PARENT SESSION
Oral Session #84: Statistical Ecology.
Presiding: L. Subhash
Thursday, August 8. 9:00 AM to 11:30 AM. Mesquite Room, Radisson.
Estimating stage-specific daily survival probabilities of nests when nest failure data are incomplete.
Stanley, Thomas*,1, 1 U.S. Geological Survey, Midcontinent Ecological Science Center, Fort Collins, Colorado
ABSTRACT- Estimation of daily survival probabilities of nests is common in studies of avian populations, and since the introduction of Mayfield's (1961, Wilson Bulletin 73:255-261) estimator numerous models have been developed to relax Mayfield's assumptions and account for biologically important sources of variation. In a recent paper, Stanley (2000, Ecology 81:2048-2053) presented a model for estimating stage-specific (e.g., incubation stage, nestling stage) daily survival probabilities of nests that conditions on nest type, and requires that nests be aged when they are found. Because aging a nest typically requires handling the eggs, there may be situations where nests can not or should not be aged and the Stanley (2000) model will be inapplicable. For example, nests may be inaccessible because they are high in a tree or on a cliff face, or, perhaps, the species under investigation is rare or threatened and disturbing the nest will cause abandonment. Alternatively, reliable aging methods may not exist or the aging data may have been lost or were not collected. In such cases, data for nests that fail will be incomplete and it will not be possible to apply the Stanley (2000) model. In this paper, I present a model for estimating stage-specific daily survival probabilities that conditions on nest stage for active nests, thereby obviating the need to age nests when they are found. Specifically, I derive the maximum likelihood function for the model, evaluate model performance using Monte Carlo simulations, and provide software for estimating parameters. For sample sizes as low as 50 nests, bias was small and confidence interval coverage was close to the nominal rate, especially when a reduced-parameter model was used for estimation. This model provides a robust alternative for estimating stage-specific daily survival probabilities.
KEY WORDS: nest survival, Mayfield model, stage-specific survival, maximum likelihood estimation