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Revista Brasileira de Ornitologia 26(4): 240–250. ARTICLE December 2018 Demography of the Neotropical austral migrant Elaenia albiceps chilensis (Tyrannidae) on its breeding grounds: climate and food off er eff ects 1 1 2 2,3 Paula Marcela Presti , Guillermo César Amico , Susana Patricia Bravo & Víctor Rodolfo Cueto Laboratorio Ecotono. Instituto de Investigaciones en Biodiversidad y Medioambiente (INIBIOMA), CONICET - Centro Regional Universitario Bariloche, Universidad Nacional del Comahue. Quintral 1250, Bariloche, Argentina. Centro de Investigaciones Esquel de Montaña y Estepa Patagónica (CIEMEP) - CONICET y Universidad Nacional de la Patagonia “San Juan Bosco”. Esquel, Argentina. Corresponding author: firstname.lastname@example.org Received on 04 July 2018. Accepted on 07 December 2018. ABSTRACT: Th e White-crested Elaenia (Elaenia albiceps chilensis) is a Neotropical austral migrant that breeds in Patagonian forests and overwinter in South America tropics. We investigated White-crested Elaenia demography and the environmental conditions the specie is subjected at the northwest of Patagonia as a fi rst attempt to elucidate its population dynamic. We studied the species abundance, individuals' body condition, survival, productivity of young and site fi delity according to changes in rainfall patterns and food supply, during three breeding seasons (2009 to 2012). We color banded 361 adult and juvenile White-crested Elaenias. During the fi rst studied season, precipitations were remarkably above the mean and ripe fruit supply was lower than in the other seasons, whereas the abundance of arthropods remained similar along the study. Th e species abundance decreased 50% across the study, while adult apparent survival rate, the number of breeding females, young productivity and site fi delity were 50% lower in the fi rst season in comparison to the following seasons. Females presented lower body condition at arrival in the fi rst two studied periods. Site fi delity diminished after unfavorable breeding season (i.e. low young productivity and fruit supply), especially for males, although they were more faithful than females and had a slightly higher apparent survival rate. Our results suggest that White-crested Elaenia demography is aff ected by changes in its main food resource supply (fl eshy fruits) during the breeding season, indicating that this part of the annual cycle could be fundamental for its population dynamic. KEY-WORDS: body condition, breeding season, frugivory, Patagonian forest, population dynamic, site fi delity, survival, White- crested Elaenia. INTRODUCTION greater parental care) that is compensated with higher adult survival (see review in Martin 1996 & Russell et Th e study of demography and the factors that regulate al. 2004). Th roughout South America information is contrasting, with some studies indicating a higher adult populations are among the most important approaches survival from tropical to temperate latitudes (Martin to understand population trends. Birds demographic (abundance, survival and reproductive success) and 1996) and others pointing to a lack of such trend (Karr behavioral features (site fi delity, space use and dispersal) et al. 1990, França & Marini 2010), or even to variations are regulated by both intrinsic and extrinsic factors (e.g. among phylogeny and regions for tropical birds (Blake & Loiselle 2013). Although this trend has been mainly physical and nutritional traits of individuals and food or suggested for resident species, it also applies to species weather variations, respectively; Martin 1996, Newton 1998). Th ese factors interact with each other in positive that perform regional or long distance migrations (Martin and negative ways, and their implications in a population 1996, Russell et al. 2004, Blake & Loiselle 2013). are expected to vary according to the species life history Among behavioral features site fi delity is one that can be aff ected by species life history as well as by (Newton 1998). environmental quality, conditioning migratory birds' Among demographic features, diff erences in life history between North and South Hemisphere birds abundance (Holmes & Sherry 1992). Site fi delity will be suggest that Southern hemisphere species have lower favorable if the area allows individuals to pair a previous reproductive success (as indicated by smaller clutch sizes, successful partner or be more competitive because of prior territory ownership, as well as if they are able to higher nest predation rates, more nesting attempts and Revista Brasileira de Ornitologia 26(4): 2018 Demography of the migratory White-crested Elaenia Presti et al. identify the distribution and availability of resources as abundance (Brown et al. 2007), diet (Grigera 1982, food, refugees or nestling sites (Newton 2008). Contrary, Brown et al. 2007), foraging behavior (Chust et al. 2012, site fi delity will be disadvantageous for migrants