What does the Denver Museum of Nature & Science do with 52,000 bird specimens? Detective work. Museum guests see only a small part of the collection in the wildlife exhibits. The rest receives specialized care and study in the underground Avenir Collections Center, which is part preservation facility, part laboratory. Here in the Museum’s vault, curators solve ecological mysteries.
This summer, Garth Spellman, PhD, curator of ornithology, and his assistants, (pictured in the photos) investigated clues in the collections center and in the field to put science one step closer to solving two puzzling and important cases: the “Case of the Star Crossed Vireos” and the “Case of the Missing Finches.” The long-term survival of these Colorado songbirds may depend on getting a break in the case.
The Case of the Star Crossed Vireos: If you see a little olive-green bird with a yellowish-white belly and lively black eyes singing a sweet tune, it might be a warbling vireo. Or it might be a warbling vireo. That’s because there are two subspecies—eastern (V. gilvus gilvus) and western (V. gilvus swainsoni). These little birds began to differentiate during the last ice age. Over 2.5 million years, V. g.swainsoni started to get little bigger and changed its tune.
Today, for the first time in a long, long time, their range overlaps along Colorado’s Front Range. What happens when formerly separated populations (in this case, subspecies) begin to breed again? Often, closely related bird species produce viable young. These mixed individuals are called hybrids. Are these hybrids as healthy as their parents or are they less fit? What does it mean for conservation? If the hybrids are less fit, should the subspecies be managed as a single species or two separate species? To answer any of these questions, scientists first need to know if the subspecies are producing hybrid young.
Dr. Spellman and his assistants, Boulder high school students Aja Hammond and Tammy Zhang,took the case to the lab and then to the field. In the lab, Aja and Tammy found you can discriminate between the two types of warbling vireo by their measuring their bodies and listening to their songs. The next step was to see if these differences might matter at all to the birds!
It’s hard to find clues when the suspects are high in the treetops, so the science team used a singing decoy featuring songs from both western and eastern warbling vireos. The detectives listened, and the birds responded, but they reacted as though the songs were a single tune. This clue suggests that the subspecies are interbreeding. What does this mean for the birds’ future?
Back at the Museum’s lab, Dr. Spellman has begun to map the genetics of several hundred vireo specimens. He sends tissue samples of each bird to an outside laboratory. The result is a long list of molecules (adenine, thymine cytosine, and guanine) that spell out each bird’s genetic code. Dr. Spellman will compare the birds’ DNA to determine how often the eastern and western warbling vireos interbreed and if there are any consequences. The case continues …
The Case of the Missing Finches: Fifty years ago, Colorado’s high alpine meadows were filled with the song of the brown-capped rosy-finch. These little birds with pinkish bellies glean insects from residual winter snowfields above 10,000 feet. Unfortunately, their numbers have declined by 90 percent over the past five decades. In the species’ southernmost range, Colorado’s Sangre de Cristo Mountains, it was feared they were gone altogether. What happened to the brown-capped rosy-finch? Dr. Spellman and his coinvestigators from the Bird Conservancy of the Rockies, Colorado Parks and Wildlife, CU Boulder, CSU, and UC Santa Cruz took the case.
First, Luke George, PhD, of Bird Conservancy of the Rockies, ventured to the Sangre de Cristos to determine if there were any rosy finches left. He found a few breeding pairs. Where did all the birds go? Did declining snow impact their food source? Were there other stresses on the population?
Back in the lab, Dr. Spellman has access to brown-capped rosy-finch specimens going back a century. A single feather can reveal clues about the bird’s diet and stress levels. Have the birds become more stressed or nutritionally deprived over time?
Dr. Spellman and fellow detectives have begun to sequence the DNA of the brown-capped and other rosy-finches. These species began differentiating at the end of the last ice age. What clues lie waiting to be discovered in their genes? Can the clues help conservationists save the species? How can state wildlife managers and other government agencies use the findings discovered by the Museum and its partners to ensure a rosier future for this little bird? The case continues …