[mou] Bird Behavior-Sad

[Jim Barrett]

The last sentence of your first paragraph posed the rhetorical question "It 
also seems.... that eventually this could sway the balance of birds in a 
negative way."  The following excerpt from a larger article ( 
http://www.michigan.gov/dnr/0,1607,7-153-10370_12145_12202-32591--,00.html#cowbirds 
) illustrates  how the presence (or, successfully, the absence) of cowbirds 
can impact a bird population (read, especially, the 3rd and 4th paragraphs):

[excerpt]
Brown-headed Cowbirds

The brown headed cowbird (Molothrus ater), once called the "buffalo bird," 
was common in the open plains. Cowbirds followed the vast herds of American 
bison and then cattle, eating the insects that swarmed around the hoofs of 
the grazing herds. Unable to move with the wandering herds while maintaining 
a nest, these birds developed an unusual behavior; they began to lay their 
eggs in the nests of other birds. The cowbird chicks, which hatch earlier 
than most songbirds, are more aggressive and will out-compete their nest 
mates for food. This added competition reduces the number of non cowbird 
young that fledge.

As land in Michigan was opened up during logging and agricultural 
development, cowbirds moved into the new areas, and the Kirtland's warbler 
was an extremely vulnerable host. The egg laying activity of the cowbirds 
began to impact the Kirtland's warbler population.

Studies have revealed that when one cowbird egg is laid in a warbler nest, 
only one to three warbler chicks may survive. If two cowbird eggs are laid 
and hatched in a warbler's nest, none of the warbler chicks survive. Heavy 
cowbird parasitism is believed to have been a major factor in the decline of 
the Kirtland's warbler population. In 1972, the U.S. Fish and Wildlife 
Service, in cooperation with the USDA Forest Service, Michigan Department of 
Natural Resources, and the Michigan Audubon Society, began controlling 
cowbirds with large live traps that are placed in Kirtland's nesting areas 
during spring and early summer. The traps, which are baited with millet, 
water, and several live cowbirds, are checked daily and any trapped cowbirds 
are euthanized. Non target species are released unharmed. Since 1972, an 
average of 4,000 cowbirds per year have been removed from Kirtland's warbler 
breeding areas.

Kirtland's warbler reproductive success has improved dramatically since 
cowbird trapping began. The nest parasitism rate has declined from the 1966 
71 average of 69% to less than 5%. Average clutch size has increased from 
2.3 eggs per nest to more than four. The average number of young warblers 
fledged per nest increased from less than one to almost three birds during 
the same period. The 2002 annual census counted over 1000 singing males for 
the second year in a row.


From: "Farrel Graves" <bgraves@usfamily.net>
To: "mou" <mou-net@cbs.umn.edu>
Subject: [mou] Bird Behavior-Sad
Date: Tue, 11 Jul 2006 08:04:56 -0500

Like most things in life hearing or even reading about a problem doesn't 
drive home a point like seeing it first hand. From reading I knew cow birds 
lay eggs in other birds nests. One day I spotted a chipping sparrow (several 
are at our feeders) hopping through the grass with this really big bird 
hopping right behind it. The bigger bird almost appeared big enough to harm 
the sparrow if it landed on it. And it stayed on the sparrows heels. Then I 
realized the sparrow was searching for food to feed the big bird. It was a 
cow bird. I witnessed it begging for food for a couple of weeks. It looked 
so odd. The sad part is the chipping sparrow had none of it's own with it. 
After reading more I realized the bigger bird out muscled the sparrow babies 
and likely rooted them out of the nest. It's really a shame that some birds 
can't realize the difference. It also seems (since the cow birds are not 
only big but also hatch earlier than the birds in the host nest) that 
eventually this could sway the balance of birds in a negative way.

I have a picture if anyone is interested. It looks like the sparrow is 
putting it's head into the mouth of a lion...


--- http://USFamily.Net/dialup.html - $8.25/mo! -- 
http://www.usfamily.net/dsl.html - $19.99/mo! ---