Coping with captivity: takeoff speed and load-lifting capacity are unaffected by substantial changes in body condition for a passerine bird.

Captivity presumably challenges the physiological equilibrium of birds and thus influences flight ability. However, the extent to which captive birds exhibit altered features underpinning maximum flight performance remains largely unknown. Here, we studied changes in physiological condition and load-lifting performance in the Eurasian tree sparrow (Passer montanus) over 15, 30 and 45 days of captivity. Sparrows showed body mass constancy over time but also an increased hematocrit at 15 days of captivity; both relative pectoralis mass and pectoralis fat content increased at 30 days. However, maximum takeoff speed and maximum lifted load remained largely unchanged until 45 days of captivity. Wingbeat frequency was independent of captivity duration and loading condition, whereas body angle and stroke plane angle varied only with maximum loading and not with duration of captivity. Overall, these results suggest that captive birds can maintain maximum flight performance when experiencing dramatic changes in both internal milieu and external environment.