Neotropical Migratory Songbird Research Articles

Migratory connectivity of a Neotropical migratory songbird revealed by archival light-level geolocators.

Understanding migratory connectivity is critical for interpreting population dynamics, seasonal interactions, and for the implementation of conservation strategies of migratory species. We evaluated the migratory connectivity of a Neotropical migratory songbird, the Ovenbird (Seiurus aurocapilla) using archival light-level geolocators deployed at two breeding and four nonbreeding locations while incorporating Ovenbird abundance as prior information using Bayes' Rule. We also included band recoveries submitted to the United States Geological Survey's Bird Banding Laboratory to assess connectivity of areas where geolocators were not deployed. We created a probabilistic map of origin for each capture site and mapped spring migration routes between nonbreeding and breeding locations. We found a complete separation of eastern and western populations of Ovenbirds throughout the annual cycle. Breeding Ovenbirds from western Canada spent the nonbreeding season throughout Central America and migrated through central North America during spring migration. Birds breeding in the northeastern United States were distributed throughout the central Greater Antilles in the Caribbean and migrated through eastern North America during spring migration. Fall migration routes were not included because the timing of migration coincided with fall equinox when latitudinal estimates are unreliable. However, longitudinal estimates suggest no overlap between eastern and western populations during fall migration. Ovenbirds with geolocators attached in Jamaica bred in the northeastern United States with the highest posterior probability of origin found in Massachusetts, while Ovenbirds captured in Florida and Puerto Rico bred primarily in the mid-Atlantic. Incorporating Ovenbird abundance as a prior into geolocator estimates decreased the area of origin by 90.37% ± 1.05% (mean ± SE) for the breeding season and 62.30% ± 1.69% for the nonbreeding season, compared to geolocator estimates alone. Ovenbirds exhibited strong migratory connectivity between breeding and nonbreeding season, which has important implications for various aspects of the ecology, evolution, and conservation.

Intratropical migration of a Nearctic-Neotropical migratory songbird (Catharus fuscescens) in South America with implications for migration theory

Abstract:Recent advances in tracking technology have revealed significant intratropical movement of Nearctic–Neotropical migratory songbirds during their non-breeding season. We report the movement of 25 veeries (Catharus fuscescens) over multiple seasons (2009–2013) through equatorial rain forests of South America. Veeries initially settled on the Brazilian Shield geological formation but undertook an intratropical migration to a second South American region in January, February or March. Consequently, our study is the first to track individual forest passerines to document an annual migration from the Brazilian Shield to the Guiana Shield and into lowland regions of Amazonia. The movement and settlement patterns showed no spatiotemporal relationships with Nearctic–Neotropical migration, remained in accordance with the flood pulse of the Amazon basin, and were spatially and temporally complex suggesting relatively ancient ancestral origins. The ability to isolate the migration event from Nearctic–Neotropical migration is an important contribution to the ongoing discourse regarding the evolution of trans-hemispheric migration in the genus Catharus.

Connecting breeding and wintering grounds of Neotropical migrant songbirds using stable hydrogen isotopes: a call for an isotopic atlas of migratory connectivity

