Methods to Estimate Golden Eagle Populations

A multi‐state, time‐removal model for population dynamics of cliff‐nesting raptors

Abstract

Cliff‐nesting raptors present considerable challenges for population estimation due to their sparse distribution across remote landscapes and the multiple occupancy states (e.g., unoccupied, occupancy without breeding, breeding occupancy) through which we observe their nesting territory dynamics. To increase the efficiency and spatial inference of surveys, we developed 2 versions of a multi‐state, time‐removal model: 1 for long‐term monitoring studies and the other for population inventories or single‐season surveys in which there is no prior knowledge of nest locations. We focused our development of these methods in the context of a combined aerial and ground‐based survey approach, which permits efficient surveying at landscape scales. The approach, however, is also applicable to designs restricted to ground surveys. For long‐term monitoring of species with alternative nests, we formulated a version of the model that accounts for state uncertainty at the territory level caused by a failure to observe all nests within a territory. Simulations based on the long‐term monitoring model indicated adequate (near nominal) coverage and low relative bias (<0.05) for nearly all parameters. In the simulation study for the inventory model, population size estimates showed negligible bias for a survey duration of 90 minutes. We applied our approach to a long‐term study of golden eagles (Aquila chrysaetos) in Alaska and demonstrated that the maximum effort spent on any nesting territory could be reduced by up to almost 90% of that recommended by standard protocols.

Mizel, J. D.,C. L. McIntyre, S. B. Lewis, M. S. Lindberg, and J. H. Schmidt. 2018. A multi‐state, time‐removal model for population dynamics of cliff‐nesting raptors. Journal of Wildlife Management 82:1701-1710. doi:10.1002/jwmg.21526