Wednesday, June 18, 2008

There Goes the Neighborhood

I originally started putting this together in late April, but left it incomplete until now. With all of my recent "neighborhood" talk I thought this one's time has come - what happens when your neighborhood attracts "undesirables."

Originally from 26 April 2008
I mentioned Brown-headed Cowbirds in a recent post as their frequency of sightings reaches its spring peak in our neighborhood, but I left it at merely commenting on their looks. I'll venture that there are others, maybe even a silent majority, that find the rich brown and lustrous black subtly stunning, but most don't discuss cowbirds unless they are racing to the reasons to hate them.

Cowbirds may be the most vilified bird in North America. Every breeding season you'll find anti-cowbird rants as they make their annual rounds on the Internet, a digital harbinger of spring on par with the noticable increase in posts to birding listserves.


Why hate cowbirds? Easy. They're brood parasites, meaning they're pretty lax in the parental care department. They don't bother with the whole nest building, incubation, or nestling feeding scene. They don't provide care for them once they fledge. Those activities are pretty costly energy expenditures, so they lay their eggs in active nests built by another species and let the "host" parents do the child rearing. If your goal is to simply spread your genes, what better way than to lay all that care and investment on surrogates who'll do it for you? Very productive for the cowbird, but with a potential serious downside for many host species, which usually fledge fewer young, if any at all.

The female cowbird may even eject a host egg from the nest when she deposits hers, and the cowbird nestling(s) will typically hatch sooner and grow faster, outcompeting its nestmates for food. Even if the host's nestlings don't starve in the nest, they typically fledge in such poor condition the odds of survival are significantly stacked against them.


It's a pretty blunt strategy, and clearly, it works. Estimates of their population range from 20 to 40 million birds across North America, where they survive, and thrive, from central Mexico to southern Canada. Couple that with the knowledge that cowbird parasitism is listed as a influential factors in the decline of the endangered Kirtland's Warbler in Michigan and Black-capped Vireo in Oklahoma and Texas and you've got to ask, "so, what's not to hate?"

Well, in my estimation, their breeding strategy is not exactly the problem. Species that evolved with cowbirds through the millenia have learned how to deal with cowbird parasitism. They usually recognize a cowbird egg in their nest, eject it, or scrap everything they've done and start over, building a new nest right over the old eggs.

Agonistic behavior: one male "bowing" to the other to show dominance.

It's the species that have only recently encountered cowbirds that are in trouble, the species that have no history with them. These are typically neotropical migrants who inhabit large, unbroken tracts of forest where cowbirds did not historically tread. Now that the forests have been so fragmented the cowbirds are able to penetrate and exploit these naive forest-dwelling birds. Layer the parasitism with additional pressures such as loss of habitat, increased nest predation, pesticide applications, and possibly factors not yet recognized, and you've got a recipe for reproductive unsuccess.

Is it fair to hate the native cowbird for an ingrained behavior, coded in its genes, that's evolved over thousands of generations? That individual under your feeder, or displaying in the bare-limbed tree, or chasing that Yellow Warbler through the foliage, is not consciously scheming, it's merely doing what it does. Cowbirds do what cowbirds do, we've just enabled them to do it more proficiently, and to exploit species that don't know how to react.


And given that, I don't hate the cowbirds, I hate the fact we humans have so drastically upset the system. Now we're in the unenviable position of attempting to manage that system to return some sort of balance, which always seems to muck things up even more. One thing I've learned in our small scale attempts to manage our "neighborhood," meaning our yard: once you monkey with it, you've got to keep at it, and it will be years (if not longer) to evaluate your success.

"Thoreau says 'give me a wildness no civilization can endure.' That's clearly not difficult to find. It is harder to imagine a civilization that wildness can endure, yet this is just what we must try to do. Wildness is not just the 'preservation of the world,' it is the world."
-- Gary Snyder

-

13 comments:

Cindy said...

quote:

' I don't hate the cowbirds, I hate the fact we humans have so drastically upset the system. Now we're in the unenviable position of attempting to manage that system to return some sort of balance, which always seems to muck things up even more. One thing I've learned in our small scale attempts to manage our "neighborhood," meaning our yard: once you monkey with it, you've got to keep at it, and it will be years (if not longer) to evaluate your success'

well said! I live 15 min. away from breeding Kirtlans' and worked with the recovery team doing counts.. the program was successful, but has tasken a hit.. no doubt the warblers will too.Time will tell-
we've created the very edge environs that cowbirds gravitate to.. difficult to blame a species of bird for that.

noflickster said...

Hi Cindy,

First, thanks for dropping by, and for commenting! Having yet to see a Kirtland's Warbler I envy your neighborhood, though (as you obviously know) that species certainly presents a sobering reality check. This year's discovery of a nest in Wisconsin was pretty heartening.

Regarding the cowbird trapping program, I get that we have to do something, but it frustrates me that it's partially at the expense of a species that didn't do anything wrong.

Maybe it's just me, but I find it hard to pretend we're the noble ones, protecting the Kirtland's from the evil cowbird, when it's a situation that we could prevented a long time ago.

Of course, live and learn . . . wasn't it Aldo Leopold who admonished keeping every cog wheel was a precaution to intelligent tinkering?
-Mike

Cindy said...