if the Cueto et al. 2016a), functional role (Mazia et al. 2009, site diminishes in quality or represents an unpredictable Cavallero et al. 2013, Bravo et al. 2015), and migration habitat (Switzer 1993). In addition, site fi delity can routes (Marini & Cavalcanti 1990, Capllonch et al. 2011, diff er according to sex, age and competitive condition, Cueto et al. 2016b, Bravo et al. 2017), but its survival has generating diff erences in dispersal and habitat use patterns never been studied, as well as the relationship between its (Latta & Faaborg 2002). demographic parameters with environmental factors. Environmental factors are relevant causes of Th e aim of our study was to analyze the demography demographic variation in resident and migratory bird of the White-crested Elaenia through the analysis of populations. Food limitation can be a fundamental changes in abundance, productivity of young, survival, factor aff ecting body condition and, consequently, site fi delity and body condition, related with food off er breeding success and survival (Martin 1987). Factors and precipitation variability during the breeding season. such as precipitation, habitat quality and resource spatial We aim to improve our knowledge about the factors distribution, will aff ect food abundance and availability, aff ecting its population at temperate latitudes of South aff ecting diff erently the population (Wilson et al. America. 2011). Th e eff ects of those environmental factors on the population can be quantifi ed by measuring diff erent METHODS external variables that indicates habitat quality (Benson & Bednarz 2010) as well as estimating the individuals' body condition by their body mass or fat deposits (Labocha Study site & Hayes 2012). On the other hand, unusual weather conditions, sometimes related with periodic climatic We conducted our study from October to March of three consecutive breeding seasons (2009/10, 2010/11 events, aff ect the sizes of bird populations (Sillett et al. 2000). Some studies suggest that southern temperate and 2011/12) in a Patagonian mixed forest of Nothofagus birds' survival either is reduced after periods with unusual dombeyi (Coihue) and Austrocedrus chilensis (Ciprés o o precipitation, rainy (Th omson & Estades 2012) or dry de la Cordillera) at Steff en Lake (41 30'S; 71 35'W, (Sagario 2010). Th erefore, it is expected that climate 550 m a.s.l). Th is is a representative and well protected area of the temperate forest of southern South America variations also aff ect migratory birds' demography at southern South America. inside Nahuel Huapi National Park, at the northwest All these theories about the factors controlling of Argentinean Patagonia (Mermoz et al. 2009). At the population dynamics remain slightly evaluated in study site, the forest is characterized by a canopy above 20 passerine birds of South America, been mainly studied m of height and an understory (< 10 m) with fl eshy fruit shrubs, mainly Aristotelia chilensis (Maqui) and Schinus in tropical species (Karr et al. 1990, Martin et al. 2000, Parker et al. 2006, Blake & Loiselle 2013). Th us, there patagonicus (Laura). is still little information for temperate latitudes of South Th e climate is cold-temperate with precipitations America and migratory birds of the Neotropical austral concentrated in autumn and winter (April–September). system, despite some advances for diff erent passerine Annual mean precipitation in the study area is 1264 mm (for 1993–2012 period) and annual mean temperature is families in survival (Willson & Pendleton 2008, Sagario 2010, Th omson & Estades 2012), site fi delity (Jahn et al. 9.1 C (for 2000–2012 period), with a maximum mean o o 2009) and life history traits (e.g. parental care, Llambías temperature of 15 C (January) and a minimum of 3.5 C et al. 2015). (July) (data from Station N 2300 “Lago Steff en”, Red Th e White-crested Elaenia (Elaenia albiceps Hidrológica Nacional, Subsecretaría de Recursos Hídricos de la Nación). chilensis) is the most abundant Neotropical austral migrant passerine at the Patagonian forest (Grigera et al. We established two permanent plots on the northern 1994, Ippi et al. 2009). Th is tyrant fl ycatcher arrives up margin of the lake, separated 1000 m by a small bay. Th e to mid-October to breed and start its migration to the plots area were 4 ha (Plot 1) and 7 ha (Plot 2) and we tropics between mid-February and March (Fitzpatrick gridded them in 25 x 25 m squares, for bird and food resource surveys (68 squares for P1 and 109 squares for 2004, Bravo et al. 2017). It is a frugivorous-insectivorous species with an important role as the main disperser of P2). Both plots had the same vegetation composition and seed of endemic plants of the Patagonian forest (Armesto structure, representing a well-preserved mixed forest with et al. 1987, Amico & Aizen 2005) and as a controller three types of patches: open areas, young forest and old of herbivorous insects of Nothofagus trees (Mazia et forest (see Bravo et al. 2015), therefore we pooled the data for the analysis. al. 2009). Th ere are studies of White-crested Elaenia Revista Brasileira de Ornitologia 26(4): 2018 Demography of the migratory White-crested Elaenia Presti et al. Bird surveys were randomly placed, tided horizontally on an exposed branch of a shrub or tree, two meters above the ground, Scientifi c nomenclature and common name follow operated for an average of 15 days per month depending the recommendation by the South American Checklist on weather conditions. After the survey, we counted the Committee (Remsen-Jr. et al. 2018). To get demographic number of captured individuals at each trap. data of the White-crested Elaenia we used capture-mark- We evaluated fruit production of Aristotelia chilensis recapture method. We captured birds using 24 mist nets (Elaeocarpaceae), the main fl eshy-fruited shrub consumed of 12 m × 3 m, 38 mm mesh size (12 per plot). Nets were by White-crested Elaenia at the study site (Bravo et al. distributed along the area separated at least 50 m from 2015). We randomly selected 10 individuals in each plot each other, arranged in fi xed places at every capture session and counted the number of ripe fruits every 15 days from to register the mist net of every captured and recaptured November to March. We used a semi-quantitative index bird in order to study site fi delity. During every breeding from 0 to 5 (Saracco et al. 2004), where 0: no fruits, 1: season, nets were opened for two consecutive days per 1–10 fruits, 2: 11–50 fruits, 3: 51–100 fruits, 4: 101–500 month in both plots (in similar month dates along every fruits, and 5: 501–1000 fruits. session), since sunrise and for at least fi ve hours. Every captured bird was banded with numbered Precipitation patterns aluminum and a unique combination of color bands. We weighted birds to the nearest 0.1 g with a 30 g spring To assess the potential eff ect of climate on the White- scale in every capture occasion and measured their tarsus crested Elaenia's demography and their food abundance, length to estimate their arrival and departure body we analyzed the variations on precipitation at the study condition (details below). We aged individuals by the site. Precipitation data were available from the weather presence (adult) or lack (juvenile) of the characteristic station N° 2300 - “Lago Steff en” (Red Hidrológica white crown (Schulenberg 2009). To determine the Nacional, Subsecretaría de Recursos Hídricos de la Nación), sex and reproductive status of birds, we registered the for the period 1993–2012. We considered wet or dry development of the incubation patch (females) and months to be those with monthly rainfall above or below cloacal protuberance (males) following Ralph et al. one standard deviation of the average monthly rainfall for (1993), and used the diff erences in wing and tail length a 20-years period of climatic data (Ropelewski & Folland between females and males for sexing non-breeding birds 2000). following Cueto et al. (2015). When an individual did not match with those criteria of sexing it was classifi ed as Data analysis “unsexed adult”. From November to February, after net sampling, Bird abundance and productivity of young: In order to we surveyed each plot to relocate those banded birds compare bird abundance among breeding seasons, that remained at the study site to complete their capture we calculated the season capture rate for each bird history for survival and site fi delity estimates. Searches category (female and male in breeding and non-breeding were carried out systematically by walking through the conditions; and juveniles) as the total number of captures study area during fi ve hours after sunrise and three hours per 100 h of net eff ort. We used the data from November before sunset, at least once per day for a mean of 10 days to February, and excluded from the analysis birds captured or until no new banded birds were seen after searching in October and March that did not remain in the study for 10 h. We registered the identity of each banded bird site in the summer (i.e. those individuals that were just found and its location on the grid. Th e position of every passing through). Juveniles capture rate in every season relocated bird was recorded estimating the distance and was used as a measure of productivity of young (du Feu angle respecting a reference point of the grid, using a & McMeeking 1991). compass. We also recorded eventual encounters while Relative body condition: We generated an index collecting environmental data. of body condition using the residuals of the linear regression between every bird tarsus length and their Arthropods and fruit abundance body mass (Labocha & Hayes 2012). Positive residuals indicated that birds were in relatively good condition, Arthropod abundance was estimated using blue sticky i.e. they were heavy for their size, and negative residuals traps (Young 2005). We used blue because it is neutral indicated