From the theory of bird flight energetics (due mainly to Pennycuick) a simple model is derived which identifies the flight speed of breeding birds that results in most food for the young. Only flights between foraging areas and the young, with no foraging during travel flights are considered. A parent bird trying to maximize amount of food delivered to its young should fly faster, at the penalty of increased energy expenditure on travel, than the maximum range speed (which involves minimum energy cost per unit distance flown). Regardless of the distances flown, birds should increase speed as long as the concomitant increment in travel costs can be more than compensated by foraging in the travel time saved. The higher the food availability and, hence, the rate of net energy gain during foraging, the higher the optimal speed during travel flights. This prediction is testable without knowledge of the bird''s power-v.-speed curve or its maximum range speed.
