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TIMING OF NEST DEPARTURE IN THE THICK‐BILLED MURRE AND RAZORBILL: TESTS OF YDENBERG’S MODEL
Author(s) -
Hipfner J. Mark,
Gaston Anthony J.
Publication year - 1999
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(1999)080[0587:tondit]2.0.co;2
Subject(s) - hatching , biology , nest (protein structural motif) , intraspecific competition , ecology , variation (astronomy) , zoology , demography , biochemistry , physics , sociology , astrophysics
Marine birds of the family Alcidae exhibit extreme variation in the mass and age at which offspring leave the nest. A previously proposed, theoretical model of intraspecific variation in optimal timing of nest departure in alcids predicts that: (1) variation in growth rate among chicks will result in negative correlations between departure mass and departure age, and (2) in the absence of seasonal declines in chick growth rates (such declines are consistent features of alcid biology), variation in timing of hatching among chicks will cause both mass and age at departure to decline with hatching date. We tested these predictions for Thick‐billed Murres and Razorbills, two alcids that employ a unique development strategy. To control for the confounding effects of seasonal variation in growth rates, caused at least in part by variation in the characteristics of adults breeding at different times, we switched eggs at random among breeding pairs in each of two years for both study species. Contrary to prediction 1, there were no significant negative correlations between departure mass and departure age, and in fact, there was one significant positive relationship. Contrary to prediction 2, departure mass did not decline with hatching date; in agreement with prediction 2, departure age often declined with date. Our results suggest that, for Thick‐billed Murres and Razorbills: (1) variation in growth rate probably does not influence timing of nest departure in the manner outlined in the model, and (2) it is unlikely that variation in hatching date affects the departure decision in the manner predicted by the model. Based on our experimental results, and previously reported observations of Thick‐billed Murres, we develop alternative hypotheses, emphasizing the roles of parental quality and wing growth (rather than increase in mass), to explain the close correspondence between the model’s predictions and patterns in the timing of nest departure within the Alcidae that are reported frequently.