The flight speed of parent birds feeding young

Abstract

I review previous models of the speed at which parent birds should fly when delivering food to their young. Norberg gives a graphical method of finding a parent's best flight speed. This speed maximizes the overall rate at which energy is delivered to the young. An alternative assumption is that a parent maximizes the net rate of delivery of energy. I suggest that in general we cannot distinguish between net rate and overall rate on the basis of whether the parent feeds itself. The best way to distinguish between these currencies may be to use qualitative predictions. I present new results on the effect of a constraint on energy expenditure on the parent's optimal speed. I show that the optimal speed when foraging should be less than the optimal speed when traveling. I also analyse the advantage to a parent of flying faster than the maximum range speed and evaluate previous empirical studies of the speed at which parent birds fly. Only one study claims that parent birds fly at the speed identified by Norberg, but I raise doubts about this claim. © Journal of Avian Biology.