Tag Archives: nature

Don Cowlione: How Cowbirds Run A Songbird Mafia

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If I were to imprint on you one main point stringing together every article I’ve ever written for Badass Biology, I hope it would be this: nature has produced no shortage of jerks. I say “jerk” like it’s a bad thing, but take the time to think about the word and you’ll realize “jerk” becomes a bit endearing when we’re talking about nature.

First, let’s review what it means to be called a “jerk” species. First, a jerk has to be abundant enough to merit some sort of attention or recognition, but not more abundant than non-jerks, otherwise the jerk strategy would be much less effective. This population size balance is very delicate, but jerks seem to manage it well.  Second, being a jerk means going against some established natural norm. Usually, jerks exploit some mutually beneficial arrangement between individuals, leaving another party to carry their weight for them. It’s a pretty clever strategy if I say so myself. Third, present a jerk with an opportunity and it’s likely to get snagged. Another admirable trait in favor of biological jerks

Back to the point, Planet Earth has lots of jerks. Consider the bluestreak cleaner wrasse. On Southeast Asian reefs, cleaner wrasse set up cleaning stations where they pick off the tiny parasites that live in the skin of larger fish. This arrangement seems to work for everyone (except the parasites, unfortunately); the wrasse get dinner while the larger fish get a good skin treatment. Some jerk wrasses, let’s call them “wrasseholes”, like to instead bite big chunks out of the mucus membranes on these fish instead, turning this mutualistic interaction into a parasitic one.

To be honest, it’s not that I find this interaction all that neat. The main reason I bring this up is to mention that it DID spawn an article in Discover Magazine with a really clever name: Cheater Cheater Mucus Eater.

Sure, jerks are great and all. My favorite? This little guy:

Awwwwww. SO PRETTYYYYYYY.

Adorable, right? What about now?

The Birdfather

Why yes, I AM proud of this joke.

Make no mistake. This stone cold killa is ruthless, even enough so that I’d put the word “killa” in an article that I’m reasonably sure a future employer will read.

So what about this little bird makes it so much of a wrassehole? To start, an introduction. This is the brown-headed cowbird, a member of the family Icteridae, which consequently means nothing at all to me but sounds pretty badass all the same. What distinguishes cowbirds is that they are notorious brood parasites. They find nests belonging to other aviary families, mostly songbirds but varying from hummingbirds to birds of prey, lay their eggs next to theirs, and let those other poor bird parents feed, raise, protect, bathe, clothe, and attend PTA meetings of cowbird babies. As of 1999, approximately 140 species of birds have been documented raising cowbird young.

Here’s what’s odd about this. I’m sure you’ve guessed that cowbirds are able to get away with this sneaky business because their eggs and young look an awful lot like the birds they’re parasitizing. They don’t. More often than not, cowbird eggs are either much larger than the eggs of their host AND a different color and pattern. Moreover, cowbird chicks are gigantic when they hatch, making little songbird chicks look tiny by comparison.

One of these eggs is a parasitic cowbird’s. Can you guess which one? Did you guess the one on the bottom left? You did!? Very good!

You may be asking yourself, “why do these other birds raise babies that aren’t their own?” Right now, I’m asking myself, “have I smelled like this all day?”, but that’s really of no consequence to anyone (except my wife, I guess).

Oddly, one theory explaining why the hosts hadn’t murdered these little guys is, and I’m serious, that the host birds don’t have the cognitive ability to recognize that these chicks are different from the others. It seems odd to me that the same birds can relocate their nests among thousands of other similar-looking forest objects with near-identical colors and patterns would not be able to recognize that one of their babies is a freakish monster.

Meanwhile, I only learned today that I live 5 minutes from a major interstate highway, but I’m confident that there’s no gigantic monster baby living in my house. One of our cats is pretty large, sure, but I’m not convinced I’m her father or anything.

No, the real reason host don’t viciously murder cowbird young is pretty sinister. In 2007, two researchers from the University of Florida set up a field experiment where they manipulated cowbird presence in predator-free nests of host birds. In “ejector” nests, the researchers removed cowbird eggs from host nests, mimicking a host that rejected a cowbird egg,  whereas “acceptor” nests saw through the raising of a strange foreign cowbird hatchling. In all, 56% of ejector nests saw some the destruction of host bird eggs, but only 6% of acceptor nests were ruined. What happened?

Cowbirds happened. Females, actually. These jerks monitored the nests of their hosts, checking in on the progress of their young from time to time. If cowbirds found that their babies weren’t receiving the star treatment (or weren’t in the nest at all), the cowbirds would lay ruin to the eggs of the host bird. Essentially, these birds were exhibiting mafia behavior, laying down some pretty severe consequences if the host rejects the parasite.

What’s equally sinister is the explanation for destruction in the 6% of acceptor nests. Why kill the young of a nest that’s satisfactorily caring for your own young? Simple: murder creates room in the nest for more cowbirds.

In summation, I quite admire cowbirds. In a group of organisms whose ability to distinguish which egg is their own is questionable, these ladies are clever. It’s pretty rare to see such a sophisticated racket exist in animals with brains the size of beans. Think about the cognitive power cowbirds need to keep track of which nests are parasitized, then decide on whether to murder or not murder depending on what they see. I gotta say I’m impressed.

So, like a Don collecting tribute from his corner of Little Italy, cowbirds command respect. They’re clever, manipulative, aggressive, greedy, and all of it is so sinisterly bundled in a package that I’d rather enjoy petting.  Plus, it’s nice to know that some species out there gives others an offer they can’t refuse.

How settlers and cows changed the face of south Texas prairies.

