What attracts birds to newly mown pasture? Decouplingthe action of mowing from the provision of short swards

Many bird species flock to forage on newly mown grass swards. Several potential benefitsare offered by such swards, including increases in prey availability (flush of foliar prey,reduced physical obstruction to surface and soil prey) and a foraging environment withfewer visual obstructions, so allowing predators to be detected more easily. We performeda field experiment using captive Common StarlingsSturnus vulgarisforaging in bottomlessenclosures on newly mown swards (within 1 h) and old mown swards (48 h). We performedthe experiment during winter months and standardized sward height to exclude other confoundingeffects in order to determine the temporal benefits of mowing for species foragingon soil invertebrates. We found no differences in the vigilance or time budgets of Starlingsforaging on newly or old mown swards. Intake efficiency (prey captured per 100 roots) wasgreater on newly mown swards, suggesting that Starlings used less energy to obtain their preyon that substrate. It is possible that mowing alters the microclimate of the soil and sward,causing invertebrate availability to decline over time, which causes the lower foragingefficiency. Mowing is a technique often used to manipulate grassland habitats in ecologicalresearch; it has recently been advocated as a conservation management tool for winteringbird populations. We suggest that care should be taken when designing such studies to avoidconfounding the factors under investigation with temporal changes in prey availability.

Claire L. Devereux, Mark J. Whittingham, John R. Krebs, Esteban Fernandez Juricic & Juliet A. Vickery, Ibis (2006), 148 , 302-306