Bald eagle winter roost characteristics in Lava Beds National Monument, California

Abstract

This study provided a survey of bald eagle ( Haliaeetus leucocephalus ) winter roost habitat (in 4 km 2 of potential roost areas) in southern Lava Beds National Monument, California. A systematic-clustered sampling design ( n =381 plots) was used to compare forest stand characteristics in two primary roost areas (Caldwell Butte and Eagle Nest Butte) and two potential roost areas (Hidden Valley and Island Butte). A 100 percent inventory of roost trees in Caldwell Butte ( n =103 trees) and Eagle Nest Butte ( n =44 trees) showed they were spatially clumped and restricted to 12.7 percent and 2.8 percent, respectively, of the study areas. Roost trees, primarily ponderosa pine ( Pinus ponderosa ), averaged 81.1 ± 1.3 cm dbh (mean ± 1 S.E.) compared to non-roost trees (>35 cm dbh) that averaged 52.2 ± 1.0 cm dbh. Roost trees were generally taller and more open-structured than non-roost trees. All four study sites had adequate numbers of mid-sized trees (10 to 50 cm dbh) to replace the current stock of older, larger roost trees. However, seedling and small trees (<10 cm dbh) in the roost areas were spatially clumped and few, suggesting that maintaining a continuous population of roost trees may be a problem in the distant future. Long-term studies of changing winter roost habitat and eagle use are essential to protect the bald eagle in the northwestern US.