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Core and transient species in an Amazonian savanna bird assemblage

Core and transient species in an Amazonian savanna bird assemblage Revista Brasileira de Ornitologia, 22(4), 374-382 ARTICLE December 2014 Core and transient species in an Amazonian savanna bird assemblage 1 1,2,3 Roberta Lúcia Boss and José Maria Cardoso da Silva Programa de Pós-Graduação em Biodiversidade Tropical – PPGBio, Universidade Federal do Amapá (UNIFAP), Departamento de Pós-Graduação, Bloco I, Jardim Marco Zero, CEP 68.902-280, Macapá, AP, Brazil. Conservation International. 2011 Crystal Drive, Suite 500, Arlington, VA 22202, USA. Corresponding author: jmcs0765@gmail.com Received on 16 April 2014. Accepted on 17 September 2014. ABSTRACT: In this paper, we report the number of core and transient bird species in an Amazonian savanna site and assess their ecological differences. We conducted our study at Campo Experimental do Cerrado (CEC) da Embrapa–Amapá, 48 km north of Macapá (0˚2'5" N / 51˚2'2" W), Amapá, Brazil. Forty points were monitored on a monthly basis over the course of one year, using the unlimited-distance point counts in a plot of 360 hectares of well-preserved and relatively homogeneous upland savanna from September 2006 to August 2007. Species were classified in core (recorded in the area in nine or more months), transient (recorded in the area in four or less months) and intermediate (the ones recorded between five and eight months). Species were also classified according to feeding guilds and habitat preferences. Statistical analyses were made to compare core and transient species. We recorded 72 species in the plot, of which 36 were transients, 12 were intermediates, and 22 were core. Core species have higher abundances than transient species. Core species are found mostly in the savanna while transient species also occur in other habitats within the landscape. Both core and transient groups presented well-marked seasonal variation in abundance. Recruitment explains abundance variation for core species, while differences in the availability of food resources in the site explains variation of the abundance in transient species. We predict that plot-level (not more than 500 hectares) bird assemblages in South American savannas will be composed of a small number of abundant and habitat-restricted species that occupy the site almost year round, combined with a high number of low abundant transient species that are habitat generalists and use the plot only during limited periods of their annual life cycle. KEYWORDS: conservation biogeography, landscape dynamics, local assemblages, South America, tropical savannas. INTRODUCTION patches within a landscape, landscapes within a region, and entire regions (Wiens 1992). Therefore, a thorough The most common approach to biodiversity conservation understanding of the major patterns of biological is to identify and protect natural features such as movements from the local to the regional scales is a critical step towards the design of conservation systems ecosystems and threatened species, whose distributions can be mapped and targeted through conservation that maintain ecological flows and enable the resilience of management activities (Watson et al. 2011). While such populations against the effects of global changes (Watson an approach is important, the conservation of species and et al. 2011). ecosystems cannot be achieved unless the ecological and One concept that has not yet been fully explored in conservation biogeography is the important distinction evolutionary processes that sustain them are understood and maintained (Cowling et al. 1999, Fuller et al. 2001). between core and transient species (Grinnell 1922, One of the most important ecological processes to be Magurran & Henderson 2003). Core species are those documented for any conservation plan is the movement that persist in a habitat patch (or site) through time of organisms (Bennett et al. 2009). Organisms move at and transient species are those that occur intermittently in a habitat patch (or site) as a result of dispersal from different scales and for many purposes: to find food and shelter, for social interactions, to track resources that vary surrounding habitats or regions (Coyle et al. 2013). irregularly over space and time, for seasonal migration, Core and transient species usually differ in their and to disperse and establish in new locations (Bennett ecological requirements as well as their abundance et al. 2009). patterns (Magurran & Henderson 2003, Magurran 2007). Core species are predicted to be locally abundant, Movements of populations and species link habitat Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva habitat-restricted, and follow a lognormal abundance of Macapá (0˚2'5" N / 51˚2'2" W), Amapá, Brazil. The distribution, whereas transient species are predicted to be CEC protects 796 ha of well-managed South American rare, habitat generalist, and follow the log series abundance upland savannas. distribution model (Magurran 2007, Belmaker 2009). The CEC landscape has four major habitat types: Core and transient species arise in local assemblages upland savannas, wet grasslands, gallery forests, and through different mechanisms. Core species are influenced anthropic areas. Upland savannas compose the matrix mostly by local-scale factors that allow the persistence of of the landscape. They occupy nutrient-poor soils, with the species in a habitat patch, whereas transient species strong to medium acidity, low in organic matter and with are influenced mostly by regional factors that govern the frequent iron concretions. Savanna vegetation is low, with number of species that potentially could move into the few (usually no more than 100 per hectare) short (up to 4-6 habitat patch from the surrounding landscape (Coyle et m) trees (Silva et al. 2011). The grass Trachypogon plumosus al. 2013). and the sedge Bulbostylis spadicea dominate the ground Tropical avian assemblages are well known to exhibit (Sanaiotti et al. 1997). Wet grasslands are found in narrow temporal and spatial variation in their species’ richness valleys where soils are shallow and permanently inundated. and abundance at the site scale (Karr 1976, Loiselle 1988, Narrow belts of Mauritia martiniana palms can be used Poulin et al. 2001). These variations are usually correlated to identify the position of these wet grasslands. Gallery with the availability of fruit, flowers, seeds, and insects forests are linear formations (usually 15-25 m tall) that are that are, in turn, impacted by seasonal changes in rainfall restricted to wide valleys formed by the permanent streams and associated soil moisture cycles (Karr 1976). In regions that cut the landscape. Tree species such as Jacaranda with long dry seasons, resource availability is low during copaia and Symphonia globulifera as well as palms such the dry season and high during the wet season (Poulin et as Euterpe oleracea are the most common species in these al. 2001, Blendiger 2005). Resource scarcity during the gallery forests. Anthropic areas used for agriculture and dry season can create ecological ‘crunches’ or ‘bottlenecks’ agro-forestry experiments are small in size and are located that limit species’ abundances and biotic interactions and near the CEC’s housing and laboratory facilities. processes (Wiens 1977, 1992). The climate is hot (average temperature of 27 C) Temporal variance in abundances of tropical birds and humid (average relative humidity of 81%). Average at the site scale can be caused by population recruitment annual precipitation from 1961 to 1990 is around 2,700 and mortality (Blake & Loiselle 1991) but short-term mm with a well-marked dry season from August to (e.g., < 3 months) variations in abundance can be caused November, when total monthly rainfall is below 50 mm. by movements of individuals into or out of a site (Martin & Karr 1986). Movements by individuals have been suggested as an