and breeding (Maher and Lott 1995). Individuals were captured with mist nets and marked with metal bands provided by a Brazilian environmental agency (CEMAVE/ICMBIO) and unique combinations of plastic colored bands. We also marked nestlings. Observations were made with binoculars, primarily in the morning (0500–1400 hours), from August 2003 to January 2006, using the focal sampling method (Martin and Bateson 1993). Observations were made mostly inside the sample grid, but we also did inspections in a 300-m buffer area around it. We observed color-banded birds for as long as possible, registering their location in a map of the grid and also marking them with a GPS. We conducted successive observations of the territory of each group until new observations resulted in no increase in the territory area by verifying effort–territory size curves. Territories were mapped and their areas measured by the convex polygon method (Odum and Kuenzler 1955), which consists of joining the outermost observation points for each group with a straight line. Polygons were considered the territories of groups. We used AutoCAD version 14.0 (AutoDesk, San Rafael, California, USA) to draw polygons and calculate their areas. Territory sizes were measured in five distinct periods, three in breeding seasons (August–December in 2003, 2004, and 2005) and two in nonbreeding seasons (January–July in 2004 and 2005). Group Size Group was defined as the association among individuals living in the same territory. Most groups were composed of one pair of adults and helpers of different age classes (see Duca and Marini 2013). We made censuses of color-banded birds every half-year, before and after the breeding seasons (June and December, respectively; Duca and Marini 2013). To search for marked birds in the groups, we monitored all territories as described above. Birds were sexed and aged by plumage, according to Duca and Marini (2013). Group size was defined by counting all individuals in each group during field monitoring, and also during the censuses of marked individuals conducted before and after breeding seasons (June and December, respectively). The size of the groups at the end of breeding seasons was estimated without fledglings born in that season because they did not participate in territory defense when the group settled there at the start of the breeding season. Dispersal among Territories We assessed the distance moved and sex of individuals that changed territories (dispersed). The number of territories passed over by individuals leaving their natal territories was used as a dispersal estimate. We defined the distance dispersed on the basis of the mean diameter of territory areas (201 ± 19 m, n = 28) in the breeding season of 2004. We counted the number of territories that each individual dispersed across from the natal territory and estimated the average length of a territory as ∼200 m. Statistical Analysis Differences in territory sizes among years and seasons (breeding and nonbreeding) were assessed with analysis of variance (ANOVA). We used analysis of covariance (ANCOVA) to verify differences in territory sizes among years, considering group size (number of birds in each group) as a covariate. Post hoc tests (least significant difference) were performed to identify differences in territory size between years. Linear regression was used to assess the relation between territory size and group size. Chi-square tests were used to assess the difference between the distances (number of territories) dispersed by males and females. This test was also used to assess differences between the numbers of males and females that dispersed or remained in their natal territory. Normality of data was verified by Kolmogorov-Smirnov tests. We set significance at α = 0.05 and performed statistical analysis using the BioStat version 5.0 (Ayres and Ayres 2000) statistical package. Results are reported as means ± SD. Results We captured and banded 253 individuals. All territories considered here had at least two individuals marked with plastic colored bands, and ∼88% of the individuals inside the sample grid were banded. Territories had small overlapping areas, and intrusions into the neighboring territories beyond the limits of overlap were not recorded (Figure 1). These overlapping areas of territories can be considered “border-disputed areas” because a group could forage there only for a short time before being detected by the neighboring group. Once the individuals of a group perceived the presence of a neighboring group, they started agonistic behaviors that always ended with individuals of both groups leaving the area of overlap. When two groups met in these areas, all individuals defended the territory. Nearly always, individuals vocalized intensely and flew from one perch to another many times, but physical aggression among individuals of different groups was rare. We recorded 217 encounters of groups in the border-disputed areas of 39 territories. These encounters were recorded in all months of the year, and the agonistic behavior reported above was observed in all of them. We recorded 6 individuals (2 males and 4 females) from different territories that stayed in their territories for >3 yr, and 10 individuals (5 males, 3 females, and 2 subadults of unknown sex) that stayed in their territories for 2 yr. This occurred in spite of switching of other individuals from the groups. Spatial distribution of territories was held almost constant throughout the study (Figure 1). Territory Size The mean number of points marked in each territory was 168 ± 12.1, but the cumulative territory area curves of all groups stabilized with a mean of 123 ± 22.3 points. Territory size ranged from 2.1 to 5.3 ha, and averaged 3.7 ± 0.6 ha, considering the five sampling periods. In the nonbreeding and breeding seasons, territories averaged 3.6 ± 0.6 ha (n = 83) and 3.8 ± 0.6 ha (n = 51), respectively (Table 1 and Figure 2), without significant variation between seasons (ANOVA: F1,129 = 1.45, P = 0.23). Considering both seasons together (breeding and nonbreeding), the territory size was smaller in 2005 than in 2003 and 2004 (ANOVA: F2,129 = 6.05, P = 0.003; Table 1). However, the core areas of territories were basically the same over time. When we considered territories only from breeding seasons, the difference in territory sizes was significant only between 2003 and 2005 (ANOVA: F2,80 = 3.74, P = 0.03; Table 1 and Figure 2). Group sizes ranged from 2 to 8 individuals and averaged 3.4 ± 1.2 individuals. Mean size of the groups was 3.2 ± 1.1 individuals in the breeding seasons and 3.6 ± 1.2 individuals in the nonbreeding seasons (Table 1). Analysis considering group sizes as covariate also indicated significant differences in territory sizes among years, with territory sizes correlated to group sizes (Table 2). However, there was no significant difference in the number of individuals per group among years (ANOVA: F2,131 = 1.29, P = 0.28). There was a positive relation between territory size and group size (linear regression: r2 = 0.362, P < 0.001; Figure 3). Dispersal among Territories We recorded 44 dispersal events (movements of individuals) between territories. Of these, 15 individuals (34%) were males and 29 (66%) were females. Most individuals of both sexes dispersed distances equal to one territory in length, and only females dispersed farther than two territories (Figure 4). Nevertheless, there was no significant difference between the number of territories dispersed by males and females (χ2 = 2.23, df = 1, P = 0.26). We recorded 48 individuals that remained in the same territory for at least two consecutive breeding seasons. Of these, 26 (54%) were males, 14 (29%) were females, and 8 (17%) were subadults with undetermined sex. Overall, males tended to stay in the same territory whereas females tended to disperse (χ2 = 7.31, df = 1, P = 0.01). Discussion Territory Size The White-banded Tanager is a resident species that defends its territory throughout the year. Following a functional classification of avian territories based on Hinde (1956), the White-banded Tanager has a type “A” territory within which all activities are done, including those related to feeding and breeding. Considering the definition of “territory” proposed by Noble (1939) and Pitelka (1959), the White-banded Tanager's territory corresponds to its home range. The territorial behavior presented by the White-banded Tanager corroborates the hypothesis that predicts year-long territories and stable neighborhoods for tropical birds (revision in Stutchbury and Morton 2001). The stability of territory occupancy was positively correlated with abundance for Amazonian birds (Stouffer 2007). The year-long territory defense presented by the White-banded Tanager is common for insectivorous Neotropical birds (Fedy and Stutchbury 2005, Lopes and Marini 2006, Sogge et al. 2007), but this pattern is not expected for frugivorous ones (Morton 1973). However, the White-banded Tanager has a generalist diet and foraging tactic (Alves 1991). Also, there are variations in basic patterns of territorial defense, especially for species with cooperative breeding (Stutchbury and Morton 2001). Therefore, the territorial behavior of White-banded Tanager corroborates the literature related to year-long territory defense. Most territories of White-banded Tanagers remained with their same boundaries over time, regardless of turnover among individuals in the groups. Although the mean territory size decreased in 2005, the territories shrank but continued to occupy the same core area over time. Possibly, the hypothesis that a territory's shape is mainly determined by the ability to defend its limits rather than by foraging conditions (Eason 1992) applies to this White-banded Tanager population. We could not determine whether any group had dominance over overlapping areas among territories. More studies about agonistic interactions among social groups and foraging time spent in different portions of the territories should answer this issue. The average territory size of White-banded Tanagers in our study (3.7 ha) was similar to the 4.3 ha found by Alves (1990) for the territory of a group in another population in the Federal District, Brazil. The territory of the White-banded Tanager is relatively small for a medium-sized passerine (29 g) that lives in social groups of ≤8 individuals. Low density and large size of territories have been described for a guild of Amazonian birds (Stouffer 2007). No Amazonian birds defended territories smaller than 3 ha (mean = 9 ha), and the average territory size for omnivorous species with body mass similar to that of the White-banded Tanager (23–35 g) was 9.5 ha (Terborgh et al. 1990). The mean territory size for species of Thraupidae was 5.3 ha (Terborgh et al. 1990). The territory size of Atlantic Forest birds was also small for species with body mass lower than (Mendonça and Gonzaga 1999, Duca and Marini 2005) or similar to (Duca et al. 2006) that of White-banded Tanagers. In the Cerrado biome, some passerines defended smaller and larger territories than White-banded Tanagers, regardless of body mass (Table 3). These comparisons suggest that variation in territory size among species with similar body mass is explained by another factor, not considered here. The positive correlation between the number of individuals per group and territory size of White-banded Tanagers suggests a relationship between the demand of the group for resources and the area of habitat necessary to supply it. Because individuals adjust territory size to ensure the resource necessary for survivorship and breeding, two hypotheses can be considered to explain this relationship. The first predicts a positive correlation between body mass and territory size (Perrins and Birkhead 1983), and the other predicts a negative correlation between food abundance and territory size (Gass 1979, Smith and Shugart 1987). Studies with other species corroborate both hypotheses (Burke and Nol 1998, Duca et al. 2006, Hussell 2012), but there is evidence that prey abundance is not the main factor determining territory size in Neotropical birds (Duca and Marini 2005). That White-banded Tanager territory size was smaller in 2005 than in 2003 and 2004 may be related to the higher survival rate of juveniles in the breeding season of 2005, given that adult survival rate did not vary significantly between those years (see Duca and Marini 2013). We might even think that the higher number of juvenile survivors enhanced competition and that the territory size became smaller. This effect of competition is corroborated by the fact that fecundity was lower in 2005 (Duca and Marini 2013). However, the density remained stable throughout the sampling period and, thus, we did not expect a density effect in territory size in 2005. Because the density did not vary over time, it was not possible to assess how the density could affect the territory size of White-banded Tanagers. Because the study area presented evidence of habitat saturation (Duca et al. 2009, Duca and Marini 2013), we suggest that the territories of White-banded Tanagers are close to the smallest possible size they can present. In general, territory size decreases with increasing density, but there is a minimum size of territory to supply the needs of individuals (Hixon 1980, Perrins and Birkhead 1983). Therefore, the territorial behavior poses a limit to population size, producing a density effect on the population, as demonstrated by Yamagishi and Ueda (1986). Also, an increase in occupation of poor habitats may result from an increase in density (Preston et al. 1998). Territory sizes may vary with resource distribution, regardless of the degree of habitat saturation (Doerr and Doerr 2006). However, the best explanation for differences in territory size among White-banded Tanagers was the relationship with group size. Territory size of White-banded Tanagers did not vary significantly between nonbreeding and breeding seasons (Figure 2). Variations in territory sizes between seasons were not observed among Atlantic