Thomas B. Ryder

Population demography of Gray Catbirds in the suburban matrix: sources, sinks and domestic cats

Understanding factors that limit the productivity and survival of birds in rapidly changing human-dominated landscapes are key to managing future population persistence. To date, few studies have quantified both nest success and post-fledging survival for birds breeding within the suburban matrix. Here, we estimated nest success and juvenile post-fledging survival for Gray Catbirds (Dumatella carolinensis) and used those site-specific parameters to model source–sink dynamics at three sites in suburban Washington DC (USA). Cumulative nest success probability varied substantially among suburban sites and indicated that in some cases suburban habitats may provide suitable breeding sites for passerine birds. In addition, we documented the effects of sex and brood size on post-fledging survival rates and determined the role of predation on dispersing fledglings. Like nest success, estimates of post-fledging juvenile survival also varied among sites and highlight the importance of site-specific demographic estimates in urban habitats. Predation accounted for 79% of all mortalities, with 47% of known predation events attributable to domestic cats (Felis catus). Our models of source–sink dynamics underscore the importance of seasonal recruitment parameters for calculating population growth rate and subsequent persistence. This study provides parameter estimates for two critical life history stages in the avian annual cycle in the suburban matrix and posits that predation drives differential nest and post-fledging survival within human-dominated environments.ZusammenfassungUm zu gewährleisten, dass Populationen in der Zukunft fortbestehen, liegt ein Schlüssel im Verständnis der Faktoren, die in sich rasant verändernden, menschendominierten Lebensräumen die Produktivität und das Überleben von Vögeln begrenzen. Bis heute haben nur wenige Studien sowohl den Bruterfolg als auch das Überleben nach dem Ausfliegen von Vögeln untersucht, die in der suburbanen Matrix brüten. Wir haben hier den Bruterfolg und die Überlebensrate von Jungvögeln der Katzendrossel (Dumatella carolinensis) nach dem Ausfliegen bestimmt und verwendeten diese ortsabhängigen Parameter für eine Modellierung der Quellen-Senken-Dynamiken an drei Standorten in Vorstädten von Washington DC (USA). Die kumulierte Bruterfolgswahrscheinlichkeit unterschied sich stark zwischen den Standorten und wies darauf hin, dass in einigen Fällen Vorstadthabitate durchaus passende Brutplätze für Singvögel bieten. Zusätzlich dokumentierten wir den Einfluss von Geschlecht und Brutgröße auf die Überlebensraten nach dem Ausfliegen und bestimmten die Rolle von Prädation auf dispergierende Jungvögel nach dem flügge werden. Ebenso wie der Bruterfolg variierten die Schätzungen der Überlebensraten der Jungvögel nach dem Ausfliegen zwischen den Standorten und unterstreichen die Bedeutung ortsspezifischer demographischer Bestimmungen in städtischen Lebensräumen. Prädation war in 79% die Todesursache, dabei gingen 47% der Prädationsereignisse auf Hauskatzen (Felis catus) zurück. Unsere Modelle der Quellen-Senken-Dynamiken betonen die Bedeutung saisonaler Rekrutierungsparameter zur Berechnung von Wachstumsraten und darauf folgendem Fortbestehen von Populationen. Die vorliegende Arbeit erlaubt Parameterschätzungen für zwei kritische Lebensphasen im Jahreszyklus von Vögeln in der Vorstadtmatrix und stellt heraus, dass in menschendominierten Lebensräumen Prädation maßgeblich zu Unterschieden in der Überlebensrate im Nest und nach dem Ausfliegen führt.

Social networks in the lek-mating wire-tailed manakin (Pipra filicauda)

How social structure interacts with individual behaviour and fitness remains understudied despite its potential importance to the evolution of cooperation. Recent applications of network theory to social behaviour advance our understanding of the role of social interactions in various contexts. Here we applied network theory to the social system of lek-mating wire-tailed manakins (Pipra filicauda, Pipridae, Aves). We analysed the network of interactions among males in order to begin building a comparative framework to understand where coordinated display behaviour lies along the continuum from solitary to obligately cooperative dual-male displays in the family Pipridae. Network degree (the number of links from a male to others) ranged from 1 to 10, with low mean and high variance, consistent with the theory for the evolution of cooperation within social networks. We also assessed factors that could predict social and reproductive success of males. Four network metrics, degree, eigenvector centrality, information centrality and reach, some of which assess circuitous as well as the shortest (geodesic) paths of male connectivity, predicted male social rise. The duration of a males territorial tenure during the 4 years of the study predicted his probability of siring offspring.

