Year after year, the same black-headed grosbeak returns from Mexico to the Oxbow Park and Preserve, where he’s been netted three times as part of a study of birds at the site near the northern city limits of Durango.
The grosbeak is one of 55 birds that have returned to the 38-acre preserve along the Animas River multiple times, according to a Monitoring Avian Productivity and Survivorship report.
Researchers know the birds are return visitors because they have been caught at least twice.
All told, more than 90 species have been identified in the Oxbow Preserve as part of a study, said Lynn Wickersham, an owner of Animas Biological Studies, which is running the study.
“That highlights the real quality and importance of that habitat,” she said.
In the grosbeak’s case, he was likely born in the Oxbow, or near there, and returned to breed, said Brian Magee, land-use coordinator for Colorado Parks and Wildlife.
“He’s 6, at least 6; he’s probably been to Mexico six times,” Magee said.
When Colorado Parks and Wildlife and the city of Durango started funding the study four years ago, little data about the birds at the site existed, Magee said. The two split the cost of the $14,000 study in 2017, Parks and Recreation Director Cathy Metz said.
Now, researchers and trained volunteers have gathered enough data to get insight into individual birds and to set a baseline for what to expect in future years at the site, Wickersham said. The baseline could allow researchers to detect how the construction of a parking lot, restrooms and boat ramp at Oxbow Park will impact the birds. Although it might be hard to tie changes in bird population directly to development, she said.
But right now, it’s a busy place during the summer. In eight days of netting, researchers tend to capture between 260 and 290 birds, she said.
“We don’t have a plethora of rare species. We have a good amount of relatively common species, in relatively good abundance, and that’s worth preserving in and of itself. ... One of the goals of Parks and Wildlife is to keep common species common,” Magee said.
Song birds are facing a variety of threats. For example, the number of birds that rely on insects for food, such as the northern rough-winged swallow, are declining across North America, Wickersham said.
It is possible that the birds might be dying from insecticides or as the climate changes. As insects start to hatch earlier, the birds are missing the insects on their migratory paths, she said.
To help contribute to a greater understanding about trends, the birds captured at Oxbow Preserve are banded with a unique number so they can be tracked as part of a national database. This allows researchers to identify the birds again if they are captured at one of the other MAPS sites.
The Oxbow Preserve is the only location where MAPS studies are done in Southwest Colorado.
The city set out to do the study for five years, but it could be extended beyond next year, Metz said.