FreeLists / va-bird / [va-bird] Re: Cowbird Mafia

[Barbara Chambers <bj.chambers@xxxxxxx>]

My understanding is that this is only one study done in Ill. or Ind.   
There needs to be a lot more research done on this.  It has always  
been general knowledge with us birders that cowbirds lay eggs and go  
on.  Never thinking about the egg any more.   This study gives us an  
interesting new twist to consider.  It was the male that tore up the  
nests, was my understanding.  Perhaps they hang around, and the  
females go on.

I was always fascinated with the very large flocks of cowbirds in the  
fall of each year.  How do they find one another?   How do the  
Juveniles of that year find the adults? and do they ever have  
"family" groups as such?  It just looks like one large cowbird  
convention to me.   And it has to be call and song that gets them  
together again, but the young birds had not heard that "voice" in the  
nest.   So it is in the egg!  It is a remarkable thing considering.

And I must admit that I hate seeing the cowbird eggs in our bb box  
nests, but they fledge before the bbs and there is at least one  
bluebird that survives to also fledge.  I would prefer it not happen  
but it is not EVERY box, and all species need their methods of  
breeding.  It is the only parasitic bird on our continent, we can  
handle that.

However, it also seems to me that there are more and more cowbirds as  
we cut back all the woodlands to build housing and malls,  leaving  
only "edges"  for our other birds and making it all that much easier  
for the cowbirds to find a nest to drop an egg in.  And I have read  
that a female can lay 70 eggs in a season!  So if I remove one of  
them I won't feel too badly.

Barbara


On Jun 14, 2007, at 2:29 PM, John Broman wrote:

> This raises the question of how a cowbird knows its deposited egg  
> has been removed.  I thought Cowbirds developed this parasitic  
> behavior due to never staying in one place on enough to nest  
> (following the cattle).  Perhaps if the urban cowbirds don't have  
> cattle to follow around, they have time to see if their egg  
> deposits are still safe.
> And while we're discussing Cowbirds...I'm still puzzled by the  
> anger some birders have for them.  It seems to me this behaviour is  
> what nature developed.  Any similarity to dead-beat dads should not  
> be held against the birds.  Are we anthropomorphising too much  
> here?  We don't consider a lion cruel for taking down a gazelle for  
> lunch, do we?
>
> John Broman
> Lovettsville, VA
>
>
> On 13/Jun/2007 23:44 Sandy Hevener wrote ..
>> And the other side of the cowbird egg story:
>>  (From March 10, 2007 Science News)
>> *
>> Mafia Cowbirds: do they muscle birds that don't play ball? * By   
>> S. Milius
>> Cowbirds in Illinois that sneak their eggs into other birds' nests
>> retaliate violently if their scam gets foiled, researchers say.
>>
>> The brown-headed cowbirds of North America outsource nest building  
>> and
>> chick raising. female cowbirds dart into other birds' nests,  
>> quickly lay
>> eggs, and rush away. The nest owners are left to care for big  
>> demanding
>> cowbird chicks.
>>
>> Why don't the dupes throw out the odd eggs? When scientists removed
>> cowbird eggs from warbler nests, more warbler eggs later got  
>> smashed or
>> carried off than did eggs in nests with cowbird eggs in place. It was
>> cowbird retaliation, conclude Jeffrey P. Hoover of the Illinois  
>> Natural
>> History Survey in Champaign and Scott K. Robinson of the Florida  
>> Museum
>> of Natural History in Gainesville.
>>
>> That's the first evidence of gangsterlike behavior in cowbirds,  
>> say Hoover.
>>
>> A decade of monitoring prothonotary warblers in nest boxes in
>> souther-Illinois swamps gave Hoover the idea for the new  
>> experiment. The
>> nest boxes sit on poles coated with axle grease to thwart raccoons,
>> snakes, and most other raiders. Egg-laying cowbirds still strike, and
>> Hoover had for years left the cowbird eggs alone. In 2002, he and  
>> other
>> researchers removed cowbird eggs. Nest vandalism suddenly increased.
>>
>> No one saw the vandals, but Hoover and Robinson turned to an idea put
>> forward in 1979 by Israeli biologist Amotz Zahavi. He'd suggested  
>> that
>> by tending the weird-looking eggs and chicks, the foster parents  
>> protect
>> their own progeny. In a rare test of the idea, cuckoos retaliated
>> against magpies in Spain that rejected cuckoo eggs, scientists  
>> reported
>> in 1995.
>>
>> In the new experiment, the researchers recorded egg damage in only 6
>> percent of the warbler nests where cowbird eggs remained  
>> unmolested. In
>> contrast, 56 percent of nests were vandalized after the researchers
>> removed the cowbird eggs. When the scientists removed the cowbird  
>> eggs
>> but added new fronts to the nestt boxes with holes too small for
>> cowbirds, there was no damage
>> So, the nest thrashes are cowbirds, Hoover and Robinson conclude in a
>> paper now online for an upcoming Proceedings of the National  
>> Academy of
>> Sciences.
>>
>> When the cowbird eggs stayed in the next, some warbler chicks starved
>> because the pushy cowbird nestlings took so much of the food. Yet  
>> with
>> the retaliation attacks, the nests where cowbird eggs had been  
>> removed
>> produced, on average, only 40 percent as many warblers as the
>> cowbird-fostering nest did, say Hoover.
>>
>> "This is a surprising result," says Stephen Rothstein of the  
>> University
>> of California, Santa Barbara.
>>
>> Rothstein hasn't tested whether cowbirds retaliate, but he says, "My
>> bet, before this paper, would have been defnitely no." He's now
>> reconsidering but says, "I'd like to see more direct evidence to  
>> date,
>> "
>> such as video.
>>
>> So would Naomi Langmore of the Australian National University in
>> Canberra.  Still, she describes the evidence as compelling."
>>
>>
>>
>>
>> "Best evidence of  date, " Says Rebecca Kilner of the University of
>> Cambridge in England.
>>
>> Comment: Hummmmm. Wonder if we should throw cowbird eggs from the  
>> nest?
>>
>>
>> Posted by:
>>
>> Sandy Hevener
>> General Delivery
>> Blue Grass, VA 24413
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> You are subscribed to VA-BIRD. To post to this mailing list,  
>> simply send
>> email to va-bird@xxxxxxxxxxxxxx To unsubscribe, send email to
>> va-bird-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject  
>> field.
>
>
> You are subscribed to VA-BIRD. To post to this mailing list, simply  
> send email to va-bird@xxxxxxxxxxxxxx To unsubscribe, send email to
> va-bird-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field.
>

You are subscribed to VA-BIRD. To post to this mailing list, simply send email 
to va-bird@xxxxxxxxxxxxxx To unsubscribe, send email to
va-bird-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field.