important cause of the variance in tropical METHODS bird abundances (Martin & Karr 1986, Silva et al. 2011), We set 40 sampling points within a plot of 360 hectares but very few studies have evaluated the contribution of core and transient species on the richness and abundance of local of well-protected and relatively homogeneous upland assemblages (Karr & Freemark 1983, Poulin et al. 2001). savanna located at 0˚2'5" N / 51˚2'2" W. We set points Here we report for the first time the numbers of core at least 300 m apart to maintain sample independence and transient bird species in a 360-ha plot of relatively and at least 300 m from any habitat edge. We used this distance because Tubelis et al. (2004) found that forest uniform Amazonian upland savanna. We assessed the variation of the bird assemblages in this plot over a one- birds do not move more than 200 m within the savannas year period. Then we identified the core and transient in central Brazil. Our goal with this approach was to species and evaluated how these two groups of species sample the avifauna in the most homogenous savanna differ in their species richness, abundance, feeding area possible, avoiding the influence of other habitats in the landscape as well as edges or transitional vegetation. habitats, and habitat use. In addition, we evaluated how species richness and abundance of the core and transient To study the bird assemblages within the plot, we groups vary over time. We used our findings to propose used the unlimited-distance point count method (Blondel some general predictions on the contribution of the core et al. 1970). For 10 min we noted all birds seen or heard and transient species for site-level bird assemblages in in each point. For species that travel in groups, when we heard but did not see the birds, we assumed that the group South American upland savannas. size was the average from when we did see and count a group of the same species. We noted the species seen while STUDY AREA the observer walked between points, but these sightings were not included in the quantitative analyses. The order Our field research was conducted at Campo Experimental of point sampling changed every month to eliminate any do Cerrado (CEC) of Embrapa–Amapá, 48 km north Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva bias. RB conducted all monthly censuses from September monthly in the plot. We calculated the monthly abundance 2006 to August 2007, always between 06h00 and 08h00. for each species, summing up its number of detections in She used a Pentax 8X40 binocular and a Sony TCD5 PRO all 40 points (Maron et al. 2005). By summing up monthly II tape-recorder with a Sennheiser ME67 microphone. abundances of species, we were able to calculate monthly Following Coyle et al. (2013), we classified each abundances for the entire core and transient species groups species as core if it was present in the plot for at least as well as the annual abundance for each species. two-thirds of the period of time that was surveyed (nine We used the Kolmogorov-Smirnov test to test if months or more) and transient if it was present in no more the species abundance distributions of core and transient than one-third of the surveyed period (four months or groups were different. We used the Median Test to less), regardless of whether the species was recorded or not determine if species classified as core and transient breeding in the plot. Intermediate are those species that differed in their annual abundances. We used the G-Test were neither classified as core nor as transients. We used to evaluate if proportions of core and transient species this pragmatic approach to minimize misclassification at among feeding guilds as well as habitat use categories the expense of excluding a small fraction of intermediate were different. We used the G-Test for goodness-of-fit to species from analyses. a uniform distribution to determine whether abundances Species were also classified as habitat-restricted if and species richness of core and transient groups showed they were recorded in the landscape only in the upland any variation over time. We used Biostat 5.0 (Ayres et al. savannas; they were classified as habitat non-restricted 2007) for all statistical analyses. Latin and English names when they were also found in other natural habitats of the bird species follow Remsen et al. (2014). within the landscape. Our classification is based on qualitative data collected by RB during our study period in other habitats as well as the information reported by RESULTS Silva et al. (1997) for our study area. We recorded 72 species in the plot, corresponding to We classified bird species into six major guilds based on their diet. These feeding guilds are: (RS) 37.2% of all species recorded in the entire site until raptors + scavengers (including families of Cathartidae, now (Boss 2009). The presence of species in the plot Accipitridae and Falconidae); (IN) insectivores; (IF) over the year follows the expected bimodal pattern insectivore-frugivore; (FG) frugivore-granivore; (GR) (Figure 1) with 36 transients, 12 intermediates and 22 core species. Intermediate species were Colinus cristatus, granivore; and (NE) nectarivore. We used personal field experience and literature (Silva 1995, Silva et al. 1997, Columbina passerina, Thalurania furcata, Amazilia Sick 1997) to classify species into feeding guilds. fimbriata, Heliactin bilophus, Caracara cheriway, Milvago We calculated the monthly richness for core and chimachima, Amazona ochrocephala, Amazona amazonica, transient groups as well as for each feeding guild by Myiarchus ferox, Cyclarhis gujanensis, Piranga flava, Thraupis palmarum, and Sporophila plumbea. summing up the number of species of each group recorded FIGURE 1. Temporal occupancy of bird species in the 360-ha plot of upland savanna in Amapá, Brazil. The temporal occupancy of a species is the number of surveyed months in which the species was recorded as present. Core species were those recorded in nine or more months and transient species were those recorded in four our less months. Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva The abundance distribution patterns of core and different (G = 3.97, df = 5, p < 0.55). In contrast, core transient groups (Figure 2) are significantly different (KS, and transient species are very different in their habitat use Dmax = 0.91, p < 0.001). Core species are significantly (G = 27.2, df = 1, p < 0.0001) because most of the core more abundant than transient species (Median Test,  = species (68.2%) are found only in savannas, whereas most 36.6, p < 0.001). The frequencies of core and transient of the transient species (94.4%) occur in two or more species among the five guild categories (Figure 3) are not habitats (Table 1). FIGURE 2. Abundance distributions patterns of core (black) and transient (white) bird species recorded in a 360-ha plot of an upland savanna in Amapá, Brazil. FIGURE 3. Numbers of core (black) and transient (white) species among five feeding guilds recorded in a 360-ha plot of an upland savanna in Amapá, Brazil. Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva TABLE 1. List of bird species recorded during one year in a 360 hectares of savanna upland at Campo Experimental do Cerrado, Embrapa-Amapá, Amapá, Brazil. Core species are those found during at least nine months while transient species were reported in less than four months. Feeding guilds are: RS (raptors + scavangers), IN (insectivores), IF (insectivore-frugivore), FG (frugivore-granivore), GR (granivore), and NE (nectarivore). Habitat categories are: (1) restricted to upland savanna; (2) recorded in other habitats in the broad landscape. Annual abundance is the total number of detections of the species over one year. Feeding Annual Species English Name Habitat Guild Abundance CORE SPECIES Geranoaetus albicaudatus White-tailed Hawk RS 2 27 Patagioenas cayennensis Pale-vented Pigeon FG 2 129 Zenaida auriculata Eared Dove FG 1 103 Aratinga aurea Peach-fronted Parakeet FG 1 161 Eupetomena macroura Swallow-tailed Hummingbird NE 2 38 Colaptes campestris Campo Flicker FI 1 23 Lepidocolaptes angustirostris Narrow-billed Woodcreeper IN 1 153 Elaenia flavogaster Yellow-bellied Elaenia FI 2 331 Elaenia chiriquensis Lesser Elaenia FI 1 185 Suiriri suiriri Suiriri Flycatcher FI 1 332 Xolmis cinereus Gray Monjita IN 1 327 Tyrannus albogularis White-throated Kingbird FI 1 131 Tyrannus melancholicus Tropical Kingbird FI 2 102 Tyrannus savana Fork-tailed Flycatcher FI 1 816 Myiarchus swainsoni Swainson’s Flycatcher FI 1 256 Troglodytes aedon House Wren IN 2 38 Mimus saturninus Chalk-browed Mockingbird FI 2 134 Neothraupis fasciata White-banded Tanager FI 1 552 Cypsnagra hirundinacea White-rumped Tanager FI 1 486 Emberizoides herbicola Wedge-tailed Grass-Finch GR 1 273 Ammodramus humeralis Grassland Sparrow GR 1 554 Sturnella magna Eastern Meadowlark GR 1 56 TRANSIENT SPECIES Theristicus caudatus Buff-necked Ibis IN 2 6 Cathartes aura Turkey Vulture RS 2 1 Buteogallus meridionalis Savanna Hawk RS 2 2 Rupornis magnirostris Roadside Hawk RS 2 6 Burhinus bistriatus Double-striped Thick-knee IN 2 6 Columbina talpacoti Ruddy Ground-Dove GR 2 1 Patagioenas speciosa Scaled Pigeon FG 2 1 Leptotila verreauxi White-tipped Dove FG 2 6 Guira guira Guira Cuckoo IN 2 6 Chordeiles pusillus Least Nighthawk IN 2 4 Phaethornis ruber Reddish Hermit NE 2 3 Phaethornis superciliosus Long-tailed Hermit NE 2 3 Chrysolampis mosquitus Ruby-topaz Hummingbird NE 1 12 Anthracothorax nigricollis Black-throated Mango NE 2 3 Campephilus melanoleucos Crimson-crested Woodpecker FI 2 4 Herpetotheres cachinnans Laughing Falcon RS 2 5 Falco femoralis Aplomado Falcon RS 2 4 Forpus passerinus Green-rumped Parrotlet FG 2 2 Thamnophilus doliatus Barred Antshrike IN 2 1 Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva Feeding Annual Species English Name Habitat Guild Abundance Formicivora rufa Rusty-backed Antwren IN 2 2 Synallaxis albescens Pale-breasted Spinetail IN 2 5 Phaeomyias murina Mouse-colored Tyrannulet FI 2 4 Euscarthmus rufomarginatus Rufous-sided Pygmy-Tyrant IN 1 1 Tolmomyias flaviventris Yellow-breasted Flycatcher FI 2 1 Megarynchus pitangua Boat-billed Flycatcher FI 2 7 Myiarchus tyrannulus Brown-crested Flycatcher FI 2 5 Vireo olivaceus Red-eyed Vireo FI 2 2 Hylophilus pectoralis Ashy-headed Greenlet FI 2 15 Turdus leucomelas Pale-breasted Thrush FI 2 10 Schistochlamys melanopis Black-faced Tanager FI 2 2 Ramphocelus carbo Silver-beaked Tanager FI 2 3 Volatinia jacarina Blue-black Grassquit GR 2 2 Oryzoborus angolensis Chestnut-bellied Seed-Finch GR 2 3 Molothrus bonariensis Shiny Cowbird FI 2 4 Sturnella militaris Red-breasted Blackbird GR 2 3 Euphonia chlorotica Purple-throated Euphonia FI 2 3 Core species represented most (90.6%) of all seasonal variation in abundance was found for both core detections over the year (Figure 4b). Monthly species (G = 309.5, df = 11, p < 0.0001) and transient (G = 26.25, richness of core (G = 6.36, df = 11, p = 0.84) and transient df = 11, p < 0.0001) groups (Figure 4b). Both groups (G = 0.32, df = 11, p = 0.32) groups did not differ from presented their highest abundance values from October a uniform distribution (Figure 4a). However, significant to February, with a clear peak in November (Figure 4b). FIGURE 4. Monthly variations in the species richness (a) and total number of detections (b) of core (black) and transient (white) bird species recorded in a 360-ha plot of an upland savanna in Amapá, Brazil. Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva DISCUSSION array of landscapes that compose the South American savannas. Populations of both core and transient species We recorded that only 22 species (30.5%) are core, with most of the species being transients. However, core exhibited marked seasonality and followed roughly species represented 90.6% of all detections in one year the same variation pattern. Overall, bird abundance is and are on average more abundant than transient species. high from October to February and low from March to September. The five months in which bird abundance Therefore, although species’ richness in the site is mostly is higher coincides with the last two months of the dominated by transient species, abundance is dominated by core species. dry season and the first three months of the rainy one. Core species are mostly restricted to savannas, while Although fruits and insects are available year-round in transient species occupy other habitats in the landscape. tropical savannas (Silvério & Lenza 2010, Silva et al. 2011), the availability of these resources peaks during the This finding is supported by findings in other tropical transition between dry and rainy seasons (Sanaiotti & bird assemblages. For instance, Poulin et al. (2001) found that transient birds represented a large portion of the Cintra 2001). It is also during this period that most of the local assemblages of tropical arid and semi-arid habitats species breed in the plot (Boss 2009), a pattern that has in northern Venezuela. Martin and Karr (1986) suggested been observed in other tropical savannas as well (Sanaiotti & Cintra 2001, Silvério & Lenza 2010). that transients are an important component of tropical The overlap between breeding period and higher forest bird assemblages, but they did not present their proportions. abundance indicates that recruitment is the simplest The core species recorded in our research site are explanation for the increase of the detections of also found frequently in other savannas in central South core species at the local level (Martin & Karr 1986). However, there are six species (Elaenia flavogaster, Elaenia America and some of them are amongst the most abundant chiriquensis, Tyrannus albogularis, Tyrannus melancholicus, species (Silva 1995, Sick 1997, Tubelis & Calvacanti 2000, Cintra & Sanaiotti 2005, Aleixo & Poletto 2007). Tyrannus savanna, and Myiarchus swainsoni) that have In addition, five core species (Lepidocolaptes angustirostris, populations that breed in central South America and Suiriri suiriri, Mimus saturninus, Neothraupis fasciata, and are known to migrate northwards during the austral migration (Chesser 1994). Therefore, it is also possible Cypsnagra hirundinacea) are considered as nuclear species that individuals coming from migratory populations of in the mixed-species flocks that are found in most of the South American upland savannas (Tubelis 2007). those species and stopping by the site during some days or Combining our findings with general theories on weeks may also contribute to the variation in abundance bird assemblages, we can make some general predictions of these core species. Finally, core species might have been more abundant during the breeding period because they about the proportions of core and transient species in were more vocal and consequently their detectability other South American upland savannas. At the local scale (up to 500 ha), we predict that savanna bird assemblages increased. More studies are required to evaluate these will be composed of a small number of abundant and hypotheses. habitat-restricted species that occupy the site almost year- Because transient species are expected to track resources across the landscape more frequently than round, combined with a high number of low abundant core species, the variation in the abundance observed transient species that are habitat generalists and use the site only during some periods of their annual life cycle. for transient species can be explained by the high Because local diversity is a consequence of regional concentration of insects, fruits, and flowers during some diversity plus habitat selection (Ricklefs 2004), we can periods of the year in the plot. The abundance of food resources during the end of the dry season and beginning also predict that the number of core species in a given of the rainy season possibly attracts several species from savanna site will increase with the