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Smoke from the 416 Fire may have negatively affected birds in the 38-acre Oxbow Preserve last summer near northern Durango city limits.

Researchers and volunteers captured 166 birds in the preserve, 40 percent fewer than in past years, according to the Monitoring Avian Productivity and Survivorship (MAPS) report. The study was in its fifth year.

To track bird populations, researchers and volunteers capture birds in nets at the Oxbow Preserve and band them with unique numbers so they can be tracked at similar MAPS stations across the continent. The data informs national bird population trends.

The study, jointly funded by the city of Durango and Colorado Parks and Wildlife, could be used as a baseline to help determine if construction of a boat ramp at Oxbow Park has an impact on the number of birds.

Smoke from the 416 Fire did not cause a statistically significant decline in the number of birds captured in the preserve, but it did raise questions about bird behavior, health and survival, the report said.

“Maybe some birds were more sensitive and maybe they didn’t make it because they took in too much smoke, but there is no way to fully know that,” said Lynn Wickersham, an owner of Animas Biological Studies, the company running the study. It is also possible some birds abandoned their nests, she said.

Researchers and volunteers also spent fewer hours netting birds last year compared with some prior years because of the smoke, the report said. Last year, researchers netted birds from May to early August.

Despite the air pollution, 65 species were spotted in the preserve this year, the report said. During all five years of the study, 95 species have been observed flying in or above the preserve.

Black-capped chickadees, yellow warblers, house wrens and rufous hummingbirds were among the most common birds to be netted last year at the Oxbow Preserve.

“It’s a really good, high-quality bird habitat,” Wickersham said.

The study also reveals birds returning to the preserve year after year.

For example, a yellow warbler, first captured at the preserve in 2014, was recaptured at the preserve in 2015 and 2018. It is estimated to be 7 years old.

“Those birds are making an incredible life history,” said Brian Magee, land-use coordinator for CPW. Many of these birds are migrating down to South America each year, he said.

A $20,000 grant from Great Outdoors Colorado could sustain the study for two more years, he said. The grant would require the city and CPW to contribute $3,000 annually for two years.

Parks and Recreation Director Cathy Metz said she supports funding the study because it informs management of the preserve, but a decision has not yet been made about funding.

If the study continued, the data could help determine if construction of a boat ramp, parking lot and changing rooms in Oxbow Park, adjacent to the preserve, have an effect on the birds. Staging for construction is expected to start in March, Metz said.

During construction, the city is required to watch for the southwestern willow flycatcher, an endangered species that has been spotted in the area previously during a MAPS study, Metz said.

If the bird is spotted in Oxbow, construction will be halted and moved to a different area during the bird’s breeding season, she said.

Overall, Magee said he is happy with the city’s management of the preserve.

“The city’s done a really good job of going slow with development out there and being thoughtful of what they want to do in terms of balancing access with preservation,” he said.

mshinn@durangoherald.com