JUVENILE SURVIVAL IN A POPULATION OF NEOTROPICAL MIGRANT BIRDS

Determination of population productivity of Neotropical migrant birds and assessment of breeding habitat quality have been based on populati on densities and nesting success. Data on juvenile survival improve ou r estimates of population productivity, provide information on factors during the post-fledging period that affect this productivity and, wi th comparative data, enable us to better assess breeding habitat quali ty. We present the first estimate of post-fledging juvenile survival i n a population of Neotropical migrant birds. We studied post-fledging survival in a population of Wood Thrush (Hylocichla mustelina) in sout hern Missouri, (U.S.) an area hypothesized to contain source populatio ns. Nesting success during our study period was 0.266, and individual survival within the nest was 0.245. Post-fledging survival during the first 8 weeks after fledging was 0.423. Survival varied significantly between post-fledging weekly age classes, with survival of weeks 1, 2, 3, and 4 through 8 being 0.716, 0.930, 0.637, and 1.00, respectively. Probability of prediction varied by weekly age class and may have bee n related to behaviors occurring at different stages. Post-fledging su rvival was not correlated with nestling mass and did not change throug hout the course of the breeding season. Analysis of the source/sink st atus of the population based on our estimates of nesting success and p ost-fledging survival indicates that young were being produced below r eplacement levels during our study period. Large-scale management deci sions should take into account potential fluctuations in the productiv ity of Neotropical migrant populations over time. Data on post-fledgin g juvenile survival are needed from other populations of Neotropical m igrant birds to more accurately assess differential productivity betwe en populations and better assess breeding habitat quality.