Nocturnal Singing by Marsh Wrens

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Abstract
We quantified nocturnal singing by Marsh Wrens (Cistothorus palustria) at Delta Marsh, Manitoba [Canada], and determined nightly and seasonal patterns of this behaviour in order to assess its costs and potential functions. Male Marsh Wrens sang intensively between 01:00 and 03:00 throughout the breeding season at rates approaching their daytime singing rates. Environmental conditions and moon phase did not appear to influence nocturnal singing activity and there was considerable individual variation. Pairing and reproductive success of male Marsh Wrens were not correlated with their nocturnal singing activity. The behavior could serve to attract nocturnally migrating females, stimulate reproductive behavior of females, facilitate male-male interactions in the face of acoustic interference and aggression from other species during the day, or affect the songs learned by offspring. Since males of this species sing at night throughout the breeding season, however, no one function is likely responsible for this behavior.