Data for: Negative effects of agricultural intensification on the food provisioning rate of a declining aerial insectivore

The historical rise of intensive agricultural practices is hypothesized to
be related to declines of grassland and aerial insectivorous birds.
Drivers of declines may also influence the overall abundance and spatial
distribution of insects within agricultural landscapes. Subsequently, the
food provisioning rate of birds breeding within more agro-intensive
landscapes may be impacted. Lower provisioning rates in agro-intensive
landscapes may lead to reduced growth rate, body condition or fledging
success of nestlings but also to diminished body condition of food
provisioning adults. Results from a previous study supported this
hypothesis as the fledging success and proxies of nestling body condition
were lowest for an aerial insectivore breeding in more agro intensive
landscapes. Of the multiple hypotheses put forward to explain these
correlations, one mechanism may act through variation in food provisioning
rates. In this study, we expounded on this hypothesis using data derived
from the aforementioned study system and assessed if provisioning rates to
nestlings and food provisioning behavior of adults varied across a
gradient of agricultural intensification in a declining aerial
insectivore, the Tree Swallow (Tachycineta bicolor). We found that the
hourly provisioning rate was lower in agro-intensive landscapes, and yet
travel distances were longest within less agro-intensive landscapes. Our
results highlight that, in order to maximize long term average gain rates,
Tree Swallows breeding within agro-intensive landscapes must forage with
greater intensity, perhaps at a cost to themselves, or else costs will
transfer to growing broods. Our work provides further evidence that
agricultural intensification on the breeding grounds can contribute to the
declines of aerial insectivores in part through a trophic pathway.