Forest birds (Duca and Marini 2005, Duca et al. 2006). However, changes in territory size were noted in other birds. For example, the territory of two pairs of Hawaii Creepers (Fringillidae: Oreomystis mana) in Hawaii increased 346% and 180% (VanderWerf 1998), and California Gnatcatchers (Polioptilidae: Polioptila californica) in the temperate region increased 78% in the nonbreeding season (Preston et al. 1998). On the other hand, 39 territories of bird species in the temperate region were larger in the breeding season (Møller 1990). An increase in territory size in the nonbreeding season can be related to looser territorial defense in this season, enabling the expansion of territory boundaries (VanderWerf 1998). The hypothesis of behaviors to prevent extrapair copulation displayed by males was considered to explain the increase in territory size in the breeding season (Møller 1990). None of these hypotheses seems to be related to the territorial system of the White-banded Tanager, because this species shows spatially fixed and stable territory location throughout the year. Dispersal among Territories White-banded Tanagers tend to disperse distances equivalent to mean diameters of territories, establishing in territories adjacent to their parents. This tendency was observed in several tropical birds (e.g., Willis 1974, Dowsett 1985, Greenberg and Gradwohl 1997) and seems to be a pattern among birds with cooperative breeding (see Brown 1987). In some monogamous tropical birds, juveniles live in their parents' territory for many months (e.g., Morton et al. 2000), thus having more chances to compete for vacancies in neighboring territories that can arise at any time of the year (Stutchbury and Morton 2001). This strategy has been associated with a greater individual likelihood of attaining a breeder status in cooperative groups (Brown 1987). Also, competition for vacant territories occurs mainly between individuals of neighboring territories (Greenberg and Gradwohl 1997). Only female White-banded Tanagers dispersed distances farther than two territories. The difference in dispersal between males and females has been reported for other species. For example, males settling in neighboring territories and females dispersing longer distances were described for the Superb Fairywren (Maluridae: Malurus cyaneus; Rowley 1965) and the Florida Scrub-Jay (Corvidae: Aphelocoma coerulescens), in which males also remain on their home territory (Woolfenden and Fitzpatrick 1978). Similarly, there was a higher tendency for male White-banded Tanagers to remain at their home territories and females to disperse. On the other hand, Greenberg and Gradwohl (1997) showed that 37% of banded individuals of the Checker-throated Antwren (Thamnophilidae: Myrmotherula fulviventris) moved to neighboring territories at least once, irrespective of sex. Conclusion The White-banded Tanager is a resident species that defends its territory throughout the year. All individuals in the group defended their territory, which had the same core area over time, regardless of members' substitutions. This species has a dispersal pattern whereby individuals predominantly occupy neighboring territories, in accordance with former studies that have considered this a typical pattern for cooperative-breeding birds and also for populations in saturated environments. Our data also suggest a different dispersal pattern between males and females, but this point needs better quantitative data to be confirmed. The lack of vacant spaces among territories and the existence of adults not breeding but cooperating with breeding pairs suggest habitat saturation and that the White-banded Tanager population in our study site may be regulated by a density-dependent effect. Our results show that a density-dependent effect can promote the evolution of cooperative breeding behavior based on the unavailability of breeding habitat. Acknowledgments This study was funded by CNPq and the Fundação O Boticário de Proteção À Natureza. PEQUI—Pesquisa e Conservação do Cerrado provided institutional support. We thank ESECAE/SEMARH for authorization to conduct this study. C.D. was supported by a fellowship from CAPES/CNPq, and M.Â.M. was supported by a research fellowship from CNPq. We thank all our friends from Laboratório de Ecologia e Conservação de Aves at Universidade de Brasília for help during field work. We thank R. B. Cavalcanti, R. Macedo, M. A. S. Alves, R. Young, and A. C. Guaraldo for suggestions that improved the manuscript. We also thank anonymous reviewers who kindly made suggestions on the manuscript. Literature Cited Alves , M. A. S (1990) . Social system and helping behavior in the White-banded Tanager (Neothraupis fasciata) . The Condor 92 : 470 – 474 . Google Scholar Crossref Search ADS WorldCat Alves , M. A. S (1991) . Dieta e táticas de forrageamento de Neothraupis fasciata em cerrado no Distrito Federal, Brasil (Passeriformes: Emberizidae) . Ararajuba 2 : 25 – 29 . WorldCat Alves , M. A. S. , and R. B. Cavalcanti (1990) . 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Simultaneous territory mapping of male Fan-tailed Warblers (Cisticola juncidis) . Journal of Field Ornithology 57 : 193 – 199 . WorldCat Figure 1. Open in new tabDownload slide Map of South America, with location of the sample grid (*) and distribution of White-banded Tanager territories (numbers) in Estação Ecológica de Águas Emendadas during the nonbreeding season in 2004. Closed polygons represent well-sampled territories, and open polygons represent territories with unsatisfactory samples. Open polygons with dotted line represent territories that were recorded but not monitored. Figure 1. Open in new tabDownload slide Map of South America, with location of the sample grid (*) and distribution of White-banded Tanager territories (numbers) in Estação Ecológica de Águas Emendadas during the nonbreeding season in 2004. Closed polygons represent well-sampled territories, and open polygons represent territories with unsatisfactory samples. Open polygons with dotted line represent territories that were recorded but not monitored. Figure 2. Open in new tabDownload slide Territory sizes of White-banded Tanagers during the breeding (B) and nonbreeding (NB) seasons in Estação Ecológica de Águas Emendadas, 2003–2005. Points above and below the bars represent outlier values. Figure 2. Open in new tabDownload slide Territory sizes of White-banded Tanagers during the breeding (B) and nonbreeding (NB) seasons in Estação Ecológica de Águas Emendadas, 2003–2005. Points above and below the bars represent outlier values. Figure 3. Open in new tabDownload slide Correlation between territory size and group size of White-banded Tanagers in Estação Ecológica de Águas Emendadas. Figure 3. Open in new tabDownload slide Correlation between territory size and group size of White-banded Tanagers in Estação Ecológica de Águas Emendadas. Figure 4. Open in new tabDownload slide Percentage of the male and female White-banded Tanagers that remained in the same territory, and the