What you are about to read is udderly amazing. This being an article about the great state of Texas, currently my home, the steaks are high to make this one funny and I butter deliver. If you have any bull with what I have to say, go hoof it or I’ll get cheesed. At least give me the chance to milk this topic before you give me beef. Regardless, much of this article isn’t black and white, and I hope too that in some way you will find this article amoosing. Anyway, let’s herd this along, I’m getting hungry. Agriculture.

Cow Title

How settlers and cows changed the face of south Texas prairies.

Texas: the home of wide open skies, twenty acres, barbecues, and pecan pies. American culture paints an idyllic and rugged picture of Texas. Cowboys herd cattle through vast expanses of fence-less plains. Prairies full of lush grasses as far as the eye can see. The picture in your head probably isn’t too far off from this:

Photo credit: Pondero (http://pawndero.wordpress.com/)

Had you visited central or south Texas 120 years ago, this would’ve been largely accurate. However, over a span of a few decades, an alarmingly large portion of Texas has transformed from a landscape of endless grass to something much much uglier:

What you see nowadays is mesquite, prickly pear cactus, and some small brushy shrubs displacing the miles and miles of grasslands that historically covered much of Texas. How did it get this way? And, more importantly, can we blame something else for it besides ourselves?

Even if you’ve never seen the Lion King, you’re likely still aware of cyclical nature of life. Among these cycles is succession. A habitable area becomes damaged by some event, like an eruption or a bulldozer clearing land for farming. The vacuum of space and resources left behind gets colonized first by r-selected species. These species are really good at dispersing over wide distances and taking root in new places unaided by other species. The unfortunate cost to being an r-selected species is that it’s generally very hard to compete, especially with k-selected species that take longer to colonize a disturbed area but competitively dominate more easily once they’ve done so. So, over time, a community of plants or animals can shift from being primarily r-selected to k-selected, completing the cycle of succession until the next disturbance event.

A typical course of succession on a plot of cleared land. R-selected strategists invade first, but are gradually out-competed by hardier but slower-growing k-selected species like hardwoods. Heh. Hardwoods.

Prior to about the 1880s, the most common form of disturbance in south Texas was fire. Prairie grasses would naturally form dense expanses of flammable material, and the slightest spark could create wildfires that spread for miles. The constant and intense winds blowing from the Gulf would aid in spreading fires over vast distances, removing all the built-up grasses and allowing new ones to take root. Another consequence of these natural fires is that shrubs, cacti, and trees, all more k-selected than the weedy grasses, could not colonize the prairie successfully because the odds of surviving these fires was so low. And because it took such a long time for these plants to move into a space, even one cleared by fire, they never really became dominant in these regions because fires were so common.

The catalyst that sparked change in Texas prairies was the large influx of cattle ranchers in the late 19th century. Early Texas ranchers understood the importance of fires and would perform yearly burns of ranchlands, and it was clear that the annual new growth of grasses improved the health and size of their cattle making for tastier Ribeyes and jucier Sirloins. However, once the density of cattle began to explode, grazing on these grasses intensified, leaving empty patches clear of the combustible material necessary for fires to destroy old growth. Fires became less and less effective and spread to a fraction of the area and intensity that they were mere decades before.

Here’s where the opportunistic k-selected species began to invade. With reduced damage by fires, seedlings of mesquite, oak, and various shrubs had a better chance of setting up a home on the range. Once they did, the shade they created further drove down the density of flammable grasses and added more space between plants, inhibiting fires even further. The end result facilitated the invasion of other plant types including a host of cacti and small shrubs.

Why does any of this matter? Put simply, economic growth in the region took a heavy blow. In a surprisingly well maintained old-ass report published by the U.S. Dept. of Agriculture in 1908, the consequences of bushes on ranching and farming became clear: “South Texas is being rushed under the plow to escape the invasion of bushes. Large tracts which could have been bought a few years ago for a dollar or less per acre…now cost $5 or $10 an acre to clear of woody growth…many thousands of acres are already lost, at least to the present generation, for the bushes are so well intrenched that the cost of clearing would greatly exceed the value of the land”.

Despite these difficulties, the face of south Texas is likely to continue to change. The currently dominant plant species in the area are only transitory, and often they give way to larger trees that can outcompete the smaller brush. Many experts think reforestation is a likely consequence in the coming decades, though a gradual one. Swampify isn’t a word, but it should be.

I want to make clear that despite the usage of the term “south Texas”, the area impacted by mesquite invasion is friggin massive. The amount of land encompassed between Houston, the Rio Grande valley to the south, and the border town of Del Rio to the west is roughly the size of the state of South Carolina; some 32,000 square miles. And these boundaries only generally reflect the affected areas because these are among the only Texas towns I can name off the top of my head. Regardless, the difficulty of this invasion has undoubtedly shaped Texas history and the outcomes of economic competition with other Southern states.

The overall point of cases like these is that human beings have a profound and measurable impact on the land from which we obtain our livelihoods. The issue of responsible land management is arguably one of the greatest problems facing our generation. Properly managing sensitive natural areas is crucial for the future of economic growth and development.  Unfortunately for us, it’s almost never clear what the best approach is to battling habitat degradation. What would have worked in south Texas? Limiting the density of cattle? Denying settlers the opportunity to buy arable land? Freezing growth in a developing Texas? Eating more cows? I am seriously hungry.

Since I’ve moved to Texas, I’ve gotten the chance to do a lot of characteristically “Texas-y” things. I’ve saved a friend’s beer while floating the rapids on the San Marcos. I’ve hiked Guadalupe Peak. I’ve stopped on the highway to take pictures of the springtime explosion of Texas Blue Bonnets. I’ve seen the millions of bats at Devil’s Sinkhole and seen Kemp’s Ridley turtle hatchlings make a run for it on Padre Island. Hell, I’ve even yelled at cows from a moving vehicle. Enjoy these things while they last, because those cows may just eat all your land to death. The end.