Migratory animals face severe time and energy constraints during their annual cycle. These constraints may be exacerbated in young animals by conditions experienced during development that can affect both phenotype and phenology. For young migratory songbirds, the period between fledging and autumn migration, the post‐fledging period, is believed to represent a time of intense selective pressure. However, there has yet to be a study that has assessed post‐fledging survival for the entirety of the post‐fledging period, probably due to the challenge of following juveniles as they move broadly across the landscape (tens to hundreds of kilometres). To overcome this challenge, we used an automated radiotelemetry array spanning 60 000 km2 in southern Ontario, Canada, and miniature digital radiotelemetry tags to track 216 juvenile Barn Swallows Hirundo rustica continuously from fledging to migration. We hypothesized that young that fledged in better condition and earlier in the breeding season would have higher survival relative to birds fledging in poorer condition, because they have more energy to deal with resource constraints, and that early‐fledging birds would depart on migration earlier than late‐fledging birds because there is probably a fixed period of time required post‐fledging to prepare for migration. We found that average cumulative apparent survival was 42% and that condition in the nest was a strong positive predictor of post‐fledging apparent survival. We also found that birds that fledged earlier in the season departed on migration earlier in the autumn relative to late‐fledging birds. Contrary to our prediction, average apparent survival was equal for early‐ and late‐fledging birds. Our results suggest that factors during development that promote better nestling condition are critical for predicting future apparent survival prior to migration. Differences in annual apparent survival between early‐ and late‐fledging songbirds, as commonly observed, may be driven by events occurring at later stages of the annual cycle.
The globe skimmer dragonfly, Pantala flavescens Fabricius (Odonata: Libellulidae), is a long-distance migrant, well adapted to exploiting ephemeral waterbodies. This species occurs in Japan every summer, but overwintering has only been recorded on subtropical Ishigaki Island. It is not known from where the summer immigrants originate, nor what proportion of the globe skimmers seen in Japan are of local origin. We analyzed stable hydrogen isotope (δ 2H) composition of wings of 189 P. flavescens captured at six sites in Japan from August to September in 2016 (n = 57) and from April to November in 2017 (n = 132). We determined that the majority of individuals were immigrants. Individuals of probable Japanese origin occurred only later in the year and were of lower mass on average than immigrants. Immigrants potentially originated from a broad area as far west as northern India and the Tibetan Plateau and, especially late in the season, as near as northcentral China and the Korean peninsula. However, for April samples, the most parsimonious interpretation suggested southern origins, in northern Myanmar to southern China, or possibly Borneo-Sulawesi. Our investigation underlines the power of combining stable isotope data with other information such as wind speed and direction, arrival dates, and body mass to estimate origins and to understand the life history of this and other insects.
Determining the source areas of harvested individuals is important for effective conservation and management of migratory game birds. Banding has provided much information about source areas, but obtaining samples of marked individuals representative of all potential breeding areas is difficult for most species. To add to previous knowledge of harvest derivation based on banding data and to assist with regulatory decisions, we used stable hydrogen isotope (d 2 H) techniques to estimate natal and molt source areas of Blue-winged Teal (Spatula discors) harvested in southern Canada in 2014 and 2017. We found that most birds harvested in southern Saskatchewan, southern Manitoba, northern Ontario, and southern Ontario likely originated in the prairie and boreal plains regions of Canada and the United States, which is the core production area for the species. Based on feather d 2 H values, some birds harvested in Ontario may have also originated in Ontario. Our results differ from those of a long-term analysis of band recovery data that revealed that most Blue-winged Teal harvested in Ontario originated in the eastern part of the province and areas along the lower Great Lakes and southwestern Quebec. We found that nearly all birds harvested in Ontario in our study likely originated from areas north and west of the province. Together, banding and stable isotopes likely provide the best information available on source areas of harvested birds for regulatory decision making. RESUMEN.Areas de origen de Spatula discors cazadas en Ontario y Prairie Canad a con base en is otopos estables: implicaciones para el manejo sostenible Es importante determinar las areas de origen de animales de caza para la conservaci on efectiva y el manejo de aves de caza migratorias. El anillamiento ha provisto mucha informaci on sobre estas areas, pero obtener muestras de individuos marcados que sean representativas de todas las areas de reproducci on potenciales es dif ıcil para la mayor ıa de las especies. Con el fin de contribuir con informaci on previa del origen de las aves cazadas con base en datos de anillos y para asistir en la toma de decisiones regulatorias, utilizamos t ecnicas de isotopos estable de hidr ogeno (d 2 H) para estimar areas de nacimiento y muda de Spatula discors cazadas en el sur de Canad a entre 2014 y 2017. Encontramos que la mayor ıa de las aves fueron cazadas en el sur de Saskatchewan, el sur de Manitoba, el norte de Ontario y el sur de Ontario probablemente se originaron en la regi on de praderas y planicies boreales de Canad a y Estados Unidos, el cual es el area nuclear de reproducci on de esta especie. Con base en los valores de d 2 H de las plumas, algunas aves que fueron cazadas en Ontario pueden, tambi en, haberse originado en Ontario. Nuestros resultados difieren de los resultados de los an alisis de largo plazo utilizando datos de anillos recuperados que suger ıan que la mayor ıa de Spatula discors cazados en Ontario se originaban en la regi on este de la provincia y las areas a lo largo de la regi on baja d...
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