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.