Evol Ecol Res 3: 179-190 (2001)     Full PDF if your library subscribes.

Precocial nest departure in the Alcidae

R.C. Ydenberg*

Behavioral Ecology Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada

e-mail: ydenberg@sfu.ca


The avian family Alcidae is unique among birds in having species with widely divergent developmental modes. In all alcids, the juvenile phase is composed of a period spent in the nest and a subsequent period at sea completing growth; the age at transition varies greatly between species. Previously, semi-precocial (species completing more than half of growth in the nest before departure to the sea) and intermediate (one-quarter to one-third of growth) alcid species have been modelled. Here a model is developed to investigate selective factors favouring the evolution of precocial nest departure in the Ancient Murrelet Synthliboramphus antiquus. The fitness-maximizing age to make the transition from nest to sea (nest departure) is calculated under various assumptions, for both parents and offspring. The model shows that the potential for growth at sea following nest departure is the strongest factor influencing the age at departure. A second important factor is the danger posed by predators to provisioning parents, while the two-egg clutch of murrelets (most other alcids lay a single egg) is less important. There is a small region of the parameter space (with high ocean growth and dangerous provisioning) within which precocial nest departure is favoured from the point of view of both parents and offspring. The zone of conflict between parents and offspring is also narrow. These results are evaluated with respect to the precocity hypothesis of Gaston.

Keywords: alcid nest departure, Ancient Murrelet, growth–mortality trade-off, parent–offspring conflict, precocity.

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