Data sets for Interacting effects of cold snaps, rain, and agriculture on the fledging success of a declining aerial insectivore

Climate change predicts the increased frequency, duration, and intensity
of inclement weather periods, such as unseasonably low temperatures (i.e.,
cold snaps) and prolonged precipitation. Many migratory species have
advanced the phenology of important life history stages, and as a result
will likely be exposed to these periods of inclement spring weather more
often, thus risking reduced fitness and population growth. For declining
avian species, including aerial insectivores, anthropogenic landscape
changes such as agricultural intensification are another driver of
population declines. These landscape changes may affect the foraging
ability of food provisioning parents, and reduce the survival of nestlings
exposed to inclement weather, through for example pesticide exposure
impairing thermoregulation and punctual anorexia. Breeding in
agro-intensive landscapes may thus exacerbate the negative effects of
inclement weather under climate change. We observed that a significant
reduction in the availability of insect prey occurred when daily maximum
temperatures fell below 18.3°C, and thereby defined any day where the
maximum temperature fell below this value as a day witnessing a cold snap.
We then combined daily information on the occurrence of cold snaps and
measures of precipitation to assess their impact on the fledging success
of Tree Swallows (Tachycineta bicolor) occupying a nest box system placed
across a gradient of agricultural intensification. Estimated fledging
success of this declining aerial insectivore was 36.2% lower for broods
experiencing four cold snap days during the 12 days post hatching period
versus broods experiencing none, and this relationship was worsened when
facing more precipitation. We further found that the overall negative
effects of a brood experiencing periods of inclement weather was
exacerbated in more agro-intensive landscapes. Our results indicate that
two of the primary hypothesized drivers of many avian population declines
may interact to further increase the rate of declines in certain landscape
contexts.