Osprey baby boom on the Westport River


By Bruce Burdett

The Westport osprey nursery is a bustling place as near-record numbers of youngsters fill nests along both branches of the river.

"We are seeing pretty amazing numbers said Gina Purtell of Mass Audubon's Allens Pond headquarters.

The number of eggs (231) was way up this year, the number of chicks (159) from those eggs its up, but it is the number of fledged birds — 136 —  (that survived to near the age of flight) that is really surprising. "Most of the chicks that hatched managed to fledge and that is very uncommon … We're seeing many nests with three and four young ones."

The weather deserves a good deal of credit, she and others suspect.

"We've had a couple of big storms and rains but none of the typical three-day runs of bad weather that usually wipe out clutches," Ms. Purtell said.

Those prolonged storms are exhausting for parents and often deadly for chicks.

The fathers can't get out and bring back fish as well as they should and the chicks don't get a chance to dry out from a days' long chilly soaking.

"So they are hungry, wet and cold, a lethal combination," Ms. Purtell said. Birds still in the downy stage, without their outer protective feathers, are especially vulnerable.

Alan Poole, who has led studies of Westport's osprey population for years, has even looked into whether nest building skills play a role in survival during such bad years, Ms. Purtell said. Do youngsters born into well-shaped, quick-drying nests fare better than those whose parents are less adept?

Ms. Purtell and volunteers, among them Judy and Harold Isaksen, spent recent weeks banding as many of the young birds as they could among the 74 Westport River area nests.

"You have to get them at just the right age." Not too young and not so old that you risk spooking them off the nest before they are ready."

And you need cooperative mothers.

Most of them "hover overhead and watch very carefully. You feel like you are an interloper, an alien."

A few make their displeasure more obvious.

"One mom was so aggressive that we had to give up. She was dive bombing us with her talons at the ready." The mother avoided contact but came much too close for comfort.

The chicks, on the other hand, "are usually fairly passive. They  grab onto us with their talons but stay quiet."

Because they are aware that banding is disturbing to chicks and parents alike, "We make it very quick — we tuck them under our arms, attach the band and put them back. It takes all of about seven seconds."

Sometimes their visits even help the birds. At one nest they found a youngster that had tumbled overboard. They put him back onto the nest.

This is an especially busy time for the Westport River osprey, especially the parents.

That large fledge number reflects the fact that many nests were especially successful this year — "lots more with three and four fledglings instead of none or one."

Which means parents have a lot more mouths to feed in the weeks before the youngsters learn to feed themselves.

In early August, "the young ones are still at the fumbling around stage when it comes to catching fish. They still want to be fed by mom and dad."

While they are encouraged by the dramatic increase in fledge numbers, observers say that doesn't necessarily translate into  overall osprey population growth in the Westport area.

"The population as a whole has been remaining fairly steady, another thing that Mr. Poole and others have been looking into.

Lots of factors come into play.

Although most of the youngsters that have made it this far will migrate south, many won't survive to return to Westport in two years (they spend the first full year at the southern end of their migration and don't come back until they are ready too mate.)

Risks include predators such as great horned owls, angry fish farmers in their southern range (Cuba, Central America etc.), storms and food supply.

"Here the population hinges on the herring population" which they rely on for at least half of their food. If too many young ones stay in Westport, they could find food, nests (the river area is limited to 80 platform nests - 74 are now in place) and mates.

The experience of one Westport male describes while not all mate every year.

Returning to Westport in 2013, "He was swept offshore and had to struggle to get back. He was a week late getting back to Westport and by then another male had moved in. That sort of thing is also built into the system … if they all mated successfully every year, the population growth could not be sustained," Ms. Purtell said.


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