Integrating information from geolocators, weather radar, and citizen science to uncover a key stopover area of an aerial insectivore

Abstract

Determining the distribution of stopover and overwintering areas of migratory animals is essential for understanding population dynamics and building predictive models. Tree Swallows (Tachycineta bicolor) are small songbirds that breed across North America. Data from Doppler weather radar and eBird indicate that Tree Swallow numbers increase throughout October and November in southeastern Louisiana, but then decrease during December. We thus hypothesized that southeastern Louisiana is a stopover area used by Tree Swallows during fall migration before they move to farther overwintering areas. We tested this hypothesis by attaching light-logging geolocators to Tree Swallows at five breeding sites spanning the species' breeding range from British Columbia to Nova Scotia, and then tracking their fall migration routes, stopover sites, and wintering locations. Of 38 individuals that returned in the following breeding season, 11 birds from three breeding sites (Saskatchewan, Wisconsin, and Ontario) used southeastern Louisiana as a stopover site. Arrival date and duration of stay closely matched observations from both eBird and radar data. From Louisiana, most Tree Swallows continued their migration to one of three wintering sites: peninsular Florida, the Bahamas, or the Yucatán Peninsula, whereas two birds remained until spring within 200 km of the stopover area. Our results (1) suggest that southeastern Louisiana is an extended stopover site for Tree Swallows that originate from a wide geographic range on the breeding grounds; and (2) demonstrate how geolocators, combined with other sources of movement information, reveal habitat use throughout the annual cycle.

Severe recent decrease of adult body mass in a declining insectivorous bird population

“…The use of geolocators has recently proved extremely useful in identifying nonbreeding ranges and migratory connectivity in another declining North American aerial insectivore, the purple martin (Progne subis) [63]. Similar projects are underway in tree swallows, and a single year of geolocator data has so far allowed the identification of an important stopover site in Louisiana [51]. Our work provides further incentives for such logistically challenging endeavours, as understanding population decline in aerial insectivores will involve disentangling complex interactions between multiple environmental factors, especially for migratory species occupying diverse habitats during their lifecycle.…”

Distribution of Nearctic-Neotropical migratory birds along a South American elevation gradient during spring migration

“…The migrant community as a whole showed large annual variations in abundance, which might be attributed to varying food availability (Wolfe et al 2014), weather patterns (Liechti 2006, Laughlin et al 2013, annual variation in productivity (Rodenhouse et al 2003, Hoye et al 2012, or most likely a combination of all of these factors Holmes 2002, Mitchell et al 2011). Individual species needs and preferences, as well as annual variation, must be taken into account when designing conservation and management strategies for Nearctic-Neotropical migrants during stopover Holmes 1996, Faaborg et al 2010).…”

Full Issue

“…For raptors, songbirds, and monarch butterflies, broad breeding catchment areas were defined using stable hydrogen isotopes in feather samples (Wassenaar and Hobson 1998, Dunn et al 2006, Nelson et al 2015. Combined with weather radar (migration volume and direction; Laughlin et al 2013) and large-scale telemetry studies (stopover behavior, migration orientation; Taylor et al 2011) breeding and wintering catchment areas of migrants, and migratory connectivity, could be refined (Nelson et al 2015). This would allow correlation of trends with underlying changes in habitat or land use on the inferred breeding or wintering grounds.…”