Range‐wide populations of a long‐distance migratory songbird converge during stopover in the tropics

Abstract

Geographic convergence during migration influences the extent to which animal populations may experience carry‐over effects across periods of the annual cycle. When most individuals of a population share geographic areas during a given priod, carry‐over effects are likely stronger than when individuals occupy multiple areas. We used genetic data and stable isotope (δ2H) measurements from feathers and claws to describe the likely breeding and wintering geographic origins of a long‐distance migratory songbird (Gray‐cheeked Thrush, Catharus minimus) moving through northern Colombia in spring and fall migration. Furthermore, we used these data coupled with regional occupancy surveys to assess whether individuals from various breeding populations converge during migration and evaluated whether geographic origin, age, or sex affected stopover strategies. We found that range‐wide breeding populations of Gray‐cheeked Thrush converged in northern Colombia in an area spanning <1% of the breeding range, especially during a prolonged spring stopover in the Sierra Nevada de Santa Marta. Breeding (but not winter) origin, sex, and age influenced arrival date and body condition upon arrival at stopover sites where populations converged. Birds from more northerly breeding latitudes, males and adults generally arrived earlier and in lower body condition than those with more southerly breeding origins, females, and juveniles. Our work and other studies suggest that areas in northern Colombia may function as ecological bottlenecks for Gray‐cheeked Thrush because they concentrate individuals from across the breeding range, provide critical resources, and impose constraints during migration. Future studies quantifying the effects of high‐convergence areas on fitness and survival of individuals and their demographic consequences are required to assess their roles as ecological bottlenecks.

High spatiotemporal overlap in the non‐breeding season despite geographically dispersed breeding locations in the eastern whip‐poor‐will (Antrostomus vociferus)

“…competition for food) and independent (e.g. extreme weather events) regulation can play an important role at migratory bottlenecks (Cardenas‐Ortiz et al, 2020; Newton, 2006), and conserving high‐quality habitat in this region will be particularly important (Bayly et al, 2018; Gómez et al, 2019). Circumvention of the Gulf of Mexico in this species contrasts with other Neotropical migrants that maintain longitudinal separation on southward migration before crossing over the Gulf (e.g.…”

Migratory connectivity then and now: a northward shift in breeding origins of a long-distance migratory bird wintering in the tropics

“…We then transformed this isoscape into an expected feather δ 2 H (δ 2 H f ) surface using the calibration equation estimated for feathers of canopy-foraging Neotropical migrants [50]: d 2 H f ¼ À17:57 þ 0:95 (d 2 H p ). We followed a likelihood framework for geographical assignment extensively used for Neotropical migratory birds [50][51][52] and obtained a cumulative surface of likely breeding origins for every individual from each time period. Briefly, this procedure involves obtaining likelihoods of each individual belonging to a given 30 × 30 km cell on the breeding grounds and then transforming them to a probability surface by dividing by the total sum of likelihoods [50,53].…”

Combining Models of Environment, Behavior, and Physiology to Predict Tissue Hydrogen and Oxygen Isotope Variance Among Individual Terrestrial Animals

“…Several studies have investigated the causes of within-site amongindividual isotopic variance through exploratory approaches such as correlation analysis and model selection (e.g., Clegg et al, 2003;Meehan et al, 2003;Smith and Dufty, 2005;Langin et al, 2007;Reese et al, 2018; see also Hobson et al, 2012;Nordell et al, 2016). Relationships between feather δ 2 H values and age have been observed for several taxa (e.g., Meehan et al, 2003;Smith and Dufty, 2005;Langin et al, 2007;Haché et al, 2012;Studds et al, 2012;Gomez et al, 2019) and attributed to age-related differences in diet, access to water, metabolism (Meehan et al, 2003;Langin et al, 2007;Storm-Suke et al, 2012), and/or evaporative water loss (Wolf and Martinez del Rio, 2000;Meehan et al, 2003, McKechnie et al, 2004Smith and Dufty, 2005; but see Kirkley and Gessaman, 1990;Marder et al, 2003). Differences in the magnitude and patterns of local among-individual variance observed for shore birds (Wunder et al, 2005;Rocque et al, 2006), raptors (Meehan et al, 2003;Smith and Dufty, 2005), and passerines (Langin et al, 2007) have been attributed to differences in molt phenology and evaporative water loss among these taxa (Smith and Dufty, 2005).…”