Community structure of raptors in the páramo landscape of the Ecuadorian Andes

Introduction: Habitat alterations result in biodiversity loss, particularly in regions with high levels of diversity and endemism. Raptors are an essential part of the functionality and stability of ecosystems and indicators of habitat quality. In the paramo grassland ecosystems in the high Andes of Northern South America, raptors contain a high concentration of threatened species. Objective: To describe the raptor community structure and determine the species associations. Methods: We made monthly raptor counts in eight transects from October 2021 to September 2022 and used a principal component analysis to determine species associations. Results: We identified 149 individuals (seven species, three families) in two communities: abundant (Carunculated Caracara, Variable Hawk, Andean Condor and Turkey Vulture; PCI = 47 %), and scarce (Cinereous Harrier, Peregrine Falcon and Aplomado Falco; PCII = 27 %). Conclusion: We provide a valid description and understanding of raptor community structure, identifying two communities and the dynamics between them. The first is characterized by an increased abundance of generalist and regionally common species, when the abundance of these species decreases, the second community is defined, characterized by an increase in the abundance of specialist and rare species at the local scale.

Introducción: Las alteraciones del hábitat provocan la pérdida de biodiversidad, especialmente en regiones con altos niveles de diversidad y endemismo. Las aves rapaces son una parte esencial de la funcionalidad y estabilidad de los ecosistemas, y son indicadores de la calidad del hábitat. En los ecosistemas de páramo en los Andes del norte de Sudamérica, hay una concentración de especies rapaces amenazadas. Objetivo: Describir la estructura de la comunidad de aves rapaces y determinar las asociaciones entre las especies. Métodos: Hicimos conteos mensuales de rapaces en ocho transectos, de octubre 2021 a setiembre 2022 y usamos un análisis de componentes principales para determinar las asociaciones entre especies. Resultados: Identificamos 149 individuos (siete especies, tres familias) en dos comunidades: abundantes (e.g., Caracara Curiquingue, Gavilán Variable, Cóndor Andino y Gallinazo Cabecirrojo; PCI = 47 %), y poco abundantes (e.g., Caracara Curiquingue, Gavilán Variable, Cóndor Andino y Gallinazo Cabecirrojo; PCII = 27 %). Conclusiones: Nuestro enfoque proporciona una descripción y comprensión válida de la estructura de la comunidad de rapaces. Identificamos dos comunidades y la dinámica entre ellas. La primera se caracteriza por una mayor abundancia de especies generalistas y regionalmente comunes, cuando la abundancia de estas especies disminuye, se define la segunda comunidad, caracterizada por un aumento de la abundancia de especies especialistas y raras a escala local.

Comprehensive inventory of páramo birds and their habitat affinities in a conservation hotspot, the Macizo del Cajas Biosphere Reserve, southern Ecuador

The páramo ecosystem is a significant centre of Andean bird diversity with high concentrations of threatened species. The Macizo del Cajas Biosphere Reserve's páramos are a district of the biogeographic páramo province of northern Andes and are therefore considered a conservation hotspot with representative bird diversity. To enhance regional conservation efforts, comprehensive inventories of bird species that occupy this páramo are required. We present an updated bird inventory for the páramos of Macizo del Cajas and included validated records from eBird and GBIF databases along with records from continuous monitoring across this páramo landscape for five years. We also provide notes on habitat affinity and important new, rare, restricted range, and threatened birds. We report 112 bird species within the reserve, including five endemics, and three globally and 12 nationally threatened species. Finally, we discuss the use of habitat affinities as indicators of biodiversity patterns in páramo to improve conservation tools for key habitats.

El ecosistema de páramo es un centro importante de diversidad de aves andinas con altas concentraciones de especies amenazadas. Los páramos de la Reserva de la Biosfera Macizo del Cajas son un distrito biogeográfico de la provincia del páramo de los Andes del norte y por tanto, son un punto crítico de conservación con una diversidad de aves representativa. Inventarios exhaustivos de la avifauna que ocupa este páramo son requeridos para asegurar esfuerzos de conservación regional. El presente estudio brinda un inventario actualizado de aves de los páramos del Macizo del Cajas. Se incluyen registros verificados desde eBird y GBIF, así como registros de cinco años continuos de monitoreo a través del paisaje de páramo. Además, se incluyen notas acerca de la afinidad de hábitat y registros importantes, nuevos, raros y de aves amenazadas. En total, se reportan 112 especies de aves dentro de la reserva, incluyen cinco endémicas, tres globalmente amenazadas y 12 a escala nacional. Finalmente, se discute el uso de la afinidad de hábitat como indicador de los patrones de biodiversidad en el páramo para mejorar herramientas de conservación para hábitats clave.