relatively poorer condition. We used a two-way in terms of attracting or repelling insects (Ausden & ANOVA to examine the diff erences of body condition Drake 2006). Each trap was of 10 × 20 cm, attached between breeding seasons, arrival from spring migration inside a plastic transparent cylinder of 15 cm diameter (October–November) and departure from the breeding to prevent that leaves, branches and rain aff ect its capture study site (February–March) of females and males. Given effi ciency. We used 28 blue sticky traps (14 per plot) that the unequal sample sizes, we used Type III method to Revista Brasileira de Ornitologia 26(4): 2018 Demography of the migratory White-crested Elaenia Presti et al. compute the sum of squares (Shaw & Mitchell-Olds for all returning White-crested Elaenias individuals and 1993). Comparisons of treatments after ANOVA were by sexes, through a diff erence of proportions test (Agresti performed using the Kramer modifi cation of Tukey's test 2002). We used a Bonferroni correction to adjust when (Day & Quinn 1989) using the free software InfoStat more than one test was performed on related data. We (2014). considered the data from November to March for the Survival: We estimated apparent annual survival analysis and used the free software InfoStat (2014). rate between two breeding season intervals (2009/10 to We estimated the displacement distance between 2010/11 and 2010/11 to 2011/12) as the probability of the fi rst capture and the fi rst recapture or relocation an individual survive and return to the same breeding of individuals in every breeding season. For this, the area. Th is is an approximation of the real survival rate, position of the mist nets and relocation position of every because it does not account for permanent or temporal bird were georeferenced in a metric coordinate system, emigration (Lebreton et al. 1992). We used captures, using the free software Quantum Gis 1.8.0-Lisboa recaptures and relocation data of 269 birds, considering (QGIS Development Team, 2012). We performed a T only adult birds as we never recaptured or relocated test (Agresti 2002) to compare the displacement distance any marked juvenile. We excluded from the analysis between sexes and between returning periods: 2009/10 the individuals that were captured just once and were to 2010/11 versus 2010/11 to 2011/12, and 2009/10 to not relocated during the season (i.e., likely transient 2010/11 versus 2009/10 to 2011/12 displacement. individuals). We fi tted Cormack-Jolly-Seber (CJS) mark- Arthropods and fruit variations: Abundance of recapture models to assess apparent annual survival arthropods was assessed by calculating a relative abundance rate and capture probability (Lebreton et al. 1992). index per trap (RAI = number of caught individuals / We confi rmed models goodness-of-fi t and lack of over- number of trapping days) and then estimated the average dispersion using the median c procedure (Burnham of all traps for the season. We evaluated diff erences & Anderson 2002). We modeled apparent survival in arthropod abundance among seasons by using one probability () as constant, varying in time (years) and factor Analysis of Variance with Repeated Measures between sexes, and examined the infl uence of these two (Winer 1971), because we counted arthropods in the covariates together, as additive and interactive eff ects. same points at every season. We used the Tukey multiple We considered capture-recapture-relocation probability comparison test for comparing means when season (p) constant in time and equal among sexes. We based factor was signifi cant (Winer 1971). We tested equality our decision on sampling eff ort as we systematically and symmetry of covariance matrices (Winer 1971). sampled the plots with mist nets and active search since Data violated the symmetry assumption, so we used the the arrival of the birds till their departure, compensating Greenhouse-Geiser procedure (Lower Bound Epsilon possible diff erences in detection caused by changes in correction = 0.5) to adjust the degrees of freedom of females and males behavior during their breeding period within-subject eff ects (Winer 1971). For ripe fruit off er, (as incubation and territorial defense). Th e relative we calculated the proportion of individuals that off ered importance of each model was compared using: Akaike›s no ripe fruits (index 0), less than 50 ripe fruits (indexes Information Criterion adjusted for small sample size 1 and 2), and those that off ered more than 50 ripe fruits (AICc), the diff erence of AICc between models (ΔAICc), (indexes 3 to 5). For each category, we evaluated the their weights (wi) and deviance (Burnham & Anderson diff erence in abundance of ripe fruit between seasons 2002). Models with a ΔAICc < 2 of the top model were using a test for diff erence of proportions (Zar 2010). considered to have equal support, so we model-averaged ANOVAs, the Tukey comparisons and all assumption survival estimates (Burnham & Anderson 2002). Model tests were performed on the free software InfoStat (2014). averaging generated an annual mean apparent survival rate for each sex and breeding period, with their standard RESULTS errors and confi dence intervals. We performed this analysis in R (version 3.1.1 2014, Th e R Foundation for Statistical Computing) using the RMark package (version Bird abundance and productivity of young: We banded 361 2.1.8; Laake & Rexstad 2008) that provides an interface adult and juvenile White-crested Elaenias and recaptured to the software MARK (version 7.2; White & Burnham 44 individuals during 5394 mist netting hours (Table 1). Complementary we relocated 25 adults that were 1999). Site fi delity: We analyzed it as the percentage of adult not recaptured in nets but detected by active search. birds banded in a previous fi eld season that were recaptured We did not recapture or relocate any marked juvenile or relocated in a subsequent fi eld season. We compared after its hatching year. Male capture during October- the diff erences in annual return rates between breeding November represented 69% of all captures. Th e latest captured individuals towards the end of the breeding seasons (2009/10 to 2010/11 vs. 2010/11 to 2011/12) Revista Brasileira de Ornitologia 26(4): 2018 Demography of the migratory White-crested Elaenia Presti et al. season (March) were mainly juveniles. Captures of new ΔAICc criterion (Table 2). Results from model averaging individuals decreased almost 50% between the fi rst revealed that the mean apparent annual survival rate was and last studied seasons (Table 1). During 2009/10 we equally low for females and males for the fi rst interval but registered the lowest percentage of breeding females males tended to increase its survival more than females (28%) and the lowest productivity of young, while for towards the following breeding season (Table 3). the following seasons the percentage of breeding females Site fi delity: From 231 banded and sexed adult exceeded that of non-breeders (68% for 2010/11 and White-crested Elaenias, 69 individuals returned the 73% for 2011/12) and the productivity of young following breeding seasons. Within those faithful birds, increased (Fig. 1). 14 individuals returned all the studied seasons and 12 Relative body condition: White-crested Elaenias skipped from the fi rst season (2009/10) to the third arrived in relatively good condition only during the (2011/12), not being recapture or relocated during the 2011/12 breeding season (F = 3.42, P < 0.001; Fig. second season (2010/11). Annual return rate varied 2, 169 2A), presenting the lowest condition during 2009/10, signifi cantly between breeding seasons, being higher for especially females. Th e condition for the departure period 2010/11 to 2011/12 period (Zc = -0.13, P = 0.028) in did not present a statistical diff erent variation between a) Female Male breeding seasons (F = 1.72, P = 0.187; Fig. 2B) or sexes 2, 66 1.5 (F = 21.58, P = 0.060). 1, 169 Survival : The best fi tted model indicated a variation 0.5 in apparent annual survival rate between breeding seasons, being 50% lower for 2009/10–2010/11 interval -0.5 in relation to 2010/11–2011/12 (0.41 ± 0.07 vs. 0.80 -1 ± 0.15). Models that considered survival vary among -1.5 seasons and sexes had a great support following AICc and -2 2009-2010 2010-2011 2011-2012 Breeding season b) 2 Female Male 1.5 0.5 -0.5 -1 -1.5 -2 2009-2010 2010-2011 2011-2012 Breeding season Figure 2. Body condition variation of the migratory White- Figure 1. Abundance by sex reproductive status and juvenile crested Elaenia females and males, during: a) arrivals and b) productivity of the migratory White-crested Elaenia along three departures in three breeding seasons, at Nahuel Huapi National breeding seasons, at Nahuel Huapi National Park, Patagonia, Park, Patagonia, Argentina. Boxes represent the mean condition Argentina. Total adults, includes all captured individuals in every period (± SE - Standard Error). Condition was derived with more than one year old (i.e. breeding and non-breeding as the residuals of a linear regression between body mass and individuals). Breeding birds were defi ned by the presence of tarsus length. Positive residuals indicate better condition. developed incubation patch (female) and cloacal protuberance Asterisk indicates the statistically diff erent season. (male) and Juveniles by the lack of the white crown. Table 1. Captures and recaptures of the migratory White-crested Elaenia by sex and age, in three breeding seasons (October to March) at Nahuel Huapi National Park, Patagonia, Argentina. Individuals that did not match with the criteria of sexing were left as “unsexed adults”. Breeding Total banded birds Females Males Juveniles Unsexed Total captures and seasons adults recaptures 2009–2010 152 61 85 3 3 152 2010–2011 136 55 68 27 4 154 2011–2012 73 46 33 23 2 104 Total 361 162 186 53 9 410 Revista Brasileira de Ornitologia 26(4): 2018 Birds’ body condition at departure Birds’ body condition on arrival (residual) (residual) Demography of the migratory White-crested Elaenia Presti et al. Table 2. Models results for the apparent annual survival rate () and recapture (p) probability of the migratory White- crested Elaenia in three breeding seasons at Nahuel Huapi National Park, Patagonia, Argentina (n = 269). Models are arranged by Akaike's Information Criterion adjusted for sample size (AICc). (.) Parameter is constant; k: number of parameters; wi: model weight. Model k AICc ΔAICc w Deviance (time) p (.) 