Not many birds can lay claim to being the only species in their entire family. But, taxonomically, ospreys are just that.
Due to significant genetic differences from other raptorial birds (hawks), they have been placed in a family of their own, the Pandionidae. They are special in a number of ways – they are one of few bird species, and the only hawk, that has successfully colonized all the continents, except Antarctica.
This success is due, in part, to having little competition for food resources. They have the unique ability among hawks to plunge-dive into the water, feet first, to as deep as one meter to capture the fish that constitute virtually their entire diet. They do this in both fresh and salt waters, from the Arctic to the tropical seas.
If you are a casual bird observer here, you may confuse ospreys with bald eagles. Both build large stick nests, but eagle nests are nearly always in trees. Osprey nests, these days, are more frequently on man-made structures, like power poles, nest platforms built specifically for them, or, coastally, on channels markers.
Two easily seen nests are on the power poles along Hwy. 34 at Long Lake and in Lake George, near the public access. Ospreys are also considerably smaller than eagles, are very light below, and in flight show a crooked wing shape instead of the straight wingspan of eagles.
Ospreys typically mate for life, but pairs do not remain together all year. Though both sexes provision food for their young, the females migrate south in August, leaving the male to provide the last few weeks of parenting until the young become independent.
Ospreys are serious long-distance migrants. Most of those that nest in the upper Midwest end up wintering in the Caribbean or in South America, some as far as southern Brazil. The females, on average, winter farther south than the males, then reunite with their mate at the nest at the end of spring migration.
All this information on distribution throughout the year has come from birds that have either been banded by biologists or, more recently, applied with radios and tracked via satellite. Tracking of young birds has revealed that most young return to nest for the first time within 50 km of where they were raised.
As successful as ospreys have been as a species, their survival, like that of other fish-eating birds, was threatened between the 1950s and 1970s by hatching failure due to eggshell thinning. It is well known now that ingestion of DDT, which was found in high concentrations in their fish prey, was the direct cause of eggshell thinning. Osprey populations along the northeastern coast declined 90 percent during those years.
Bald eagles were also very seriously affected. With the banning of DDT in 1972 and subsequent return of captive-bred birds to the wild, populations of both species gradually rebounded. Today, both are thriving. Their recoveries are considered to be one of the great bird conservation successes and attest to the value of all the hard work conducted by biologists to make it happen.
Marshall Howe is a retired biologist with the U.S. Fish and Wildlife Service. He specialized in bird population studies. Howe has been a Park Rapids resident since 2010.