Individual condition, but not fledging phenology, carries over to affect post‐fledging survival in a Neotropical migratory songbird

Abstract

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.

Full lifetime perspectives on the costs and benefits of lay‐date variation in tree swallows

“…The lifetime perspective developed here has allowed us to extend the scope of fitness consequences beyond single breeding seasons, and the lay‐date effects we have seen on offspring recruitment and lifetime number fledged mirror those detected in another well‐studied swallow (Saino et al 2012, Raja‐Aho et al 2017, cf. Evans et al 2019).…”

“…Such challenges could include enduring harsh early‐season environmental conditions such as inclement weather (e.g., Ramos et al 2002), low food availability (e.g., Young 1994, Bowlin and Winkler 2004), high levels of predation (e.g., Borgmann et al 2013), or competition for scarce nesting sites or mates (e.g., Smith 2006). Several studies of timing of breeding have explored the connection between quality and date experimentally (reviewed in Verhulst and Nilsson 2008) or by examining facets of fitness beyond reproduction (Brinkof et al 2002, Brown et al 2015, Low et al 2015, Needham et al 2017, Evans et al 2019). However, in the latter cases, breeding adults have usually been followed only to the season just after the focal breeding attempt.…”

Nutritional consequences of breeding away from riparian habitats in Bank Swallows: new evidence from multiple endogenous markers

“…The preservation of aquatic systems will support not only riparian specialists such as Bank Swallows but also other insectivorous songbirds using the same riparian habitat ( Blancher and McNicol, 1991 ; Brown et al , 2002 ; Deschênes et al , 2003 ; Twining et al , 2018a ; Jackson et al , 2020 ) and similar forested riparian habitats ( Gray, 1993 ; Rottenborn, 1999 ; Lussier et al , 2006 ; Pennington et al , 2008 ; Rubin et al , 2019 ). Understanding foraging ranges of Bank Swallows from inland and lakeshore sites using radiotelemetry (see Evans et al , 2020 ) will also help evaluate costs and benefits of using natural versus aggregate pits in this species.…”

Fledgling Bachman’s Sparrows in a longleaf pine ecosystem: survival, movements, and habitat selection

“…Few other investigators have examined how individual condition influences fledgling survival. Even within nests, the condition or age of individual nestlings can vary due to asynchronous hatching or differential feeding rates (Evans et al 2020). Conditions experienced in the nest likely have carryover effects during the post‐fledging period.…”