RESUMO
The tropical Andes are characterized by extreme topographic and climatic complexity, which has likely contributed to their outstanding current species diversity, composed of many range-restricted species. However, little is known about how the distribution and abundance of highly mobile organisms, like long-distance migratory birds, varies across different land covers, elevations, and climatic conditions within the Andes. We conducted 1,606 distance-sampling point counts across the Colombian Andes, spanning elevations from 253 to 3,708 m, a range of precipitation regimes and representative land covers. We then employed a novel application of a multispecies hierarchical modeling approach to evaluate how elevation, local land cover, aboveground woody biomass, cloud cover, precipitation, and seasonality in precipitation shape the abundance of the migratory land bird community in the Andes. We detected 1,824 individuals of 29 species of migratory land birds, six of which were considered incidental in our study region. We modeled the abundance of the remaining 23 species, while considering observer and time of day effects on detectability. We found that both elevation and land cover had an overriding influence on the abundance of migratory species across the Andes, with strong evidence for a mid-elevation peak in abundance, and species-specific responses to both variables. As a community, migratory birds had the highest mean abundance in shade coffee plantations, secondary forest, and mature forest. Aboveground woody biomass did not affect the abundance of all species as a group, but a few showed strong responses to this variable. Contrary to predictions of a positive correlation between abundance and precipitation, we found no evidence for community-level responses to precipitation, aside for a weak tendency for birds to select areas with intermediate levels of precipitation. This novel use of a multispecies model sheds new light on the mechanisms shaping the winter distribution of migratory birds and highlights the importance of elevation and land cover types over climatic variables in the context of the Colombian Andes.
Assuntos
Aves , Florestas , Animais , Biodiversidade , Biomassa , Aves/fisiologia , Humanos , Estações do Ano , Especificidade da EspécieRESUMO
Temporal variation in the connectivity of populations of migratory animals has not been widely documented, despite having important repercussions for population ecology and conservation. Because the long-distance movements of migratory animals link ecologically distinct and geographically distant areas of the world, changes in the abundance and migratory patterns of species may reflect differential drivers of demographic trends acting over various spatial scales. Using stable hydrogen isotope analyses (δ2H) of feathers from historical museum specimens and contemporary samples obtained in the field, we provide evidence for an approximately 600 km northward shift over 45 years in the breeding origin of a species of songbird of major conservation concern (blackpoll warbler, Setophaga striata) wintering in the foothills of the eastern Andes of Colombia. Our finding mirrors predictions of range shifts for boreal-breeding species under warming climate scenarios and habitat loss in the temperate zone, and underscores likely drivers of widespread declines in populations of migratory birds. Our work also highlights the value of natural history collections to document the effects of global change on biodiversity.
Assuntos
Passeriformes , Aves Canoras , Migração Animal , Animais , Colômbia , Estações do AnoRESUMO
Body mass is one of the most important phenotypic attributes in animal ecology and life history. This trait is widely used in the fields of ecology and macroevolution, since it influences physiology, morphological functions, and a myriad of ecological and social interactions. In this data set, our aim was to gather a comprehensive bird and mammal body mass data set from northern South America. We report body mass, discriminated by sex, for 42,022 individual birds and 7,441 mammals representing 1,317 bird species (69% of Colombia's avifauna) and 270 mammal species (51% of Colombian mammals) from the Neotropics. The data were sourced from vouchers collected between 1942 and 2020 and from individuals captured and released at banding stations over the last two decades for birds (2000-2020) and the last decade for mammals (2010-2020), by 10 research groups and institutions in Colombia. This data set fills gaps identified in other similar databases, as it focuses on northern South America, a highly diverse Neotropical region often underrepresented in morphological data sets. We provide wide taxonomic coverage for studies interested in information both at regional and local scales. There are no copyright restrictions; the present data paper should be appropriately cited when data are used for publication. The authors would appreciate learning about research projects, teaching exercises, and other uses given to this data set and are open to contribute in further collaborations using these data.
