How to Stop a Bird-Murdering Cat

Photo from The Atlantic

This month in bird news: a few weeks ago, I had a story in The Atlantic online about one way we might mitigate a serious threat to native birds: getting eaten by pet and stray cats. Ed Yong at National Geographic, as well as blogs at Smithsonian and Mental Floss, gave the piece a nod. Long-time readers, thank you so much for supporting my writing over the years.

Also, for the 30 Rock fans among us: the headline chosen for the story made me think of "The Rural Juror" episode. I think "bird murder" would have fit in well with Barbara Walter's interview with Jenna:

Winter Travelers

Rusty Blackbirds are one of the fastest declining species in North America. In the same family as orioles, red-winged blackbirds, and grackles, it has lost between 85 and 99 percent of its population over the last 40 years. This past weekend, we saw two pairs of Rusties in our neighborhood in St. Louis county. 

 One of the pairs (male on the left, female on the right.) Their buffy-colored eyebrow and the rusty ends of their feathers distinguish them from other small blackbirds.

Both pairs together.

Rusty Blackbirds typically forage in bottomland forests with standing water. They flip over leaves, looking for small arthropods. They arrived shortly after a rainstorm and after my dad had blown the leaves into piles, so the yard must have looked like a good place to eat. Traditionally, they winter in the bottomlands of the American South and breed in boreal forests in the Northeast U.S. and Canada. Both habitats have suffered serious damage in the past century.

They were following a group of European Starlings. Migratory birds, especially blackbirds and starlings, often form mixed flocks for protection from predators. There's also evidence that Rusties, which have smaller beaks than grackles, follow other blackbird species around and pick up the scraps from nuts that the larger birds have cracked open. 

It was truly special to see the Rusties so close to my home. It's a species that I have learned much about: my research adviser at Truman surveyed the birds in their wintering grounds and is an expert on their ecology. But their existence was somewhat theoretical until I saw them through my front door. It was fascinating to realize that they were only midway on their journey to Arkansas or Mississippi. Reflecting on how a small songbird carries itself thousands of miles every year is always a source of wonder for me.

Egrets at Columbia Bottoms

This morning, my mom and I drove to Columbia Bottom Conservation Area for the my last birding trip in the St. Louis region for a while. Just north of the city, stacks of shipping containers and freight warehouses transition in just a few miles to the broad floodplains of the confluence of the Mississippi and Missouri rivers.  I had never been to the park before, and was impressed with the shorebird, wading bird, and duck diversity that the broad wet meadows and mudflats support. 

After spotting  a few Killdeer and Lesser Yellowlegs foraging in a roadside puddle, we were impressed with a flock of over 200 Great Egrets packed in the tall grasses of a marsh.

Neither of us had seen so many egrets in one place before. We set up a scope to get a closer look and see if any Snowy Egrets were tucked in among the others. (They would have black bills rather than orange.) We didn't see any Snowies, but there were at least two Great Blue Herons strutting around the edges of the flock. You can get a fairly high resolution picture by pressing a camera phone up to a spotting scope, though this picture isn't the best example.

We spooked a few Egrets as we drove by. 

Looking to the other side of the road, we saw a large lake lined with a seemingly endless flock of egrets, at least twice as large as the ones nearer to us. You can see them in the distance of this photo as a line of white on the far side of the lake.

We also found a flock of 150+ ducks beside a smaller group of egrets. In their duller non-breeding plumage, they gave us some trouble in identification, but seeing the band of white on the underside of their wings, dark eyestripe, and blotch of white behind the beak (the last two aren't so easy to see in this picture) allowed us to identify them as Blue-winged Teals. 

We followed the road until it took us to the Missisippi River. An Army Corps of Engineers pumping station had a large scale for reading the flood level. Strange to think that those heights are plausible; the bank in this photo is already 15 feet above the water level. 

