Great blue herons return to midvalley rookeries
March 12, 2002
A flock of great blue herons apparently have realized just how good they had it on the Rock Bottom Ranch in the midvalley.
Four or five pairs of the birds visited the nature preserve this month, much to the delight of conservationists at the Aspen Center for Environmental Studies. At least 10 mating pairs of herons migrated off the ACES-owned property last May and June.
The herons’ decision to abandon their nests in cottonwoods along the Roaring Fork River baffled wildlife experts last year. There was speculation they were driven away by everything from an unusually hot spring and summer to construction in the vicinity.
Rock Bottom co-manager Matthew Coen said he is encouraged that the birds are returning since herons are an “indicator species” of healthy ecosystems. He said people who visit the ranch always inquire about the plight of the herons.
But his enthusiasm comes with caution. Coen said raptors have relaxed in the old heron nests this winter, making the birds skittish about hanging around.
“They’re kind of jockeying for position,” he said.
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Bald eagles and hawks prey on young herons. The eagles typically migrate out of the valley in the spring, so they won’t pose a threat much longer, Coen noted.
Great blue herons often return to traditional nesting areas, or rookeries, around mid-February, according to Jeanne Beaudry, executive director of the Roaring Fork Conservancy. Once they lay eggs – usually between two and six – the incubation period can be as short as 28 days, she said.
The young feast on regurgitated fish provided by their parents until they fledge in 55 to 90 days, Beaudry said. Then they go their separate ways to other grounds.
It’s common for herons to return to the rookery where they were raised. They often rebuild the huge nests they left behind. But sometimes they abandon a rookery.
“It’s so unpredictable why they will pick up and leave a nest,” said Beaudry.
Their departure from Rock Bottom was ironic because ACES had gone to great lengths to secure the wildlife habitat and protect it from development.
In a rare land purchase, ACES raised nearly $2.8 million to purchase 115 acres. ACES noted in fund-raising materials in 1999 that the land it eyed along with adjacent property provided the largest aggregation of great blue heron nests in the valley.
The old Sanders Ranch property provides another important nesting area. The Roaring Fork Conservancy has a conservation easement on 54 acres of the old ranch, where the Bair Chase Golf and Rod Club will be developed this year. Twelve heron nests were lost when a huge ponderosa pine on the property blew over last year.
The herons resettled in two other ponderosa pines – one within the conservancy’s easement and one on a neighboring property. They returned last month.
Combined, there are 10 to 12 mating pairs in what appears to be a thriving population in the Sanders Ranch area, Beaudry said.