Multiple lines of evidence suggest the persistence of the Ivory-billed Woodpecker (Campephilus principalis) in Louisiana.

The history of the decline of the Ivory-billed Woodpecker is long and complex, but the status of the species since 1944, when the last widely accepted sighting in continental North America occurred, is particularly controversial. Reports of Ivory-billed Woodpeckers have continued, but none has reached the threshold of quality for general acceptance by ornithologists or the birdwatching public. In 2021, the U.S. Fish and Wildlife Service opened for public comment a proposal to declare the species extinct. Here, we present evidence suggesting the presence of the Ivory-billed Woodpecker at our study site, based on a variety of data collected over a 10-year search period, 2012-2022. These data are drawn from visual observations, ~70,000 h of recordings by 80-100 acoustic recording units, ~472,550 camera-hours by as many as 34 trail cameras, and ~1089 h of video drawn from ~3265 drone flights. Using multiple lines of evidence, the data suggest intermittent but repeated presence of multiple individual birds with field marks and behaviors consistent with those of Ivory-billed Woodpeckers. Data indicate repeated reuse of foraging sites and core habitat. Our findings, and the inferences drawn from them, suggest that not all is lost for the Ivory-billed Woodpecker, and that it is clearly premature for the species to be declared extinct.

Two is better than one: Coupling DNA metabarcoding and stable isotope analysis improves dietary characterizations for a riparian-obligate, migratory songbird.

While an increasing number of studies are adopting molecular and chemical methods for dietary characterization, these studies often employ only one of these laboratory-based techniques; this approach may yield an incomplete, or even biased, understanding of diet due to each method's inherent limitations. To explore the utility of coupling molecular and chemical techniques for dietary characterizations, we applied DNA metabarcoding alongside stable isotope analysis to characterize the dietary niche of breeding Louisiana waterthrush (Parkesia motacilla), a migratory songbird hypothesized to preferentially provision its offspring with pollution-intolerant, aquatic arthropod prey. While DNA metabarcoding was unable to determine if waterthrush provision aquatic and terrestrial prey in different abundances, we found that specific aquatic taxa were more likely to be detected in successive seasons than their terrestrial counterparts, thus supporting the aquatic specialization hypothesis. Our isotopic analysis added greater context to this hypothesis by concluding that breeding waterthrush provisioned Ephemeroptera and Plecoptera, two pollution-intolerant, aquatic orders, in higher quantities than other prey groups, and expanded their functional trophic niche when such prey were not abundantly provisioned. Finally, we found that the dietary characterizations from each approach were often uncorrelated, indicating that the results gleaned from a diet study can be particularly sensitive to the applied methodologies. Our findings contribute to a growing body of work indicating the importance of high-quality, aquatic habitats for both consumers and their pollution-intolerant prey, while also demonstrating how the application of multiple, laboratory-based techniques can provide insights not offered by either technique alone.

Genetic confirmation of a hybrid between two highly divergent cardinalid species: A rose-breasted grosbeak (Pheucticus ludovicianus) and a scarlet tanager (Piranga olivacea).

Using low-coverage whole-genome sequencing, analysis of vocalizations, and inferences from natural history, we document a first-generation hybrid between a rose-breasted grosbeak (Pheucticus ludovicianus) and a scarlet tanager (Piranga olivacea). These two species occur sympatrically throughout much of eastern North America, although were not previously known to interbreed. Following the field identification of a putative hybrid, we use genetic and bioacoustic data to show that a rose-breasted grosbeak was the maternal parent and a scarlet tanager was the paternal parent of the hybrid, whose song was similar to the latter species. These two species diverged >10 million years ago, and thus it is surprising to find a hybrid formed under natural conditions in the wild. Notably, the hybrid has an exceptionally heterozygous genome, with a conservative estimate of a heterozygous base every 100 bp. The observation that this hybrid of such highly divergent parental taxa has survived until adulthood serves as another example of the capacity for hybrid birds to survive with an exceptionally divergent genomic composition.