RESUMO
Migratory birds travel vast distances and the timing of migratory flights can affect survival and the ability to reproduce. For Neotropical migrant songbirds, early spring departure from wintering sites, early arrival to the breeding grounds and higher reproductive success have been related to the use of suitable habitats and environmental conditions during the non-breeding season. However, how migratory strategies are shaped by winter habitat choice is largely unknown due to the general inability to track birds from specific wintering habitats to stopovers or breeding destinations. We assessed how winter habitat (native forest vs. shade-grown coffee plantations) relates to spring departure date and migration pace in Swainson's Thrush Catharus ustulatus. We also determined the effect of departure date and total migration duration on the arrival date of birds detected near or within their breeding range. We used a novel application of Motus radiotelemetry arrays to track individuals from their wintering grounds in the Andes of South America along their migratory journey to North America. We found variation in migratory strategies between habitats, with birds wintering in native forest departing later than birds in coffee. We present isotopic evidence for native forest being of higher quality than shade-coffee for Swainson's Thrush and hypothesize that moister conditions in forest, as shown by stable isotope (δ13 C) analysis of thrush whole blood, provides favourable pre-migratory conditions allowing birds to delay departure from wintering grounds. Habitat, between-site and -year variation in departure date, suggests that birds made facultative adjustments to winter habitat quality and environmental conditions. Independent of habitat, birds that departed later migrated faster and this pattern was maintained along the migration route (n = 44). Migrating earlier and slower or later and faster was unlikely to result in significant differences in arrival time to breeding destinations. Our findings reveal underappreciated complexity in migratory decisions by long-distance migrants that contrast with the current paradigm of earlier departures and arrival from optimal habitats. The next step is to understand the relative fitness benefits of early versus late schedules or whether each strategy is an equally good response to experienced conditions.
Las aves migratorias viajan largas distancias y la fecha de sus vuelos migratorios puede afectar su supervivencia y habilidad para reproducirse. Para las aves migratorias Neotropicales canoras, salir más temprano de los sitios de invernada, llegar más temprano a los sitios de reproducción y tener mayor éxito reproductivo, está relacionado con el uso de hábitats y condiciones medioambientales adecuadas durante la época no reproductiva. Sin embargo, la forma en que las estrategias migratorias son moldeadas por la selección del hábitat invernal es en gran parte desconocida debido a la inhabilidad general de rastrear las aves desde hábitats de invernada específicos hasta los sitios de descanso o de reproducción. Determinamos la relación entre el hábitat de invierno (bosque nativo vs. plantaciones de café con sombra), la fecha de salida durante la migración de primavera y el número de días usados durante la migración por la mirla buchipecosa Catharus ustulatus. También determinamos el efecto de la fecha de salida y la duración total de la migración en la fecha de llegada de las aves detectadas cerca o dentro de su rango de reproducción. Usamos la novedosa red de radio telemetría Motus para rastrear individuos desde sus sitios de invernada en las montañas de los Andes en Sudamérica a lo largo de su viaje migratorio hasta Norte América. Encontramos variación en las estrategias migratorias entre hábitats, las aves invernando en bosque nativo salieron más tarde que las aves invernando en cafetales. Presentamos evidencia isotópica, que sugiere que el bosque nativo es de mejor calidad que las plantaciones de café con sombra. Hipotetizamos que condiciones más húmedas en el bosque, indicadas por análisis de isotopos estables (δ13 C) de la sangre de las mirlas, proveen condiciones favorables antes de la migración permitiendo a las aves retrasar su salida de los territorios de invernada. La variación en la fecha de salida entre hábitats, años y sitios, sugiere que las aves hicieron ajustes facultativos a la calidad del hábitat de invierno y a las condiciones medio ambientales. Independientemente del hábitat, las aves que salieron más tarde migraron más rápido, y este patrón fue mantenido a lo largo de la ruta migratoria (n = 44). Fue poco probable que migrar más temprano y más lento o más tarde y más rápido resultara en diferencias significativas en la fecha de llegada a los sitios de reproducción. Nuestros resultados revelan una subestimada complejidad en las decisiones migratorias de las aves y contrastan con el paradigma actual de salida y llegada más temprana en aves que usan hábitats óptimos. El siguiente paso es entender los beneficios relativos de migrar temprano versus tarde en el desempeño o si cada estrategia es una respuesta igualmente buena a las condiciones experimentadas.
Assuntos
Aves Canoras , Migração Animal , Animais , América do Norte , Estações do Ano , América do SulRESUMO
Long-distance migratory organisms are under strong selection to migrate quickly. Stopovers demand more time than flying and are used by individuals to refuel during migration, but the effect of fuel loads (fat) acquired at stopover sites on the subsequent pace of migration has not been quantified. We studied stopover behaviour of Grey-cheeked Thrush (Catharus minimus) at a site in northern Colombia and then tracked their migration using an intercontinental radio-telemetry array. Tracking confirmed long-distance flights of more than 3000 km, highlighting the key importance of a single stopover site to the migration strategy of this species. Our results suggest that these songbirds behave as time-minimizers as predicted by optimal migration theory, and that fuel loads acquired at this South American stopover site, together with departure date, carry-over to influence the pace of migration, contributing to differences in travel time of up to 30 days in birds subsequently detected in the U. S. and Canada. Such variation in the pace of migration arising from a single stopover site, likely has important fitness consequences and suggests that identifying important fuelling sites will be essential to effectively conserve migratory species.