House sparrows selectively eject parasitic conspecific eggs and incur very low rejection costs

• Published in: Behavioral ecology and sociobiology 2011-10, Vol.65 (10), p.1997-2005
• Main Authors: Soler, Manuel, Ruiz-Castellano, Cristina, del Carmen Fernández-Pinos, María, Rösler, Anja, Ontanilla, Juan, Pérez-Contreras, Tomás
• Format: Article
• Language: English
• Subjects: Animal behavior; Animal Ecology; Animal nesting; Animal reproduction; Behavioral Sciences; Biomedical and Life Sciences; Bird nesting; Birds; Breeding; Brood parasitism; Eggs; Female animals; Infanticide; Life Sciences; Male animals; Original Paper; Parasites; Parasitism; Passer domesticus; Sparrows; Swallows; Zoology
• ISSN: 0340-5443; 1432-0762
• DOI: 10.1007/s00265-011-1209-z

Most host species of obligate interspecific brood parasites are under strong selection because such parasitism, e.g., that involving evictor nestmates, is highly costly. Egg rejection is one of the most efficient host defences against avian brood parasites. Many hosts have thus evolved egg-recognition ability and rejection behaviour. However, this defensive mechanism has not evolved in most species where only intraspecific brood parasitism occurs, probably because (1) the eggs of conspecific females are very similar in appearance, making egg rejection less likely to emerge, and (2) such parasitism is frequently less costly than interspecific parasitism. Using a captive population of house sparrows (Passer domesticas) with a low breeding density, we here provide new evidence showing that this species actually has a fine capacity to discriminate conspecific eggs and to eject them (44.2% of foreign eggs ejected) while incurring very low rejection costs (4.2% of own eggs ejected). This result contradicts those previously found in high-density house sparrow populations in which very high rejection costs and very high clutch desertion rates were reported, probably as a consequence of intraspecific competition and infanticide provoked by the high breeding density. The house sparrow has only rarely been reported as the host of an interspecific brood parasite, which implies that it is a newly described example of an altricial species in which egg ejection has evolved and is maintained in response to intraspecific brood parasitism.