Explore the vast range of titles available.

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.

To maximize fitness, organisms must assess and select suitable habitat. Early research studying birds suggested that organisms consider primarily vegetation structural cues in their habitat choices. We show that experimental exposure to singing in the post-breeding period provides a social cue that is used for habitat selection the following year by a migrant songbird, the black-throated blue warbler (Dendroica caerulescens). Our experimental social cues coerced individuals to adopt territories in areas of very poor habitat quality where individuals typically do not occur. This indicates that social information can override typical associations with vegetation structure. We demonstrate that a strong settlement response was elicited because post-breeding song at a site is highly correlated with reproductive success. These results constitute a previously undocumented, but highly parsimonious mechanism for the inadvertent transfer of reproductive (public) information from successful breeders to dispersers. We hypothesize that post-breeding song is a pervasive and reliable cue for species that communicate vocally, inhabit temporally autocorrelated environments, produce young asynchronously and/or abandon territories after reproductive failure.

1. Demographic data from both breeding and non-breeding periods are needed to manage populations of migratory birds, many of which are declining in abundance and are of conservation concern. Although habitat associations, and to a lesser extent, reproductive biology, are known for many migratory species, few studies have measured survival rates of these birds at different parts of their annual cycle. 2. Cormack-Jolly-Seber models and Akaike's information criterion model selection were used to investigate seasonal variation in survival of a Nearctic - Neotropical migrant songbird, the black-throated blue warbler, Dendroica caerulescens. Seasonal and annual survival were estimated from resightings of colour-ringed individuals on breeding grounds in New Hampshire, USA from 1986 to 2000 and on winter quarters in Jamaica, West Indies from 1986 to 1999. Warblers were studied each year during the May-August breeding period in New Hampshire and during the October-March overwinter period in Jamaica. 3. In New Hampshire, males had higher annual survival (0.51 ± 0.03) and recapture probabilities (0.93 ± 0.03) than did females (survival: 0.40 ± 0.04; recapture: 0.87 ± 0.06). In Jamaica, annual survival (0.43 ± 0.03) and recapture (0.95 ± 0.04) probabilities did not differ between sexes. Annual survival and recapture probabilities of young birds (i.e. yearlings in New Hampshire and hatch-year birds in Jamaica) did not differ from adults, indicating that from the time hatch-year individuals acquire territories on winter quarters in mid-October, they survive as well as adults within the same habitat. 4. Monthly survival probabilities during the summer (May-August) and winter (October-March) stationary periods were high: 1.0 for males in New Hampshire, and 0.99 ± 0.01 for males in Jamaica and for females in both locations. 5. These annual and seasonal survival estimates were used to calculate warbler survival for the migratory periods. Monthly survival probability during migration ranged from 0.77 to 0.81 ± 0.02. Thus, apparent mortality rates were at least 15 times higher during migration compared to that in the stationary periods, and more than 85% of apparent annual mortality of D. caerulescens occurred during migration. 6. Additional data from multiple species, especially measures of habitat-specific demography and dispersal, will improve our understanding of the relative impacts of the breeding, migratory, and winter periods on population dynamics of migratory birds and thus enhance future conservation efforts.