3 373.38 0.00 0.49 4.75 (time * sex) p (.) 5 374.54 1.16 0.27 1.77 (time + sex) p (.) 4 374.86 1.48 0.23 4.17 (.) p (.) 2 382.42 9.04 0.01 15.84 (sex) p (.) 3 383.60 10.22 0.00 14.97 Table 3. Apparent annual survival rate and capture probability estimates (measured as capture, recapture and relocation) for the migratory White-crested Elaenia in three breeding seasons at Nahuel Huapi National Park, Patagonia, Argentina. Estimates correspond to model averaging of the best-fi tted models that indicated that survival varied by time and sex-class. 95% Confi dence Interval Parameter Breeding seasons interval Sex Estimate SE lcl ucl 2009–2010 to 2010–2011 Female 0.40 0.09 0.25 0.58 Male 0.41 0.08 0.28 0.56 Survival () 2010–2011 to 2011–2012 Female 0.74 0.17 0.34 0.94 Male 0.84 0.17 0.30 0.98 Capture probability (p) Constant in time - 0.49 0.09 0.32 0.66 relation to the fi rst interval (Table 4). Considering the P = 0.772). Females tended to displace more than males birds that returned across the entire study and those that when they returned (n = 30, 118 m ± 86 m vs. n = 54, skipped the second studied season, site fi delity of 2011/12 76 ± 78 m on average, respectively. t = 2.25, P = 0.027). season increased from 33% to 49% (54 individuals), Precipitation variability: Th e fi rst study year was an increasing the above-mentioned diff erence with the fi rst unusual rainy year, with an important input during the interval. Fidelity did not vary signifi cantly between sexes October–March period (638 mm) that was almost two (Zc = -0.11, P = 0.084), but males tended to return in standard deviations above the historical record (371 mm). greater proportion than females towards 2011/12 (Table At the following breeding seasons, precipitation was close 4). to average (347 and 390 mm, respectively; Fig. 3). With respect to territory fi delity, only three males Arthropods and fruit off er. Arthropod abundance was moved between plots along the study, less than 1500 m. similar among seasons (F = 3.027; P = 0.093; Fig. 4) 2, 27 Th e mean displacement between seasons was: 94 ± 100 but ripe fruit production varied notably between seasons. m for 2009/10 to 2010/11 seasons, 85 ± 71 m between Th e proportion of plants without ripe fruits was higher 2010/11 to 2011/12 , and 102 ± 84 m for birds that in the fi rst study season than the two following breeding were banded in 2009/10 and only relocated in 2011/12. seasons (Fig. 5, test for more than two proportions, Zc = Th ere were no signifi cant diff erences between the mean 22.86, P = 0.003), while plants with more than 50 ripe displacement of the fi rst and second period (t = 0.42, P = fruits were higher in the second and third seasons (Zc = 0.676), neither between the fi rst and the third (t = -0.29, 6.94, P = 0.031; Fig. 5). Revista Brasileira de Ornitologia 26(4): 2018 Demography of the migratory White-crested Elaenia Presti et al. Table 4. Site fi delity (annual return rate) of the migratory White-crested Elaenia in three breeding seasons at Nahuel Huapi National Park, Patagonia, Argentina. Estimation is presented as the percentage and number of adult birds that returned from a previous banding season, by sex-class and for the complete studied population. Total estimation includes birds captured at 2009/10 that returned at 2011/12, not being recaptured or relocated during 2010/11. Returns include both recaptures in nets and relocations of color-banded individuals. Returning individuals Banding and returning seasons All Females Males 2009/2010 to 2010/2011 20% (29) 20% (12) 20% (17) 2010/2011 to 2011/2012 33% (28) 19% (9) 50% (19) Total 30% (69) 24% (26) 35% (43) Figure 5. Diff erences in Aristotelia chilensis ripe fruit off er between three breeding seasons of the migratory White-crested Elaenia, at Nahuel Huapi National Park, Patagonia, Argentina. Figure 3. Rainfall anomalies during three breeding seasons of Th e percentage of Aristotelia chilensis plants within every fruit the migratory White-crested Elaenia at Steff en Lake, Nahuel off er score is shown for each season. Huapi National Park, Patagonia, Argentina. Values are expressed in standard deviations from an average climatic data of a 20-year period. Wet and dry years were those with annual DISCUSSION rainfall respectively above and below one standard deviation (dashed lines) from the mean. Our results suggest that the demography of migratory White-crested Elaenia is aff ected by environmental