About Brown-headed Cowbirds

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About Brown-headed Cowbirds

Postby Mike O on Sat Jun 16, 2012 8:24 pm

I have a nesting Northern Cardinal in my backyard and I suspect that one of the three eggs in the nest is from a Cowbird. The egg is bigger and has an overall darker look due to more brown spots. I would like to see baby Cardinals fledge this year as opposed to Cowbirds again. What to do, or should I let nature take its course. Thanks in advance

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Re: About Brown-headed Cowbirds

Postby Jeff Hunt on Sun Jun 17, 2012 6:55 am

If it were me, I would confirm the egg is a brown headed cowbird one and it would be gone, no questions asked.

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Re: About Brown-headed Cowbirds

Postby Ruth on Sun Jun 17, 2012 7:14 am

I do not see that Brown-headed Cowbirds are protected by the Migratory Birds Convention Act according to this list from Environment Canada http://www.ec.gc.ca/nature/default.asp? ... 9AAA86EC-1
Would the female cowbird return to check if the egg was still there? Personally, I would destroy it based on sentiment alone.
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Re: About Brown-headed Cowbirds

Postby AlvanBuckley on Sun Jun 17, 2012 7:44 am

I think that from an evolutionary standpoint, it doesn't make sense to kill the egg.

If the Cardinals can determine that the egg doesn't belong to them, they will remove it, abandon the nest, or build a new nest on top of the existing one and start again.
Arguably, by helping the Cardinals survive and pass on their genes, you're helping to ensure that this will occur in future generations. But if they can figure it out for themselves they'll pass on the lesson, or genes, to their offspring - and their offspring will hopefully be more likely to have offspring that'll survive as well.

Just being a devils advocate here ;)
I wouldn't blame you for destroying it though.

A related story: there was a pair of Yellow Warblers that built a nest which a Cowbird parasitized and laid her own egg in. The Yellow Warblers somehow figured this out and built a new nest on top of the original nest - thereby killing the previous eggs. The Cowbird (or another one) laid their egg in this new nest again and once again the Yellow Warblers somehow figured out that one of the eggs didn't belong to them. So they built yet another nest. This continued until, apparently, there was a stack of 5 nests!
Here's an article about that if you don't believe me (I didn't believe the story at first):
http://opinicon.wordpress.com/2010/01/1 ... tack-nest/
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Re: About Brown-headed Cowbirds

Postby Peter C. on Tue Jun 19, 2012 1:27 pm

Mike O wrote:I have a nesting Northern Cardinal in my backyard and I suspect that one of the three eggs in the nest is from a Cowbird. The egg is bigger and has an overall darker look due to more brown spots. I would like to see baby Cardinals fledge this year as opposed to Cowbirds again. What to do, or should I let nature take its course. Thanks in advance

Mike Osborne


I'm very unhappy with this sort of intervention. The Brown-headed Cowbird is a perfectly legitimate Canadian bird, albeit one that has been helped out a lot by human-caused habitat change (creating the open habitat that allowed the species to expand beyond its former range). Interventions should only be applied to species whose survival would otherwise be threatened by parasitism, e.g. Kirtland's Warbler; any other species should be left to cope (and they're a lot more threatened by other types of direct human activity than they are by Cowbird parasitism - but that's a whole other story).

And no, I don't like to use "slippery slope" arguments, but the next thing you know, people will be "getting rid of" grackles and jays, because they are notorious nest robbers. People in the nineteenth century practically obliterated the accipiters on this continent, based on the that sort of thinking.

When it comes to the nests of wild birds (and that encompasses everything outside of an aviary), my policy is a strict "hands off".
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Re: About Brown-headed Cowbirds

Postby bernie2112 on Tue Jun 19, 2012 8:48 pm

I too appreciate the sentiment - however Cow Birds do come back and check and will destroy the original eggs (and perhaps leave a few more) - so if there is only one out of several - you might want to leave them alone. As well, who knows the Cardinal will react if you fuss with any of the eggs.

Cheers,

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Re: About Brown-headed Cowbirds

Postby Quentin on Thu Jun 21, 2012 5:15 pm

Here is what I have researched about Brown-headed Cowbirds...

This bird is a brood parasite; it lays its eggs in the nests of other small perching birds. The Brown-headed Cowbird eggs have been documented in nests of at least 220 host species, including hummingbirds and raptors. The young cowbird is fed by the host parents at the expense of their own young. Brown-headed Cowbird females can lay 36 eggs in a season. More than 140 different species of birds are known to have raised young cowbirds.

Host birds sometimes notice the cowbird egg, to which different host species react in different ways. Rejection manifests in three forms: nest desertion (Blue-gray Gnatcatcher), burying of the egg under nest material (Yellow Warbler), and physical ejection of the egg from the nest (Brown Thrasher). The cowbird nestlings are also sometimes expelled from the nest.

Parasite response

It seems that Brown-headed Cowbirds periodically check on their eggs and young after they have deposited them. Removal of the parasitic egg may trigger a retaliatory reaction termed "mafia behavior". According to a study by the Florida Museum of Natural History published in 1983, the cowbird returned to ransack the nests of a range of host species 56% of the time when their egg was removed. In addition, the cowbird also destroyed nests in a type of "farming behavior" to force the hosts to build new ones. The cowbirds then laid their eggs in the new nests 85% of the time.

Human intervention

Humans sometimes engage in cowbird control programs, with the intention of protecting species negatively impacted by the cowbirds' brood parasitism. A study of nests of Bell's Vireo highlighted a potential limitation of these control programs, demonstrating that removal of cowbirds from a site may create an unintended consequence of increasing cowbird productivity on that site, because with fewer cowbirds, fewer parasitized nests are deserted, resulting in greater nest success for cowbirds.

I'm with Peter on this... leave nature to take it's course.
Last edited by Quentin on Thu Jun 21, 2012 5:21 pm, edited 1 time in total.
Adopt the pace of nature: her secret is patience.
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Re: About Brown-headed Cowbirds

Postby kellie on Thu Jun 21, 2012 5:18 pm

Others have stated what I would've stated... destroying the Brown-headed Cowbird egg isn't the right choice. Also consider that once you touch the nest, other eggs, etc., you'll be leaving a traceable path of human scent for some predators to follow to the nest (raccoons, squirrels, chipmunks, and others use their nose to seek out bird nests). Also, it's illegal to destroy any native wildlife, including nests, eggs, etc., under the Migratory Birds Convention Act.

Maybe your efforts could be better focussed on the reason for the apparent increase of Brown-headed Cowbirds. It seems like forest fragmentation is one of the main reasons why their population has shown a steady increase since about the mid-twentieth century--they prefer forest edges, and every time a forest has a road build through it, the availability of their preferred habitat increases. Like some other examples, basically we've destroyed one kind of habitat that is required for some species, and simultaneously "created" desirable habitat for others.

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Re: About Brown-headed Cowbirds

Postby Mike O on Thu Jun 21, 2012 8:55 pm

I decided just after posing the question that I should leave the nest alone for a couple reasons. First is I'm not 100% sure it is a Cowbird egg and second I think deep down I just didn't think I had the right to interfere. The nest has remained as it was and nature shall take its own course. For a moment I forgot the birds in my backyard are wild and should not be treated like weeds among flowers and pluck them out and discard one in favour of the other. Thank you all for your information and opinions on this matter.

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