ADOPTION OR INFANTICIDE - OPTIONS OF REPLACEMENT MALES IN THE EUROPEAN STARLING

The behaviour of a male bird towards a potential mate and her clutch m ay depend both on his expected paternity and on the likelihood that sh e will produce a replacement clutch if he commits infanticide. In this study we evaluate the choices made by replacement male European starl ings Sturnus vulgaris. By removing males before and during laying, we induced other males, mainly neighbours, to mate with the reproductivel y active females. When the original male was removed before laying, a new male adopted the subsequent clutch in 14 out of 15 cases. When ten females were widowed during their laying period, replacement males ne ver adopted their clutches. The paternity of replacement males was a f unction of when they replaced the former male. When replacement occurr ed more than 3 days before egglaying, the new male fathered nearly all offspring; when it occurred the day before laying, the new male still fathered more than every second young. When the original male was rem oved during his mate's laying period, in five out of ten cases a repla cement male committed infanticide by throwing out the eggs, but this o nly occurred in one out of 15 cases when removal took place before lay ing. The evidence for infanticide actually being committed by the repl acement male was circumstantial. Four out of six of the females affect ed by apparent infanticide produced replacement clutches in which the male presumably had higher paternity than in the original clutch. In a ll cases, the male adopted the replacement clutch. In five cases when the original male was removed during laying, the neighbours neither ad opted the brood nor committed infanticide, although they sometimes wer e seen courting the widowed female and copulating with her. These case s occurred later during laying than those were males comitted infantic ide. The time from infanticide to the laying of the replacement clutch tended to increase as infanticide was committed later in the laying s equence. We conclude that strategies of potential replacement males ar e influenced by their expected paternity in the current brood and the probability that the female will produce an early replacement clutch.