August 7, 2008
At a symposium entitled “Avian CSI” I heard about sophisticated ways that biologists learn intimate details about birds from tiny pieces of recovered evidence. A team of Smithsonian scientists is especially good at identifying bird remains – even mere specks exhumed from the guts of a giant snake.
It turns out that Everglades National Park has a growing demand for experts in snake-meal identification. Wild Burmese pythons, most likely released by fed-up pet owners, have graduated from amusing 10-o’clock-news material into a growing, self-sustaining, and hungry population. Park officials have now captured and killed more than 600 of the snakes. Some contained a full complement of eggs ready for laying.
A host of remarkable birds call the Everglades home, including stunners like the roseate spoonbill, scarlet ibis, reddish egret, and the endangered wood stork and threatened limpkin. And necropsies of captured pythons have turned up plenty of feathers covered in fragrant python digestive slurry. But park officials had no idea which birds they came from. So they turned to Carla Dove and the “feather lab” at the National Museum of Natural History.
To clinch her IDs, Dove uses deceptively low-tech methods that hinge on experience and close observation. There are so many sources of DNA in a python’s stomach that genetic analyses are complicated. Instead, Dove painstakingly cleans feathers and bones, using a fume hood to suck out the most offensive of the smells. Sometimes, she said, she runs down the hall to dry her feathers with the hand dryer in the women’s bathroom.
She puts cleaned feathers under a microscope to analyze their microscopic structure, which differs reliably among different groups of birds. (Here, the distinctive barbules of a common backyard mourning dove.) Dove uses traditional light microscopes instead of electron microscopes because she needs to see into the sample, not just the surface. The final step is to compare python meals with the reference specimens in the Museum’s enormous collection.
So far, the team has identified some 29 species from the bowels of Everglades pythons. Victims include everything from the meatball-sized house wren to the 4-foot tall great blue heron. Rails, coots, and gallinules – slender birds of the marshes – are most frequently eaten, but at least one limpkin and one wood stork have vanished down python throats. One meal even included a magnificent frigatebird, a tropical seabird with a seven-foot wingspan whose closest roosting site is 10 miles away.
The work is fascinating, but Dove says she hopes people think twice before releasing the python they’ve grown tired of into the Everglades. Even so, she says, the population may already be too well established to bring back under control. But the work does point out the way museum collections can yield unexpected dividends.
“A hundred and fifty years ago, when people started this collection,” Dove said, “They could not have imagined the uses we would put these specimens to” – including identifying birds involved in airplane strikes as well as ancient DNA studies. “But they’re crucial to the work we do today. It’s a reminder that we need to continue these collections for purposes we may not have dreamed of yet.”
(Image: Burmese python by Roy Wood, National Park Service; mourning dove feather courtesy Carla Dove)