distances (number of territories) dispersed during the study period (2003–2006), in Estação Ecológica de Águas Emendadas. Figure 4. Open in new tabDownload slide Percentage of the male and female White-banded Tanagers that remained in the same territory, and the distances (number of territories) dispersed during the study period (2003–2006), in Estação Ecológica de Águas Emendadas. Table 1. Mean (± SD) group size (number of individuals) and mean territory size (ha) of White-banded Tanagers in Estação Ecológica de Águas Emendadas during the nonbreeding (NB) and breeding (B) seasons from 2003 to 2005, and post hoc test results (least significant difference test) showing P values from an analysis of variance to verify variations in territory sizes between years, using data from both seasons and only the breeding seasons. Significant values are in bold. Open in new tab Table 1. Mean (± SD) group size (number of individuals) and mean territory size (ha) of White-banded Tanagers in Estação Ecológica de Águas Emendadas during the nonbreeding (NB) and breeding (B) seasons from 2003 to 2005, and post hoc test results (least significant difference test) showing P values from an analysis of variance to verify variations in territory sizes between years, using data from both seasons and only the breeding seasons. Significant values are in bold. Open in new tab Table 2. Results of an analysis of covariance that assessed variations in territory sizes among years, using group size as the covariate, for White-banded Tanagers in Estação Ecológica de Águas Emendadas. Significant values are in bold. Open in new tab Table 2. Results of an analysis of covariance that assessed variations in territory sizes among years, using group size as the covariate, for White-banded Tanagers in Estação Ecológica de Águas Emendadas. Significant values are in bold. Open in new tab Table 3. Body mass (g) and territory size (ha) of birds from the Cerrado biome, Brazil. Open in new tab Table 3. Body mass (g) and territory size (ha) of birds from the Cerrado biome, Brazil. Open in new tab Author notes Current address: Universidade Vila Velha, Vila Velha, Espírito Santo, Brazil © 2014 American Ornithologists' Union http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Auk: Ornithological Advances Oxford University Press

Territorial system and adult dispersal in a cooperative-breeding tanagerTerritory and dispersal of a tanager

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References (69)

Publisher
Oxford University Press
Copyright
© 2014 American Ornithologists' Union
ISSN
0004-8038
eISSN
1938-4254
DOI
10.1642/AUK-13-005.1
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Abstract

Abstract Latitudinal differences in territorial behavior are considered to have great influence on differences in life-history strategies of Nearctic and Neotropical birds. Most territorial behavior of tropical birds has particularities that cannot be explained only by theories from studies of birds in temperate regions. We evaluated the territorial system of the cooperative-breeding White-banded Tanager (Neothraupis fasciata) in central Brazil's savanna and present results on stability of territory site occupation, relationship between territory size and group size, and dispersal patterns. Territories (n = 27, mean per season) were monitored for 3 yr in a protected area in the cerrado of central Brazil and were defined by the minimum convex polygon method. Territory size averaged 3.7 ± 0.6 ha, and was defended by all individuals of groups of 2–8 individuals (mean = 3.4 ± 1.2). We recorded 44 dispersal events between territories, and most individuals dispersed distances equal to one territory in length. Males tended to stay in the same territory, whereas females dispersed. Our results support hypotheses that predict year-long territory defense for tropical birds. Territory size reflected group size, corroborating the hypothesis that individuals adjust the territory size to ensure the amount of resources for survival. Resumo Diferenças latitudinais no comportamento territorial exercem influencia nas estratégias da história de vida de aves da região neártica e neotropical. O comportamento territorial de aves tropicais apresenta particularidades que não podem ser explicadas apenas com base em teorias provenientes de estudos realizados na região temperada. Nós avaliamos o sistema territorial de um traupídeo com reprodução cooperativa, cigarra-do-campo (Neothraupis fasciata), em uma área de Cerrado do Brasil central, apresentando resultados a respeito da estabilidade de ocupação do território, relação entre tamanho do território e número de indivíduos no bando, e padrões de dispersão. Os territórios (n = 27, média por estação) foram monitorados durante três anos em uma unidade de conservação do Brasil central e foram estimados pelo método do polígono convexo. O tamanho médio dos territórios foi de 3,7 (± 0.6) ha. O número de indivíduos nos bandos variou de 2 a 8 (média: 3.4 ± 1.2) indivíduos e todos participaram da defesa do território. Foram registrados 44 eventos de dispersão entre territórios, sendo que a maioria dos indivíduos dispersaram distâncias equivalentes à largura média de um território. Machos tenderam a permanecer no mesmo território e fêmeas a dispersarem. Os resultados apresentados corroboram a hipótese que prediz a defesa do território durante todo o ano para aves tropicais. O tamanho do território foi diretamente relacionado com o tamanho do grupo, corroborando a hipótese que os indivíduos ajustam o tamanho dos territórios para garantir a quantidade de recursos necessários para a sobrevivência. Palavras chave: Cerrado, cigarra-do-campo, dispersão por sexo, Neothraupis fasciata, savana Neotropical, tamanho de área de vida Introduction Latitudinal differences in territorial behavior are considered to have great influence on differences in life-history strategies of Nearctic and Neotropical birds. Most territorial behavior of tropical birds has particularities that cannot be explained only by theories from studies of birds in temperate regions. In the tropics, year-long territory defense is common and adult survival is high, so opportunities for territory acquisition may be scarce (Stutchbury and Morton 2001). For insectivorous species it is common to defend year-round territories, but this behavior is not expected for frugivorous birds (Morton 1973, Buskirk 1976). Territorial intrusions are rare among tropical birds (Gorrell et al. 2005, Duca et al. 2006, Freitas and Rodrigues 2012) but common in temperate species (Preston et al. 1998), a behavior often associated with extrapair mating behavior (Gowaty et al. 1989, Meek and Robertson 1994). Some tropical birds occupy the same territory over time, and adult turnover is low (Duca et al. 2006, Woltmann and Sherry 2011, Freitas and Rodrigues 2012), a characteristic that can maintain stability between neighboring territories. Even when owners are replaced, the new owner of a vacant territory tends to adjust its boundaries similar to those of the original territory (Greenberg and Gradwohl 1986). Eason (1992) suggested that the territory site should be determined more by the ability to defend it than by quality. An explanation for stability of territory occupancy is based on the minimum territory size necessary to obtain enough resources to supply the foraging demand and, thus, respond to fluctuating foraging conditions (Greenberg and Gradwohl 1986, 1997). According to Hixon (1980), there is an optimization of territory sizes whereby the need for foraging habitat regulates the minimum size, and intraspecific competition determines the maximum size. The main resources that birds can defend in their territories include food, breeding sites, and mates (Perrins and Birkhead 1983). The influence of food availability in territory size can be illustrated by the relationship between the area of territories and body mass of species. Studies of species with similar diet demonstrated that territory sizes were related to body mass of different species (Schoener 1968, Duca et al. 2006). This relationship is expected for species defending territories where all breeding and feeding activities occur (Perrins and Birkhead 1983). The relationship between food availability and territory size can also be expected for species living in cooperative groups, because larger groups demand more food. Territory acquisition has been carefully studied in cooperative birds in the tropical region, where juveniles often inherit their natal territory or use them as a refuge from which to compete for breeding positions on nearby territories (Stutchbury and Morton 2001). Several studies have demonstrated that individuals can use their helper status as an intermediate step for breeder status in the population (Grimes 1980, Brown and Brown 1984, Rabenold 1985). Moreover, individuals should be more reluctant to divorce or engage in breeding dispersal in a more saturated environment, where their chances of finding a new mate or territory are probably low (Doerr and Doerr 2006). Some species have sex-biased dispersal tendency (Greenwood 1980). Male Great Tits (Parus major) captured in their natal territories had lower dispersal probability than females (Dhondt 1979). This pattern was also recorded in other populations (Dhondt and Hublé 1968) and confirmed by studies of sex ratio, showing that male Great Tits have a higher tendency to stay near their natal territory, whereas females prevail among dispersing individuals (Payevsky 2006). Here, we describe the territorial system and dispersal pattern of a near-threatened bird species, the White-banded Tanager (Neothraupis fasciata). It is the only species in this genus, uncommon to locally fairly common in the Cerrado (Neotropical savanna). It is a generalist forager that takes both insects and fruits (Alves 1991) and constructs a basket-shaped nest <1 m above ground (Alves and Cavalcanti 1990, Duca and Marini 2011). It has a cooperative breeding system (Alves 1990, Manica and Marini 2012) and is frequently observed in mixed-species flocks sharing sentinel function with White-rumped Tanager (Cypsnagra hirundinacea; Ragusa-Netto 2000). Our objective was to describe the territorial system and adult dispersal pattern of White-banded Tanagers. Specifically, we assessed the following issues of territoriality: (1) stability of the territory location and size (breeding vs. nonbreeding seasons and years), (2) relation between territory size and group size, and (3) dispersal pattern by sex. Methods Study Area We studied the White-banded Tanager in a 10,547-ha protected area, Estação Ecológica de Águas Emendadas (ESECAE) (15°29–15°36′S, 47°31–47°41′W) in Distrito Federal, Brazil. There are 287 bird species in ESECAE (Bagno 1998), or 35% of the total birds known for the Cerrado biome (Silva 1995). ESECAE is an isolated protected area currently surrounded by farms, small rural properties, and a city. The local vegetation is a mosaic ranging from grassland to dense and closed woodland and gallery forest. Local climate is markedly seasonal. The rainy season is from October to April, and the remainder of the year is exceptionally dry (Nimer 1979). White-banded Tanagers were studied mostly in a 100-ha grid established in 2002 in the interior (>1 km from the border) of the reserve. The grid is a 1 × 1 km square, divided into four hundred 50 × 50 m squares. The topography is nearly flat at an altitude of ∼1,040 m. The area is covered with a mosaic of different vegetation physiognomies typical of Cerrado patches of grasslands (campo limpo), open cerrado (campo sujo), shrubby grassland (cerrado ralo), and cerrado sensu stricto (cerrado típico) (Ribeiro and Walter 1998). Territory Size The territory was defined as the area used for living and breeding (Maher and Lott 1995). Individuals were captured with mist nets and marked with metal bands provided by a Brazilian environmental agency (CEMAVE/ICMBIO) and unique combinations of plastic colored bands. We also marked nestlings. Observations were made with binoculars, primarily in the morning (0500–1400 hours), from August 2003 to January 2006, using the focal sampling method (Martin and Bateson 1993). Observations were made mostly inside the sample grid, but we also did inspections in a 300-m buffer area around it. We observed color-banded birds for as long as possible, registering their location in a map of the grid and also marking them with a GPS. We conducted successive observations of the territory of each group until new observations resulted in no increase in the territory area by verifying effort–territory size curves. Territories were mapped and their areas measured by the convex polygon method (Odum and Kuenzler 1955), which consists of joining the outermost observation points for each group with a straight line. Polygons were considered the territories of groups. We used AutoCAD version 14.0 (AutoDesk, San Rafael, California, USA) to draw polygons and calculate their areas. Territory sizes were measured in five distinct periods, three in breeding seasons (August–December in 2003, 2004, and 2005) and two in nonbreeding seasons (January–July in 2004 and 2005). Group Size Group was defined as the association among individuals living in the same territory. Most groups were composed of one pair of adults and helpers of different age classes (see Duca and Marini 2013). We made censuses of color-banded birds every half-year, before and after the breeding seasons (June and December, respectively; Duca and Marini 2013). To search for marked birds in the groups, we monitored all territories as described above. Birds were sexed and aged by plumage, according to Duca and Marini (2013). Group size was defined by counting all individuals in each group during field monitoring, and also during the censuses of marked individuals conducted before and after breeding seasons (June and December, respectively). The size of the groups at the end of breeding seasons was estimated without fledglings born in that season because they did not participate in territory defense when the group settled there at the