Bird data
We collated data for 6 North American migratory species for which
analysis has been previously conducted to identify genetically distinct
populations: Willow Flycatcher (Empidonax traillii ; WIFL), Yellow
Warbler (Setophaga petechia ; YEWA), Wilson’s Warbler
(Cardellina pusilla ; WIWA), Common Yellowthroat (Geothlypis
trichas ; COYE), American Redstart (Setophaga ruticilla ; AMRE),
and Painted Bunting (Passerina ciris ; PABU). A total of 3326
genetic samples were available and distributed widely across the
breeding and wintering ranges of these species (Figs. S1–S6).
Migratory connectivity was estimated using high-resolution genetic
markers data compiled by the Bird Genoscape Project
(www.birdgenoscape.org). Data and
methodology for mapping migratory connectivity using genetic markers is
described in detail in a set of species-specific papers (Bay et
al. 2021; DeSaix et al. 2023a; Rueda-Hernández et al.2023; Ruegg et al. 2014, 2020, 2021, Bobowski et al. in
review ). Briefly, for each species, DNA was sampled from individuals
across the species’ breeding ground and RAD-seq (WIFL, YEWA, PABU and
WIWA) or whole genome sequencing data (COYE and AMRE) were used for an
initial estimate of population structure. For all species except AMRE, a
subset of 96–158 SNPs were identified for each species that could
accurately assign individuals to breeding population using population
assignment tests (Moran & Anderson 2018). These subsets of SNPs were
used to genotype additional birds from the breeding grounds as well as
individuals sampled across the wintering grounds. For the whole genome
sequencing, genome-wide SNPs were identified that could accurately
assign individuals to breeding populations and the genotype likelihoods
of these data were used for population assignment (DeSaix et al.2023b). Taking advantage of the population structure and isolation by
distance signals on the breeding ground, we estimated breeding location
for each wintering sample.
This procedure resulted in 26 genetically distinct breeding populations,
whose seasonal distributions are shown in Figs. S1–S6. We removed
populations with low quality data (i.e. with fewer than 10 sampled
individuals, or fewer than 3 distinct locations for sampled individuals,
or fewer than 2 occupied ecoregions during at least one season), thus
removing 4 populations: YEWA East, COYE California, AMRE Mid-West and
PABU Louisiana. Analyses were performed using the remaining 22
genetically distinct populations.