Ardea
Official journal of the Netherlands Ornithologists' Union

login


[close window] [previous abstract] [next abstract]

Nur N. (1988) The cost of reproduction in birds: an examination of the evidence. ARDEA 76 (2): 155-168
The cost of reproduction plays a critical role in theories of the evolution of life history strategies, yet several recent reviews conclude that good evidence is lacking that, in particular, survival decreases with an increase in clutch or brood size. Some have therefore minimized the importance of the cost of reproduction as an evolutionary force. I review six studies which manipulated brood size, five of which provide evidence of a cost of reproduction (reduced survival or future fecundity); the experimental design of the sixth was such that an effect of brood size on survival, if there was one, would be difficult to detect. Correlations of adult survival with natural (unmanipulated) brood size are difficult to interpret owing to the likelihood that females respond to environmental condition or their own condition by altering clutch size. As a result of the phenotypic adjustment of clutch size, the largest clutches tend to be reared under the best conditions and the latter influence observed survival. I present a model which predicts that if females optimally adjust clutch size to condition(s) then there will often (but not always) arise a positive correlation between clutch size and observed survival, even though a cost of reproduction is present. I review four nonmanipulative studies each of which provides support for the existence of adaptive adjustment of clutch size and/or the manifestation of a cost of reproduction. Campbell's data on Pied Flycatchers are re-analyzed; they demonstrate a significant negative correlation between brood size and female survival and significant year-to-year variation in this relationship. Adaptive adjustment in clutch size may be more significant among older breeders than among first-time breeders. I conclude that the empirical record supports well the hypothesis of a cost of reproduction associated with rearing larger broods.


[close window] [previous abstract] [next abstract]