Ejaculate allocation by male sand martins, Riparia riparia

Males of many species allocate sperm to ejaculates strategically in respons e to variation in the risk and intensity of sperm competition. The notable exception is passerine birds, in which evidence for strategic allocation is absent. Were we report the results of a study testing for strategic ejacul ate allocation in a passerine bird, the sand martin (Riparia riparia). Natu ral ejaculates were collected from males copulating with a model female. Ej aculates transferred in the presence of a rival male contained significantl y more sperm than ejaculates transferred in the absence of a rival male. Th ere was no evidence that this difference was due to the confounding effects of the year of ejaculate collection, the identity of the model female, the colony, the stage of season or the period of the day in which ejaculates w ere collected. A more derailed examination of the ejaculate patterns of ind ividual males: achieved by the DNA profiling of ejaculates, provided additi onal evidence for strategic allocation of sperm.