To run or to fly: low cost versus low risk escape strategies in blackbirds

When escaping from predators, ground-foraging birds could choose between two escape strategies with different costs: running or flying. We simulated predator attacks on blackbirds Turdus merula to investigate the factors influencing blackbirds to select between these strategies. The probability that blackbirds would fly increased as flight initiation distance decreased, suggesting that they may trade-off benefits of delaying escape with a costly escape strategy. The probability of flying also increased as the number of potential predators increased, indicating an increase in perceived predation risk with the number of non-attacking predators. Running was more likely to be used in the mornings and flying in the afternoons, suggesting a possible mass-dependent predation risk effect or restrictions in the use of costly escape strategies when energetic reserves are lower. Juvenile blackbirds tended to fly away more often than adults, probably to compensate for their less reliable risk assessments due to lack of experience. We conclude that different factors act independently on choosing an optimal escape strategy, and that the decision about when to escape (flight initiation distance) is associated with the decision about how to escape (escape strategy), which in turn can affect the decision about how far to escape (distance fled).