There is an overdue and urgent need to establish patterns of migratory connectivity linking breeding grounds, stopover sites, and wintering grounds of migratory birds. Such information allows more effective application of conservation efforts by applying focused actions along movement trajectories at the population level. Stable isotope methods, especially those using stable hydrogen isotope abundance in feathers ( 2 Hf) combined with Bayesian assignment techniques incorporating prior information such as relative abundance of breeding birds, now provide a fast and reliable means of establishing migratory connectivity, especially for Neotropical migrants that breed in North America and molt prior to fall migration. Here we demonstrate how opportunistic sampling of feathers of 30 species of wintering birds in Cuba, Venezuela, Guatemala, Puerto Rico, and Mexico, regions that have typically been poorly sampled for estimating migratory connectivity, can be assigned to breeding areas in North America through both advanced spatial assignment to probability surfaces and through simpler map lookup approaches. Incorporating relative abundance information from the North American Breeding Bird Survey in our Bayesian assignment models generally resulted in a reduction in potential assignment areas on breeding grounds. However, additional tools to constrain longitude such as DNA markers or other isotopes would be desirable for establishing breeding or molt origins of species with broad longitudinal distributions. The isotope approach could act as a rapid means of establishing basic patterns of migratory connectivity across numerous species and populations. We propose a large-scale coordinated sampling effort on the wintering grounds to establish an isotopic atlas of migratory connectivity for North American Neotropical migrants and suggest that isotopic variance be considered as a valuable metric to quantify migratory connectivity. This initiative could then act as a strategic template to guide further efforts involving stable isotopes, light-sensitive geolocators, and other technologies.

Physiological assessment of the effects of changing water levels associated with reservoir management on fattening rates of neotropical migrants at a stopover site.

Riparian habitat makes up a small fraction of the landscape but provides important stopover habitat for migratory birds. Hydroelectric dam operations cause fluctuations in water levels that can change the amount or quality of riparian habitat, which in turn might affect potential fattening rates of migrant birds. Here we used plasma metabolite analysis to estimate variation in fattening rate in relationship to variable water levels associated with reservoir management in four species of neotropical migratory songbirds using riparian habitat at a dam-impacted stopover site in Revelstoke, British Columbia, Canada. Residual plasma triglyceride, our measure of estimated fattening rate, varied systematically with time of day and Julian date and varied consistently among species, but did not vary with age or sex. Controlling for potentially confounding variables, we found no inter-annual variation in estimated fattening rate, even though there were marked differences in water levels among years. Likewise, there was no relationship between daily variation in water levels and estimated fattening rate. Data on feather isotopes (δD), indicative of migratory origin, did not add explanatory power to our models. There was inter-annual variation in plasma glycerol and β-hydroxybutyrate levels and significant, though weak, relationships between these metabolites and water level (higher metabolite levels when drier) that might indicate effects on 'body condition' independent of fattening rate. Our study suggests that, at present, although hydroelectric dam operations influence water levels in the Arrows Lake Reservoir and adjacent riparian habitats, this does not significantly impact fattening rates of migratory passerines using these habitats.

Using audio lures to improve golden‐winged warbler (Vermivora chrysoptera) detection during point‐count surveys

ABSTRACTThe golden‐winged warbler (Vermivora chrysoptera) is a Neotropical migratory songbird listed as a “Bird of Conservation Concern” by the U.S. Fish and Wildlife Service. To manage golden‐winged warblers, it is important to develop effective survey techniques for conservation research and monitoring. We conducted point counts in 1–8‐year‐old aspen (Populus sp.) stands in the northern Lower Peninsula of Michigan (USA), during 2011, to estimate detection probability of golden‐winged warblers, with and without an electronic broadcast of a golden‐winged warbler song (i.e., audio lure). We compared audio lure effectiveness for detecting golden‐winged warblers during fixed‐ (50‐m radius) and variable‐radius point counts. Golden‐winged warbler detection estimates were = 0.84 (95% CI = 0.39–0.98) and = 0.22 (0.11–0.40) for fixed‐radius point counts, with and without audio lure, respectively. For variable‐radius point counts, golden‐winged warbler detection estimates were = 0.79 (CI = 0.51–0.93) and = 0.57 (0.42–0.71), with and without audio lure, respectively. We also estimated the number of 3‐minute sub‐counts required to achieve detection probability ≥95% for both radii, with and without audio lures. We found that 2 sub‐counts with audio lure resulted in >95% detection probability for golden‐winged warblers at both radii. Without audio lure, 12 and 4 sub‐counts were required for fixed and variable radii, respectively. Regardless of survey technique, golden‐winged warbler detection probability was always <1.0, which highlights the importance of accounting for imperfect detection of golden‐winged warblers. Our results indicate that the use of an audio lure is an effective design technique for improving detectability of golden‐winged warblers. © 2014 The Wildlife Society.