It takes two to tango: reproductive skew and social correlates of male mating success in a lek-breeding bird

Variance in reproductive success among individuals is a defining characteristic of many social vertebrates. Yet, our understanding of which male attributes contribute to reproductive success is still fragmentary in most cases. Male–male reproductive coalitions, where males jointly display to attract females, are of particular interest to evolutionary biologists because one male appears to forego reproduction to assist the social partner. By examining the relationship between social behaviour and reproductive success, we can elucidate the proximate function of coalitions in the context of mate choice. Here, we use data from a 4-year study of wire-tailed manakins (Pipra filicauda) to provide molecular estimates of reproductive skew and to test the hypothesis that male–male social interactions, in the context of coordinated displays, positively influence a males reproductive success. More specifically, we quantify male–male social interactions using network metrics and predict that greater connectivity will result in higher relative reproductive success. Our data show that four out of six leks studied had significant reproductive skew, with success apportioned to very few individuals in each lek. Metrics of male social affiliations derived from our network analysis, especially male connectivity, measured as the number of males with whom the focal male has extended interactions, were strong predictors of the number of offspring sired. Thus, network connectivity is associated with male fitness in wire-tailed manakins. This pattern may be the result of shared cues used by both sexes to assess male quality, or the result of strict female choice for coordinated display behaviour.

ESTIMATING MIGRATORY CONNECTIVITY OF GRAY CATBIRDS (DUMETELLA CAROLINENSIS) USING GEOLOCATOR AND MARK-RECAPTURE DATA

ABSTRACT. Understanding the connectivity between breeding and nonbreeding populations of migratory birds is fundamental to our knowledge of biological phenomena such as population dynamics and dispersal. Moreover, our ability to quantify migratory connectivity has inevitable consequences for both conservation and management of species that utilize distinct geographic locations. Technology is rapidly advancing our ability to track birds throughout the annual cycle and to collect data on the degree of connectivity among breeding and nonbreeding populations. We combined two direct methods, mark—recapture (n = 17) and geolocation (n = 6), to estimate the migratory connectivity of breeding and nonbreeding populations of Gray Catbirds (Dumetella carolinensis). Data from geolocators show that birds breeding in the Mid-Atlantic overwinter in both Cuba and southern Florida. Mark-recapture data supported our geolocator results but also provided a broader spatial perspective by documenting that Mid-Atlantic and Midwestern populations occupy distinct geographic localities during the nonbreeding period. This research underscores the importance of geolocators, as well as other tools, to advance our understanding of migratory connectivity. Finally, our results highlight the potential value of U.S. Geological Survey (USGS) Bird Banding Laboratory mark-recapture data, which are often underutilized in ornithological research.

Quantifying drivers of population dynamics for a migratory bird throughout the annual cycle.

Worldwide, migratory species are undergoing rapid declines but understanding the factors driving these declines is hindered by missing information about migratory connectivity and the lack of data to quantify environmental processes across the annual cycle. Here, we combined range-wide information about migratory connectivity with global remote-sensing data to quantify the relative importance of breeding and non-breeding environmental processes to persistent long-term population declines of a migratory songbird, the wood thrush (Hylocichla mustelina). Consistent with theoretical predictions about population limitation of migratory birds, our results suggest that habitat loss and climate have contributed to the observed declines in wood thrush breeding abundance, yet the relative importance of breeding versus non-breeding factors is population-specific. For example, high-abundance core breeding populations appear to be more limited by habitat loss, whereas low-abundance, peripheral populations appear to be limited by climate-driven seasonal interactions. Further, our analysis indicates that the relative impact of breeding habitat loss is at least three to six times greater than the impact of equivalent non-breeding habitat loss and therefore the steepest regional declines have likely been driven by the loss of breeding habitat. These results underscore the need for population-specific conservation strategies implemented throughout the annual cycle to reverse long-term declines.

A TEST OF THE ENVIRONMENTAL HOTSPOT HYPOTHESIS FOR LEK PLACEMENT IN THREE SPECIES OF MANAKINS (PIPRIDAE) IN ECUADOR

Abstract Lekking is classified as a form of male-dominance polygyny in which males lack control of resources essential for the acquisition of females. Of particular interest to behavioral ecologists has been the mechanistic basis of male spatial aggregation and the maintenance of site fidelity over time. The “hotspot” hypothesis has been proposed as both an ultimate and proximate mechanism by which males aggregate in locations where females are likely to be encountered. The hypothesis has been extended to include areas of the environment that act to constrain females’ use of space. Here, we test a prediction of this hypothesis for three species of manakins (Pipridae): that leks are located in places where fruit, the main food for these frugivorous birds, is plentiful. We compared four lek sites with four non-lek control sites of Golden-headed (Pipra erythrocephala), Wire-tailed (P. filicauda), and White-crowned (P. pipra) manakins in an Amazonian forest in Ecuador. Our results show that lek sites had higher fruit biomass than control sites. Moreover, lek sites had more plants bearing ripe fruit as well as a higher fruit biomass per plant than control sites. Thus, our results support the environmental hotspot hypothesis as an explanation for current lek site occupancy and suggest that fruit availability may also explain the placement of traditional manakin lekking sites. We also discuss a potential direct benefit for subordinate male manakins derived from the notion of central-place foraging and public information-sharing. Una Prueba de la Hipótesis de que Puntos que Concentran Recursos Explican la Ubicación de las Asambleas de Cortejo en Tres Especies de Saltarines (Pipridae) en Ecuador

