Jeffrey F. Kelly

Technology on the Move: Recent and Forthcoming Innovations for Tracking Migratory Birds

Basic questions about the life histories of migratory birds have confounded scientists for generations, yet we are nearing an era of historic discovery as new tracking technologies make it possible to determine the timing and routes of an increasing number of bird migrations. Tracking small flying animals as they travel over continental-scale distances is a difficult logistical and engineering challenge. Although no tracking system works well with all species, improvements to traditional technologies, such as satellite tracking, along with innovations related to global positioning systems, cellular networks, solar geolocation, radar, and information technology are improving our understanding of when and where birds go during their annual cycles and informing numerous scientific disciplines, including evolutionary biology, population ecology, and global change. The recent developments described in this article will help us answer many long-standing questions about animal behavior and life histories.

Insights into Wilson's Warbler migration from analyses of hydrogen stable-isotope ratios

Our ability to link the breeding locations of individual passerines to migration stopover sites and wintering locations is limited. Stable isotopes of hydrogen contained in bird feathers have recently shown potential in this regard. We measured hydrogen stable-isotope ratios (δD) of feathers from breeding, migrating, and wintering Wilsons Warblers. Analyses of feathers from museum specimens collected throughout the western portion of the breeding range indicate that δD values are significantly negatively related to latitude of collection (R2=0.52), which is an indication that δD values are a good descriptor of breeding latitude. Analyses of feathers collected from birds migrating through the Bosque del Apache National Wildlife Refuge, New Mexico (USA), revealed a significantly positive relationship between δD values and the timing of autumn migration (R2=0.34), but not the timing of spring migration. This pattern indicates that Wilsons Warblers that bred furthest north migrated earliest in the autumn. Finally, analysis of feathers collected on the wintering grounds indicate that the hydrogen isotope ratio is significantly positively related to wintering latitude (R2=0.80), which indicates that birds that bred furthest north wintered furthest south. In combination, these patterns suggest that in the western portion of their range, Wilsons Warblers have a leapfrog migration system in which the northern-most breeding birds pass through New Mexico early in the autumn to arrive on the wintering grounds in southern Central America, the southern edge of the Wilsons Warblers winter range. We know of no other literature documenting or suggesting that Wilsons Warbler engage in leapfrog migration. We think the novelty of these results is a reflection of the potential for stable-isotope techniques to revise our understanding of bird migration.

Combining genetic markers and stable isotopes to reveal population connectivity and migration patterns in a Neotropical migrant, Wilson's warbler (Wilsonia pusilla)

We used results from the analysis of microsatellite DNA variation and hydrogen stable‐isotope ratios to characterize the population structure of a neotropical migrant passerine, the Wilsons warbler (Wilsonia pusilla). The resulting information was then used to infer migration patterns and population connectivity between breeding grounds in North America and overwintering areas in Mexico and Central America. The microsatellite data revealed genetic structure across the North American continent; populations in the west were found to significantly differ from the east. Minimal genetic structure was observed among western sites. The lack of isolation by distance and low variance in FST values suggests that gene flow could play an ongoing role in limiting genetic differentiation among sites in the western part of the distribution. However, additional information including estimates of effective population size and the proximity of the population to equilibrium is required before the role of gene flow can be assessed fully. Analysis of isotope data showed a negative relationship between latitude and hydrogen isotope ratios in breeding ground individuals. There was a positive relationship between wintering ground latitude and hydrogen isotope ratios for individuals that were genetically western in origin. This is consistent with a leapfrog pattern of migration, in which genetically western birds from the northernmost breeding areas overwinter at the most southerly locations in Central America. Additionally, isotopic ratios of western birds suggest that coastal breeders overwinter in western Mexico, while western birds from further inland and at high elevations overwinter in eastern Mexico. Using information from both genetic an isotopic approaches will probably be useful for identifying patterns of migration and population connectivity between breeding and overwintering areas, both important issues for conservation efforts, and may also contribute to investigation of the evolution of migration.

COMBINING ISOTOPIC AND GENETIC MARKERS TO IDENTIFY BREEDING ORIGINS OF MIGRANT BIRDS

A quantitative method for linking reproductive and nonreproductive phases of migratory life cycles is fundamental to understanding the biology of migratory organisms. Here we combine genetic (mtDNA) and biochemical (stable isotope) information to examine seasonal movements in the Swainsons Thrush (Catharus ustulatus), a Neotropical migrant. We show that when these intrinsic markers are used in concert, they can predict the site-specific origin of thrushes with 76–80% accuracy. Genetic and isotope data needed for these classifications can be obtained from migratory organisms at any phase of the life cycle. We demonstrate how this classification analysis can be used to infer breeding origins of samples gathered during the nonreproductive phases of the life cycle. Based on these results, we argue that further integration of methodologies will refine the scale at which linkages between reproductive and nonreproductive phases of the life cycle can be quantified.