Integrating DNA-Based Prey Occurrence Probability into Stable Isotope Mixing Models.

The introduction of laboratory methods to animal dietary studies has allowed researchers to obtain results with accuracy and precision, not possible with observational techniques. For example, DNA barcoding, or the identification of prey with taxon-specific DNA sequences, allows researchers to classify digested prey tissues to the species-level, while stable isotope analysis paired with Bayesian mixing models can quantify dietary contributions by comparing a consumer's isotopic values to those derived from their prey. However, DNA-based methods are currently only able to classify, but not quantify, the taxa present in a diet sample, while stable isotope analysis can only quantify dietary taxa that are identified a priori as prey isotopic values are a result of life history traits, not phylogenetic relatedness. Recently, researchers have begun to couple these techniques in dietary studies to capitalize on the reciprocal benefits and drawbacks offered by each approach, with some even integrating DNA-based results directly into Bayesian mixing models as informative priors. As the informative priors used in these models must represent known dietary compositions (e.g., percentages of prey biomasses), researchers have scaled the DNA-based frequency of occurrence of major prey groups so that their normalized frequency of occurrence sums to 100%. Unfortunately, such an approach is problematic as priors stemming from binomial, DNA-based data do not truly reflect quantitative information about the consumer's diet and may skew the posterior distribution of prey quantities as a result. Therefore, we present a novel approach to incorporate DNA-based dietary information into Bayesian stable isotope mixing models that preserves the binomial nature of DNA-based results. This approach uses community-wide frequency of occurrence or logistic regression-based estimates of prey occurrence to dictate the probability that each prey group is included in each mixing model iteration, and, in turn, the probability that each iteration's results are included in the posterior distribution of prey composition possibilities. Here, we demonstrate the utility of this method by using it to quantify the prey composition of nestling Louisiana waterthrush (Parkesia motacilla).

Temporal stability in species richness but reordering in species abundances within avian assemblages of a tropical Andes conservation hot spot.

As the pace of environmental change increases, there is an urgent need for quantitative data revealing the temporal dynamics of local communities in tropical areas. Here, we quantify the stability of avian assemblages in the highly threatened, but poorly studied, Andean biodiversity hot spot. We evaluated the temporal variation in species richness and community composition of local bird assemblages in three habitat types (native forest, introduced forest, native shrub) using a unique, relatively long-term data series from Cajas National Park and Mazán Reserve in the southern Andes of Ecuador. We sampled birds with mist nets using a standardized protocol over 11 years, from 2006 to 2016. Species richness remained stable over time across habitats, but community composition changed in the native forest. In particular, we observed taxonomic reordering in the native forest, in which the evenness in the distribution of abundances of taxa decreased over time. This finding is consistent with other studies where species richness remained constant over time while community composition changed. Our study highlights the value of long-term studies in the tropical Andes as we show that species composition of birds in a montane forest is changing, consistent with global trends in biodiversity change.

La tasa acelerada del incremento en el cambio ambiental crea la necesidad urgente de datos cuantitativos que expongan la dinámica temporal de comunidades locales en áreas tropicales. En este manuscrito, cuantificamos la estabilidad de ensambles de aves un área altamente amenazada pero poco estudiada, el hot­spot de biodiversidad Andino. Evaluamos la variación temporal en riqueza y composición del ensamble de aves local en tres tipos de hábitat (bosque nativo, bosque introducido, matorrales nativos) usando una serie de datos de largo plazo relativo, obtenidos en el Parque Nacional Cajas y la reserva Mazan, en los Andes del sur del Ecuador. Las aves se estudiaron con redes de neblina por medio de protocolos estandarizados por 11 años, desde 1996 al 2016. La riqueza de especies permaneció estable en el tiempo en todos los hábitats, pero la composición de especies cambió en el bosque nativo. En particular, observamos un reorden taxonómico en el bosque nativo, en el cual existió una diminución en la equitatividad de las distribuciones de las especies en el tiempo. Este resultado es consistente con otros estudios que encuentran que la riqueza de especies permanece constante en el tiempo mientras que la composición de la comunidad cambia. Nuestro trabajo resalta el valor de los estudios de largo tiempo en los Andes tropicales al demostrar que la composición de aves está cambiando, y concuerda con los patrones globales de cambio de la biodiversidad.