start of the breeding season. Dispersal among Territories We assessed the distance moved and sex of individuals that changed territories (dispersed). The number of territories passed over by individuals leaving their natal territories was used as a dispersal estimate. We defined the distance dispersed on the basis of the mean diameter of territory areas (201 ± 19 m, n = 28) in the breeding season of 2004. We counted the number of territories that each individual dispersed across from the natal territory and estimated the average length of a territory as ∼200 m. Statistical Analysis Differences in territory sizes among years and seasons (breeding and nonbreeding) were assessed with analysis of variance (ANOVA). We used analysis of covariance (ANCOVA) to verify differences in territory sizes among years, considering group size (number of birds in each group) as a covariate. Post hoc tests (least significant difference) were performed to identify differences in territory size between years. Linear regression was used to assess the relation between territory size and group size. Chi-square tests were used to assess the difference between the distances (number of territories) dispersed by males and females. This test was also used to assess differences between the numbers of males and females that dispersed or remained in their natal territory. Normality of data was verified by Kolmogorov-Smirnov tests. We set significance at α = 0.05 and performed statistical analysis using the BioStat version 5.0 (Ayres and Ayres 2000) statistical package. Results are reported as means ± SD. Results We captured and banded 253 individuals. All territories considered here had at least two individuals marked with plastic colored bands, and ∼88% of the individuals inside the sample grid were banded. Territories had small overlapping areas, and intrusions into the neighboring territories beyond the limits of overlap were not recorded (Figure 1). These overlapping areas of territories can be considered “border-disputed areas” because a group could forage there only for a short time before being detected by the neighboring group. Once the individuals of a group perceived the presence of a neighboring group, they started agonistic behaviors that always ended with individuals of both groups leaving the area of overlap. When two groups met in these areas, all individuals defended the territory. Nearly always, individuals vocalized intensely and flew from one perch to another many times, but physical aggression among individuals of different groups was rare. We recorded 217 encounters of groups in the border-disputed areas of 39 territories. These encounters were recorded in all months of the year, and the agonistic behavior reported above was observed in all of them. We recorded 6 individuals (2 males and 4 females) from different territories that stayed in their territories for >3 yr, and 10 individuals (5 males, 3 females, and 2 subadults of unknown sex) that stayed in their territories for 2 yr. This occurred in spite of switching of other individuals from the groups. Spatial distribution of territories was held almost constant throughout the study (Figure 1). Territory Size The mean number of points marked in each territory was 168 ± 12.1, but the cumulative territory area curves of all groups stabilized with a mean of 123 ± 22.3 points. Territory size ranged from 2.1 to 5.3 ha, and averaged 3.7 ± 0.6 ha, considering the five sampling periods. In the nonbreeding and breeding seasons, territories averaged 3.6 ± 0.6 ha (n = 83) and 3.8 ± 0.6 ha (n = 51), respectively (Table 1 and Figure 2), without significant variation between seasons (ANOVA: F1,129 = 1.45, P = 0.23). Considering both seasons together (breeding and nonbreeding), the territory size was smaller in 2005 than in 2003 and 2004 (ANOVA: F2,129 = 6.05, P = 0.003; Table 1). However, the core areas of territories were basically the same over time. When we considered territories only from breeding seasons, the difference in territory sizes was significant only between 2003 and 2005 (ANOVA: F2,80 = 3.74, P = 0.03; Table 1 and Figure 2). Group sizes ranged from 2 to 8 individuals and averaged 3.4 ± 1.2 individuals. Mean size of the groups was 3.2 ± 1.1 individuals in the breeding seasons and 3.6 ± 1.2 individuals in the nonbreeding seasons (Table 1). Analysis considering group sizes as covariate also indicated significant differences in territory sizes among years, with territory sizes correlated to group sizes (Table 2). However, there was no significant difference in the number of individuals per group among years (ANOVA: F2,131 = 1.29, P = 0.28). There was a positive relation between territory size and group size (linear regression: r2 = 0.362, P < 0.001; Figure 3). Dispersal among Territories We recorded 44 dispersal events (movements of individuals) between territories. Of these, 15 individuals (34%) were males and 29 (66%) were females. Most individuals of both sexes dispersed distances equal to one territory in length, and only females dispersed farther than two territories (Figure 4). Nevertheless, there was no significant difference between the number of territories dispersed by males and females (χ2 = 2.23, df = 1, P = 0.26). We recorded 48 individuals that remained in the same territory for at least two consecutive breeding seasons. Of these, 26 (54%) were males, 14 (29%) were females, and 8 (17%) were subadults with undetermined sex. Overall, males tended to stay in the same territory whereas females tended to disperse (χ2 = 7.31, df = 1, P = 0.01). Discussion Territory Size The White-banded Tanager is a resident species that defends its territory throughout the year. Following a functional classification of avian territories based on Hinde (1956), the White-banded Tanager has a type “A” territory within which all activities are done, including those related to feeding and breeding. Considering the definition of “territory” proposed by Noble (1939) and Pitelka (1959), the White-banded Tanager's territory corresponds to its home range. The territorial behavior presented by the White-banded Tanager corroborates the hypothesis that predicts year-long territories and stable neighborhoods for tropical birds (revision in Stutchbury and Morton 2001). The stability of territory occupancy was positively correlated with abundance for Amazonian birds (Stouffer 2007). The year-long territory defense presented by the White-banded Tanager is common for insectivorous Neotropical birds (Fedy and Stutchbury 2005, Lopes and Marini 2006, Sogge et al. 2007), but this pattern is not expected for frugivorous ones (Morton 1973). However, the White-banded Tanager has a generalist diet and foraging tactic (Alves 1991). Also, there are variations in basic patterns of territorial defense, especially for species with cooperative breeding (Stutchbury and Morton 2001). Therefore, the territorial behavior of White-banded Tanager corroborates the literature related to year-long territory defense. Most territories of White-banded Tanagers remained with their