A test of the condition-bias hypothesis yields different results for two species of sparrowhawks (Accipiter)

The determination of body condition of birds is important for many field st udies. However, when using trapping methods based on food as a lure, the sa mple of trapped birds could be biased toward individuals in poor physical c ondition. We provide information on body mass, body condition, and sex and age ratio of Levant Sparrowhawks (Accipiter brevipes) and Eurasian Sparrowh awks (Accipiter nisus) caught in flat, southern Israel, during spring migra tion. We compared physical condition of birds trapped in baited traps to ph ysical condition of birds trapped in mist nets (no bait). The body mass and index of physical condition of migrating Levant Sparrowhawks trapped in ba ited traps was lower than birds trapped in mist nets. By comparison no diff erences were detected in body mass and condition index of migrating Eurasia n Sparrowhawks caught by the different trapping methods. The differences fo und in condition of Levant Sparrowhawks trapped with and without food suppo rt the predictions of the condition-bias hypothesis; however, data from the Eurasian Sparrowhawk do not. The extent to which biases occur may be diffe rent even for closely related species.