I feel much the same.. and I'm not ashamed to admit that viewing cowbirds in baited pens always made me very very sad. It's not easy to pass by the cages without feeling a sense of 'so this is what it comes to?' extermination is ugly in my eyes.
I'm hoping that a sustainable population will someday be a reality in both Michigans' UP and Wisconsin as well. And yes, I certainly agree that we've tinkered our way into a fine mess. I still have hope but it's difficult to reconcile the ongoing destruction of so much habitat at a rate that boggles the mind.

N8 said...

The vilification of the BH Cowbird is especially ironic given the excitement some birders can show over a vagrant Bronzed or Shiny Cowbird.

Same ecological niche, same nest predatory habits, but by virtue of their rarity they somehow avoid the bad rap.

noflickster said...

Cindy - ditto, ditto, ditto!

n8 - excellent point! It is funny, in an odd sort of way, that layering the cloak of rarity on top of (essentially) the same bird somehow masks the same behaviors that condemn the Brown-headed Cowbird. I suppose most people who find the Shiny or Bronzed Cowbird in the U.S. are too busy "twitching," and the subsequent endorphine release hinders certain neurotransmitters from connecting the dots. At least, that's my working hypothesis today.
-Mike

N8 said...

Maybe birders figure since they're so rare, how much damage can they really do to native bird populations?

I know from experience though. A couple weeks ago a Shiny Cowbird was reported just about 10 miles from my house and got the local twitchers all riled up (including me, to be fair : ) ). But it only stuck around one day and was never relocated. It was that and your post here that got me thinking about it.

But as for the BHCO, I always thought they got the shaft. Nest predation is a pretty elegant solution to the nomadic lifestyle once you get past the harm they do, or as you point out, we did.

scienceguy288 said...

Cowbirds are notorious nest thieves, but so are many other birds that are not so villainized like cukoos.

noflickster said...

n8 - interesting points. A topic for another post (not necessarily by me, either . . . hint hint) is that element of colonization. I've always been fascinated by the fact we ho-hum the House Sparrow while putting Eurasian Tree Sparrows high on the "gotta have it" list. One we love, one we love to hate. I would think the House Sparrow would be more interesting to birders - more adaptable, not like that near-failure, can't-hold-their-own Tree Sparrow. Of course, that then opens the door to the "birder" definition debate: lister vs. birdwatcher or what have you.

It could go on for hours . . . and hours, and hours. . . .

Scienceguy288 - I think you've hit the central theme: all three species (BH Cowbirds, Black-billed and Yellow-billed Cuckoos) are native, but only one is a really, really prolific brood parasite. In fact, only the cowbird is an obligate parasite: it couldn't build a nest if you pointed it to wikihow.
The cuckoos do build, and use, their own nests, with only some parasitism of other nests. And, according to the Birds of North America Online account, some of that parasitism is intraspecific. Yellow-billed Cuckoos are reported to parasitize eleven host species, cowbirds parasitize 220 species. YB Cuckoos are declining and have been extirpated in several states, cowbird numbers are climbing.

I think both of you (and me) are coming up with the same downfall: it doesn't pay to be too successful. As Bill O'Reilly might say (so I hear), where am I going wrong?

Thanks for commenting, I'm really enjoying this discussion!
-Mike

mon@rch said...

I would rather have these cowbirds as your neighbors than mine! Also found this discussion very interesting!

The Zen Birdfeeder said...

Nicely done, taking on a tough subject. Do you think we would feel different about this bird if it looked like a Scarlet Tanager?

djbrown said...

Awesome post! I cannot hate cowbirds either, but instead, have to admire their evolution. Struggled with this when I recently saw an exhausted Hooded Warbler frantically trying to feed "its" young...cowbird.
You are so right; the problem is us (as always),not them.

noflickster said...

Hi mon@rch - Always better to have those unwanteds in someone else's backyard! ;-)

I really like djbrown's comment: I admire the adaptation, but I'm conflicted when seeing the effect on other species. Similarly, I admire species that have adapted to the cowbird's strategy by building a new nest over the parasitized clutch, kind of a, "Take that!" to the cowbird.

Coevolution is really an amazing process to witness.

Zenbirdfeeder, great question. My daughter loved the first Japanese beetle she saw with it's iridescent colors and bold attitude. But when she realized how many there were in our yard, and how much damage they cause (which we were able to witness first hand), she "saw" them differently. (No doubt influenced by the stream of near-profanity from my wife and I upon seeing our chewed up native plants.)

So, Scarlet Tanager-looking brood parasites might get a pass for a while, but once we understood their behavior some (maybe not everyone) would look at them differently. There are those who actively try to attract starlings to their feeders because they're beautiful; I wonder if they see them differently when bluebirds and Tree Swallows are evicted or killed on their nests.

At least, that's what I think!

Thanks again, all, for stopping by and chatting!
-Mike

The Zen Birdfeeder said...

I’ve included a link to this post in my monthly “Zen Nature Lessons” post. Thanks and keep up the good work!

http://wildbirdsunlimited.typepad.com/the_zen_birdfeeder/2008/07/zen-nature-lessons.html

Locations of visitors to this page