When do helpers help? Food availability and helping in the moorhen,Gallinula chloropus

Summary The importance of food availability as a constraint upon cooperative behaviour was examined by providing supplementary food on some breeding territories of a population of moorhens (Gallinula chloropus). First brood juveniles on territories provided with food were more likely to feed their younger second brood siblings. Supplementary feeding improved the physical condition of juveniles above that of unfed conspecifics, and birds in better condition were more likely to be helpers. Helpers on fed territories also provided more food to siblings than did their counterparts on unfed territories, enabling parent birds to reduce their work rates. Results are discussed in relation to the benefits which may accrue to helpers and the energetic costs of cooperation which may act as proximate constraints upon potential helpers.