Growth‐Mortality Trade‐Offs and the Evolution of Juvenile Life Histories in the Alcidae

• Published in: Ecology
• Main Author: Ydenberg, R. C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1989
• Subjects: Common Murre
• Online Access: http://dx.doi.org/10.2307/1938208; http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2307%2F1938208; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2307%2F1938208; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.2307/1938208

The juvenile life history of each of the 22 living species in the avian family Alcidae is composed of a period in the nest followed by a move to the ocean (fledging), where development is completed. The age, degree of development, and the mass of the alcid chick at fledging are extraordinarily variable, both between and within species. The available information suggests that nests are safe places (the daily mortality of chicks there is low) relative to the ocean, but that growth in the nest is slow relative to that attainable at sea, because of the parental travel time between the nest and feeding areas. The chick therefore faces a trade—off in deciding when to make the transition from nest to ocean. A dynamic programming model incorporating (1) the differential growth and mortality in the nest and ocean habitats, and (2) assumptions about the relation between size and survival, accurately predicts the fledging age and mass of the Common Murre (the only species for which reasonable estimates are available). The model suggests explanations for some other phenomena associated with the reproduction of alcids and other northern seabirds, namely the seasonal decline in mass at fledging, and the negative relation of mean fledging age and mass observed between colonies in several species. The optimal fledging policy is also considered from the point of view of the parents. There are many indications that visits to the nest endanger the parents' lives, and hence parents should be @`reluctant" provisioners, leading to conflict between parents and their offspring. This evolutionary conflict and its implications forour understanding of avian life histories are discussed.