Within-season nesting dispersal and molt dispersal are linked to habitat shifts in a Neotropical migratory songbird

Dispersal decisions of songbirds are relatively well understood between breeding seasons, but far less is known about dispersal between nesting attempts and during the molting period. There are several non-mutually exclusive hypotheses for why birds disperse during breeding and molt including: (1) avoiding predation, (2) because of depleted resources, or (3) seeking higher quality habitat. In this study, we evaluated the above hypotheses by radio-tracking a Neotropical migrant, the Wood Thrush (Hylocichla mustelina), during breeding and molt. During breeding, 30% (7/23) of females moved territories within-season. Females were not more likely to move off-territory following nest predation, and dispersing females were not in poorer nutritional state than non-dispersing females prior to the move. However, females occupying nest sites with large trees, high canopy height and percent canopy cover, and low percent ground cover were more likely to move off-territory for their second nest to sites with few large trees, a low canopy height and cover, and high percent ground cover. During the molting period, 61% (28/46) of birds moved off-territory to molt. Molting areas were associated with more shrubs and fruiting trees compared with breeding territories. There were no sex or age effects as to whether a bird molted on or off their breeding territory. We suggest that off-territory movements during the nesting period are to seek more suitable nesting vegetation, rather than specifically avoiding predation or because of reduced resource availability. This study has additionally shown that, without radio-telemetry, detecting off-territory movements during breeding is difficult and neglecting to include these movements may result in an underestimation of annual productivity.

Juvenile Survival in a Neotropical Migratory Songbird Is Lower than Expected

Attempts to estimate and identify factors influencing first-year survival in passerines, survival between fledging and the first reproductive attempt (i.e. juvenile survival), have largely been confounded by natal dispersal, particularly in long-distance migratory passerines. We studied Prothonotary Warblers (Protonotaria citrea) breeding in nest boxes to estimate first-year survival while accounting for biases related to dispersal that are common in mark-recapture studies. The natal dispersal distribution (median = 1420 m; n = 429) and a distance-dependent recruitment rate, which controls for effects of study site configuration, both indicated a pattern of short-distance natal dispersal. This pattern was consistent with results of a systematic survey for birds returning outside the nest box study sites (up to 30 km in all directions) within a majority (81%) of total available bottomland forest habitat, further suggesting that permanent emigration outside of the study system was rare. We used multistate mark-recapture modeling to estimate first-year survival and incorporated factors thought to influence survival while accounting for the potential confounding effects of dispersal on recapture probabilities for warblers that fledged during 2004–2009 (n = 6093). Overall, the average first-year survival for warblers reared without cowbird nestmates was 0.11 (95% CI = 0.09–0.13), decreased with fledging date (0.22 early to 0.03 late) and averaged 40% lower for warblers reared with a brood parasite nestmate. First-year survival was less than half of the rate thought to represent population replacement in migratory passerines (∼0.30). This very low rate suggests that surviving the first year of life for many Neotropical migratory species is even more difficult than previously thought, forcing us to rethink estimates used in population models.

