Data for: Early life conditions influence fledging success and subsequent local recruitment rates in a declining migratory songbird, the Whinchat Saxicola rubetra

Life history traits and environmental conditions influence reproductive
success in animals, and consequences of these can influence subsequent
survival and recruitment into breeding populations. Understanding
influences on demographic rates is required to determine the causes of
decline. Migratory species experience spatially and temporally variable
conditions across their annual cycle, making identifying where the factors
influencing demographic rates operate challenging. Here, we use the
Whinchat Saxicola rubetra as a model declining long-distance migrant bird.
We analyse 10 years of data from 247 nesting attempts and 2519
post-fledging observations of 1193 uniquely marked nestlings to examine
the influence of life history traits, habitat characteristics and weather
on survival of young from the nestling stage to local recruitment into the
natal population. We detected potential silver spoon effects where
conditions during the breeding stage influence subsequent apparent local
recruitment rates, with higher recruitment for fledglings from larger
broods, and recruitment rate negatively related to rainfall that chicks
experienced in-nest. Additionally, extreme temperatures experienced pre-
and post-fledging increased fledging success and recruitment rate.
However, we could not determine whether this was driven by temperature
influencing mortality during the post-fledging period or later in the
annual cycle. Brood size declined with hatching date. In-nest survival
increased with brood size and was highest at local temperature extremes.
Furthermore, nest survival was highest at nests surrounded with 40–60%
vegetation cover of Bracken Pteridium aquilinum within 50m of the nest.
Our results show that breeding phenology and environmental factors may
influence fledging success and recruitment in songbird populations, with
conditions experienced during the nestling stage influencing local
recruitment rates in Whinchats (i.e. silver spoon effect). Recruitment
rates are key drivers of songbird population dynamics. Our results help
identify some of the likely breeding season mechanisms that could be
important population drivers.