The winter closure of the Rio Grande Trail between Rock Bottom Ranch and Catherine Store has paid big dividends for deer, elk, bear, mountain lions, songbirds and countless other critters, according to a wildlife biologist hired to monitor conditions.

“You’ve actually helped create out there a winter haven,” Jonathan Lowsky, of Colorado Wildlife Sciences, told the Roaring Fork Transportation Authority board of directors Thursday.

Lowsky was hired by the RFTA board in 2007 to monitor wildlife use of the closed trail corridor during the winter. The popular trail is closed from Dec. 1 to April 30 each year. RFTA’s board will consider next month if it wants to alter the closure or leave it alone.

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Lowsky recommended expanding the closure by starting it earlier in the fall. He suggested closing the gates Nov. 15 rather than Dec. 1. Lowsky said deer would benefit if the trail corridor was available, without human disruption, during early snowfall.

Over the past five years, Lowsky has used motion-detection cameras, personal observations and examination of tracks to assess what wildlife is using the trail corridor when the 2.5-mile stretch is closed for winter. The section butts up against the prime wildlife habitat of The Crown and overlooks the Roaring Fork River.

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Lowsky said his analysis shows an abundance of species is thriving.

“We can’t say for certain there was an increase, but we can say for certain there wasn’t a decrease,” he said.

Among his findings:

• There were 3,796 detections of 13 mammal species over the five winters through 2011.

“As expected, detections of elk and mule deer tracks were the most abundant,” Lowsky wrote in a report. “Voles and the long-tailed weasels that prey on them were third and fourth most abundant, respectively. Bobcats, coyotes, mountain lions, mountain cottontails, pine squirrel, red fox and rock squirrels were also among the species detected.”

• There were 1,376 detections of 75 bird species.

“Species known to be sensitive to human activity – blue-gray gnatcatcher, plumbeous vireo – and species requiring riparian habitat – gray catbird, yellow warbler – are present within the trail corridor in substantial numbers and population trends are not declining and may be increasing,” Lowsky’s report said.

• Forty-three bald eagles and nine golden eagles were found in the trail corridor.

• The great blue heron colony’s fate doesn’t seem tied to trail use in spring. A pair of golden eagles found the heron chicks in 2009 and singlehandedly caused abandonment of the colony in 2009. The eagles “found it was a really good buffet for their kids,” Lowsky said.

In 2010, only one nest survived with two fledging young. Last year, 16 young herons fledged, thanks to their own efforts to fight off the eagles.

“The adult herons just sat and watched,” Lowsky said. The eagles ate a bunch of babies once again, but the fact that some of the young figured out they could fight off the eagles probably bodes well for the future of the colony, according to Lowsky.

Based on the detections of animals, Lowsky said he considers the winter closure a big success. When asked if there was empirical data that indicated opening the trail to cross-country skiers and hikers during the winter would have a negative effect on wildlife, Lowsky said the outcome would be certain, particularly with deer and elk.

“You disturb them enough, they won’t come back,” he said.

Lowsky’s full report is available at http://www.rfta.com/traildocs.html. RFTA is accepting public comments via the website through Feb. 24 on the winter closure and the report findings.

scondon@aspentimes.com