More than just nestlings: incidence of subcutaneous Philornis (Diptera: Muscidae) nest flies in adult birds.

Philornis flies Meinert (Diptera: Muscidae) have been documented parasitizing over 250 bird species, some of which are endemic species threatened with extinction. Philornis parasitism is hypothesized to affect nestlings disproportionately more than adult birds because limited mobility and exposed skin of nestlings increase their vulnerability to parasitism. We used a comprehensive literature review and our recent fieldwork in the Dominican Republic, Puerto Rico, and Grenada to challenge the idea that parasitism by subcutaneous Philornis species is a phenomenon primarily found in nestlings, a fact that has not been quantified to date. Of the 265 reviewed publications, 125 (49%) reported incidences of parasitism by subcutaneous Philornis, but only 12 included the sampling of adult breeding birds. Nine of these publications (75%) reported Philornis parasitism in adults of ten bird species. During fieldwork in the Dominican Republic, Puerto Rico, and Grenada, we documented 14 instances of parasitism of adult birds of seven avian species. From literature review and fieldwork, adults of at least fifteen bird species across 12 families and four orders of birds were parasitized by at least five Philornis species. In both the published literature and fieldwork, incidences of parasitism of adult birds occurred predominantly in females and was frequently associated with incubation. Although our findings indicate that Philornis parasitism of adult birds is more common than widely presumed, parasite prevalence is still greater in nestlings. In the future, we recommend surveys of adult birds to better understand host-Philornis relationships across life stages. This information may be essential for the development of effective control measures of Philornis to ensure the long-term protection of bird species of conservation concern.

Avian community characteristics and demographics reveal how conservation value of regenerating tropical dry forest changes with forest age.

Expansion of secondary forests following the abandonment of agriculture may have important implications for bird conservation, but few studies have examined the dynamics of this process. We studied bird use of a chronosequence of differently-aged abandoned pastures regenerating to dry forest to better understand how the value of these habitats to birds changes over time. In a five year study on Hispaniola, we recorded 7,315 net captures of 60 species of landbirds in sites that began the study at two, five, 10, and 20 years post-abandonment, and in mature native dry forest. Twenty-five species made up 97% of all net captures. Highest capture rates were in the two youngest sites. These early-successional habitats had many over-wintering Neotropical migrants; among residents, granivores and frugivores predominated. In contrast, both the twenty-year-old and mature forest sites had few migrants, more resident insectivores and omnivorous species, and a greater proportion of endemics. Age and sex ratios, body condition and site persistence suggest early successional sites were sub-optimal for most over-wintering migrants, but habitat improved with age for three migratory species; results for permanent residents varied among species. Remnant trees and understory shrubs in the agroecological matrix likely contributed to avian diversity in regenerating dry forest sites, and proximity to mature forest also likely affected the diversity and abundance of birds in regenerating habitat. Our study shows that regenerating forests do not fully compensate for loss of mature dry forest habitat, even after 24 years of regeneration; natural restoration of complex microhabitats in dry forest sites converted to agriculture may take decades or longer. The highest value of regenerating forests may be as habitat for some over-wintering Neotropical migrants, and in creating a buffer zone that enhances biodiversity conservation by re-integrating these lands into the protected tracts of mature forest needed by the islands more unique and endemic bird species.

Stream acidification and reduced aquatic prey availability are associated with dietary shifts in an obligate riparian Neotropical migratory songbird.

