Effects of Duckling Body Condition on Hunting Vulnerability in Juvenile and Immature Common Eiders Somateria mollissima

Thomas Kjær Christensen

body condition ； duckling ； eider ； hunting ； Somateria mollissima

Wildlife Biology

7卷2期（2001 / 06 / 01）

97 - 104

英文

Condition related pre-breeding hunting vulnerability in the common eider Somateria mollissima, i.e. the relationship between body condition attained as a duckling and the probability of being shot, was analysed from recoveries of hunter-retrieved birds ringed in the Stavns Fjord colony in Denmark during 1991-1995. Mean duckling cohort condition showed significant variation between years, but the proportions of birds retrieved during the first three seasons were similar (4.9%±1.4 SD). The proportion of birds retrieved by hunters declined from 3.9% in the first year to 0.64% and 0.38% in the second and third year, respectively. A condition bias was found in first-year retrieved birds in the cohorts with the highest and poorest mean condition, but not in the cohorts of intermediate condition. In accordance with a priori predictions regarding condition related non-hunting mortality during the period between marking and the opening of the hunting season, the direction of the bias was negative (hunters retrieved poor individuals compared to cohort mean) in the cohort of high mean condition, and positive (hunters retrieved good individuals compared to cohort mean) in the cohort of poor mean condition. Despite significant variation in cohort condition, the duckling condition of individuals retrieved during their first season from the cohorts of high and poor mean condition was comparable. The condition of first-year retrieved birds was not significantly different from the condition of birds retrieved during their second and third year, when all years were pooled. As there is a significant positive relationship within cohorts between duckling condition and recruitment of (female) eiders, the present results suggest, 1) that hunting vulnerability in the eider is related to a specific (poor) level of body condition attained prior to fledging, and 2) that hunting tends to remove the poorest individuals present at the time when the hunting season opens.