Courtship Feeding
photograph of a Forester's Tern, which is closely related to Common Tern, carrying a fish by Tom Grey	During the breeding season you may have watched one adult bird feed another. Whether it occurs when pairs are first getting established or sometime later after incubation has begun, this behavior is known as "courtship feeding." In most species males present solid or regurgitated food to the soliciting female. In species in which the females do the courting, the roles may be reversed. Courtship feeding is frequently seen in terns. For instance, in an effort to lure females to their territories in the nesting area, a male Common Tern carries a fish around the breeding colony and displays it to prospective mates. After a pair bond is formed, during the "honeymoon period" the male tern actually feeds the female, and soon thereafter they begin to copulate.
During the following five to ten days, both sexes feed themselves, but the male also frequently feeds the increasingly dependent female. For the few days prior to egg laying the female is fed almost exclusively by the male, but this activity declines rapidly as the second and third eggs are laid. It is generally thought that courtship feeding serves more than a ceremonial or pair-bonding function -- that it provides the female with considerable nutritional benefit. In turn, the number of eggs and total clutch weight are partly determined by the female's nutritional status. Careful measurements suggest that the total weight of a Common Tern's clutch is correlated with the amount of food the male delivers, especially during the honeymoon. Male Common Terns in one Massachusetts colony were unable to deliver as much food to their mates as males in a second colony. In the colony where the males were less successful, the females laid fewer and lighter eggs. Thus the amount of food the male provides may limit female reproductive output. If the female's nutritional status is so critical to her reproduction, why does she gradually stop feeding herself prior to egg laying? The probable answer is that she is too heavy to hunt efficiently. Before laying her three egg clutch a female Common Tern weighs half again as much as she does when not breeding. Terns forage by cruising at low speed and making precise dives at fishes. A female's additional weight would increase the energy requirements of flight, and perhaps make controlled dives too difficult. This does not mean that improving the female's nutrition is the only function of courtship feeding. In gulls, it is also an important inducement to copulation (as it may be in the Common Tern). It may also serve to facilitate the formation of the pair bond and reduce aggression between the male and female. Still, when a male warbler, crossbill, chickadee, or tern is seen feeding a female, it seems apparent that he is increasing his own reproductive success by keeping her fat and healthy.
SEE: Average Clutch Size; Visual Displays. Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.