Impact of Climatic Variation on Galapagos Mockingbird Social Organization.
We studied cooperative breeding of Nesomimus parvulus over 13 years (1978-90) across a broad range of climatic conditions. Variation in annual rainfall strongly influenced demography, but had few direct effects on social behavior, Indirect effects were pronounced. The frequencies of polygyny and associated joint nesting decreased with adult sex ratio. Along with destiny, mate availability determined the proportion of males that bred and, secondarily, the proportion that helped. Sex ratio did not affect the proportion of females that bred, but the proportion helping decreased with availability of males because mate-sharing females most often acted as helpers. Polygyny benefits males but it usually rare because monogamous females have higher reproductive success than females sharing mates. The frequency of plural breeding varied with population age structure. By favoring flexible reproductive behavior, climatic and demographic variation ultimately accounts for the occurrence of polygyny, joint nesting, and plural breeding.
|Main Author:||Curry, R. L.|
|Other Authors:||Grant, P. R.|