Canopy characteristics affect reproductive success of golden‐cheeked warblers

AbstractThe golden‐cheeked warbler (Setophaga chrysoparia), listed by the U.S. Fish and Wildlife Service as endangered in 1990 due primarily to habitat loss and fragmentation, is a Neotropical migrant songbird that breeds exclusively in mature juniper–oak (Juniperus–Quercus) woodlands in central Texas, USA. Previous studies suggested suitable breeding habitat consists of >35% canopy closure (with 50–70% cover optimal), and ≥10% oak composition. However, little is known about this species' habitat relationships at the southwestern edge of its breeding range. Therefore, within this portion of the species' breeding range, we investigated influences of canopy closure and tree species composition on pairing and reproductive success of golden‐cheeked warblers during 2009 and 2010. We used remote sensing and ground sampling to acquire variables to describe habitat characteristics, and we estimated pairing for breeding and reproductive success by golden‐cheeked warblers. We found successfully breeding pairs in areas with >20% canopy cover, 35% juniper composition, and only 3% oak composition. A logistic model for pairing success retained juniper, oak, and the interaction between these 2 variables, and the model for reproductive success retained juniper, canopy closure, study area, and the interaction between canopy closure and study area. Our results expand our knowledge of habitat conditions that warblers use for breeding, thus expanding the range of habitat management options available for this species during breeding season. © 2012 The Wildlife Society.

Brood size and late breeding are negatively related to juvenile survival in a Neotropical migratory songbird

ABSTRACT. Widespread decline of Neotropical migrant songbirds requires better understanding of the mechanisms driving juvenile mortality. We used mark—resight encounter histories of 3,990 banded fledglings (1998–2002) to test whether late breeding or large brood size negatively affected apparent annual and migration—wintering survival probability of juvenile Purple Martins (Progne subis). We estimated apparent annual juvenile survival (φa, fledging to 1 year old) by resighting individuals as adults at regional breeding colonies and at a premigratory roost. We tested for carryover effects of fledge week and brood size on migration—wintering survival (φm, premigratory roost to 1 year old) using two encounter occasions per season (premigratory roost, breeding colony) to partition annual survival into premigration versus migration—wintering survival. Annual survival (± SE) was 0.27 ± 0.027 and the best model (model weight = 0.93) included week of fledging and brood size, with survival probability decreasing w...

Influence of forest management on pre- and post-fledging productivity of a Neotropical migratory songbird in a highly fragmented landscape

Little is known about the effects of forest management on fledgling survival in birds, despite the fact that this is a key determinant of overall productivity. In 2005–2006, we compared male density, nesting success, and fledgling survival of Hooded Warblers (Wilsonia citrina Boddaert, 1783) among forest fragments that were reference sites (n = 3; not logged in >21 years) or had received either a standard selection system harvest (n = 3) or a heavy cut (n = 5) within the past 6–10 years. Density tended to be higher in logged sites than reference sites, but cumulative probability of nest survival (0.22 ± 0.02; 21 days) did not differ among treatments. Brown-headed Cowbird (Molothrus ater (Boddaert, 1783)) parasitism was significantly higher in recently logged sites, and reference sites produced significantly more Hooded Warbler young per successful nest than standard selection harvest sites. Logging treatment did not have a strong negative effect on fledgling survival, and overall, 51% (33/65) of fledglings survived until three weeks after fledging. Standard selection harvest sites had the highest Hooded Warbler density (0.2 males/ha) but also the lowest seasonal productivity (0.84 independent fledglings/female), raising the possibility of an ecological trap. The estimated number of daughters produced per female per year that are expected to survive to breeding age was lower for all treatments (reference, 0.26; selection, 0.17; heavy cut, 0.32) than the expected annual mortality probability of adult females (0.4–0.6). Forest fragments in this region appear to be population sinks, regardless of extent of partial harvest within the fragment.

Range-wide effects of breeding- and nonbreeding-season climate on the abundance of a Neotropical migrant songbird

