Brood parasitism in the sand martin, Riparia riparia: evidence for two parasitic strategies in a colonial passerine

Sand martin parentage was studied at a large breeding colony in central Sco tland. Multilocus DNA fingerprinting was used during the 3-year study to ex clude some social parents as true parents, and thereby determine the freque ncy of monogamy, quasiparasitism (QP), intraspecific brood parasitism (ISBP ) and extrapair fertilization (EPF) amongst 45 broods and 167 nestlings. Mo nogamous parentage characterized the majority of broods (60%), so most chic ks were the offspring of their social parents (81%). QP (involving a male's extrapair mate laying in his nest) was found in 9% of broods and 2.4% of c hicks and ISBP (or 'egg dumping') in 4% of broods and 1.8% of chicks. A sub stantial proportion of offspring arose from EPFs, affecting 36% of broods a nd 14% of chicks. On present evidence, the relatively high frequency of QP found in sand martins is unusual. We propose that its observed frequency is unlikely to be due to chance events and may represent a female-driven stra tegy. (C) 1998 The Association for the Study of Animal Behaviour.