Sleeping Behavior of Purple Martins

Abstract

The behavior of purple martins (P. subis) at nightfall and the birds'' sleeping arrangements, each night, from spring arrival until premigratory flocking began were studied. Martins slept in martin houses until about June 15, after which they commonly slept in trees. Birds that were firmly established on a territory slept in a room of that territory. Some pairs of birds slept together in the same room and others did not. This behavior was determined by the males. Pairs that occupied their territories for a week or longer often slept together. While building nests, pairs began to prefer certain rooms for sleeping. During egg laying and incubation, all females slept in the nest. They slept with the young and probably brooded them at night until the nestlings were 13-15 days old. Some females ceased sleeping with the nestlings after 2 wk, and these females either slept in a tree or resumed sleeping with their mates. Many vagrant martins slept in martin houses, often on occupied territories. Martins frequently called from 0300 h until daybreak. Purple martins probably copulate in martin houses at night, probably in the early morning. Pairs'' sleeping together facilitates mating. Nocturnal copulation benefits males by minimizing cuckoldry and neighbor interference. Females benefit by being less vulnerable to gang rapes. Pairs also may sleep together to conserve heat on cool spring nights.