Geographic variation in the population dynamics of a species can result from regional variability in climate and how it affects reproduction and survival. Identifying such effects for migratory birds requires the integration of population models with knowledge of migratory connectivity between breeding and nonbreeding areas. We used Bayesian hierarchical models with 26 years of Breeding Bird Survey data (1982-2007) to investigate the impacts of breeding- and nonbreeding-season climate on abundance of American Redstarts (Setophaga ruticilla) across the species range. We focused on 15 populations defined by Bird Conservation Regions, and we included variation across routes and observers as well as temporal trends and climate effects. American Redstart populations that breed in eastern North America showed increased abundance following winters with higher plant productivity in the Caribbean where they are expected to overwinter. In contrast, western breeding populations showed little response to conditions in their expected wintering areas in west Mexico, perhaps reflecting lower migratory connectivity or differential effects of winter rainfall on individuals across the species range. Unlike the case with winter climate, we found few effects of temperature prior to arrival in spring (March-April) or during the nesting period (May-June) on abundance the following year. Eight populations showed significant changes in abundance, with the steepest declines in the Atlantic Northern Forest (-3.4%/yr) and the greatest increases in the Prairie Hardwood Transition (4%/yr). This study emphasizes how the effects of climate on populations of migratory birds are context dependent and can vary depending on geographic location and the period of the annual cycle. Such knowledge is essential for predicting regional variation in how populations of a species might vary in their response to climate change.

Interannual flexibility in breeding phenology of a Neotropical migrant songbird in response to weather conditions at breeding and wintering areas

Changes in climate that affect breeding phenology can have important ramifications for the population dynamics of migratory wildlife. In birds, predicted changes in global climate raise concerns over the ability of migratory species, especially long-distance migrants, to adapt to changes in spring weather conditions. At a riparian breeding site in southern Manitoba, we found that over 3 decades (1974 to 2003), migratory yellow warblers (Dendroica petechia) exhibited considerable plasticity in their timing of clutch initiation in response to mean May temperatures at the breeding site. Spring arrival dates estimated during the last 9 y of our study were also highly variable and correlated with mean May temperatures. By contrast, we found no support for an effect of the El Niño/Southern Oscillation, a climatic phenomenon known to affect weather conditions on wintering grounds of yellow warblers, on spring arrival dates or timing of breeding. This suggests that El Niño/Southern Oscillation did not have carry-over effects on spring arrival dates or timing of clutch initiation. The results from our study are consistent with the timing of breeding in Neotropical migrant songbirds being flexible and closely coupled with spring temperatures (mean daily May temperatures) at breeding sites. These findings are important for predicting how sensitive long-distance migrant birds may be to changes in spring conditions caused by climatic warming.

Moisture as a determinant of habitat quality for a nonbreeding Neotropical migratory songbird

Identifying the determinants of habitat quality for a species is essential for understanding how populations are limited and regulated. Spatiotemporal variation in moisture and its influence on food availability may drive patterns of habitat occupancy and demographic outcomes. Nonbreeding migratory birds in the neotropics occupy a range of habitat types that vary with respect to moisture. Using carbon isotopes and a satellite-derived measure of habitat moisture, we identified a moisture gradient across home ranges of radio-tracked Northern Waterthrush (Seiurus noveboracensis). We used this gradient to classify habitat types and to examine whether habitat moisture correlates with overwinter mass change and spring departure schedules of Northern Waterthrush over the late-winter dry season in the tropics. The two independent indicators of moisture revealed similar gradients that were directly proportional to body mass change as the dry season progressed. Birds occupying drier habitats declined in body mass over the study period, while those occupying wetter habitats increased in body mass. Regardless of habitat, birds lost an average of 7.6% of their mass at night, and mass recovery during the day trended lower in dry compared with wet habitats. This suggests that daily incremental shortfalls in mass recovery can lead to considerable season-long declines in body mass. These patterns resulted in consequences for the premigratory period, with birds occupying drier habitats having a delayed rate of fat deposition compared with those in wet habitats. Taken together with the finding that males, which are significantly larger than females, are also in better condition than females regardless of habitat suggests that high-quality habitats may be limited and that there may be competition for them. The habitat-linked variation in performance we observed suggests that habitat limitation could impact individual and population-level processes both during and in subsequent periods of the annual cycle. The linkage between moisture and habitat quality for a migratory bird indicates that the availability of high-quality habitats is dynamic due to variation in precipitation among seasons and years. Understanding this link is critical for ascertaining the impact of future climate change, particularly in the Caribbean basin, where a much drier future is predicted.