Streams and their surrounding riparian habitats are linked by reciprocal exchanges of insect prey essential to both aquatic and terrestrial consumers. Aquatic insects comprise a large proportion of total prey in riparian habitats and are opportunistically exploited by terrestrial insectivores; however, several species of songbirds are known to preferentially target aquatic prey via specialized foraging strategies. For these songbirds, reduced availability of aquatic insects via stream acidification may result in compensatory changes in provisioning during the nesting period, thereby influencing both adult and nestling diet composition. In this study, we used DNA metabarcoding to test the hypothesis that an obligate riparian Neotropical migratory songbird, the Louisiana Waterthrush (Parkesia motacilla), expands its diet to compensate for the loss of preferred aquatic prey taxa (primarily pollution-sensitive Ephemeroptera, Plecoptera, and Trichoptera) as a result of stream acidification. Our results revealed that both adult and nestling waterthrush exhibited an increase in dietary richness and niche breadth resulting from the consumption of terrestrial prey taxa in acidified riparian habitats. In contrast, compensatory dietary shifts were not observed in syntopic Neotropical migrant species known to primarily provision terrestrial prey taxa. In addition to providing support for our hypothesis that waterthrush compensate for stream acidification and aquatic prey limitations by expanding their diet, our findings highlight the vulnerability of Louisiana Waterthrush to anthropogenic disturbances that compromise stream quality or reduce the availability of pollution-sensitive aquatic insects.

DNA metabarcoding of nestling feces reveals provisioning of aquatic prey and resource partitioning among Neotropical migratory songbirds in a riparian habitat.

Riparian habitats are characterized by substantial flows of emergent aquatic insects that cross the stream-forest interface and provide an important source of prey for insectivorous birds. The increased availability of prey arising from aquatic subsidies attracts high densities of Neotropical migratory songbirds that are thought to exploit emergent aquatic insects as a nestling food resource; however, the prey preferences and diets of birds in these communities are only broadly understood. In this study, we utilized DNA metabarcoding to investigate the extent to which three syntopic species of migratory songbirds-Acadian Flycatcher, Louisiana Waterthrush, and Wood Thrush-breeding in Appalachian riparian habitats (Pennsylvania, USA) exploit and partition aquatic prey subsidies as a nestling food resource. Despite substantial differences in adult foraging strategies, nearly every nestling in this study consumed aquatic taxa, suggesting that aquatic subsidies are an important prey resource for Neotropical migrants nesting in riparian habitats. While our results revealed significant interspecific dietary niche divergence, the diets of Acadian Flycatcher and Wood Thrush nestlings were strikingly similar and exhibited significantly more overlap than expected. These results suggest that the dietary niches of Neotropical migrants with divergent foraging strategies may converge due to the opportunistic provisioning of non-limiting prey resources in riparian habitats. In addition to providing the first application of DNA metabarcoding to investigate diet in a community of Neotropical migrants, this study emphasizes the importance of aquatic subsidies in supporting breeding songbirds and improves our understanding of how anthropogenic disturbances to riparian habitats may negatively impact long-term avian conservation.

Long-term monitoring reveals an avian species credit in secondary forest patches of Costa Rica.

Degraded and secondary forests comprise approximately 50% of remaining tropical forest. Bird community characteristics and population trends in secondary forests are infrequently studied, but secondary forest may serve as a "safety net" for tropical biodiversity. Less understood is the occurrence of time-delayed, community-level dynamics such as an extinction debt of specialist species or a species credit resulting from the recolonization of forest patches by extirpated species. We sought to elucidate patterns and magnitudes of temporal change in avian communities in secondary forest patches in Southern Costa Rica biannually over a 10 year period during the late breeding season and mid-winter. We classified birds caught in mist nets or recorded in point counts by residency status, and further grouped them based on preferred habitat, sensitivity to disturbance, conservation priority, foraging guild, and foraging strata. Using hierarchical, mixed-effects models we tested for trends among species that share traits. We found that permanent-resident species increased over time relative to migrants. In both seasons, primary forest species generally increased while species typical of secondary forest, scrub, or edge declined. Species relatively sensitive to habitat disturbance increased significantly over time, whereas birds less sensitive to disturbance decreased. Similarly, generalists with higher habitat breadth scores declined. Because, we found very few changes in vegetation characteristics in secondary forest patches, shifts in the avian community toward primary forest species represent a species credit and are likely related to vegetation changes in the broader landscape. We suggest that natural regeneration and maturation of secondary forests should be recognized as a positive conservation development of potential benefit even to species typical of primary forest.

Dynamics of avian haemosporidian assemblages through millennial time scales inferred from insular biotas of the West Indies.