changes on its breeding grounds. Th e three seasons of our study had contrasting climatic conditions, with the fi rst season having a remarkable increase in rainfall respecting the historical average for the study area. Th is climatic variation was refl ected in changes in the supply of ripe fruits of Aristotelia chilensis, but not in the abundance of understory arthropods. Th e increase in rainfall during the fi rst season resulted in few days of full sun, likely leading to the inability of Aristotelia chilensis shrubs to produce ripe fruits, a relationship widely documented for others species (Aalders et al. 1969, Patten & Proebsting 1986, Spayd et al. 2002). During that fi rst season a lower Figure 4. Variation in arthropods abundance between three proportion of females became reproductive (28%), which breeding seasons of the migratory White-crested Elaenia, at was refl ected in a low productivity of young. Besides, Nahuel Huapi National Park, Patagonia, Argentina. Values birds' relative body condition tended to be lower than represent the mean arthropods abundance index (number of the following seasons and both survival and site fi delity individuals captured per sticky trap per survey days, ± SE - Standard Error) for every season. diminished by 50% after that period. Revista Brasileira de Ornitologia 26(4): 2018 Demography of the migratory White-crested Elaenia Presti et al. Previous studies have shown the impact of food recent studies revealed White-crested Elaenias returns to limitation in reproductive status and success of resident their wintering areas in the Brazilian Cerrado and Atlantic and migratory birds, as birds adapt their reproductive Forest by routes with diff erent habitat structure and cycle according to food availability (Martin 1987, Sherry refueling opportunities (Bravo et al. 2017), indicating that & Holmes 1995, Marshall et al. 2002, Jahn et al. 2014). a good body condition at departure could be fundamental For example, females of Parus major are able to modify to survive the journey between breeding and wintering their laying date so it coincides with periods of higher sites. According to that, the poor relative body condition caterpillar abundance (their main food item) and higher of birds during arrival and departure of the fi rst season temperatures, promoting nesting success (van Noordwijk could enhance birds' mortality during autumn migration, et al. 1995). With respect to the infl uence of arthropods diminishing survival values between breeding seasons. supply on White-crested Elaenias demography, we found Th is relationship between rainy breeding seasons with the that slightly variations in foliage arthropods abundance reduction in the species departure body condition has also did not aff ect bird's reproductive status and productivity been reported by previous studies (González et al. 2004). of young, neither body condition or survival. Similar Our results reinforce the need of demographic studies results were reported for Nearctic-Neotropical migrants across the entire annual cycle to improve our knowledge (Vireo olivaceus, Marshall et al. 2002, and Seiurus of White-crested Elaenia population dynamic. aurocapilla, Vernouillet et al. 2014) and for White-crested In addition, our mean apparent annual survival Elaenias breeding at central Chile (González et al. 2004). estimate (60%) is higher than the mean reported for Consistent with Cueto et al. (2016a) that found changes other migratory Flycatchers of comparable size and in the species foraging behaviour related with fruit off er behavior, breeding at temperate North America (50%; variations at the same study site, we conclude that fruit Karr et al. 1990, Koronkiewicz et al. 2006) but similar is the main food resource aff ecting White-crested Elaenia to tropical resident fl ycatchers (Johnston et al. 1997, reproductive success and demography during the breeding França & Marini 2010, Blake & Loiselle 2013). Our period. Our work represents a primary approximation results reinforce the hypothesis of higher survivorship of the eff ect of food limitation in White-crested Elaenia of southern hemisphere tropical and temperate birds demography and reinforces the importance of more respecting to northern hemisphere ones (Martin 1996). detailed study for a complete understanding of the role of Nevertheless, this trend requires more research including food resources on the species population dynamic. the hypothesis of reproduction cost, nest predation rate Decrease in new individuals capture rate along our and adult mortality, that have been mainly verifi ed for study years could be considered as an indirect measure North American and tropical birds (Martin et al. 2000, of low immigration rate, caused by a poor infl ux of new Martin 2015). birds to the population (Newton 1998). Th is could be Regarding migratory behavior, the higher capture due to events of lower reproductive success (as in the rate of White-crested Elaenia males comparing to