Lidar remote sensing variables predict breeding habitat of a Neotropical migrant bird

A topic of recurring interest in ecological research is the degree to which vegetation structure influences the distribution and abundance of species. Here we test the applicability of remote sensing, particularly novel use of waveform lidar measurements, for quantifying the habitat heterogeneity of a contiguous northern hardwoods forest in the northeastern United States. We apply these results to predict the breeding habitat quality, an indicator of reproductive output of a well-studied Neotropical migrant songbird, the Black-throated Blue Warbler (Dendroica caerulescens). We found that using canopy vertical structure metrics provided unique information for models of habitat quality and spatial patterns of prevalence. An ensemble decision tree modeling approach (random forests) consistently identified lidar metrics describing the vertical distribution and complexity of canopy elements as important predictors of habitat use over multiple years. Although other aspects of habitat were important, including the seasonality of vegetation cover, the canopy structure variables provided unique and complementary information that systematically improved model predictions. We conclude that canopy structure metrics derived from waveform lidar, which will be available on future satellite missions, can advance multiple aspects of biodiversity research, and additional studies should be extended to other organisms and regions.

Migratory double breeding in Neotropical migrant birds

Neotropical migratory songbirds typically breed in temperate regions and then travel long distances to spend the majority of the annual cycle in tropical wintering areas. Using stable-isotope methodology, we provide quantitative evidence of dual breeding ranges for 5 species of Neotropical migrants. Each is well known to have a Neotropical winter range and a breeding range in the United States and Canada. However, after their first bout of breeding in the north, many individuals migrate hundreds to thousands of kilometers south in midsummer to breed a second time during the same summer in coastal west Mexico or Baja California Sur. They then migrate further south to their final wintering areas in the Neotropics. Our discovery of dual breeding ranges in Neotropical migrants reveals a hitherto unrealized flexibility in life-history strategies for these species and underscores that demographic models and conservation plans must consider dual breeding for these migrants.

Estimating Territory and Home-range Sizes: Do Singing Locations Alone Provide an Accurate Estimate of Space Use?

ABSTRACT. Documenting space-use patterns of animals is important for understanding their ecology and providing for their conservation. The concept of territory refers to a defended area, whereas the concept of home range refers to any area used by an animal during its normal activities. Few studies have explored quantitatively how these areas differ, and the use of these terms in the literature has, at times, been inconsistent. Many studies attempt to estimate territory size of a bird by territory mapping, which involves using locations obtained by following a singing bird. This is often assumed to be an effective measure of territory size, but few studies have examined the efficacy of this technique. Here, we used radiotelemetry to estimate breeding home-range and territory sizes of Swainson's Warbler (Limnothlypis swainsonii), a Neotropical migrant songbird. We found that territories were much larger than had been estimated by territory-mapping methods and suggest that researchers use caution when assum...

LANDSCAPE STRUCTURE AND SPATIAL SCALE AFFECT SPACE USE BY SONGBIRDS IN NATURALLY PATCHY AND HARVESTED BOREAL FORESTS

Abstract Knowledge of how landscape structure influences patterns of animal space use is critical to developing sustainable landscape management practices. For breeding songbirds that defend a territory embedded within a larger home range, effects of structural change on movement may be manifested at multiple spatial scales. We used radio-telemetry to assess within-territory and home range space use as functions of the proportion of clearcut-harvested versus naturally unforested land for two species of Neotropical migrant songbirds. We tested whether these relationships varied with spatial scale by assessing landscape structure in both the local neighborhood (115 m radius around an individual's territory center) and across the landscape (1250 m radius). Territory size for riparian-associated male Northern Waterthrushes (Seiurus noveboracensis) was curvilinearly related to the proportion of harvested versus naturally unforested land and varied by greater than two orders of magnitude. Waterthrush territorie...