Although introduced hemosporidian (malaria) parasites (Apicomplexa: Haemosporida) have hastened the extinction of endemic bird species in the Hawaiian Islands and perhaps elsewhere, little is known about the temporal dynamics of endemic malaria parasite populations. Haemosporidian parasites do not leave informative fossils, and records of population change are lacking beyond a few decades. Here, we take advantage of the isolation of West Indian land-bridge islands by rising postglacial sea levels to estimate rates of change in hemosporidian parasite assemblages over a millennial time frame. Several pairs of West Indian islands have been connected and separated by falling and rising sea levels associated with the advance and retreat of Pleistocene continental glaciers. We use island isolation following postglacial sea-level rise, ca. 2.5 ka, to characterize long-term change in insular assemblages of hemosporidian parasites. We find that assemblages on formerly connected islands are as differentiated as assemblages on islands that have never been connected, and both are more differentiated than local assemblages sampled up to two decades apart. Differentiation of parasite assemblages between formerly connected islands reflects variation in the prevalence of shared hemosporidian lineages, whereas differentiation between islands isolated by millions of years reflects replacement of hemosporidian lineages infecting similar assemblages of avian host species.

Use of data on avian demographics and site persistence during overwintering to assess quality of restored riparian habitat.

Monitoring responses by birds to restoration of riparian vegetation is relatively cost-effective, but in most assessments species-specific abundances, not demography, are monitored. Data on birds collected during the nonbreeding season are particularly lacking. We captured birds in mist nets and resighted banded birds to estimate species richness and diversity, abundance, demographic indexes, and site-level persistence of permanent-resident and overwintering migrants in remnant and restored riparian sites in California. Species richness in riparian remnants was significantly higher than in restored sites because abundances of uncommon permanent residents were greater in remnants. Species richness of overwintering migrants did not differ between remnants and restored sites. Responses among overwintering migrants (but not permanent residents) to remnant and restored riparian sites differed. Capture rates were higher in remnant or restored riparian sites for 7 of 10 overwintering migratory species. For Lincoln's Sparrows (Melospiza lincolnii) and White-crowned Sparrows (Zonotrichia leucophrys) proportions of older birds were significantly higher in remnants, even though capture rates of these species were higher in restored sites. Overwinter persistence of 4 migrant species was significantly higher in remnant than in restored sites. A higher proportion of Hermit Thrushes (Catharus guttatus, 56.3%), older Fox Sparrows (Passerella iliaca, 57.1%), Lincoln's Sparrows (59.7%), and White-crowned Sparrows (67.8%) persisted in remnants than restored sites. Our results suggest restored riparian sites provide habitat for a wide variety of species in comparable abundances and diversity as occurs in remnant riparian sites. Our demographic and persistence data showed that remnants supported some species and age classes to a greater extent than restored sites.

Ancient islands and modern invasions: disparate phylogeographic histories among Hispaniola's endemic birds.

With its large size, complex topography and high number of avian endemics, Hispaniola appears to be a likely candidate for the in situ speciation of its avifauna, despite the worldwide rarity of avian speciation within single islands. We used multilocus comparative phylogeography techniques to examine the pattern and history of divergence in 11 endemic birds representing potential within-island speciation events. Haplotype and allele networks from mitochondrial ND2 and nuclear intron loci reveal a consistent pattern: phylogeographic divergence within or between closely related species is correlated with the likely distribution of ancient sea barriers that once divided Hispaniola into several smaller paleo-islands. Coalescent and mitochondrial clock dating of divergences indicate species-specific response to different geological events over the wide span of the island's history. We found no evidence that ecological or topographical complexity generated diversity, either by creating open niches or by restricting long-term gene flow. Thus, no true within-island speciation appears to have occurred among the species sampled on Hispaniola. Divergence events predating the merging of Hispaniola's paleo-island blocks cannot be considered in situ divergence, and postmerging divergence in response to episodic island segmentation by marine flooding probably represents in situ vicariance or interarchipelago speciation by dispersal. Our work highlights the necessity of considering island geologic history while investigating the speciation-area relationship in birds and other taxa.

Conserving migratory land birds in the new world: do we know enough?

