Subject: window kills
Date: Sep 6 16:44:44 1994
From: Dennis Paulson - dpaulson at ups.edu


Gene Hunn made a good point in questioning the statistics of window-kill
mortality in birds. I can only point out that this estimate was, amazingly,
arrived at independently in two different studies. Klem (1990) gave the
original estimate of 1-10 birds per building (the range of
100,000,000-1,000,000,000 in the U.S.), but unfortunately I don't have a
copy of his paper (J. Field Ornithol. 61: 120-128) so I don't know what his
methodology was.

Erica Dunn, in the paper I cited previously, received data from 5500
Project Feeder Watch households. Only 507 of them reported window kills in
that period. Obviously this is an underestimate, because I know full well
that we in fact don't detect them all. Some get lost in the shrubbery,
others are taken by predators. However, the figure likewise may be an
overestimate, because the people who participated had lots of feeders
attracting birds to their yards. So - ??? Her final figure was 0.85
birds/yard/4-month winter period--obviously the figure would be higher for
the entire year. So that's only a paltry 100 million, if that's how many
buildings there are. I don't know where they got *that* estimate, presumbly
from the U.S. population and average family size; I guess the homeless
aren't included. As Gene wrote, and as both of the above authors cautioned,
a lot more information is needed.

But I don't think my yard is too atypical, and we have >1 predator
kill/year, especially cats, and at least 1 window kill/year. We need to
have volunteers do door-to-door surveys on the general populace comparable
to the Feeder Watch surveys, and we need to pay close attention to such
variables as latitude, season, and # and type of birds fed (there are good
data for Feeder Watch). Gene made the point about "well lighted and
exceptionally tall" buildings, but I think the majority of window kills may
be in suburban and country homes with big picture windows located in
more-or-less natural habitats; looks like a straight flight through the
woods. That's where a lot of breeding and migrant birds meet their demise.
At the Slater and Burke museums we receive a constant supply of window- and
cat-killed birds, and when we think that only a few people are actually
saving them, we have a lot of respect for this source of mortality. I think
most of the people on Tweeters might be shocked by my rather conservative
estimate of a mortality of *hundreds* of sharp-shinned hawks every winter
in King County alone.

Both of the above authors, responsibly, tried to make suggestions about how
to reduce this mortality. Guess what--cessation of feeding might be the
most significant one. It would reduce cat kills, window kills, and the
spread of communicable diseases. This might be significant to populations,
it might not. After all, many of us feed birds winter after winter and
don't see a diminution of bird populations around our houses. But
individual birds *are* dying because of our bird feeders. And probably
individual birds survive better because we feed them during the winter,
too. What a tradeoff!

Dennis Paulson