Individuals within a population vary in important fitness components, such as reproductive success. In general, females can maximize the number of young they produce by altering either the number of young per breeding attempt or the number of breeding attempts per season. In short-lived species, and especially in small passerine birds, number of breeding attempts per season varies markedly among individuals. Here, we evaluated factors influencing whether female Blackthroated Blue Warblers (Dendroica caerulescens) initiated additional nests after a successful breeding attempt (i.e. double-brooded). The percentage of females that laid a second clutch after successfully fledging a first brood ranged from 0 to 87% and averaged 53% (n = 7 years). Multiple logistic regression and AIC sub(c) model selection indicated that double-brooded females bred in territories with greater food availability and produced heavier nestlings than single-brooded females. Female age, male age, date of first breeding attempt, and number of young in the first clutch were not included in the best-fit model. Older females, however, produced heavier fledglings, and females mated to older males occurred on territories with greater food availability, indicating that age contributed to individual variation in reproductive output. Because the proportion of females that produce multiple broods within a season can have a substantial effect on the annual fecundity of a population, variation among females and among the territories they occupy (i.e. habitat quality) are key factors influencing population dynamics in this and other multibrooded, shortlived species.Poner Nidadas Dobles o No? Variacion Individual en el Esfuerzo Reproductivo en Dendroica caerulescensOriginal Abstract: Los individuos de una misma poblacion varian en componentes importantes de la adecuacion, como el exito reproductivo. En general, las hembras pueden maximizar el numero de crias que producen alterando ya sea el numero de crias por intento reproductivo, o el numero de intentos reproductivos por estacion. En especies de vida corta, especialmente en aves paserinas pequenas, el numero de intentos reproductivos por estacion varia marcadamente entre individuos. En este estudio evaluamos los factores que determinan si las hembras de la especie Dendroica caerulescens inician nidos adicionales luego de un intento reproductivo exitoso (i.e. nidadas dobles). El porcentaje de hembras que pusieron una segunda nidada despues de haber producido volantones exitosamente en su primer intento estuvo entre 0 y 87%, con un promedio de 53% (n = 7 anos). Analisis de regresion logistica multiple y de seleccion de modelos con base en el criterio de informacion de Akaike indicaron que las hembras con nidadas dobles se reprodujeron en territorios con mayor disponibilidad de alimento y produjeron pichones mas pesados que las hembras que pusieron solo una nidada. La edad de las hembras, la edad de los machos, la fecha del primer intento reproductivo y el numero de pichones de la primera nidada no fueron parte del modelo con el mejor ajuste. Sin embargo, las hembras de mayor edad produjeron volantones mas pesados, y las hembras apareadas con machos mas viejos se encontraron en territorios con mayor disponibilidad de alimento, lo que indica que la edad contribuyo a la variacion individual en el rendimiento reproductivo. Debido a que la proporcion de las hembras que producen nidadas multiples en una estacion reproductiva puede tener un efecto sustancial sobre la fecundidad anual de una poblacion, la variacion entre las hembras y entre los territorios que ocupan (i.e. calidad de habitat) son factores claves que influencian la dinamica de las poblaciones en esta y en otras especies de vida corta con nidadas multiples.

Understanding the breeding origins of migratory birds captured on their wintering grounds has important management and conservation implications for declining populations of songbirds. Stable isotopes have recently been used to infer origins for species where application of conventional markers fails. A natural method of linking wintering birds to breeding populations, and one that has not been previously applied to stable isotopes, is based on likelihood. Using a likelihood assignment rule, birds are associated with the breeding population under which their realized isotope signature is most likely to have been generated. We report the first illustration of using likelihood-based assignment with stable isotope data. Moreover, within a probability-based framework for assignment, we argue that a more natural formulation of the assignment problem should be based on the probability of origin given the observed data, or the posterior probability of origin. The relationship between posterior assignment and that based on simple likelihood is embodied in Bayes Rule, which establishes a clear linkage between the distribution of the breeding population (i.e., relative abundance) and probability of origin. We demonstrate likelihood and posterior assignment using a large data set on Black-throated Blue Warblers (Dendroica caerulescens). Our results suggest that relative abundance is likely to be a more crucial consideration in the presence of less geographically structured isotopes, when the distribution of abundance is highly non-uniform, or when the range of the species is geographically restricted.

In short-lived species, fecundity strongly influences population size. For those species with multiple breeding attempts per breeding season, variance in fecundity is best explained by the number of breeding attempts. For birds, multiple brooding may be influenced by food availability. Here, we report results of a food supplementation experiment that tests the role of food as a mechanism driving variation among individuals in the frequency of multiple brooding in a Neotropical migrant songbird, the Black-throated Blue Warbler (Dendroica caerulescens). Supplementally fed females produced more second broods, spent less time foraging and more time loafing, and stayed closer to their nests than did control females. Fed and control females did not differ in the number or mass of young fledged from the first nesting attempt. Supplemental food increased the probability that females would initiate second broods in both a low and an average food year, suggesting that this population is food limited during the breeding season in most years. Our results thus demonstrate that food availability can strongly influence annual fecundity in migratory bird species breeding in temperate forests, which, in turn, affects annual recruitment rates and population size.

Although predicted some time ago, there has been little success in demonstrating that the overall fitness of migratory birds depends on the combined influences of their experiences over all seasons. We used stable carbon isotope signatures (δ13C) in the claws of migrating black-throated blue warblers Dendroica caerulescens to infer their wintering habitats and investigated whether winter habitat selection can be linked to condition during migration. Resident bird species with low δ13C corresponded to selection of more mesic habitats, and migrating birds with low δ13C were in better condition than conspecifics with higher δ13C signatures. These findings concur with empirical observations on the wintering grounds, where dominants (mostly males) tend to exclude subordinates from mesic areas (considered to be high-quality habitats). We believe that variation in condition during migration may be one of the key factors determining differences in arrival times and condition at the breeding areas, which in turn have a major influence on reproductive success.