structural complexity of the vegetation (Mac Arthur & Mac Arthur 1961, other habitats in the landscape to the study plot, leading Karr & Roth 1971). In addition, because the number to an increment of both richness and abundance of of transient species in a site is dependent on the pool of transient species (Martin & Karr 1986). Our study also indicates that several species from species in the landscape (Belmaker 2009) and because gallery forests and wet grasslands are able to fly more than the landscape species richness correlates with landscape heterogeneity (Coyle et al. 2013), we can also predict 300 meters into the upland savannas to use resources, that the richness of transient species in a savanna bird indicating that possibly the intensity of the movements assemblage will increase with the heterogeneity of the between habitats within landscapes dominated by upland savannas are greater than was originally expected landscape in which the savanna patch is located (Coyle (Tubelis et al. 2004). Because South American savannas’ et al. 2013). These predictions can be tested by carefully designed long-term seasonal studies on sites covering an landscapes are heterogeneous landscapes subjected to Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva Bennett, A. F.; Haslem, A.; Cheal, D. C.; Clarke, M. F.; Jones, R.N.; strong environmental variability (Furley 2006), their Koehn, J. D.; Lake, P. S.; Lumsden L. F.; Lunt, I. D.; Mackey, local bird assemblages are composed mostly of species B. G.; Nally, R. M.; Menkhorst, P. W.; New, T. R.; Newell G. R.; that have a generalist feeding habit and a high capacity O’Hara T.; Quinn G. P.; Radford, J. Q.; Robinson, D.; Watson, to exploit resources in the interfaces between open and J. E. M. & Yen, A. L. 2009. Ecological processes: A key element forest physiognomies (Silva 1995, Tubelis et al. 2004). in strategies for nature conservation. Ecological Management & Restoration, 10: 192-199. Understanding the dynamics of the avian assemblages over Blake, J. G. & Loiselle, B.A. 1991. Variation in resource abundance time and space will require focus along the boundaries of affects capture rates of birds in three lowland habitats in Costa the different structural elements of the landscape because Rica. Auk, 108: 114-127. inter-habitat movements may have been underestimated Blendiger, P. G. 2005. Abundance and diversity of small-bird assemblages in the Monte desert, Argentina. Jounal of Arid in most of the studies so far (Dunning et al.1992, Silva Environments, 61: 567-587. et al. 1996). Blondel, J.; Ferry, C. & Frochot, B. 1970. La méthode des indices Our results demonstrated that few core species were ponctuels d’abondance (I.P.A.) ou des relevés d’avifaune par present in an upland savanna site over the entire year and “stations d’écoute”. Alauda, 38: 55-71. Boss, R. L. 2009. Variações espaciais e temporais em comunidades de aves that a considerable flow of individuals and species existed em uma savana amazônica no Estado do Amapá. MSc. Dissertation. across the landscape as a consequence of the resource Macapá: Universidade Federal do Amapá. dynamics. The implications of these findings for the Cavalcanti, R. B. & Joly, C. A. 2002. Biodiversity and conservation design of persistent conservation systems are clear. The priorities in the Cerrado Region, p. 351-367. In: Oliveira, P. S. & conservation of South American savannas requires large Marquis, R. J. (eds). The cerrados of Brazil. New York: Columbia University Press. protected areas covering representative entire landscapes Chesser, R. T. 1994. Migration in South America: an overview of the integrated through large-scale multiple-use corridors austral system. Bird Conservation International, 4: 91-107. designed to maximize the environmental heterogeneity Cintra, R. & Sanaiotti, T. 2005. Fire effects on the composition of of the region and thus ensure the maintenance of the a bird community in an Amazonian savanna (Brazil). Brazilian ecological and evolutionary processes that have shaped Jounal of Biology, 65: 683-695. Cowling, R. M.; Pressey, R. L.; Lombard, A. I.; Desmet, P. G. & their biota (Silva & Bates 2002, Cavalcanti & Joly 2002). Ellis, A. G. 1999. From representation to persistence requirements for a sustainable system of conservation areas in the species rich mediterranean climate desert of southern Africa. Diversity and ACKNOWLEDGMENTS Distributions, 5: 51-71. Coyle, J. R.; Hurlbert, A. H. & White, E. P. 2013. Opposing mechanisms drive richness patterns of core and transient bird We are grateful for all logistical support provided by species. The American Naturalist, 181: 83-90. Embrapa-Amapá and its team managing the research Dunning, J. B.; Danielson, B. J. & Pullian, H. R. 1992. Ecological station. B.F. Xavier assisted us during the fieldwork and J.F. processes that affect that affect populations in complex landscapes. Pacheco helped us with the identification of some species. Oikos, 65: 169-175. Fuller, R. A.; Ladle, R. J.; Whittaker, R. J. & Possingham, H. P. Susana Escudero, Alexandre Aleixo, Sérgio Borges and an 2011. Planning for Persistence in a Changing World, p. 164- anonymous referee kindly reviewed the manuscript. R.B. 189. In Ladle, R. J. & Whittaker, R. J. (eds). Conservation received a scholarship from Conservation International- Biogeography. Oxford: Blackwell Publishing Ltd. Brazil and financial support from CAPES-Program Furley, P. A. 2006. Tropical savannas. Progress in Physical Geography, 30: 105-121. SAUX. J.M.C. Silva received support from CNPq Grinnell, J. 1922. The role of the “accidental”. Auk 39:373-380. (Grants 303824/2007-7 and 472557/2007-5). This Karr, J. R. 1976. Seasonality, resource availability and community paper is based on the dissertation presented by R.B. to diversity in tropical bird communities. The American Naturalist, the Graduate Program in Tropical Biodiversity of the 110: 973-994. Universidade Federal do Amapá, Embrapa-Amapá, IEPA, Karr, J. R. & Freemark, K. E. 1983. Habitat selection and environmental gradients: Dynamics in the ‘stable’ tropics. and Conservation International. Ecological Monographs, 64: 1481-1494. Karr, J. R. & Roth, R. R. 1971. Vegetation structure and avian diversity in several New World areas. The American Naturalist, 105: 423-435. REFERENCES Loiselle, B. A. 1988. Bird abundance and seasonality in a Costa Rican lowland forest canopy. Condor, 90: 761-772. Mac Arthur, R. H. & Mac Arthur, J. W. 1961. On bird species Aleixo, A. & Poletto, F. 2007. Birds of an open vegetation enclave in diversity. Ecology, 42: 594-598. southern Brazilian Amazonia. Wilson Journal of Ornithology, 119: Magurran, A. E. 2007. 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Temporal dynamics of Neotropical Silva, J. M. C. & Bates, J. M. 2002. Biogeograhic patterns and birds with special reference to frugivores in second-growth woods. conservation in the South American Cerrado: a tropical savanna The Wilson Bulletin, 98: 38-60. Hotspot. BioScience, 52: 225-233. Poulin, B.; Lefebvre, G. & McNeil, R. 2001. Variations in bird Silva, N. A. P.; Frizzas, M. R. & Oliveira, C. M. 2011. Seasonality abundance in tropical arid and semi-arid habitats. Ibis, 135: in insect abundance in the “Cerrado” of Goiás State. Revista 432-441. Brasileira de Entomologia, 55: 79-87. Remsen, J. V.; Cadena, C.D.; Jaramillo, A.; Nores, M.; Pacheco Silvério, D. V. & Lenza, L. 2010. Fenologia de plantas lenhosas em J. F.; Pérez-Emán, J.; Robbins, M. B.; Stiles, F. G.; Stotz, D. um cerrado típico no Parque Municipal Bacabal, Nova Xavantina, F. & Zimmer, K. J. 2014. A classification of the bird species of Mato Grosso, Brasil. Biota Neotropica, 10: 205-216. South America. American Ornithologists’ Union. Disponível em Tubelis, D. P. 2007. Mixed-species flocks of birds in the Cerrado, <http://www.museum.lsu.edu/~Remsen/SACCBaseline.html>. South America: A Review. Ornitologia Neotropical, 18: 75-97. Accessed January 2014. Tubelis, D. P. & Calvacanti, R. 2000. A comparison of bird Ricklefs, R. E. 2004. A comprehensive framework for global patterns communities in natural and disturbed non-wetland open in biodiversity. Ecology Letters, 7: 1-15. habitats in the Cerrado’s central region, Brazil. Bird Conservation Sanaiotti, T. M.; Bridgewater, S. & Rattes, J. A. 1997. A floristic International, 10: 331-350. study of the savanna vegetation of the state of Amapá, Brazil, and Tubelis, D. P.; Cowling, A. & Donnelly, C. 2004. Landscape suggestions for its conservation. Boletim do Museu Paraense Emílio supplementation in adjacent savannas and its implications for the Goeldi, série Botânica, 13: 1-27. design of corridors for forest birds in the central Cerrado, Brazil. Sanaiotti, T. & Cintra, R. 2001. Breeding and migration birds Biological Conservation, 118: 353-364. in an Amazonian savanna. Studies on Neotropical Fauna and Watson, J. E.; Grantham, H. S.; Wilson, K. A. & Possingham, H. P. Environment, 36: 23-32. 