A FLEDGLING-MASS THRESHOLD GREATLY AFFECTS JUVENILE SURVIVAL IN THE HAWAII AKEPA (LOXOPS COCCINEUS COCCINEUS)

Offspring quality is all important issue in avian life-history theory, particularly with regard to birds that have low reproductive rates and extended parental care. Offspring mass has been identified as an indicator of quality in several bird species. These studies have shown that nestling mass is predictive Of Offspring survival outside the nest, but few studies have considered the role of fledgling mass. Mass during the fledgling period may change and influence juvenile Survival. Fledgling mass may be especially relevant for tropical birds that have very long fledgling periods during which food conditions randomly, or seasonally change. Here, we show that fledgling mass predicts juvenile survival in the Hawaii Akepa (Loxops coccineus coccineus), an endangered Hawaiian Honeycrceper with high annual adult survival and a two-egg Clutch. Juvenile survival of Hawaii Akepa approximated a trimodal pattern of no survival, low Survival, and high survival that corresponded to ascending mass classes. Fledglings in the highest mass class had an apparent juvenile survival probability that was more than double that of fledglings of the lower mass classes and that was statistically indistinguishable from Survival rates of adults. This mass-dependent juvenile survival has important implications for understanding the life-history evolution and population biology of the Hawaii Akepa and perhaps of other tropical birds. Received 16 January 2008,accepted,31 October 2008.