Mate and Nutrient Limitation of Egg‐laying in a Polyandrous Shorebird
1985
Lank, D. B. | Oring, L. W. | Maxson, S. J.
Spotted Sandpipers are unusual among animals in that a female's annual reproductive effort is regulated primarily by her ability to obtain mates. Males provide most of the parental care in this species. We recorded data on the abundance of food, and on the timing, number, and size of eggs laid by marked females over a 9—yr period on an island in central Minnesota, USA. The onset of egg—laying varied from year to year in association with the abundance of flying insects early in the season. After laying began, there was no relationship between food abundance and the number of size of eggs laid, the time taken to produce a clutch, or the intervals between clutches. The rate of egg—laying per female was affected, however, by rates of nest predation and by the operational sex ratio, which became increasingly female—biased over the season. Females ceased laying eggs in early July, even in years when food and mates were still available. We conclude that nutrient availability acts as a proximate factor in determining the onset of breeding, and that it may have been ultimate factor causing cessation of egg—laying. Within the season, however, the reproductive rate of individual females is primarily determined by competitive interactions with other females for males. Thus both intra and intersexual selection have important effects on fitness in this species.
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