Having had the chance to do some birding today, it was nice to note the many
passerine migrants in the area. However, the most entertaining and
interesting observation I made today was that of a few pairs of marsh wrens.
I had found 3 nests, rather easily since the birds practically pointed them
out to me, also, the cattails and bullrushes are still rather short 1 metre
in height. Two of the nests were nearly complete and the bird(s) was adding
cattail down to the interior. The third nest however, was hardly begun, it
was the shape of a small cup or bowl and was constructed of the same
materials as the others (dead woven cattail leaves) however there was not
nearly enough material present to hold eggs or repel water (no roof). I
wondered if this might be a 'dummy' nest since it was so close to one of the
other nests. I am as yet uncertain though because one of the wrens was
sitting in the flimsy nest at the time (perhaps forming its shape?).

After having watched them for a while, I was curious as to whether marsh
wrens normally make dummy nests or is this uncommon? If they do make dummy
nests, why did I not see more nests around, and wouldn't a dummy nest remain
unfinished? Why would a marsh wren bother to make an elaborate nest when
something rather flimsy might serve the same purpose? (assuming that the
purpose would be to foil predators)

On the other hand, if the purpose of making dummy nests is the male's way of
attracting females, then surely there would be more nests present per pair
of birds.

Why would these marsh wrens all make nests from dead cattail leaves? Is it
because so much of it is available at this time? Wouldn't live cattail
leaves repel water better whereas dead ones might soak up moisture and then
shrink as they dry?

It was also interesting to consider the location of the nests, all of these
nests were rather low (I suppose they do not have much choice since the
cattails themselves are short), however all of the nests seen were above
fresh water ponds whereas in the immediate vicinity was available nesting
habitat over the tidal zone. Are these birds intelligent enough to know
that making nests at this time of year over tidal water would be dangerous?
Perhaps natural selection has removed silly nesters from the coastal
population of marsh wrens. Then again, would some marsh wrens nest later in
the season over the tidal zone when the cattails are taller?


Cheers,

Don Cecile
Port Alberni, BC, CANADA V9Y 6Z5
eMAIL: dcecile at cln.etc.bc.ca