Electronic Thesis and Dissertation Repository


Master of Science




Dr. Liana Zanette


Recent manipulations show that when perceived predation risk is high, animals will chronically alter their escape behaviour, even if it affects physiological condition to such an extent that survival may be reduced. I tested the relationships amongst predation risk, mass change, and flying capacity in brown-headed cowbirds (Molothrus ater) housed in large outdoor aviaries. I measured changes in the birds’ body condition, take-off behaviour and flying capacity after manipulating the ambient level of perceived predation risk in their environment using various predator or non-predator cues. Cowbirds exposed to predator stimuli gained, rather than lost, body mass and changed their take-off behaviour, by flying at higher angles and reduced speeds. Critically, flying capacity was not affected by any of these changes. I suggest these responses may be anti-predator tactics that birds utilize to reduce starvation risk and improve their chances of predator evasion when predation risk is high.