Assessing migratory connectivity for a long‐distance migratory bird using multiple intrinsic markers

Patterns of migratory connectivity are a vital yet poorly understood component of the ecology and evolution of migratory birds. Our ability to accurately characterize patterns of migratory connectivity is often limited by the spatial resolution of the data, but recent advances in probabilistic assignment approaches have begun pairing stable isotopes with other sources of data (e.g., genetic and mark-recapture) to improve the accuracy and precision of inferences based on a single marker. Here, we combine stable isotopes and geographic variation in morphology (wing length) to probabilistically assign Wood Thrush (Hylocichla mustilena) captured on the wintering grounds to breeding locations. In addition, we use known-origin samples to validate our model and assess potentially important impacts of isotopic and morphological covariates (age, sex, and breeding location). Our results show that despite relatively high levels of mixing across their breeding and nonbreeding ranges, moderate levels of migratory connectivity exist along an east-west gradient. In addition, combining stable isotopes with geographic variation in wing length improved the precision of breeding assignments by 10% and 37% compared to assignments based on isotopes alone or wing length alone, respectively. These results demonstrate that geographical variation in morphological traits can greatly improve estimates of migratory connectivity when combined with other intrinsic markers (e.g., stable isotopes or genetic data). The wealth of morphological data available from museum specimens across the world represents a tremendously valuable, but largely untapped, resource that is widely applicable for quantifying patterns of migratory connectivity.

Characterizing avian survival along a rural‐to‐urban land use gradient

Many avian species persist in human-dominated landscapes; however, little is known about the demographic consequences of urbanization in these populations. Given that urban habitats introduce novel benefits (e.g., anthropogenic resources) and pressures (e.g., mortality risks), conflicting mechanisms have been hypothesized to drive the dynamics of urban bird populations. Top-down processes such as predation predict reduced survivorship in suburban and urban habitats, whereas bottom-up processes, such as increased resource availability, predict peak survival in suburban habitats. In this study, we use mark–recapture data of seven focal species encountered between 2000 and 2012 to test hypotheses about the processes that regulate avian survival along an urbanization gradient in greater Washington, D.C., USA. American Robin, Gray Catbird, Northern Cardinal, and Song Sparrow exhibited peak survival at intermediate and upper portions of the rural-to-urban gradient; this pattern supports the hypothesis that bott...

Decay of interspecific avian flock networks along a disturbance gradient in Amazonia

Our understanding of how anthropogenic habitat change shapes species interactions is in its infancy. This is in large part because analytical approaches such as network theory have only recently been applied to characterize complex community dynamics. Network models are a powerful tool for quantifying how ecological interactions are affected by habitat modification because they provide metrics that quantify community structure and function. Here, we examine how large-scale habitat alteration has affected ecological interactions among mixed-species flocking birds in Amazonian rainforest. These flocks provide a model system for investigating how habitat heterogeneity influences non-trophic interactions and the subsequent social structure of forest-dependent mixed-species bird flocks. We analyse 21 flock interaction networks throughout a mosaic of primary forest, fragments of varying sizes and secondary forest (SF) at the Biological Dynamics of Forest Fragments Project in central Amazonian Brazil. Habitat type had a strong effect on network structure at the levels of both species and flock. Frequency of associations among species, as summarized by weighted degree, declined with increasing levels of forest fragmentation and SF. At the flock level, clustering coefficients and overall attendance positively correlated with mean vegetation height, indicating a strong effect of habitat structure on flock cohesion and stability. Prior research has shown that trophic interactions are often resilient to large-scale changes in habitat structure because species are ecologically redundant. By contrast, our results suggest that behavioural interactions and the structure of non-trophic networks are highly sensitive to environmental change. Thus, a more nuanced, system-by-system approach may be needed when thinking about the resiliency of ecological networks.

Proximity data-loggers increase the quantity and quality of social network data

Social network analysis is an ideal quantitative tool for advancing our understanding of complex social behaviour. However, this approach is often limited by the challenges of accurately characterizing social structure and measuring network heterogeneity. Technological advances have facilitated the study of social networks, but to date, all such work has focused on large vertebrates. Here, we provide proof of concept for using proximity data-logging to quantify the frequency of social interactions, construct weighted networks and characterize variation in the social behaviour of a lek-breeding bird, the wire-tailed manakin, Pipra filicauda. Our results highlight how this approach can ameliorate the challenges of social network data collection and analysis by concurrently improving data quality and quantity.