A technique for and risks associated with entering tree dens used by blackbears

Entering dens to collect data is an important aspect of black bear (Ursus a mericanus) research. However, published literature does not describe or eva luate techniques for entering black bear dens. During winters 1995 through 1998, 109 of 151 (72.2%) radio-collared black bears in the George Washingto n and Jefferson National Forests, Virginia, used cavities in trees or snags as den sites. Safety concerns prevented us from attempt -ing to enter 25 d en trees, but we successfully entered 58 of 84 (69.0%) den trees and captur ed 166 bears (59 adults, 13 yearlings, and 94 cubs). Percentage of den tree s that we entered differed among years (P=0.077). Tree cavities that were n ot safe to enter (n=12) and den abandonment (n=7) caused most (65.5%) faile d attempts. Eight of 72 (11.1%) bears immobilized in tree dens died from ha ndling. Twenty of 94 (23.1%) cubs were orphaned due to death of, or den aba ndonment by, the sow. Den trees that we attempted but failed to enter were taller (P=0.006), had a greater diameter at breast height (dbh) (P=0.004), and had higher cavity entrances (P=0.001) than den trees we successfully en tered. Proportion of den trees falling after one year (P=0.308) and after 2 years (P= 0.481) did not differ between trees we cut to enter and uncut tr ees. We encourage biologists to assess the value, risks, and requirements f or entering den trees and to report and evaluate other techniques to enter black bear dens.