Title
Consequences of sex-specific growth on sibling competition in black-headed gulls: a sexually-size dimorphic species with scramble competition Consequences of sex-specific growth on sibling competition in black-headed gulls: a sexually-size dimorphic species with scramble competition
Author
Faculty/Department
Faculty of Sciences. Biology
Publication type
article
Publication
Berlin ,
Subject
Biology
Source (journal)
Journal of ornithology. - Berlin, 1853 - 2003
Volume/pages
148(2007) :4 , p. 495-502
ISSN
0021-8375
1439-0361
ISI
000249730900014
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
Biased mortality of the larger sex during the early developmental period has been reported for a number of size-dimorphic bird species. This can partly be explained by the fact that growing to larger size renders the larger sex more vulnerable to food shortage. However, since sibling rivalry is often size-dependent, chicks of the larger sex should have a competitive advantage. This raises the question as to why the larger sex does not always benefit from its size in sibling competition. We studied sibling competition in the black-headed gull (Larus ridibundus), a sexually-size dimorphic species with male-biased mortality. We manipulated the natural brood sex ratio and placed one male chick in direct competition with one female chick while concurrently controlling for differences in age, size and laying order. Male chicks outgrew their female siblings by 15% in asymptotic body mass and did not suffer from enhanced mortality. Female chicks tended to be more alert when the parents returned to the nest and were more persistent in gull-typical begging displays. Females were more likely to get the first food item, but they did not get more food, possibly due to a size-mediated dominance over the non-monopolizable regurgitated food. Thus, it is unlikely that sex differences in competitiveness significantly contribute to male-biased mortality in black-headed gulls. The previously reported male-biased mortality is more likely due to a disadvantage of a higher food demand and a higher sensitivity towards low egg quality, as has been shown in previous studies.
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