Raptors adapt well to life in the city

Urban raptors? Sounds oxymoronish, but it isn't.

Large winged hunters do very well in our cities. Urban habitat — cities and towns — works well for birds of prey.

There are nesting opportunities, many of them man-made, and ample food. Our yards, parks, lakes and rivers hold a feast of prey species — songbirds, mammals and fish.

Ospreys are a fine example of urban raptors. Found worldwide, ospreys are almost exclusively fish eaters. Research shows the birds usually nest no farther than 12 miles from fishable water. (How could we miss?)

In 2017 there were at least 132 active osprey nests in the greater metro area. The number comes from Vanessa Greene of Minnetonka, a volunteer who runs the Twin Cities Metro Osprey Watch.

Greene told me there were 74 nests on nesting platforms, 20 on cell or radio towers, 18 on athletic-field light standards, 17 on power poles or transmission towers, and three on other man-made structures.

Ospreys once built their stick nests in trees. Trees are so yesterday.

Last year was very successful for the birds, said Greene, who listed 13 new nesting territories. "The population continues to grow," she said.

Ospreys migrate, and are probably at winter territory by now. They are found along the Gulf Coast and deep into Central America. Some of the birds choose Caribbean islands.

We'll see them again beginning in late March. They will claim or reclaim a nesting territory. Greene says that the birds tend to return to nests previously used.

There will be some non-nesters. The average age of a breeding osprey is just under five years. Eighty percent are less than 15 years old. Osprey can live up to 25 years but most don't.

When you watch an osprey pair at an active nest, it's the male bringing fish to the nest. The female tends the chicks.

Researchers have determined that the daily meal for an osprey family of five — adults and three chicks — is 2.75 pounds of fish.

A male osprey weighs 3 to 4 pounds. Fish taken typically weigh from 6 to 10 ounces. On the small end the catch might weigh two ounces. On the large end, not often, 4 pounds, as much as the bird itself.

The bird skims the water surface, snagging its prey. A 4-pound fish would be a drag.

There are three osprey nests within a mile of our eastern Orono home. Two are on school athletic-field light standards, the third on a lakeshore platform.

I've watched osprey bring food to those schoolyard nests when I was there to photograph grandchildren's soccer games. (The object of my attention is not always on the field.)

The fish delivered have often had a golden tint to them. Koi? That would be an expensive meal for someone.

Osprey and eagle populations were shrinking prior to the mid-1970s. Widely used pesticides, particularly DDT, easily entered the food chain. Fish eaten by these birds carried the poisons.

Eagle and osprey eggshells were made thin by the chemicals. The weight of an incubating bird would break eggs.

Populations rebounded when such chemicals were banned.

Greene will process data from the 2018 season come winter. She encourages observers to report osprey nest locations to her at osprey.mn@gmail.com.

Read Jim Williams' birding blog at startribune.com/wingnut.