Over the last two centuries, engineering projects in general have sought to contain rivers and eliminate floodplains so that they can be settled for homes and farming. The path of the Missouri through the plains used to change drastically year to year as snowmelt and spring rains sprung the river from its banks, reshaping its embankments each season. Millions of amphibians spawned in the huge wetlands created in the thaws, and amphibian predators like the egrets followed in the summer. At Columbia Bottom, the Army Corps of Engineers and the Missouri Department of Conservation have collaborated to restore and protect over 4000 acres of floodplain, allowing us to see a sizable glimpse of an ecosystem type that once stretched for hundreds of miles. 

Of Swallow Wings and SUV Windshields

I often think of high-rise buildings, subways, and dams when I think about characteristic human changes to the landscape. But in terms of acreage, high-input agricultural zones have been a more widespread and comprehensive land use change in the past two centuries. This land use type includes not just the actual cornfields but also the houses, grain elevators, country highways, and small towns that support the farming. The cumulative effect has been to almost wipe out grasslands worldwide, replacing them with an ecosystem with many different pressures and opportunities than the previous one.

These changes have measurable impacts on wildlife that are often surprising. Wild populations do not merely shuffle out of the way when humans come to settle. It is always a collision. Some are killed in droves like the American buffalo. Others slowly or steadily decline over many years, like grassland songbirds. And a few special species are able to adapt and thrive in the new ecosystem.

Photo by Don DeBold

Cliff Swallows are small, handsome flycatching birds with a blue back and wings, a white belly and a red throat. They create colonies of nests on vertical surfaces made from mud they carry in their beaks. In Nebraska, biologists have been studying the habits of Cliff Swallows for over 30 years. There, the birds are not nesting on natural cliffs but the constructed ones under highway overpasses and roadway culverts. Birds with shorter wings are better able to avoid passing cars, and short wings are now the norm in these cliff swallow populations, according to Charles Brown and Mary Bomberger Brown of U. Nebraska-Lincoln and U. Tulsa. They described their findings in a paper, “Where has all the road kill gone?” published in Current Biology in 2013.

Brown and Brown compared the roadkilled birds to a sample of birds which died accidentally while the researchers used mist-netting to capture individuals for study. They saw that the roadkilled birds almost all had longer wings than the rest of the population. Over the 30-year study, fewer and fewer birds ended up on the highway shoulder, and the general population’s wings got shorter.

To understand why short wings help you dodge a Hummer, we have to consider flight physics. Longer wings lead to efficient flight and shallow, graceful takeoffs by decreasing the amount of bird mass carried by each square inch of wing. But shorter, stubbier wings allow for greater maneuverability and more vertical takeoffs. These sharply angled takeoffs, the researchers believe, are what allowed the short-winged swallows to launch away from the road surface as a car approaches more successfully than their long-winged relatives.

While the outcome has a strange beauty, the process was plainly brutal. The selection pressure was millions of unforgiving windshields. Roadway traffic kills 80 million birds a year in the U.S. alone. If you look at Brown and Brown’s figures, you’ll see that even in a moderate year, they and their students collected tens of thousands of cliff swallow corpses. And these were the cliff swallow casualties only in their Nebraska study area. Not that the butcher’s bill here is so different from that resulting from other kinds of selective pressures. Evolution works through death—new forms arise because less successful individuals die.

Yet even though we can read the cliff swallow’s story as a success of natural selection, what stands out to me is how few species have been able to adapt this well. In the same region, birds such as Henslow’s Sparrow, the Upland Sandpiper, and the Greater Prairie Chicken have faced severe declines due to the loss and fragmentation of even marginally suitable habitat. For these birds, evolution would not be a matter of changing wing length but changing their entire lifestyle, something that is probably impossible within timescales meaningful to humans. Are the opportunities that one country highway creates for Cliff Swallows balanced by the splintering of the remaining lands for declining and endangered species?

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Citation

Brown, C.R., and M.B. Brown. 2013. Where has all the road kill gone? Current Biology 23:233-234.