Cerulean Warblers exhibit parallel migration patterns and multiple migratory stopovers within the Central American Isthmus

Abstract

The Cerulean Warbler (Setophaga cerulea) is a declining Nearctic–Neotropical migratory songbird of conservation concern. Implementing full annual cycle conservation strategies to facilitate recovery has been difficult because we know little about the migratory period or strength of migratory connectivity between North American breeding and South American nonbreeding regions. Between 2014 and 2017, we deployed geolocators on 282 males at 14 study sites throughout the species’ range to (1) evaluate the strength and pattern of connectivity between breeding and nonbreeding regions, (2) identify approximate routes and stopover regions, and (3) document migration phenology. We obtained data from 26 birds and observed moderate migratory connectivity overall but documented strong parallel migration for birds breeding in two longitudinally disparate regions. Most (14 of 15; 93%) Appalachian breeders spent the stationary nonbreeding period in the Colombian/Venezuelan Andes, whereas most (5of 7; 71%) Ozark breeders spent the stationary nonbreeding period in Peru/Ecuador. The majority of spring migration (62%) was spent in Central America at multiple stopover locations between Panama and southern Mexico. The 2 migratory periods were approximately equal in duration: 38 ± 2 days (SE) in fall and 42 ± 2 days (SE) in spring. Based on the observed connectivity pattern, conservation of Appalachian breeding populations during the stationary nonbreeding period should focus on forest conservation and restoration in premontane/lower montane forests of Colombia and Venezuela, whereas Ozark breeding population conservation should focus on forest conservation and restoration efforts in Ecuador and Peru. Further conservation efforts are also needed on the breeding grounds, especially for the most sharply declining populations. And finally, conservation of forests used by Cerulean Warblers during stopover periods throughout Central America and southern Mexico, in southeastern United States coastal areas, and in the Mississippi Alluvial Valley will benefit individuals from multiple breeding locations and populations.

Novel insights into symbiont population structure: Globe‐trotting avian feather mites contradict the specialist–generalist variation hypothesis

“…This nonbreeding ground sympatry at least provides the possibility for host specialist A. protonotaria to encounter and transmit across host individuals from multiple breeding populations. In contrast, S. cerulea exhibits greater migratory connectivity; that is, individuals that breed in sympatry also tend to overwinter in sympatry (Raybuck et al, 2022). In other words, S. cerulea populations remain somewhat geographically isolated on the breeding and stationary nonbreeding grounds.…”

“…Sites were selected to maximize genetic variation via geographic distance and/or reproductive isolation. More specifically, study areas were selected based on previous research on host population genetics (Deane et al, 2013; DeSaix et al, 2019) and knowledge of each species' full annual cycle (Raybuck et al, 2022; Tonra et al, 2019). All birds were captured during the breeding season with mist nets using audio playback lures or hand nets at nesting sites.…”

“…Nonbreeding ground transmission has been posited as a potential mechanism for unexpected levels of gene flow in avian lice (Gómez-Díaz et al, 2007;Gustafsson & Olsson, 2012;Martinů et al, 2015), bat mites (Yousefi et al, 2021;Zamora-Mejías et al, 2022) and other species of feather mites (Fernández-González et al, 2018). Results herein of differing feather mite population structure give strong credence to this possibility given the knowledge of differing population dynamics and environmental contexts of hosts across their full annual cycles (Raybuck et al, 2022;Tonra et al, 2019).…”

“…Like P. citrea, S. cerulea is a Nearctic‐Neotropical migrant with a patchy breeding distribution in eastern North America. However, in contrast to P. citrea , S. cerulea is a canopy open‐cup nester that breeds in mature hardwood forests (Buehler et al, 2020; Wessels & Boves, 2021), has an estimated population size of only 530,000 individuals (BirdLife International, 2023) and exhibits moderate migratory connectivity and parallel migration (Raybuck et al, 2022). Currently, very little is known about sex‐specific S. cerulea natal or breeding dispersal.…”

Low‐coverage whole genome sequencing for highly accurate population assignment: Mapping migratory connectivity in the American Redstart (Setophaga ruticilla)

“…One potential explanation for the increase in abundance is that birds in the southern portion of the breeding range have shifted their breeding latitude northward in response to climate change, as has been documented in other Nearctic-Neotropical migrants (Gómez et al, 2021;Rushing et al, 2020). In this scenario, genetic differentiation would also likely erode between the Northern bler (Wilson et al, 2018) and Cerulean Warbler, Setophaga cerulea (Raybuck et al, 2022). Additionally, in species such as the Canada Warbler, migration routes between North and South America can concentrate in small regions of Central America, which can also affect population trends (Roberto-Charron et al, 2020).…”