Females are responsible for ejection of cuckoo eggs in the rufous bush robin.

Rufous bush robin, Cercotrichas galactotes, nests were experimentally parasitized in order to test which sex is responsible for egg ejection. We tested nests belonging to the same individuals (male, female or pair) in 2 consecutive years. Whether the eggs were rejected did not depend on environmental variables such as laying date and clutch size, and did not change between tests, when the two consecutive nests tested belonged to the same pair members, supporting the idea that some individuals reject odd eggs, while others accept them. The expected frequencies for rejection and acceptance, if females were the sex responsible for ejection behaviour, did not differ from the observed frequencies when the same female owned both the nests tested. However, the expected frequencies calculated for males as if they were the sex responsible differed from those observed, when the same male owned both the nests tested. A lower percentage of females than males changed ejection behaviour. These results show that female rufous bush robins are responsible for egg ejection. Copyright 1998 The Association for the Study of Animal Behaviour.

Nest building is a sexually selected behaviour in the barn swallow.

Females may use male nest building to assess male parental quality, and nest size would then be a sexually selected trait. In the barn swallow, Hirundo rustica, females select their partner by his tail length, a character believed to signal good genes. Both sexes participate in nest building, although male participation is negatively related to his attractiveness as reflected by tail length. We tested the hypothesis that nest building is a sexually selected trait: females paired with males of high parental quality (as shown by the male during nest building) may obtain a mate providing large amounts of parental investment, while, as has been shown previously, females mated to attractive (long-tailed) males will acquire mates with good genetic quality. Therefore, since nest building in barn swallows occurs after mating, we predicted a postmating sexual selection process by which the female invests differentially in reproduction depending on the male's nest-building effort (reflecting his willingness to invest in reproduction). The volume of material in a nest was related to the male's contribution to nest building and, in agreement with our hypothesis, in a multiple regression analysis, male tail length and nest material volume were negatively related to laying date and positively to female investment in reproduction (total number of eggs laid during the breeding season). Moreover, females paired with long-tailed males (which contribute very little to nest building), but using the same amount of nest material as females paired with short-tailed males, reduced the thickness of the nest and hence increased its capacity. Therefore, in the barn swallow two different traits appear to be sexually selected: tail length of males owing to the good genes process and nest-building ability owing to the good parent process. (c) 1998 The Association for the Study of Animal Behaviour.

Great spotted cuckoos improve their reproductive success by damaging magpie host eggs

Adult great spotted cuckoos, Clamator glandariusdamage the eggs of their magpie, Pica picahost without removing or eating them. The number of damaged magpie eggs was recorded in 360 parasitized nests of which 62.2% contained between one and eight damaged magpie eggs. Egg-destroying behaviour may be adaptive if it reduces nestling competition and/or enhances the hatching success of the cuckoo. To clarify the role of egg destruction for the reproductive success of great spotted cuckoos, unparasitized magpie nests were experimentally parasitized (without egg damage) by introducing cuckoo eggs or chicks. Egg damage was common in parasitized nests but the eggs were not damaged by the hosts. Egg damage increased the breeding success of the cuckoos, by both reducing the number of competing host chicks in the nest and increasing the likelihood that late-laid cuckoo eggs would hatch.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour