Subject: bird behavior 101
Date: Jun 11 10:56:54 2002
From: Dennis Paulson - dpaulson at ups.edu


I just read an interesting paper: Norris, D. R., and B. J. M. Stutchbury.
2001. Extraterritorial movements of a forest songbird in a fragmented
landscape. Conservation Biology 15: 729-736.

There has been much study of forest fragmentation and its effect on birds
and other organisms. One of the effects is merely to make some fragments
too small to serve as an adequate territory size for various forest birds.
But some birds nest in surprisingly small fragments, in thise case as small
as 0.7 hectares. This paper had a new twist - why a bird might be willing
to leave its territory in a fragment and fly across an open space to
another forest where others of its species are already defending
territories.

The authors studied Hooded Warblers in Pennsylvania. They were interested
in multiple effects of fragment size, and they radiotracked individual
birds. They are now making transmitters as small as 0.67 grams, not too
heavy for a 10-gram Hooded Warbler!

They found that males frequently left their isolated forest fragment and
flew across open areas into adjacent fragments or intact forest. They
stayed away an average of 29 minutes and traveled an average of 400 meters
(with a maximum of 2.5 km). The longest open area traversed was about a
half kilometer. Without much evidence, but with a strong feeling of
certainty, the authors stated that these birds were leaving their
territories and crossing quite inappropriate habitats for one reason, and
one reason alone - to seek extrapair copulations with females on adjoining
territories!

Most males stopped singing when they went off on these expeditions,
obviously to avoid being detected by other territorial males. The same
birds that sing vigorously in their own territory are sneaky little buggers
when they leave it. Unfortunately, the authors had no data on success
rates, but other researchers found that young in some nests in isolated
forest fragments that supported only one pair of warblers were of mixed
paternity, indicating that this tactic worked at least some of the time.

The drive to spread genes is a strong one.....

Dennis Paulson

Dennis Paulson, Director phone 253-879-3798
Slater Museum of Natural History fax 253-879-3352
University of Puget Sound e-mail dpaulson at ups.edu
1500 N. Warner, #1088
Tacoma, WA 98416-1088
http://www.ups.edu/biology/museum/museum.html