2011. Systematic conservation planning: Past, present and future, Sick, H. 1997. Ornitologia Brasileira. Rio de Janeiro: Nova Fronteira. p. 136-160. In Ladle, R. J. & Whittaker, R. J. (eds). Conservation Silva, J. M. C. 1995. Birds of the cerrado region, South America. Biogeography. Oxford: Blackwell Publishing Ltd. Steenstrupia, 21: 69-92. Wiens, J. A. 1977. On competition and variable environments. Silva, J. M. C.; Uhl, C. & Murray, G. 1996. Plant succession, American Scientist, 65: 590-597. landscape management, and the ecology of frugivorous birds in Wiens, J. A. 1992. The Ecology of Bird Communities. Cambridge: abandoned pastures. Conservation Biology,10: 491-503. Cambridge University Press. Silva, J. M. C.; Oren, D. C.; Roma, J. C. & Henriques, L. M. P. 1997. Composition and distribution patterns of the avifauna of an Amazonian upland savanna, Amapá, Brazil. Ornithological Monographs, 48: 743-762. Associate Editor: Alexander C. Lees Revista Brasileira de Ornitologia, 22(4), 2014 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ornithology Research Springer Journals

Core and transient species in an Amazonian savanna bird assemblage

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Revista Brasileira de Ornitologia, 22(4), 374-382 ARTICLE December 2014 Core and transient species in an Amazonian savanna bird assemblage 1 1,2,3 Roberta Lúcia Boss and José Maria Cardoso da Silva Programa de Pós-Graduação em Biodiversidade Tropical – PPGBio, Universidade Federal do Amapá (UNIFAP), Departamento de Pós-Graduação, Bloco I, Jardim Marco Zero, CEP 68.902-280, Macapá, AP, Brazil. Conservation International. 2011 Crystal Drive, Suite 500, Arlington, VA 22202, USA. Corresponding author: jmcs0765@gmail.com Received on 16 April 2014. Accepted on 17 September 2014. ABSTRACT: In this paper, we report the number of core and transient bird species in an Amazonian savanna site and assess their ecological differences. We conducted our study at Campo Experimental do Cerrado (CEC) da Embrapa–Amapá, 48 km north of Macapá (0˚2'5" N / 51˚2'2" W), Amapá, Brazil. Forty points were monitored on a monthly basis over the course of one year, using the unlimited-distance point counts in a plot of 360 hectares of well-preserved and relatively homogeneous upland savanna from September 2006 to August 2007. Species were classified in core (recorded in the area in nine or more months), transient (recorded in the area in four or less months) and intermediate (the ones recorded between five and eight months). Species were also classified according to feeding guilds and habitat preferences. Statistical analyses were made to compare core and transient species. We recorded 72 species in the plot, of which 36 were transients, 12 were intermediates, and 22 were core. Core species have higher abundances than transient species. Core species are found mostly in the savanna while transient species also occur in other habitats within the landscape. Both core and transient groups presented well-marked seasonal variation in abundance. Recruitment explains abundance variation for core species, while differences in the availability of food resources in the site explains variation of the abundance in transient species. We predict that plot-level (not more than 500 hectares) bird assemblages in South American savannas will be composed of a small number of abundant and habitat-restricted species that occupy the site almost year round, combined with a high number of low abundant transient species that are habitat generalists and use the plot only during limited periods of their annual life cycle. KEYWORDS: conservation biogeography, landscape dynamics, local assemblages, South America, tropical savannas. INTRODUCTION patches within a landscape, landscapes within a region, and entire regions (Wiens 1992). Therefore, a thorough The most common approach to biodiversity conservation understanding of the major patterns of biological is to identify and protect natural features such as movements from the local to the regional scales is a critical step towards the design of conservation systems ecosystems and threatened species, whose distributions can be mapped and targeted through conservation that maintain ecological flows and enable the resilience of management activities (Watson et al. 2011). While such populations against the effects of global changes (Watson an approach is important, the conservation of species and et al. 2011). ecosystems cannot be achieved unless the ecological and One concept that has not yet been fully explored in conservation biogeography is the important distinction evolutionary processes that sustain them are understood and maintained (Cowling et al. 1999, Fuller et al. 2001). between core and transient species (Grinnell 1922, One of the most important ecological processes to be Magurran & Henderson 2003). Core species are those documented for any conservation plan is the movement that persist in a habitat patch (or site) through time of organisms (Bennett et al. 2009). Organisms move at and transient species are those that occur intermittently in a habitat patch (or site) as a result of dispersal from different scales and for many purposes: to find food and shelter, for social interactions, to track resources that vary surrounding habitats or regions (Coyle et al. 2013). irregularly over space and time, for seasonal migration, Core and transient species usually differ in their and to disperse and establish in new locations (Bennett ecological requirements as well as their abundance et al. 2009). patterns (Magurran & Henderson 2003, Magurran 2007). Core species are predicted to be locally abundant, Movements of populations and species link habitat Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva habitat-restricted, and follow a lognormal abundance of Macapá (0˚2'5" N / 51˚2'2" W), Amapá, Brazil. The distribution, whereas transient species are predicted to be CEC protects 796 ha of well-managed South American rare, habitat generalist, and follow the log series abundance upland savannas. distribution model (Magurran 2007, Belmaker 2009). The CEC landscape has four major habitat types: Core and transient species arise in local assemblages upland savannas, wet grasslands, gallery forests, and through different mechanisms. Core species are influenced anthropic areas. Upland savannas compose the matrix mostly by local-scale factors that allow the persistence of of the landscape. They occupy nutrient-poor soils, with the species in a habitat patch, whereas transient species strong to medium acidity, low in organic matter and with are influenced mostly by regional factors that govern the frequent iron concretions. Savanna vegetation is low, with number of species that potentially could move into the few (usually no more than 100 per hectare) short (up to 4-6 habitat patch from the surrounding landscape (Coyle et m) trees (Silva et al. 2011). The grass Trachypogon plumosus al. 2013). and the sedge Bulbostylis spadicea dominate the ground Tropical avian assemblages are well known to exhibit (Sanaiotti et