Roosting behavior of a Neotropical migrant songbird, the northern waterthrush Seiurus noveboracensis, during the non‐breeding season

Several species of Nearctic‐Neotropical migratory songbirds appear to form roosting aggregations while on their wintering grounds but little is understood about the ecology of this behavior. We studied roosting behavior and patterns of roost habitat selection in the northern waterthrush Seiurus noveboracensis, during three winter years (2002–2004) in Puerto Rico using radio telemetry. Overall, red mangrove was selected for roosting disproportionately to its availability. Regardless of diurnal habitat used, 87% (n=86) of northern waterthrush selected dense stands of coastal red mangrove for roost sites. Individuals traveled up to 2 km to access roost sites in this habitat on a daily basis. The majority (8 of 14) of individuals roosted alone, while others roosted in loose aggregations near communal roosts of gray kingbirds Tyrannus dominicensis. Patterns of roost site selection did not vary by sex. Individuals showing aggressive response to playback during the day, however, selected roost sites significantly closer to the coast. Several additional migratory and resident bird species also used red mangrove for night‐time roosting habitat. Red mangrove may be a critical nocturnal roosting habitat for bird populations that live in proximity to coastal areas in the Neotropics. The benefits of nocturnal roosting behavior as well as why individuals appear to select red mangrove remain poorly understood.

Modeling Population Growth of The Ovenbird (Seiurus Aurocapilla) in the Southern Appalachians

AbstractStudies of source-sink dynamics are often prompted by concerns about negative population trends. Estimates of population trajectories are usually based on assumptions about survival rates and empirical measures of fecundity. Most models ignore the influence of the rates of renesting and multiple brooding. We used the Ovenbird (Seiurus aurocapilla) as a model Neotropical migratory songbird species to investigate the relative effects of annual female survival and components of annual fecundity on population growth rates. We applied productivity data from a three- year field study and data from Hann (1937) to several models of annual fecundity to examine the sensitivity of lambda to variations in annual female survival and the likelihood of renesting and double-brooding. Our simulations illustrate the importance of incorporating estimates of annual survival and rates of additional breeding attempts in songbird population models because population growth rates are quite sensitive to variations in these parameters. Lambda is especially sensitive to survival estimates and changes with them at the same order of magnitude. Whenever feasible, female survival and probabilities of additional breeding attempts should be estimated by direct methods. The indirect methods used in our study (annual female survival estimated from the age ratio of breeding females, and rates of renesting and double- brooding determined from the timing of reproduction) probably underestimated these parameters.Modelado del Crecimiento Poblacional de Seiurus aurocapilla en el Sur de los Apalaches

MODELING POPULATION GROWTH OF THE OVENBIRD (SEIURUS AUROCAPILLA) IN THE SOUTHERN APPALACHIANS

Studies of source-sink dynamics are often prompted by concerns about negative population trends. Estimates of population trajectories are usually based on assumptions about survival rates and empirical measures of fecundity. Most models ignore the influence of the rates of renesting and multiple brooding. We used the Ovenbird (Seiurus aurocapilla) as a model Neotropical migratory songbird species to investigate the relative effects of annual female survival and components of annual fecundity on population growth rates. We applied productivity data from a three- year field study and data from Hann (1937) to several models of annual fecundity to examine the sensitivity of lambda to variations in annual female survival and the likelihood of renesting and double-brooding. Our simulations illustrate the importance of incorporating estimates of annual survival and rates of additional breeding attempts in songbird population models because population growth rates are quite sensitive to variations in these parameters. Lambda is especially sensitive to survival estimates and changes with them at the same order of magnitude. Whenever feasible, female survival and probabilities of additional breeding attempts should be estimated by direct methods. The indirect methods used in our study (annual female survival estimated from the age ratio of breeding females, and rates of renesting and double- brooding determined from the timing of reproduction) probably underestimated these parameters. Modelado del Crecimiento Poblacional de Seiurus aurocapilla en el Sur de los Apalaches