Estimates of nest survival are commonly used as indices of reproductive productivity in a wide range of studies, including examinations of population dynamics, habitat fragmentation, and wildlife management. However, the strength of the relationship between estimates of nest survival and of seasonal fecundity has rarely been tested. To examine that relationship, we used 16 years of demographic data from an intensively studied population of individually marked Black-throated Blue Warblers (Dendroica caerulescens). We found a positive relationship between Mayfield nest-survival estimates and seasonal fecundity (i.e. number of fledglings produced per female). However, seasonal-fecundity predictions based on nestsurvival values underestimated observed seasonal fecundity by an average of 33% and population growth rate by 20%. Our results suggest that, though nest-survival estimates may be useful as indices of pressures on a population (e.g. nest predation), care is needed in using them as the basis of conservation or management strategies or to make inferences about population-level processes.Relacion entre las Estimaciones de Supervivencia de Nidos de Mayfield y la Fecundidad Estacional: una Nota de CautelaResumenLas estimaciones de la supervivencia de los nidos son usadas comunmente como indices de productividad reproductiva en un amplio espectro de estudios, incluyendo evaluaciones de dinamica poblacional, fragmentacion de habitat y manejo de fauna silvestre. Sin embargo, la fortaleza de la relacion entre las estimaciones de supervivencia de nidos y la fecundidad estacional ha sido raramente evaluada. Para examinar esta relacion, usamos datos demograficos de individuos marcados de Dendroica caerulescens de una poblacion estudiada intensamente durante 16 anos. Encontramos una relacion positiva entre las estimaciones de supervivencia de nidos de Mayfield y la fecundidad estacional (i.e. el numero de volantones producidos por hembra). Sin embargo, las predicciones de la fecundidad estacional basadas en valores de supervivencia de nidos subestimaron la fecundidad estacional observada en un 33% en promedio y la tasa de crecimiento poblacional en un 20%. Nuestros resultados sugieren que aunque las estimaciones de supervivencia de nidos pueden ser utiles como indices de presiones en una poblacion (e.g. depredacion de nidos), se debe tener cuidado al usarlas como la base de estrategias de conservacion o de manejo o para hacer inferencias sobre procesos a nivel poblacional.

The timing of settlement decisions likely influences the quality of breeding site choices. This is particularly the case in migratory birds, because the conditions that enhance breeding success are often not apparent upon arrival after migration. A strategy that addresses this problem is to adjust settlement decisions when reliable information becomes available. We used a new indirect method - dynamic site occupancy modeling - to estimate apparent movement of black-throated blue warblers Dendroica caerulescens among sites within a breeding season. Because individuals should disperse to sites that maximize their fitness, we hypothesized that warblers would move up a habitat quality gradient when opportunities arose. For our study species, that would involve moving into sites with greater shrub density and at higher elevation within northern hardwoods forest, as these two features are positively correlated with reproduction and apparent survival in this species. Although the probability of site occupancy in our study landscape remained consistent throughout the breeding season (range: 0.66-0.69), occupancy models revealed substantial support for apparent movement of individuals within the breeding season. The mean probability of emigration from a point count site was 0.21 (±0.03 SE), and the mean probability of immigration to a site not previously occupied was 0.51 (±0.05 SE). The spatial distribution of this movement was a function of habitat quality. A portion of the black-throated blue warbler population appears to arrive on the breeding grounds and settle initially in sub-optimal habitat, moving subsequently into high quality densely shrubbed habitat at higher elevations. This modeling approach provides a new means to test hypotheses about habitat selection and movement by using presence-non-detection data.

Progress toward understanding factors that limit abundances of migratory birds, including climate change, has been difficult because these species move between diverse locations, often on different continents. For black-throated blue warblers (Dendroica caerulescens), demographic rates in both tropical winter quarters and north temperate breeding grounds varied with fluctuations in the El Niño Southern Oscillation. Adult survival and fecundity were lower in El Niño years and higher in La Niña years. Fecundity, in turn, was positively correlated with subsequent recruitment of new individuals into winter and breeding populations. These findings demonstrate that migratory birds can be affected by shifts in global climate patterns and emphasize the need to know how events throughout the annual cycle interact to determine population size.