Data from: Stopover refueling, movement, and departure decisions in the White-throated Sparrow: the influence of intrinsic and extrinsic factors during spring migration

1. Differential migration timing between sex or age classes are examples
of how migratory movement strategies can differ among sub-groups within a
population. However, in songbirds, evidence for intrinsic differences in
en route migratory behavior is often mixed, suggesting that the local
environmental context may play a role in accentuating or diminishing
patterns. 2. We evaluated how multiple intrinsic and extrinsic variables
influenced refueling rates, local movement behavior, and departure
decisions in the White-throated Sparrow (Zonotrichia albicollis) during
spring migration. This species exhibits a unique genetically-based plumage
dimorphism, providing a unique class of individual in which to evaluate
patterns and processes of differential migration, in addition to sex, age,
and migration distance. 3. At a migratory stopover site, plasma metabolite
analysis was used to quantify individual variation in stopover refueling
rate. In after second year adults, automated and manual radio telemetry
was used to quantify daily activity timing, daily movement distances,
stopover duration, and departure time. Arrival timing to the stopover site
was determined using capture data. Non-breeding and previous
breeding/natal latitude were determined using analysis of hydrogen
isotopes in claws and feathers. 4. Males arrived at the stopover site 11
days on average before females, but no difference in migration timing was
observed between plumage morph or age classes. After second year adults
with more southern previous breeding latitudes arrived at stopover earlier
whereas second year birds making their first return migration arrived at
stopover in an inverse relationship to non-breeding latitude. Stopover
refueling rate did not differ between ages, sexes, or plumage morphs, and
daily departure probability of adults was higher under warmer temperatures
and favorable tailwinds. White-striped morphs moved greater distances
during stopover, initiated daily activity earlier in the morning, and
departed for migration earlier in the evening than tan-striped morphs. 5.
Our results show that while individual phenotype can influence some
aspects of local stopover-scale movement behavior, evidence for
differential stopover behavior was weak. Differential migration timing is
unlikely to result from intrinsic differences in en route refueling rate
and departure decisions, especially because the latter is strongly
influenced by meteorological conditions.