Four yellow bulldozers began cutting down cottonwood trees this week in Barr Lake State Park, alarming wildlife researchers in the middle of an annual bird-banding blitz and raising concerns about the eradication of habitat for bald eagles.

Bird Conservancy of the Rockies leaders headquartered in the park are pressing Colorado Parks and Wildlife and Farmers Reservoir and Irrigation Company (FRICO) officials to minimize the destruction by sparing as many of the park’s towering 80-year-old cottonwoods as possible.

The tree-cutting — with about 20 cottonwoods and other vegetation cleared as of Friday — marks the start of a five-year project that FRICO proposed for public safety and to increase the water-storage capacity of Barr Lake reservoir (30,057-acre-feet) by 1,500 acre-feet, according to a state document.

The reservoir holds FRICO water diverted from the South Platte River for irrigating farm fields across northeastern Colorado and supplying municipalities in north metro Denver. Colorado Division of Water Resources officials recommend the removal of vegetation along dams and dikes, including long-established cottonwoods, because roots can lead to leakage that weakens those structures.

A 1.5-mile stretch of the 8.8-mile hiking trail around the reservoir is closed until November between the dam and the Pioneer Boardwalk that allows visitors to enter a wildlife preserve. Hikers and bird watchers still can reach much of the trail via the Barr Lake Nature Center.

The park has served as a been a base for bird observation and data collection for 35 years.

“Our concern was the method and the speed at which FRICO was moving,” said Sherry Nickolaus, the conservancy’s education director, who participated