Accounting for dispersal and habitat use when estimating survival of a migrant songbird

Background/Question/Methods

Estimating demographic rates is a critical element of understanding the causes and consequences of observed changes in population size.  Losses of individuals from local populations can be driven by either the mortality or emigration rates of individuals.  However, estimation of these population parameters can be challenging even with extensive recapture or resighting data from marked individuals.  Many models for survival estimation using capture-recapture data are unable to distinguish between mortality and emigration, while basic information about dispersal distances is often biased when observations from finite study areas are more likely to include short-distance movements and do not account for the distribution of habitat on the surrounding landscape.  We developed an open-population spatial mark-recapture model for the purpose of estimating true survival and dispersal parameters for the endangered Golden-cheeked Warbler (Setophaga chrysoparia) based on a 23-year mark-resight dataset from Fort Hood, Texas.  By explicitly defining a submodel for the movement of birds and accounting for the spatial distribution of both habitat and sampling effort, we are able to link the observed capture histories and spatial data from resightings to underlying models for survival and dispersal processes.

Results/Conclusions

We estimated true annual survival at 0.70 [posterior mean] for after-hatch-year males, 0.69 for females, and 0.65 for hatch-year birds which were banded the previous year as independent young.  Estimated dispersal distances were highest for hatch-year birds and led to considerable negative bias in apparent survival estimates based on a non-spatial Cormack-Jolly-Seber model.  Because assessments of population viability are frequently sensitive to the demographic parameters selected as inputs, improved survival estimates that account for the movement behavior of organisms can provide valuable information for conservation and management planning.