Osprey nests a platform for mystery

By David Horst  sandhill7@gmail.com
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Pat Fisher is concerned about ospreys. Actually, she cares about all large birds, but this year ospreys have her very concerned.

Baby ospreys are disappearing from their nests.

An osprey chick is prepared to be weighed.

The New London bird rehabilitator tracks osprey reproduction in Waupaca, Outagamie and part of Winnebago counties. She counts how many young are in each nest, checks their general health and bands their legs for future tracking.

That’s what we were doing recently when I tagged along with Fisher and her crew and two guys from We Energies with a bucket truck.

Ospreys are bigger than a crow, smaller than an eagle. They are mostly white underneath but the tops of their wings are brown. A substantial brown stripe swooshes across each eye. To identify them in the air, look for wings that are slightly arched.

At the first stop, in Weyauwega, we found too few babies and too many adult birds.

Tim Bristol and Mark Palm from We Energies went up in the bucket to the top of the nesting platform, chasing mom from the nest. The platforms have been built to help the ospreys, and to encourage them to pick a nesting spot other than the top of a utility pole.

In this nest, Bristol and Palm found one young osprey, put it in a large plastic bin and rode the bucket back down. It was a substantial chick, but just one. Ospreys typically lay two to four eggs.
Mom continued to circle around and soon was joined by, presumably, the dad. The screech, the frantic circles of flight, said these were the concerned parents. So, Pat, why are there now three adult ospreys flying around?

Fisher said that may be part of the problem. The third bird — but wait, now there are four. The third and fourth birds, probably were from a nearby nest. The harassment can’t be helping the reproduction rate.

But at our next stop, we may have found the real answer.

Not far from the first location, a sparse nest sits on an old platform atop a utility pole. It is home to three chicks. Fisher saw them peeking out from the nest a couple of days ago. Neighbors spotted their mom just this morning.

Pat examines talons left in the nest.

The guys climb into the bucket and power up to the nest. They just hover there, not actually reaching into the nest. This can’t be good. They lower back down to conversation height and report that all they have found in the nest are feathers and talons.

An eagle or, more likely, a great-horned owl, attacked the nest and ate the young ospreys. Osprey researcher Sergej Postupalsky told Fisher that a bald eagle probably would carry the chicks away, while the owl would eat them in the nest.

Fisher is downcast. This makes at least seven chicks that have fallen victim to predation this year in the nests she checks.

“This is the first year that we’ve had so many losses. I have no idea what’s going on,” she said.

At least, we console ourselves, this time the death wasn’t caused by a human.

The DNR lists threats to ospreys as lead and mercury contamination and competition from bald eagles. The osprey is a “Species of Greatest Conservation Need” in Wisconsin. That’s improved from “threatened” (1989-2009) and “endangered” (pre-1989). Shoreline development and pollutants took the state’s population to fewer than 100 breeding pairs by 1973, according to DNR surveys. Current estimates say there are 531 nesting pairs.

Fisher and her loyal volunteers will continue the watch. She invites you to report to her any nesting failures for ospreys in your neighborhood.

Having ospreys to watch is great. So is having eagles to watch and owls flying silently in the night. But the natural world, beautiful as it is, can be an unkind place, especially when osprey chicks don’t make the cut for survival of the fittest.

David Horst’s nature column appears regularly in The Post-Crescent newspaper, Appleton, WI.