FLEXIBLE GROWTH-RATES IN FORK-TAILED STORM-PETRELS - A RESPONSE TO ENVIRONMENTAL VARIABILITY

We examined the degree that growth in Fork-tailed Storm-Petrel (Oceano droma (furcata) chicks varies among individuals and years. Data on win g chord length and body mass were collected on 10 or more chicks per y ear on the Barren Islands, Alaska, during seven years over two decades . In contrast to the apparently uniform growth rates in other storm-pe trels (e.g. Leach's Storm-Petrel [Oceanodroma leucorhoa] and British S torm-Petrel [Hydrobates pelagicus]), Fork-tailed Storm-Petrel chicks o n the Barren Islands displayed a two-fold variation in both wing growt h and mass gain. Variation in growth rate was apparent both within and among years. Correlations between wing growth and mass gain were sign ificant in only four of seven years, a finding we interpret as indicat ive of the importance of changes in food quality and quantity on growt h. The decadal changes in growth rate of this species between the 1980 s and 1990s are consistent with the regulating role that environmental variation appears to play in the growth and survival of storm-petrels . We suggest that the wide range of observed growth rates among indivi duals, years, and between decades is a response to environmental varia bility.