Foraging behaviour of the European Starling Sturnus vulgaris : a case study to explore the potential implications of climate change on ground-probing birds

Abstract

It is well established that farmland bird population declines are strongly linked to the land use and management changes associated with increased agricultural intensification. In future, climate change is predicted to be an increasingly important driver of bird population changes. A substantial number of studies have investigated the large scale impacts of climate change on species’ distribution and abundance. However, few have examined in detail specific ecological impacts of climate change on bird demographics that would allow predictions of the effects of climate on bird populations. Here I show that below-ground prey form a key part of the diet, of my study species, the Starling Sturnus vulgaris, on UK grassland in both the breeding and non-breeding season. I then show that soil moisture mediates intake rates of below-ground prey using field experiments on wild-caught Starlings. Intermediate soils provided the best foraging opportunities with both saturated and dry soils being suboptimal I then linked delivery of below-ground prey to reproductive success. A study of adult provisioning of nestlings (n= 42 nests), over a four year period, established that the delivery of below-ground prey, specifically Tipulidae larvae, was mediated by changes in soil moisture and linked to Starling reproductive success via changes in fledgling survival. Analysis of fledgling success at a range of sites (n=132) provided evidence that an increase in the mean spring (April-June) soil moisture deficit over a twenty year period was a significant driver of Starling population dynamics in Britain; even after controlling for temporal changes in starling xi populations (likely to be linked to agricultural intensification). I conclude by discussing different management options to alter soil moisture levels on grassland to benefit both ground-probing birds and the impacts on a range of other ecosystem services (e.g. reducing flood risk).