The U. S. Fish and Wildlife Service (Service) manages eagle populations under provisions of the Bald and Golden Eagle Protection Act (Act). In the Act, Congress mandated that any take of bald (Haliaeetus leucocephalus) or golden (Aquila chrysaetos) eagles authorized by the Service must be consistent with eagle preservation, which the Service interprets to mean consistent with maintaining stable populations of both eagle species. Incidental eagle take permits are sought by industries that accidentally kill eagles (e.g., wind energy companies) in order to be compliant with the law, and such permits can become controversial. Take of bald eagles was the subject of recent litigation, and as a result the Service and collaborators agreed to update our estimates of population size and demographic rates for this species. For this update, we are developing an integrated population model (IPM) to improve the formal estimates of population size and allowable take that are the basis of permit decisions for this species.
Results/Conclusions
The bald eagle IPM links data from triennial counts of occupied nesting territories, age-specific survival rates from band recovery data, and results of a meta-analysis of reproductive data to produce more accurate estimates of population size by accounting for “floating adults”, those not yet settled on a nesting territory, as a latent parameter in the model. Our expectation is that the IPM will produce more accurate estimates of bald eagle population size, as well as improvements in estimates of the vital rates that are used in models to establish sustainable take limits. By integrating data from multiple sources into a single population model, we were able to develop more biologically realistic models (e.g., accounting for covariances among life history traits), and estimate important parameters for which we did not have direct information (e.g., proportion of floaters, fecundity at low population density).