Eagle again gobbles eggs in nests as adult herons watch
BASALT – For the second year in a row, all of the great blue heron eggs in a collection of nests near Rock Bottom Ranch near Basalt have been devoured by a hungry predator.
A golden eagle raided 11 nests on May 14, according to witnesses Shep and Mary Harris, wildlife watchers who live across the Roaring Fork River from the heronry.
Shep Harris said he was outside when he heard the screech of herons. He looked up and saw about 15 adult herons circling in the sky above the nests. He knew what it meant.
“I saw it last year, too, unfortunately,” he said.
Mary Harris said some of the herons settled in towering spruce trees alongside the cottonwoods that hold their nests. They just watched as the golden eagle feasted on the eggs.
“Herons are totally capable of defending themselves,” she said, noting their large size and the sharp beaks that they can move with lightning speed. The fact that they didn’t try to fend off the eagle indicates they are young, inexperienced breeders, she said. If all herons reacted to predators like those at the Rock Bottom area this year, there wouldn’t be any herons left, she said.
The Harrises only witnessed the raid on one day. They don’t believe any of the eggs had hatched, but it was difficult to tell. The herons left the area a couple of days after the eagle had landed. A few herons returned to the nests a few days later but didn’t stay.
The heronry is abandoned, said Jonathan Lowsky, a wildlife biologist in the midvalley. His firm, Colorado Wildlife Sciences, monitors wildlife issues along the Rio Grande Trail corridor for the Roaring Fork Transportation Authority. The heronry is off the corridor but nearby.
Lowsky’s research showed that breeding pairs of herons usually have between three and five eggs, so there were probably between 33 and 55 eggs in the 11 nests. “They’re all dead,” Lowsky said.
Last year, a golden eagle raided six nests later in the spring – between May 28 and June 6 – and gobbled both eggs and chicks. It is likely that the same eagle returned to the buffet this spring. “Once they find a source of food, they’ll come back,” he said.
Lowsky said it isn’t unusual for predators like the golden eagles to eat heron eggs and chicks. “These are natural events that have happened for millennia,” he said.
And while the raid was unfortunate for the Rock Bottom heronry, he sees no evidence that great blue herons are in decline in the Roaring Fork watershed.
“The good thing is that down at Cattle Creek, there are more than 50 nests,” Lowsky said. That’s as many nests as he has witnessed there. Numbers have dwindled to as low as 15 in that site.
Other heron colonies are established at North Star Nature Preserve east of Aspen and in Woody Creek. Lowsky said he hasn’t monitored those sites yet this spring. Heronries are “dynamic entities” that change size and location with regularity, he said, further showing the incident at Rock Bottom isn’t necessarily cause for concern.
“You know what – herons are doing all right in Colorado,” Lowsky said.
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