al. 1997). Wet grasslands are found in narrow temporal and spatial variation in their species’ richness valleys where soils are shallow and permanently inundated. and abundance at the site scale (Karr 1976, Loiselle 1988, Narrow belts of Mauritia martiniana palms can be used Poulin et al. 2001). These variations are usually correlated to identify the position of these wet grasslands. Gallery with the availability of fruit, flowers, seeds, and insects forests are linear formations (usually 15-25 m tall) that are that are, in turn, impacted by seasonal changes in rainfall restricted to wide valleys formed by the permanent streams and associated soil moisture cycles (Karr 1976). In regions that cut the landscape. Tree species such as Jacaranda with long dry seasons, resource availability is low during copaia and Symphonia globulifera as well as palms such the dry season and high during the wet season (Poulin et as Euterpe oleracea are the most common species in these al. 2001, Blendiger 2005). Resource scarcity during the gallery forests. Anthropic areas used for agriculture and dry season can create ecological ‘crunches’ or ‘bottlenecks’ agro-forestry experiments are small in size and are located that limit species’ abundances and biotic interactions and near the CEC’s housing and laboratory facilities. processes (Wiens 1977, 1992). The climate is hot (average temperature of 27 C) Temporal variance in abundances of tropical birds and humid (average relative humidity of 81%). Average at the site scale can be caused by population recruitment annual precipitation from 1961 to 1990 is around 2,700 and mortality (Blake & Loiselle 1991) but short-term mm with a well-marked dry season from August to (e.g., < 3 months) variations in abundance can be caused November, when total monthly rainfall is below 50 mm. by movements of individuals into or out of a site (Martin & Karr 1986). Movements by individuals have been suggested as an important cause of the variance in tropical METHODS bird abundances (Martin & Karr 1986, Silva et al. 2011), We set 40 sampling points within a plot of 360 hectares but very few studies have evaluated the contribution of core and transient species on the richness and abundance of local of well-protected and relatively homogeneous upland assemblages (Karr & Freemark 1983, Poulin et al. 2001). savanna located at 0˚2'5" N / 51˚2'2" W. We set points Here we report for the first time the numbers of core at least 300 m apart to maintain sample independence and transient bird species in a 360-ha plot of relatively and at least 300 m from any habitat edge. We used this distance because Tubelis et al. (2004) found that forest uniform Amazonian upland savanna. We assessed the variation of the bird assemblages in this plot over a one- birds do not move more than 200 m within the savannas year period. Then we identified the core and transient in central Brazil. Our goal with this approach was to species and evaluated how these two groups of species sample the avifauna in the most homogenous savanna differ in their species richness, abundance, feeding area possible, avoiding the influence of other habitats in the landscape as well as edges or transitional vegetation. habitats, and habitat use. In addition, we evaluated how species richness and abundance of the core and transient To study the bird assemblages within the plot, we groups vary over time. We used our findings to propose used the unlimited-distance point count method (Blondel some general predictions on the contribution of the core et al. 1970). For 10 min we noted all birds seen or heard and transient species for site-level bird assemblages in in each point. For species that travel in groups, when we heard but did not see the birds, we assumed that the group South American upland savannas. size was the average from when we did see and count a group of the same species. We noted the species seen while STUDY AREA the observer walked between points, but these sightings were not included in the quantitative analyses. The order Our field research was conducted at Campo Experimental of point sampling changed every month to eliminate any do Cerrado (CEC) of Embrapa–Amapá, 48 km north Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva bias. RB conducted all monthly censuses from September monthly in the plot. We calculated the monthly abundance 2006 to August 2007, always between 06h00 and 08h00. for each species, summing up its number of detections in She used a Pentax 8X40 binocular and a Sony TCD5 PRO all 40 points (Maron et al. 2005). By summing up monthly II tape-recorder with a Sennheiser ME67 microphone. abundances of species, we were able to calculate monthly Following Coyle et al. (2013), we classified each abundances for the entire core and transient species groups species as core if it was present in the plot for at least as well as the annual abundance for each species. two-thirds of the period of time that was surveyed (nine We used the Kolmogorov-Smirnov test to test if months or more) and transient if it was present in no more the species abundance distributions of core and transient than one-third of the surveyed period (four months or groups were different. We used the Median Test to less), regardless of whether the species was recorded or not determine if species classified as core and transient breeding in the plot. Intermediate are those species that differed in their annual abundances. We used the G-Test were neither classified as core nor as transients. We used to evaluate if proportions of core and transient species this pragmatic approach to minimize misclassification at among feeding guilds as well as habitat use categories the expense of excluding a small fraction of intermediate were different. We used the G-Test for goodness-of-fit to species from analyses. a uniform distribution to determine whether abundances Species were also classified as habitat-restricted if and species richness of core and transient groups showed they were recorded in the landscape only in the upland any variation over time. We used Biostat 5.0 (Ayres et al. savannas; they were classified as habitat non-restricted 2007) for all statistical analyses. Latin and English names when they were also found in other natural habitats of the bird species follow Remsen et al. (2014). within the landscape. Our classification is based on qualitative data collected by RB during our study period in other habitats as well as the information reported by RESULTS Silva et al. (1997) for our study area. We recorded 72 species in the plot, corresponding to We classified bird species into six major guilds based on their diet. These feeding guilds are: (RS) 37.2% of all species recorded in the entire site until raptors + scavengers (including families of Cathartidae, now (Boss 2009). The presence of species in the plot Accipitridae and Falconidae); (IN) insectivores; (IF) over the year follows the expected bimodal pattern insectivore-frugivore; (FG) frugivore-granivore; (GR) (Figure 1) with 36 transients, 12 intermediates and 22 core species. Intermediate species were Colinus cristatus, granivore; and (NE) nectarivore. We used personal field experience and literature (Silva 1995, Silva et al. 1997, Columbina passerina, Thalurania furcata, Amazilia Sick 1997) to classify species into feeding guilds. fimbriata, Heliactin bilophus, Caracara cheriway, Milvago We calculated the monthly richness for core and chimachima, Amazona ochrocephala, Amazona amazonica, transient groups as well as for each feeding guild by Myiarchus ferox, Cyclarhis gujanensis, Piranga flava, Thraupis palmarum, and Sporophila plumbea. summing up the number of species of each group recorded FIGURE 1. Temporal occupancy of bird species in the 360-ha plot of upland savanna in Amapá, Brazil. The temporal occupancy of a species is the number of surveyed months in which the species was recorded as present. Core species were those recorded in nine or more months and transient species were those recorded in four our less months. Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva The abundance distribution patterns of core and different (G = 3.97, df = 5, p < 0.55). In contrast, core transient groups (Figure 2) are significantly different (KS, and transient species are very different in their habitat use Dmax = 0.91, p < 0.001). Core species are significantly (G = 27.2, df = 1, p < 0.0001) because most of the core more abundant than transient species (Median Test,  = species (68.2%) are found only in savannas, whereas most 36.6, p < 0.001). The frequencies of core and transient of the transient species (94.4%) occur in two or more species among the five guild categories (Figure 3) are not habitats (Table 1). FIGURE 2. Abundance distributions patterns of core (black) and transient (white) bird species recorded in a 360-ha plot of an upland savanna in Amapá, Brazil. FIGURE 3. Numbers of core (black) and transient (white) species among five feeding guilds recorded in a 360-ha plot of an upland savanna in Amapá, Brazil. Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva TABLE 1. List of bird species recorded during one year in a 360 hectares of savanna upland at Campo Experimental do Cerrado, Embrapa-Amapá, Amapá, Brazil. Core species are those found during at least nine months while transient species were reported in less than four months. Feeding guilds are: RS (raptors + scavangers), IN (insectivores), IF (insectivore-frugivore), FG (frugivore-granivore), GR (granivore), and NE (nectarivore). Habitat categories are: (1) restricted to upland savanna; (2) recorded in other habitats in the broad landscape. Annual abundance is the total number of detections of the species over one year. Feeding Annual Species English Name Habitat Guild Abundance CORE SPECIES Geranoaetus albicaudatus White-tailed Hawk RS 2 27 Patagioenas cayennensis Pale-vented Pigeon FG 2 129 Zenaida auriculata Eared Dove FG 1 103 Aratinga aurea Peach-fronted Parakeet FG 1 161 Eupetomena macroura Swallow-tailed Hummingbird NE 2 38 Colaptes campestris Campo Flicker FI 1 23 Lepidocolaptes angustirostris Narrow-billed Woodcreeper IN 1 153 Elaenia flavogaster Yellow-bellied Elaenia FI 2 331 Elaenia chiriquensis Lesser Elaenia FI 1 185 Suiriri suiriri Suiriri Flycatcher FI 1 332 Xolmis cinereus Gray Monjita IN 1 327 Tyrannus albogularis White-throated Kingbird FI 1 131 Tyrannus melancholicus Tropical Kingbird FI 2 102 Tyrannus savana Fork-tailed Flycatcher FI 1 816 Myiarchus swainsoni Swainson’s Flycatcher FI 1 256 Troglodytes aedon House Wren IN 2 38 Mimus saturninus Chalk-browed Mockingbird FI 2 134 Neothraupis fasciata White-banded Tanager FI 1 552 Cypsnagra hirundinacea White-rumped Tanager FI 1 486 Emberizoides herbicola Wedge-tailed Grass-Finch GR 1 273 Ammodramus humeralis Grassland Sparrow GR 1 554 Sturnella magna Eastern Meadowlark GR 1 56 TRANSIENT SPECIES Theristicus caudatus Buff-necked Ibis IN 2 6 Cathartes aura Turkey Vulture RS 2 1 Buteogallus meridionalis Savanna Hawk RS 2 2 Rupornis magnirostris Roadside Hawk RS 2 6 Burhinus bistriatus Double-striped Thick-knee IN 2 6 Columbina talpacoti Ruddy Ground-Dove GR 2 1 Patagioenas speciosa Scaled Pigeon FG 2 1 Leptotila verreauxi White-tipped Dove FG 2 6 Guira guira Guira Cuckoo IN 2 6 Chordeiles pusillus Least Nighthawk IN 2 4 Phaethornis ruber Reddish Hermit NE 2 3 Phaethornis superciliosus Long-tailed Hermit NE 2 3 Chrysolampis mosquitus Ruby-topaz Hummingbird NE 1 12 Anthracothorax nigricollis Black-throated Mango NE 2 3 Campephilus melanoleucos Crimson-crested Woodpecker FI 2 4 Herpetotheres cachinnans Laughing Falcon RS 2 5 Falco femoralis Aplomado Falcon RS 2 4 Forpus passerinus Green-rumped Parrotlet FG 2 2 Thamnophilus doliatus Barred Antshrike IN 2 1 Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva Feeding Annual Species English Name Habitat Guild Abundance Formicivora rufa Rusty-backed Antwren IN 2 2 Synallaxis albescens Pale-breasted Spinetail IN 2 5 Phaeomyias murina Mouse-colored Tyrannulet FI 2 4 Euscarthmus rufomarginatus Rufous-sided Pygmy-Tyrant IN 1 1 Tolmomyias flaviventris Yellow-breasted Flycatcher FI 2 1 Megarynchus pitangua Boat-billed Flycatcher FI 2 7 Myiarchus tyrannulus Brown-crested Flycatcher FI 2 5 Vireo olivaceus Red-eyed Vireo FI 2 2 Hylophilus pectoralis Ashy-headed Greenlet FI 2 15 Turdus leucomelas Pale-breasted Thrush FI 2 10 Schistochlamys melanopis Black-faced Tanager FI 2 2 Ramphocelus carbo Silver-beaked Tanager FI 2 3 Volatinia jacarina Blue-black Grassquit GR 2 2 Oryzoborus angolensis Chestnut-bellied Seed-Finch GR 2 3 Molothrus bonariensis Shiny Cowbird FI 2 4 Sturnella militaris Red-breasted Blackbird GR 2 3 Euphonia chlorotica Purple-throated Euphonia FI 2 3 Core species represented most (90.6%) of all seasonal variation in abundance was found for both core detections over the year (Figure 4b). Monthly species (G = 309.5, df = 11, p < 0.0001) and transient (G = 26.25, richness of core (G = 6.36, df = 11, p = 0.84) and transient df = 11, p < 0.0001) groups (Figure 4b). Both groups (G = 0.32, df = 11, p = 0.32) groups did not differ from presented their highest abundance values from October a uniform distribution (Figure 4a). However, significant to February, with a clear peak in November (Figure 4b). FIGURE 4. Monthly variations in the species richness (a) and total number of detections (b) of core (black) and transient (white) bird species recorded in a 360-ha plot of an upland savanna in Amapá, Brazil. Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva DISCUSSION array of landscapes that compose the South American savannas. Populations of both core and transient species We recorded that only 22 species (30.5%) are core, with most of the species being transients. However, core exhibited marked seasonality and followed roughly species represented 90.6% of all detections in one year the same variation pattern. Overall, bird abundance is and are on average more abundant than transient species. high from October to February and low from March to September. The five months in which bird abundance Therefore, although species’ richness in the site is mostly is higher coincides with the last two months of the dominated by transient species, abundance is dominated by core species. dry season and the first three months of the rainy one. Core species are mostly restricted to savannas, while Although fruits and insects are available year-round in transient species occupy other habitats in the landscape. tropical savannas (Silvério & Lenza 2010, Silva et al. 2011), the availability of these resources peaks during the This finding is supported by findings in other tropical transition between dry and rainy seasons (Sanaiotti & bird assemblages. For instance, Poulin et al. (2001) found that transient birds represented a large portion of the Cintra 2001). It is also during this period that most of the local assemblages of tropical arid and semi-arid habitats species breed in the plot (Boss 2009), a pattern that has in northern Venezuela. Martin and Karr (1986) suggested been observed in other tropical savannas as well (Sanaiotti & Cintra 2001, Silvério & Lenza 2010). that transients are an important component of tropical The overlap between breeding period and higher forest bird assemblages, but they did not present their proportions. abundance indicates that recruitment is the simplest The core species recorded in our research site are explanation for the increase of the detections of also found frequently in other savannas in central South core species at the local level (Martin & Karr 1986). However, there are six species (Elaenia flavogaster, Elaenia America and some of them are amongst the most abundant chiriquensis, Tyrannus albogularis, Tyrannus melancholicus, species (Silva 1995, Sick 1997, Tubelis & Calvacanti 2000, Cintra & Sanaiotti 2005, Aleixo & Poletto 2007). Tyrannus savanna, and Myiarchus swainsoni) that have In addition, five core species (Lepidocolaptes angustirostris, populations that breed in