A test of the condition-bias hypothesis yields different results for two species of sparrowhawks (Accipiter)A Test Of The Condition-Bias Hypothesis Yields Different Results For Two Species Of Sparrowhawks (Accipizter)

Determination of body condition of birds is important for many field studies. However, when using trapping methods based on food as a lure, the sample of trapped birds could be biased toward individuals in poor physical condition. We provide information on body mass, body condition, and sex and age ratio of Levant Sparrowhawks (Accipifer hrevipes) and Eurasian Sparrowhawks (Accipiter nisus) caught in Elat, southern Isr l, during spring migration. We compared physical condition of birds trapped in baited traps to physical condition of birds trapped in mist nets (no bait). The body mass and index of physical condition of migrating Levant Sparrowhawks trapped in baited traps was lower than birds trapped in mist nets. By comparison no differences were detected in body mass and condition index of migrating Eurasian Sparrowhawks caught by the different trapping methods. The differences found in condition of Levant Sparrowhawks trapped with and without food support the predictions of the condition-bias hypothesis; however, data from the Eurasian Sparrowhawk do not. The extent to which biases occur may be different even for closely related species.

Edna Gorney William S. Clark, and Yoram Yom-tov, Wilson Bull., 111(2), 1999, pp. 181-187