AN EAST-WEST COMPARISON OF MIGRATION IN NORTH AMERICAN WOOD WARBLERS

Abstract That western and eastern songbird migration routes are distinct ecological systems has been proposed for over 100 years. Nonetheless, this distinction has not been widely recognized nor have there been any comparative studies that quantitatively evaluate the differences and similarities between western and eastern songbird migration systems. We drew from previously published research on wood warblers to highlight patterns in stopover ecology that suggest fundamental differences between western and eastern migrants. In particular, we compared biogeography, evolutionary relationships, and stopover ecology of wood warblers from western and eastern North America and found: (1) multiple lines of evidence that indicate western wood warblers are geographically isolated from eastern conspecifics or congeners throughout the annual cycle, (2) eastern and western wood warbler taxa are distinct evolutionary units, (3) migrant wood warblers captured in the Southwest tended to carry lower fat loads and be comprised of more after-hatch-year birds than is typical of eastern migrants, (4) frugivory is unknown in wood warblers endemic to the Northwest or Southwest and (5) relative to other regions and seasons, riparian vegetation is heavily used by western wood warblers in the spring. We think that further examination and synthesis of these differences would yield a more mechanistic understanding of Nearctic-Neotropical avian migration. On this basis, we elaborate our view that (1) an improved understanding of western songbird migration ought to be a high priority for science, conservation, and education, and (2) large-scale coordinated research efforts would be the most effective strategy for advancing our knowledge of passerine migration in the West. Una Comparación Este-Oeste de la Migración de las Reinitas de Bosque (Parulidae) de Norte América Resumen. Por más de 100 años se ha propuesto que las rutas de migración de aves paseriformes del este y del oeste son sistemas ecológicos diferentes. Sin embargo, esta distinción no ha sido reconocida ampliamente, ni se han realizado estudios comparativos que evalúen cuantitativamente las diferencias y similitudes entre los sistemas de migración del este y del oeste. Revisamos estudios previamente publicados sobre aves de bosque de la familia Parulidae (Reinitas) para destacar los patrones ecológicos de las paradas migratorias que sugieran diferencias fundamentales entre las aves paseriformes migratorias el este y del oeste. Particularmente, comparamos la biogeografía, las relaciones evolutivas y la ecología de las paradas migratorias de las Reinitas del este y del oeste de Norteamérica y encontramos: (1) múltiples líneas de evidencia que indican que las Reinitas del oeste se encuentran geográficamente aisladas de sus coespecíficos o cogenéricos del este durante todo el ciclo anual, (2) los taxa del este y del oeste son unidades evolutivas independientes, (3) las Reinitas migratorias capturadas en el suroeste tendieron a presentar menores cargas de grasa y una mayor proporción de aves eclosionadas durante el año, que lo es típicamente observado para las aves migratorias del este, (4) la frugivoría no se conoce en las Reinitas endémicas del noroeste o sudoeste y (5) en relación a otras regiones o estaciones, la vegetación riparia es usada intensamente durante la primavera por las Reinitas del oeste. Creemos que estudios adicionales y una síntesis de estas diferencias podrían producir un mejor entendimiento mecanístico de la migración Neártico-Neotropical de aves. Basados en esto, sugerimos que (1) un mejor entendimiento de la migración de aves paserinas del oeste debería tener alta prioridad para la ciencia, conservación y educación y (2) que los esfuerzos de investigación coordinados a gran escala serían la estrategia más efectiva para progresar en nuestro conocimiento sobre la migración de las aves paserinas en el oeste.

Partly cloudy with a chance of migration: Weather, radars, and aeroecology

Aeroecology is an emerging scientific discipline that integrates atmospheric science, Earth science, geography, ecology, computer science, computational biology, and engineering to further the understanding of biological patterns and processes. The unifying concept underlying this new transdisciplinary field of study is a focus on the planetary boundary layer and lower free atmosphere (i.e., the aerosphere), and the diversity of airborne organisms that inhabit and depend on the aerosphere for their existence. Here, we focus on the role of radars and radar networks in aeroecological studies. Radar systems scanning the atmosphere are primarily used to monitor weather conditions and track the location and movements of aircraft. However, radar echoes regularly contain signals from other sources, such as airborne birds, bats, and arthropods. We briefly discuss how radar observations can be and have been used to study a variety of airborne organisms and examine some of the many potential benefits likely to aris...