central South America and Suiriri suiriri, Mimus saturninus, Neothraupis fasciata, and are known to migrate northwards during the austral migration (Chesser 1994). Therefore, it is also possible Cypsnagra hirundinacea) are considered as nuclear species that individuals coming from migratory populations of in the mixed-species flocks that are found in most of the South American upland savannas (Tubelis 2007). those species and stopping by the site during some days or Combining our findings with general theories on weeks may also contribute to the variation in abundance bird assemblages, we can make some general predictions of these core species. Finally, core species might have been more abundant during the breeding period because they about the proportions of core and transient species in were more vocal and consequently their detectability other South American upland savannas. At the local scale (up to 500 ha), we predict that savanna bird assemblages increased. More studies are required to evaluate these will be composed of a small number of abundant and hypotheses. habitat-restricted species that occupy the site almost year- Because transient species are expected to track resources across the landscape more frequently than round, combined with a high number of low abundant core species, the variation in the abundance observed transient species that are habitat generalists and use the site only during some periods of their annual life cycle. for transient species can be explained by the high Because local diversity is a consequence of regional concentration of insects, fruits, and flowers during some diversity plus habitat selection (Ricklefs 2004), we can periods of the year in the plot. The abundance of food resources during the end of the dry season and beginning also predict that the number of core species in a given of the rainy season possibly attracts several species from savanna site will increase with the structural complexity of the vegetation (Mac Arthur & Mac Arthur 1961, other habitats in the landscape to the study plot, leading Karr & Roth 1971). In addition, because the number to an increment of both richness and abundance of of transient species in a site is dependent on the pool of transient species (Martin & Karr 1986). Our study also indicates that several species from species in the landscape (Belmaker 2009) and because gallery forests and wet grasslands are able to fly more than the landscape species richness correlates with landscape heterogeneity (Coyle et al. 2013), we can also predict 300 meters into the upland savannas to use resources, that the richness of transient species in a savanna bird indicating that possibly the intensity of the movements assemblage will increase with the heterogeneity of the between habitats within landscapes dominated by upland savannas are greater than was originally expected landscape in which the savanna patch is located (Coyle (Tubelis et al. 2004). Because South American savannas’ et al. 2013). These predictions can be tested by carefully designed long-term seasonal studies on sites covering an landscapes are heterogeneous landscapes subjected to Revista Brasileira de Ornitologia, 22(4), 2014 Core and transient species in an Amazonian savanna bird assemblage Roberta Lúcia Boss and José Maria Cardoso da Silva Bennett, A. F.; Haslem, A.; Cheal, D. C.; Clarke, M. F.; Jones, R.N.; strong environmental variability (Furley 2006), their Koehn, J. D.; Lake, P. S.; Lumsden L. F.; Lunt, I. D.; Mackey, local bird assemblages are composed mostly of species B. G.; Nally, R. M.; Menkhorst, P. W.; New, T. R.; Newell G. R.; that have a generalist feeding habit and a high capacity O’Hara T.; Quinn G. P.; Radford, J. Q.; Robinson, D.; Watson, to exploit resources in the interfaces between open and J. E. M. & Yen, A. L. 2009. Ecological processes: A key element forest physiognomies (Silva 1995, Tubelis et al. 2004). in strategies for nature conservation. Ecological Management & Restoration, 10: 192-199. Understanding the dynamics of the avian assemblages over Blake, J. G. & Loiselle, B.A. 1991. Variation in resource abundance time and space will require focus along the boundaries of affects capture rates of birds in three lowland habitats in Costa the different structural elements of the landscape because Rica. Auk, 108: 114-127. inter-habitat movements may have been underestimated Blendiger, P. G. 2005. Abundance and diversity of small-bird assemblages in the Monte desert, Argentina. Jounal of Arid in most of the studies so far (Dunning et al.1992, Silva Environments, 61: 567-587. et al. 1996). Blondel, J.; Ferry, C. & Frochot, B. 1970. La méthode des indices Our results demonstrated that few core species were ponctuels d’abondance (I.P.A.) ou des relevés d’avifaune par present in an upland savanna site over the entire year and “stations d’écoute”. Alauda, 38: 55-71. Boss, R. L. 2009. Variações espaciais e temporais em comunidades de aves that a considerable flow of individuals and species existed em uma savana amazônica no Estado do Amapá. MSc. Dissertation. across the landscape as a consequence of the resource Macapá: Universidade Federal do Amapá. dynamics. The implications of these findings for the Cavalcanti, R. B. & Joly, C. A. 2002. Biodiversity and conservation design of persistent conservation systems are clear. The priorities in the Cerrado Region, p. 351-367. In: Oliveira, P. S. & conservation of South American savannas requires large Marquis, R. J. (eds). The cerrados of Brazil. New York: Columbia University Press. protected areas covering representative entire landscapes Chesser, R. T. 1994. Migration in South America: an overview of the integrated through large-scale multiple-use corridors austral system. Bird Conservation International, 4: 91-107. designed to maximize the environmental heterogeneity Cintra, R. & Sanaiotti, T. 2005. Fire effects on the composition of of the region and thus ensure the maintenance of the a bird community in an Amazonian savanna (Brazil). Brazilian ecological and evolutionary processes that have shaped Jounal of Biology, 65: 683-695. Cowling, R. M.; Pressey, R. L.; Lombard, A. I.; Desmet, P. G. & their biota (Silva & Bates 2002, Cavalcanti & Joly 2002). Ellis, A. G. 1999. From representation to persistence requirements for a sustainable system of conservation areas in the species rich mediterranean climate desert of southern Africa. Diversity and ACKNOWLEDGMENTS Distributions, 5: 51-71. Coyle, J. R.; Hurlbert, A. H. & White, E. P. 2013. Opposing mechanisms drive richness patterns of core and transient bird We are grateful for all logistical support provided by species. The American Naturalist, 181: 83-90. Embrapa-Amapá and its team managing the research Dunning, J. B.; Danielson, B. J. & Pullian, H. R. 1992. Ecological station. B.F. Xavier assisted us during the fieldwork and J.F. processes that affect that affect populations in complex landscapes. Pacheco helped us with the identification of some species. Oikos, 65: 169-175. Fuller, R. A.; Ladle, R. J.; Whittaker, R. J. & Possingham, H. P. Susana Escudero, Alexandre Aleixo, Sérgio Borges and an 2011. Planning for Persistence in a Changing World, p. 164- anonymous referee kindly reviewed the manuscript. R.B. 189. In Ladle, R. J. & Whittaker, R. J. (eds). Conservation received a scholarship from Conservation International- Biogeography. Oxford: Blackwell Publishing Ltd. Brazil and financial support from CAPES-Program Furley, P. A. 2006. Tropical savannas. Progress in Physical Geography, 30: 105-121. SAUX. J.M.C. Silva received support from CNPq Grinnell, J. 1922. The role of the “accidental”. Auk 39:373-380. (Grants 303824/2007-7 and 472557/2007-5). This Karr, J. R. 1976. 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Journal

Ornithology ResearchSpringer Journals

Published: Dec 1, 2014

Keywords: conservation biogeography; landscape dynamics; local assemblages; South America; tropical savannas

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