same boundaries over time, regardless of turnover among individuals in the groups. Although the mean territory size decreased in 2005, the territories shrank but continued to occupy the same core area over time. Possibly, the hypothesis that a territory's shape is mainly determined by the ability to defend its limits rather than by foraging conditions (Eason 1992) applies to this White-banded Tanager population. We could not determine whether any group had dominance over overlapping areas among territories. More studies about agonistic interactions among social groups and foraging time spent in different portions of the territories should answer this issue. The average territory size of White-banded Tanagers in our study (3.7 ha) was similar to the 4.3 ha found by Alves (1990) for the territory of a group in another population in the Federal District, Brazil. The territory of the White-banded Tanager is relatively small for a medium-sized passerine (29 g) that lives in social groups of ≤8 individuals. Low density and large size of territories have been described for a guild of Amazonian birds (Stouffer 2007). No Amazonian birds defended territories smaller than 3 ha (mean = 9 ha), and the average territory size for omnivorous species with body mass similar to that of the White-banded Tanager (23–35 g) was 9.5 ha (Terborgh et al. 1990). The mean territory size for species of Thraupidae was 5.3 ha (Terborgh et al. 1990). The territory size of Atlantic Forest birds was also small for species with body mass lower than (Mendonça and Gonzaga 1999, Duca and Marini 2005) or similar to (Duca et al. 2006) that of White-banded Tanagers. In the Cerrado biome, some passerines defended smaller and larger territories than White-banded Tanagers, regardless of body mass (Table 3). These comparisons suggest that variation in territory size among species with similar body mass is explained by another factor, not considered here. The positive correlation between the number of individuals per group and territory size of White-banded Tanagers suggests a relationship between the demand of the group for resources and the area of habitat necessary to supply it. Because individuals adjust territory size to ensure the resource necessary for survivorship and breeding, two hypotheses can be considered to explain this relationship. The first predicts a positive correlation between body mass and territory size (Perrins and Birkhead 1983), and the other predicts a negative correlation between food abundance and territory size (Gass 1979, Smith and Shugart 1987). Studies with other species corroborate both hypotheses (Burke and Nol 1998, Duca et al. 2006, Hussell 2012), but there is evidence that prey abundance is not the main factor determining territory size in Neotropical birds (Duca and Marini 2005). That White-banded Tanager territory size was smaller in 2005 than in 2003 and 2004 may be related to the higher survival rate of juveniles in the breeding season of 2005, given that adult survival rate did not vary significantly between those years (see Duca and Marini 2013). We might even think that the higher number of juvenile survivors enhanced competition and that the territory size became smaller. This effect of competition is corroborated by the fact that fecundity was lower in 2005 (Duca and Marini 2013). However, the density remained stable throughout the sampling period and, thus, we did not expect a density effect in territory size in 2005. Because the density did not vary over time, it was not possible to assess how the density could affect the territory size of White-banded Tanagers. Because the study area presented evidence of habitat saturation (Duca et al. 2009, Duca and Marini 2013), we suggest that the territories of White-banded Tanagers are close to the smallest possible size they can present. In general, territory size decreases with increasing density, but there is a minimum size of territory to supply the needs of individuals (Hixon 1980, Perrins and Birkhead 1983). Therefore, the territorial behavior poses a limit to population size, producing a density effect on the population, as demonstrated by Yamagishi and Ueda (1986). Also, an increase in occupation of poor habitats may result from an increase in density (Preston et al. 1998). Territory sizes may vary with resource distribution, regardless of the degree of habitat saturation (Doerr and Doerr 2006). However, the best explanation for differences in territory size among White-banded Tanagers was the relationship with group size. Territory size of White-banded Tanagers did not vary significantly between nonbreeding and breeding seasons (Figure 2). Variations in territory sizes between seasons were not observed among Atlantic Forest birds (Duca and Marini 2005, Duca et al. 2006). However, changes in territory size were noted in other birds. For example, the territory of two pairs of Hawaii Creepers (Fringillidae: Oreomystis mana) in Hawaii increased 346% and 180% (VanderWerf 1998), and California Gnatcatchers (Polioptilidae: Polioptila californica) in the temperate region increased 78% in the nonbreeding season (Preston et al. 1998). On the other hand, 39 territories of bird species in the temperate region were larger in the breeding season (Møller 1990). An increase in territory size in the nonbreeding season can be related to looser territorial defense in this season, enabling the expansion of territory boundaries (VanderWerf 1998). The hypothesis of behaviors to prevent extrapair copulation displayed by males was considered to explain the increase in territory size in the breeding season (Møller 1990). None of these hypotheses seems to be related to the territorial system of the White-banded Tanager, because this species shows spatially fixed and stable territory location throughout the year. Dispersal among Territories White-banded Tanagers tend to disperse distances equivalent to mean diameters of territories, establishing in territories adjacent to their parents. This tendency was observed in several tropical birds (e.g., Willis 1974, Dowsett 1985, Greenberg and Gradwohl 1997) and seems to be a pattern among birds with cooperative breeding (see Brown 1987). In some monogamous tropical birds, juveniles live in their parents' territory for many months (e.g., Morton et al. 2000), thus having more chances to compete for vacancies in neighboring territories that can arise at any time of the year (Stutchbury and Morton 2001). This strategy has been associated with a greater individual likelihood of attaining a breeder status in cooperative groups (Brown 1987). Also, competition for vacant territories occurs mainly between individuals of neighboring territories (Greenberg and Gradwohl 1997). Only female White-banded Tanagers dispersed distances farther than two territories. The difference in dispersal between males and females has been reported for other species. For example, males settling in neighboring territories and females dispersing longer distances were described for the Superb Fairywren (Maluridae: Malurus cyaneus; Rowley 