females fi rst studied season), or higher mortality during the non- at the beginning of the breeding season suggest that males breeding period. As White-crested Elaenia present high could be arriving earlier, a behavior that is expected in migratory connectivity between their non-breeding and territorial birds as a manner of territory acquisition breeding areas (Bravo et al. 2017), the decrease in their (Kokko et al. 2006). Th e later departure of juveniles captured rate could also be related with environmental than of adults was also reported in studies at the austral variations at their wintering sites on the Brazilian Cerrado extreme distribution of the species (Brown et al. 2007), and Atlantic Forest (for example, see Wilson et al. 2011). and is usual in immature birds without prior migration Our study represents the fi rst survival estimation for experience (Whitaker & Warkentin 2010). Concerning a Neotropical austral migrant species and revealed that site fi delity, comparisons between seasons showed a survival varied across seasons. For Nearctic-Neotropical tendency for greater dispersal after breeding periods migrants breeding at temperate latitudes of North America with low reproductive success, suggesting that White- and wintering in the tropics, the temporal variation in crested Elaenias could be more predisposed to relocate survival has been attributed to weather anomalies across after seasons with low productivity, as were reported for the areas used by birds along their life cycle (Mazerolle et Nearctic-Neotropical migrants (Haas 1998). al. 2005), as they promote decreases in food availability On the other hand, our results of site fi delity diminishing survival and productivity of young (Sillett et are higher than previous studies that just considered al. 2000, Mazerolle et al. 2005). Our results are consistent recaptured birds on its estimations reporting returning with those studies, as survival of White-crested Elaenia rates only up to 11% (e.g. Espinosa & Egli 1997, Amico & decreased after years with rainfall anomalies that aff ected Aizen 2005, Brown et al. 2007), even in long term studies ripe fruit supply. Unfortunately, there are not similar (Rozzi & Jiménez 2013). Include data of relocations studies at the species wintering sites that allows linking prevent underestimations of returning rates and improves the entire annual cycle survival process. Nevertheless, apparent annual survival estimation (Martin et al. 2017). Revista Brasileira de Ornitologia 26(4): 2018 Demography of the migratory White-crested Elaenia Presti et al. However, if we considered only recaptured birds our Argentina, for the permission to carry out the study result of site fi delity remains higher for Steff en's Lake and the institutional support in the fi eld. We also thank (19% at 41 S) comparing to the estimation of a long the students and volunteers who assisted us during fi eld term study at the species austral distribution in Navarino work, and several colleagues around Argentina and South Island (10% at 56°S). Th e lower faithfulness at Navarino America with whom we shared experiences along this could respond to its habitability conditions, as summer project. We are very grateful to both anonymous reviewers precipitations and temperatures are lower than our study whose comments highly improved our manuscript. We area, the vegetation structure varies widely in short acknowledge the support from CRUB, Universidad distances and the main fruit item consumed by elaenias Nacional del Comahue. Funding for research was (Drymis winteri fruits) are available in autumn during provided by Consejo Nacional de Investigaciones Científi cas their departure (Rozzi & Jiménez 2013). Th ese factors y Técnicas (CONICET PIP-1230 to VRC and PIP-319 could be promoting higher replacement rates of birds to SPB), Universidad de Buenos Aires (UBACyT-645 breeding at that higher latitude, indicating that Navarino to VRC and UBACyT-199 to SPB), and Idea Wild Island could be a marginal habitat for the species. Foundation (to PMP). Conclusions and future perspectives REFERENCES Previous studies have emphasized the importance for Aalders L.E., Hall I.V. & Forsyth F.R. 1969. Eff ects of partial species with low reproductive success to compensate defoliation and light intensity on fruit-set and berry development this demographic feature with higher adult and juvenile in the lowbush blueberry. Horticultural Research 9: 124–129. survival (Martin 1996, Stahl & Oli 2006). However, nd Agresti A. 2002. Categorical Data Analysis, 2 edn. New Jersey: John migratory individuals face variable conditions along their Wiley & Sons, Inc. Amico G.C. & Aizen M.A. 2005. 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Ornithology Research – Springer Journals
Published: Dec 1, 2018
Keywords: body condition; breeding season; frugivory; Patagonian forest; population dynamic; site fidelity; survival; White-crested Elaenia
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