Mass-dependent take-off ability in wintering great tits (Parus major): comparison of top-ranked adult males and subordinate juvenile females |
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Authors: | Indrikis Krams |
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Institution: | (1) Department of Sciences, Daugavpils University, Vienibas iela 13, 5400 Daugavpils, Latvia, |
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Abstract: | When birds are attacked by predators, initial take-off is crucial for survival. Theoretical studies have predicted that predation
risk in terms of impaired flight ability increases with body weight. However, studies in which attacks were simulated, and
within-individual daily changes in body weight were used to test mass-dependent take-off outside migration period, have so
far failed to show an effect of mass on velocity. In this field study I compared the mass/velocity relationships of alarmed
adult male and juvenile female great tits, Parus major. Fattening strategies differ among members of the dominance-structured basic flocks of wintering great tits, and dominant
individuals often carry significantly less amount of fat reserves than subordinates. Since the range of body weight gain/loss
is the least among dominant males, it was expected that impaired flight ability is more likely in lower-ranked female great
tits. The results show that the birds differed significantly in their daily increase of relative body weight. Average daily
weight increase of adult males was 6.2%, while it was 12.2% in juvenile females. Males were faster than females at take-off
both at dawn and at dusk. Flight velocity of males did not differ significantly between dawn and dusk, whereas females took
off at a significantly lower speed at dusk than at dawn. The results suggest that the larger fat reserves of subordinate females
needed to increase their chances of overwinter survival probably place them at increased risk of predation.
Electronic Publication |
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Keywords: | Birds Fat reserves Flight ability Predator evasion |
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