NOCTURNAL INCUBATION BY MALE BLACK TERNS

Thomas W. Custer, and Christine M. Custer
U. S. Geological Survey, Upper Mississippi Science Center, P.O. Box 818, La
Crosse, WI  54602-0818 USA

In 1996 we attached radio transmitters to 11 Black Terns, including 3 pairs, on
Trempealeau National Wildlife Refuge, Trempealeau, WI.  An automated data
recording device gathered information on the presence of radio-marked birds near
the nest every 2 to 5 min for more than 700 hours during the incubation and
nestling periods.  Males consistently incubated during the night and both members
of the pair incubated during daylight hours.  During the evening hours, breeding
females left the nesting site and spent the night 2 to 3 km away.  Preliminary
information suggests that breeding females and nonbreeding males gathered at
nighttime communal roosts.  Earlier studies have suggested that wind and waves
may be the major causes of nest loss in this species.  Because of the high potential
of nest loss in this species, nighttime incubation by the male may allow the female
to more easily renest if the eggs are lost.  The role of males and females during
nocturnal incubation is not well known for any tern species and male nocturnal
incubation may not be uncommon among terns.  


Keywords: black terns, telemetry, incubation

Thomas W. Custer, P.O. Box 818, La Crosse, WI  54602.  Voice 608 783-6451,
Fax 608 783-6066, Email tom_W_custer@nbs.gov

Poster preferred