1965) and the Florida Scrub-Jay (Corvidae: Aphelocoma coerulescens), in which males also remain on their home territory (Woolfenden and Fitzpatrick 1978). Similarly, there was a higher tendency for male White-banded Tanagers to remain at their home territories and females to disperse. On the other hand, Greenberg and Gradwohl (1997) showed that 37% of banded individuals of the Checker-throated Antwren (Thamnophilidae: Myrmotherula fulviventris) moved to neighboring territories at least once, irrespective of sex. Conclusion The White-banded Tanager is a resident species that defends its territory throughout the year. All individuals in the group defended their territory, which had the same core area over time, regardless of members' substitutions. This species has a dispersal pattern whereby individuals predominantly occupy neighboring territories, in accordance with former studies that have considered this a typical pattern for cooperative-breeding birds and also for populations in saturated environments. Our data also suggest a different dispersal pattern between males and females, but this point needs better quantitative data to be confirmed. The lack of vacant spaces among territories and the existence of adults not breeding but cooperating with breeding pairs suggest habitat saturation and that the White-banded Tanager population in our study site may be regulated by a density-dependent effect. Our results show that a density-dependent effect can promote the evolution of cooperative breeding behavior based on the unavailability of breeding habitat. Acknowledgments This study was funded by CNPq and the Fundação O Boticário de Proteção À Natureza. PEQUI—Pesquisa e Conservação do Cerrado provided institutional support. We thank ESECAE/SEMARH for authorization to conduct this study. C.D. was supported by a fellowship from CAPES/CNPq, and M.Â.M. was supported by a research fellowship from CNPq. We thank all our friends from Laboratório de Ecologia e Conservação de Aves at Universidade de Brasília for help during field work. We thank R. B. Cavalcanti, R. Macedo, M. A. S. Alves, R. Young, and A. C. Guaraldo for suggestions that improved the manuscript. We also thank anonymous reviewers who kindly made suggestions on the manuscript. Literature Cited Alves , M. A. S (1990) . Social system and helping behavior in the White-banded Tanager (Neothraupis fasciata) . The Condor 92 : 470 – 474 . Google Scholar Crossref Search ADS WorldCat Alves , M. A. S (1991) . Dieta e táticas de forrageamento de Neothraupis fasciata em cerrado no Distrito Federal, Brasil (Passeriformes: Emberizidae) . Ararajuba 2 : 25 – 29 . WorldCat Alves , M. A. S. , and R. B. Cavalcanti (1990) . 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Simultaneous territory mapping of male Fan-tailed Warblers (Cisticola juncidis) . Journal of Field Ornithology 57 : 193 – 199 . WorldCat Figure 1. Open in new tabDownload slide Map of South America, with location of the sample grid (*) and distribution of White-banded Tanager territories (numbers) in Estação Ecológica de Águas Emendadas during the nonbreeding season in 2004. Closed polygons represent well-sampled territories, and open polygons represent territories with unsatisfactory samples. Open polygons with dotted line represent territories that were recorded but not monitored. Figure 1. Open in new tabDownload slide Map of South America, with location of the sample grid (*) and distribution of White-banded Tanager territories (numbers) in Estação Ecológica de Águas Emendadas during the nonbreeding season in 2004. Closed polygons represent well-sampled territories, and open polygons represent territories with unsatisfactory samples. Open polygons with dotted line represent territories that were recorded but not monitored. Figure 2. Open in new tabDownload slide Territory sizes of White-banded Tanagers during the breeding (B) and nonbreeding (NB) seasons in Estação Ecológica de Águas Emendadas, 2003–2005. Points above and below the bars represent outlier values. Figure 2. Open in new tabDownload slide Territory sizes of White-banded Tanagers during the breeding (B) and nonbreeding (NB) seasons in Estação Ecológica de Águas Emendadas, 2003–2005. Points above and below the bars represent outlier values. Figure 3. Open in new tabDownload slide Correlation between territory size and group size of White-banded Tanagers in Estação Ecológica de Águas Emendadas. Figure 3. Open in new tabDownload slide Correlation between territory size and group size of White-banded Tanagers in Estação Ecológica de Águas Emendadas. Figure 4. Open in new tabDownload slide Percentage of the male and female White-banded Tanagers that remained in the same territory, and the distances (number of territories) dispersed during the study period (2003–2006), in Estação Ecológica de Águas Emendadas. Figure 4. Open in new tabDownload slide Percentage of the male and female White-banded Tanagers that remained in the same territory, and the distances (number of territories) dispersed during the study period (2003–2006), in Estação Ecológica de Águas Emendadas. Table 1. Mean (± SD) group size (number of individuals) and mean territory size (ha) of White-banded Tanagers in Estação Ecológica de Águas Emendadas during the nonbreeding (NB) and breeding (B) seasons from 2003 to 2005, and post hoc test results (least significant difference test) showing P values from an analysis of variance to verify variations in territory sizes between years, using data from both seasons and only the breeding seasons. Significant values are in bold. Open in new tab Table 1. Mean (± SD) group size (number of individuals) and mean territory size (ha) of White-banded Tanagers in Estação Ecológica de Águas Emendadas during the nonbreeding (NB) and breeding (B) seasons from 2003 to 2005, and post hoc test results (least significant difference test) showing P values from an analysis of variance to verify variations in territory sizes between years, using data from both seasons and only the breeding seasons. Significant values are in bold. Open in new tab Table 2. Results of an analysis of covariance that assessed variations in territory sizes among years, using group size as the covariate, for White-banded Tanagers in Estação Ecológica de Águas Emendadas. Significant values are in bold. Open in new tab Table 2. Results of an analysis of covariance that assessed variations in territory sizes among years, using group size as the covariate, for White-banded Tanagers in Estação Ecológica de Águas Emendadas. Significant values are in bold. Open in new tab Table 3. Body mass (g) and territory size (ha) of birds from the Cerrado biome, Brazil. Open in new tab Table 3. Body mass (g) and territory size (ha) of birds from the Cerrado biome, Brazil. Open in new tab Author notes Current address: Universidade Vila Velha, Vila Velha, Espírito Santo, Brazil © 2014 American Ornithologists' Union

Journal

Auk: Ornithological AdvancesOxford University Press

Published: Jan 1, 2014

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