Spatial structure in migration routes maintained despite regional convergence among eastern populations of Swainson’s Thrushes

Abstract

Background Migratory connectivity links the different populations across the full cycle and across the species range and may lead to differences in survival among populations. Studies on spatial and temporal migratory connectivity along migration routes are rare, especially for small migratory animals. Methods We used an automated radio-telemetry array to assess migratory connectivity en route and between early and later stages of the fall migration of the eastern populations of Swainson’s Thrush, and to assess the variation of migration pace between consecutive detection from the different receiving stations along the migratory journey. We tracked 241 individuals from across eastern Canada to determine if populations were mixing around the Gulf of Mexico. We also tested the influence of tagging longitude, latitude and age on migration pace. Results Migration routes varied and converged towards the northeast coast of the Gulf of Mexico, but in this region, populations maintained finer-scale spatial structure. Migration pace increased as birds progressed south, independent of age and tagging site. Conclusions We showed that for songbirds, migratory connectivity can be maintained at fine spatial scales despite the regional convergence of populations, highlighting the importance of detailed spatial tracking for identification of population specific migration routes. Overall, our study provides a portrait of migratory movements of eastern Swainson’s Thrush and a framework for understanding spatial structure in migration routes for other species.

Offshore and coastline migration of radio‐tagged Nathusius' pipistrelles

“…We defined the total minimum flight distance of the respective bat as the sum of straight lines drawn between clustered stations. A cluster of stations was defined as stations within a radius of 30 km and which were visited by the tagged bats within 30 min (see Bégin-Marchand et al, 2021). We once derivated from this, when one of the bats flew back and forth between neighboring clusters 36 km from each other (against migration direction and back).…”

Songbirds initiate migratory flights synchronously relative to civil dusk

“…We used automated radio telemetry [ 42 ] to estimate nocturnal departure time in nine species of songbirds departing six breeding or wintering sites across North America (Table 1 , Table S1 ). Most species in our study are thought to begin long-distance migration after departure from their breeding or wintering sites (see Methods), but three species are known to depart their breeding sites and primarily carry out non-migratory regional movements for days or weeks before beginning directed long-distance flights towards their wintering sites [ 43 – 46 ]. Because of this apparent variation in post-departure movement strategy, we used radio-tracking data from outside of the breeding and wintering sites to assess whether species were most likely initiating long-distance migratory flights after departure or instead first making non-migratory regional movements.…”

“… 49 (21♀, 28♂) Alaska Western USA [ 9 ] Bicknell’s Thrush (Fall) Catharus bicknelli Migration 19 (17♂, 2 unk.) Quebec Hispaniola and Cuba [ 46 ] Swainson’s Thrush (Fall) Catharus ustulatus Unk. 23 (5♀, 15♂, 3 unk.)…”

“… 23 (5♀, 15♂, 3 unk.) Quebec Central and South America [ 46 ] Swainson’s Thrush (Fall) Catharus ustulatus Regional 65 (2♀, 14♂, 49 unk.) Nova Scotia Central and South America [ 45 ] Blackpoll Warbler (Fall) Setophaga striata Regional 49 (9♀, 5♂, 35 unk.)…”

Where did the finch go? Insights from radio telemetry of the medium ground finch (Geospiza fortis)

“…Despite these concerns, telemetry in general, and Very High Frequency (VHF) radio telemetry in particular, has been used to investigate movement patterns in small birds (Kenward, 2001 ; White & Garrott, 1990 ), thus informing habitat selection (Camacho et al, 2014 ), foraging range and roosting (Ginter & Desmond, 2005 ), postfledging dispersal (Fisher & Davis, 2011 ), and migration (Bégin‐Marchand et al, 2021 ). This approach has also been used on rare occasions in Darwin's finches in the Galápagos, primarily for conservation purposes.…”