Functional significance of nest size variation in the Rufous Bush Robin Cercotrichas galactotes.

Avian nest building behaviour has generally been viewed as a result of natural selection, and several functional hypotheses have been suggested to explain variance in nest size. These include responses to predation and parasitism risk, and aspects of nest stability, clutch size, insulation and sexual display. We studied variation in nest size in the Rufous Bush Robin Cercotrichas galactotes, a songbird in which both sexes contribute in nest building. Nest size was marginally negatively associated with the probability of brood parasitism, but no relationship was found with nest predation. Four additional hypotheses of the function of nest size variance were considered. The nest support hypothesis, the clutch size hypothesis and the thermoregulation hypothesis did not explain the nest size variation found, but the sexual display hypothesis was partially supported because clutch size was positively correlated with the amount of nest material, and this nest feature also tended to be positively correlated with size of prey provided to chicks by males. Nest building behaviour in the Rufous Bush Robin can be considered a post-mating sexual display that reflects the willingness of males to invest in parental care and allows females to adjusts their reproductive effort accordingly

Palomino J.J., Martin-Vivaldi M., Soler M. & Soler J.J., ARDEA 86 (2): 177-185