Migratory bird needs must be met during four phases of the year: breeding season, fall migration, wintering, and spring migration; thus, management may be needed during all four phases. The bulk of research and management has focused on the breeding season, although several issues remain unsettled, including the spatial extent of habitat influences on fitness and the importance of habitat on the breeding grounds used after breeding. Although detailed investigations have shed light on the ecology and population dynamics of a few avian species, knowledge is sketchy for most species. Replication of comprehensive studies is needed for multiple species across a range of areas, Information deficiencies are even greater during the wintering season, when birds require sites that provide security and food resources needed for survival and developing nutrient reserves for spring migration and, possibly, reproduction. Research is needed on many species simply to identify geographic distributions, wintering sites, habitat use, and basic ecology. Studies are complicated, however, by the mobility of birds and by sexual segregation during winter. Stable-isotope methodology has offered an opportunity to identify linkages between breeding and wintering sites, which facilitates understanding the complete annual cycle of birds. The twice-annual migrations are the poorest-understood events in a bird's life. Migration has always been a risky undertaking, with such anthropogenic features as tall buildings, towers, and wind generators adding to the risk. Species such as woodland specialists migrating through eastern North America have numerous options for pausing during migration to replenish nutrients, but some species depend on limited stopover locations. Research needs for migration include identifying pathways and timetables of migration, quality and distribution of habitats, threats posed by towers and other tall structures, and any bottlenecks for migration. Issues such as human population growth, acid deposition, climate change, and exotic diseases are global concerns with uncertain consequences to migratory birds and even less-certain remedies. Despite enormous gaps in our understanding of these birds, research, much of it occurring in the past 30 years, has provided sufficient information to make intelligent conservation efforts but needs to expand to handle future challenges.

Benefits of studies of overwintering birds for understanding resident bird ecology and promoting development of conservation capacity.

Funding of ecological research and monitoring of Neotropical migratory birds on their overwintering grounds has benefited both migratory and permanent-resident species. Using examples from our work in Puerto Rico and the Dominican Republic, we demonstrate that ecological research of overwintering migrants often provides information about the ecology and demography of little-known tropical resident birds. Critically important long-term monitoring in Puerto Rico with a focus on winter residents has provided information on the relationships between annual rainfall and fluctuations in resident bird populations and survival rates. It also has alerted local biologists to declines in resident bird populations, including a decline apparently driven by the entry of a brood parasite. But migrant-focused research may also have had an underappreciated effect on the development of conservation capacity and conservation efforts in host countries. Investments in research on Neotropical migrants overwintering on Hispaniola have resulted in a huge increase in field training of students and wildlife professionals, promoted conservation awareness at local and national levels, played an important role in the growth and professionalization of key environmental organizations, spawned a growing ecotourism industry for bird-watching, and driven national park management planning and conservation efforts for all bird species. We encourage funding organizations and agencies to consider the broader impacts of funding migratory-bird research and monitoring efforts, and we encourage researchers in the tropics to use protocols that provide the most information about all the birds that use the study areas involved and to be aware of important opportunities that they may have to build capacity in host countries.

Ancient differentiation in the single-island avian radiation of endemic Hispaniolan chat-tanagers (Aves: Calyptophilus).

The simple geographic structure of island systems often makes them tractable for studies of the patterns and processes of biological diversification. The Calyptophilus chat-tanagers of Hispaniola are of general evolutionary interest because their multiple lineages might have arisen on a single island, of conservation concern because several isolated populations are nearly extinct, and taxonomically ambiguous because they have been variously lumped or split into one to four species. To explore the context of diversification of the seven extant Calyptophilus populations, we conducted a multilocus coalescent analysis based on sequences of mitochondrial ND2 and three nuclear intron loci. We then compared patterns of phylogeographic genetic variation with the morphological differences that distinguish these populations. Mitochondrial haplotypes formed two reciprocally monophyletic groups separated by a large magnitude of nucleotide divergence. Intron structure largely paralleled the geographic grouping pattern of the mitochondrial DNA (mtDNA), but these groups were only reciprocally monophyletic at one of the three introns. Also, the magnitude of between-group divergence was much lower in the introns than mtDNA genealogies. Multilocus coalescent analyses inferred a nonzero divergence time between these two major geographic groups, but suggested that they have experienced a low level of gene flow. All four markers showed substantial allele sharing within each of the two groups, demonstrating that many now separated montane populations do not have long histories of isolation. Considered in concert, our multilocus phylogeographic reconstructions support the recognition of two species within the Calyptophilus complex, and raise the possibility that these taxa differentiated prior to the fusion of the two palaeo-islands that form present-day Hispaniola.