Beyond generalities

Photographer David Leatherman studies the eating patterns of birds

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Yellow-rumped warbler, a common bird of our Colorado mountains in summer, eating a miller moth.
Daniel Leatherman

Even comprehensive ornithology guides might fail to nail down the exact species of moth a yellow-rumped warbler consumes or the type of beetle a hairy woodpecker feeds to its chicks. Photographer David Leatherman is on a mission to catalogue the complex diets of birds. Before retiring in 2005, Leatherman spent more than 30 years with the Colorado State Forest Service, developing his interest in the eating habits of birds in the mid-1980s.

“I remember seeing an orange-crowned warbler eat a particular caterpillar called the boxelder leafroller,” he says. “I wondered if anyone had ever written that combination down and put it in the literature so that we can go beyond generalities to what exactly they eat, when and where.”

This small observation became, what Leatherman calls, an obsession.

“It got out of control,” he says with a laugh. “I wrote everything down, even if I saw a bird eating a chalupa grande out of the gutter.”

Since then, Leatherman has spent decades documenting his findings through photography and his column “The Hungry Bird” in Colorado Birds, the journal of the Colorado Field Ornithologists.

Even though there are countless databases and resources dedicated to the lives of birds, Leatherman says there’s still a long way to go in terms of documenting dietary minutiae. And by capturing these particulars, Leatherman hopes to better protect bird species around the world.

“If someone asked me how they could live a better life, I’d have to know how they lived their life. Maybe I’d tell them to quit smoking, or quit staying up late, or I’d say to get a new boyfriend,” he says. “It’s [the same thing] if somebody asks how to help a bird.”

One of the benefits of more data, he says, is being able to better assist government agencies and institutions in charge of public lands and conservation. For example, if a bird population is affected by the amount of grasshoppers available to eat, then being conscious of particular pesticides used on crops can be helpful.

Another scenario could be advising fisheries on what to stock.

“There’s a fish called a gizzard shad that is often considered a trash fish by fishery biologists, but it occurs in schools in big reservoirs, and a lot of the birds go where the shad are,” he says. “I spent all of yesterday at reservoirs in Denver and Boulder County. There were some that had no birds on them and some that had a lot of birds on them, and the reason was the fish population in those reservoirs.”

Because of altering food sources, precipitated in part by climate change, the movement of local bird populations has already begun to shift. In late October, a fork-tailed flycatcher was spotted in Lafayette, Leatherman says. The bird normally migrates from Central and South America, and it was the first time it had ever been spotted in Colorado.

But warm-weather birds in the state are hardly an anomaly.

“In Colorado now, our official list of birds that has been seen is more than 500 species. Of the last 50 birds added to that list, at least 35 of those 50 are southern birds coming north, extending their range north. That is a climate change phenomenon,” he says. “The problem is if you’re a bird like the ptarmigan that lives on the tundra on the top of Colorado mountains, where do you go if you need somewhere cold?” he continues. “If you’re a bird that needs cold and wet, and it’s getting warmer and drier, where do you go if you’re at the top of the world? You’re toast.”

Leatherman is also concerned about dwindling bird populations on the Colorado grasslands and prairies, which are being used for big farms, prisons and oil wells.

He is, however, far from hopeless about the future. Through his work, Leatherman encourages hobbyist birders to branch out from just adding new bird sightings to their lists, and to instead switch their focus to capturing what the birds are eating. He urges everyone with an interest in gardening, animals and the environment to pay attention.

There’s a lot that can be done to improve the lives of birds. Whether choosing more environmentally friendly plants for your yard or changing the type of weed killer you buy, there are simple actions that start with each individual.

“We can really help the situation, our influence in our little world, our own little backyard,” he says. “If we just tweaked the way we did it, we could really make a difference.”

On the Bill: Hungry Birds: The Photography of David Leatherman. University of Colorado Museum of Natural History, Henderson Building 15th and Broadway, Boulder. www.colorado.edu/cumuseum