ARE HAZEL GROUSE BONASA-BONASIA MONOGAMOUS

The apparently monogamous social organization of Hazel Grouse Bonasa b onasia previously had been inferred only from observations of unmarked birds. Using radio-marked Hazel Grouse, we confirmed that the social organization during the breeding season was indeed monogamous, the pai r being the social unit. The pair bond, however, appeared relatively w eak, as birds were together only 37% of the time during the prelaying period. We could not document mating behaviour, but observations sugge sted that most males mated monogamously and that at least 37% of the f emales had an opportunity to mate polyandrously because of (1) the see mingly weak pair bond, (2) attentive neighbouring males, (3) larger te rritory size of unpaired males, (4) extensive movements of me unpaired males, (5) sharing of a female by two males and (6) a potentially mal e-biased sex ratio.