Tracking migrant songbirds with stable isotopes

avian biology and one of the most astounding phenomena in the natural world. In North America alone there are approximately 350 species of land birds that migrate seasonally. Most of these species weigh considerably less than 50 g and travel thousands of kilometers twice annually. Migratory biology has attracted and, in no small measure, frustrated generations of ornithologists. Much of the frustration can be traced to a simple source – namely, it is very difficult to study an individual migrating bird for any appreciable time or distance. Traditional tracking techniques, such as radio-telemetry and banding, are largely inadequate when applied to small birds that travel large distances in short time periods. Our limited ability to trace migrant birds from breeding areas through migration to wintering areas and back again has left an astonishingly large gap in our knowledge of the biology of perhaps the best known taxon in the world. Recently, Hobson and Wassenaar1 and Chamberlain et al.2 have employed stable isotope analyses in a manner that promises to narrow this gap significantly. By improving our ability to link the breeding and wintering areas of migrant individuals these techniques have the potential to revolutionize our understanding of bird migration.

Effect of Cleaning Regime on Stable-Isotope Ratios of Feathers in Japanese Quail (Coturnix Japonica)

Abstract.— Stable-isotope analysis of feathers is an increasingly important source of information on diet and movement of birds. Feathers are typically cleaned with a solvent before analysis, but the effects of this cleaning on the resulting data have not been examined critically. We conducted an experiment to determine whether a cleaning regime affected hydrogen (&dgr;D), carbon (&dgr;13C), and nitrogen (&dgr;15N) stableisotope ratios in feathers of Japanese Quail (Coturnix japonica). A paired design was used to clean feathers with 2:1 chloroform: methanol or detergent. Results after initial cleaning indicated enrichment of hydrogen by ∼40‱ in feathers treated with 2:1 chloroform: methanol-treated compared with other treatments but no correlation between treatments. We found a similar pattern among treatments for carbon, but the effect was on the order of 0.2‱. Nitrogen values showed no discernible correlation, but both uncleaned and 2:1 chloroform: methanol treatments had enriched values, on average, compared with detergent treatments. Further, variance among samples was high for hydrogen and nitrogen measurements. After recleaning with alternate treatments, differences in mean hydrogen-isotope ratios were no longer evident, data for hydrogen and carbon became less variable, and carbon maintained its initial pattern. We suggest a standard method of cleaning feathers, first with a dilute detergent solution, then with 2:1 chloroform:methanol solvent. This study has implications for increasing repeatability of hydrogen, carbon, and nitrogen stable-isotope measurements, which would increase the validity of inter-laboratory comparisons and the utility of large-scale projects using compiled data sets.

Novel statistical methods for integrating genetic and stable isotope data to infer individual-level migratory connectivity

Methods for determining patterns of migratory connectivity in animal ecology have historically been limited due to logistical challenges. Recent progress in studying migratory bird connectivity has been made using genetic and stable‐isotope markers to assign migratory individuals to their breeding grounds. Here, we present a novel Bayesian approach to jointly leverage genetic and isotopic markers and we test its utility on two migratory passerine bird species. Our approach represents a principled model‐based combination of genetic and isotope data from samples collected on the breeding grounds and is able to achieve levels of assignment accuracy that exceed those of either method alone. When applied at large scale the method can reveal specific migratory connectivity patterns. In Wilsons warblers (Wilsonia pusilla), we detect a subgroup of birds wintering in Baja that uniquely migrate preferentially from the coastal Pacific Northwest. Our approach is implemented in a way that is easily extended to accommodate additional sources of information (e.g. bi‐allelic markers, species distribution models, etc.) or adapted to other species or assignment problems.

Bottom‐up biodiversity effects increase resource subsidy flux between ecosystems

Although biodiversity can increase ecosystem productivity and adjacent ecosystems are often linked by resource flows between them, the relationship between biodiversity and resource subsidies is not well understood. Here we test the influence of biodiversity on resource subsidy flux by manipulating freshwater mussel species richness and documenting the effects on a trophic cascade from aquatic to terrestrial ecosystems. In a mesocosm experiment, mussel effects on algae were linked through stable isotope analyses to mussel-derived nitrogen subsidies, but mussel biodiversity effects on algal accumulation were not significant. In contrast, mussel biodiversity significantly increased aquatic insect emergence rates, because aquatic insects were responding to mussel-induced changes in algal community structure instead of algal accumulation. In turn, mussel biodiversity also significantly increased terrestrial spider abundance as spiders tracked increases in aquatic insect prey after a reproduction event. In a comparative field study, we found that sites with greater mussel species richness had higher aquatic insect emergence rates. These results show that, because food webs in adjacent ecosystems are often linked, biodiversity effects in one ecosystem can influence adjacent ecosystems as well.