Herons’ flight rekindles trail debate

BASALT ” The abandonment of a heron colony near Rock Bottom Ranch in the midvalley this spring has rekindled debate about the Rio Grande Trail’s effects on wildlife.

Numerous great blue herons returned to a heronry along the Roaring Fork River at the end of Hook’s Lane this spring. At least eight of 14 nests in the area were occupied as of May 6, according to Jonathan Lowsky, a wildlife biologist who works as a consultant for the Roaring Fork Transportation Authority. By May 14, all the nests were abandoned.

“It appeared they were beginning to incubate, then they just disappeared,” Lowsky said.

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The segment of the Rio Grande Trail in that part of the midvalley reopened for the season on May 1. A 2-mile stretch of the popular paved route is closed from Dec. 1 through April 30 so human users don’t disturb wildlife. The closure was put in place by RFTA, which built and maintains the Rio Grande Trail in the middle and lower valley.

Critics contend the closure should be longer so that herons don’t get flushed during the particularly sensitive time when they are incubating eggs. Jim Duke, who lives across the Roaring Fork River from the trail, has battled RFTA since the trail was proposed over its months of operation. He said he has “absolutely no doubt” the trail opening was responsible for the herons’ departure.

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He lobbied RFTA’s board of directors to extend the closure until July this year, based on what happened last year.

The heronry at Rock Bottom Ranch is divided into a west and east segment. Last year, the west segment, which is closest to the trail, was abandoned after the trail opened in May. The east segment was reduced in size.

That sparked a debate that raged the last half of last year. The Colorado Division of Wildlife advised closing the trail from Nov. 15 until the end of May. Lowsky advised RFTA to extend the closure until July 31 for one year to see how the heron colony reacted.

The trail was an instant hit with cyclists and pedestrians after it opened in fall 2006. There is pressure to keep it open for more months of the year rather than extend the closure.

RFTA’s board couldn’t come to a consensus when it reviewed the issue in January, so the closure remained as is was. Duke thinks that was a mistake. “I don’t know if we can ever get the heronry back or not,” he said.

Lowsky isn’t ready to blame the trail for the herons’ departure. If there was clear evidence, he would acknowledge it, he said. Several factors, some human and some natural, could be contributing to the birds’ flightiness, he said. Ospreys, a large fish-eating hawk that trails only bald and golden eagles in size, settled near the heron colony recently. Also, human activity picks up in the spring at Rock Bottom Ranch, which is owned by the Aspen Center for Environmental Studies and operated as a nature preserve and education center which hosts tours of school kids.

Lowsky said it is possible that the herons decided they preferred a different colony. Other colonies have been located for years at Cattle Creek farther down the Roaring Fork River, and at Northstar Nature Preserve, east of Aspen. A newer colony at Woody Creek has grown from two to four nests to 15 in recent years, Lowsky said. Meanwhile, the quality of the nest stand at the Rock Bottom Ranch colony is in decline.

“All these things in conjunction probably caused them to leave,” Lowsky said.

There is evidence that the blue herons were unsettled at Rock Bottom Ranch this year even before the trail opened. Lowsky said two or three herons returned to the colony around March 17 and the numbers swelled to seven or eight in less than one week. A homeowner in the area reported to him that the herons then disappeared. Lowsky investigated and found the birds gone from the western segment of the heronry in late March. But by early May, birds were back at both segments before they left on May 14.

Some of the herons laid eggs this spring, which usually makes them than less likely to abandon a nest.

Lowksy said the trail’s opening may have been “the proverbial straw that broke the camel’s back” this spring or it might have been coincidental that the abandonment happened shortly after the trail opened.

The good news, he said, is that great blue herons are thriving in the Roaring Fork Valley, so natural or manmade problems at Rock Bottom Ranch aren’t leading to the birds’ demise.

“The bottom line is nature happens,” Lowksy said.

scondon@aspentimes.com