Ospreys -Spring 2018
by: Virginia Andrews
Coming from above, loud, emphatic.
Nothing embodies spring like the long, drawn-out call of a hovering Osprey. The return of this big charismatic bird of prey means open water and the turn of a new season.
Alone in the genus Pandion, the Osprey has returned in more senses than one. A long-distance flier that migrates deep into the jungles of South America to avoid the northern winter, it may have traveled as many as 2,000 miles over the course of a couple of weeks. Dodging storms, bucking unfavorable winds, catching food as it can along the way, each return is an athletic feat. The prize is a chance to raise a family, to ensure the species will go on.
With light-weight backpack transmitters, researchers have followed Ospreys as they migrate, as they fish in their winter homes, and as they use the waters of the north. Every successful year is a story of survival.
But it is not just a seasonal return. The Ospreys of New England have also come roaring back from near extirpation. Roger Tory Peterson watched them as they raised their young near his home in Lyme, Conn. through the middle years of the 20th century. Suddenly there was a precipitous decline. Prior to 1940, there were about 1,000 pairs nesting between Long Island and Cape Cod. By 1970 there were less than 100 in the entire region. Without warning, they had become unable to reproduce. Like any good scientist, Peterson and other researchers wondered why.
Something, it seemed, had gone wrong with their eggs. The shells were too fragile to bear the weight of incubation by the adult. Some lacked shells altogether and were laid “sunny side up,” which however delightful as a breakfast order, is no good for embryonic development. With a series of observations and experiments, it was conclusively shown that the cause was environmental, tracked down to intensive aerial application of the pesticide DDT.
Used in attempts at mosquito control, the chemical remained in the environment. It did not readily break down, but became concentrated in the fatty tissues of living things. With each successive link in the food chain from minnow upward, the pesticide bio-accumulated, getting more concentrated at each step. As apex predators, Ospreys quickly accumulated a heavy dose. They were unable to metabolize the calcium needed for egg production.
They were certainly not the only birds to suffer, but their reliance on a fish diet made them more vulnerable. Studies showed DDT was also a potent human carcinogen. In 1972 its use was banned in the United States, although to this day it is still applied in other countries. But at that point the Ospreys of the northeast U.S. began their return from the brink.
In the 19th century, the response of human beings to the Osprey was, to say the least, mixed. Because they were seen as competing for fish, many were shot as vermin. They were completely removed from Scotland by the combined efforts of gamekeepers and egg-collectors.
In New England, on the other hand, while some were shot, others were encouraged. Farmers sometimes attracted them by putting an old wagon wheel atop a pole. Defending their nest, Ospreys would drive off marauding hawks that came to steal the farmers’ chickens. Uninterested in hens or eggs – other than their own – they were enjoyed as a kind of aerial watchdog.
In colonial days a large group of Ospreys nested together at Plum Island and a few on Martha’s Vineyard, but none on Nantucket. At that time the island was almost completely treeless. Without a place to perch or build, our island held few attractions for a nesting Osprey.
In the DDT era there were only nine Osprey nests in Massachusetts. With protection they bounced back, although their distribution changed. One new hazard they faced was a lack of suitable trees. Increased coastal development brought new utility lines, with tempting crossarms, just right for a nest. But alas, this was not, in practice, a good idea. Not only were the birds themselves getting electrocuted, they were causing major power failures.
When the solution was found, it satisfied the needs of both birds and people. Electric companies found it much more cost-effective to simply set a few unwired poles with cross-arms closer to bodies of shallow water where Ospreys wanted to be. Finding food and foundations for nests, the birds took those in preference to the ones carrying power lines. In 1969 two pairs nested on Martha’s Vineyard. On Nantucket they were seen flying over, one as early as February in 1973. In the spring and fall of 1977 there were a number of sightings near Madaket or over Long Pond.
The exact date of Nantucket’s very first Osprey pole is lost in the mists of time. In Coskata marsh, one was set up by hand by a crew of volunteers, while another was erected in Ram Pasture. In 1978 the Nantucket Electric Company put up another pole, this one at Clark’s Cove. By the early 1980s a pair was “housekeeping” at Coskata. Housekeeping is the term ornithologists use for a young couple just starting out and learning as they go.
A pair was seen carrying nesting material there in June 1981. In 1982 they successfully fledged two young. By 1983 there were two pairs on the island. In 1986 ornithologists attached the first U. S. Fish and Wildlife Service aluminum leg band to one youngster. The following year three were banded at Clark’s Cove. One interesting side note came out of that effort. Built into the nest was the entire carcass of a Great Shearwater and one wing of a Short-eared Owl.
Ospreys are known for their building and decorating style, eclectic to say the least. They use twigs, seaweed, plastic bags, landscape netting, flotsam and jetsam. Built into their nests have been ropes, Barbie dolls, rubber duckies, a coathanger. Although their diet is 99 percent fish, they often pick up and bring home whatever interesting debris catches their eye. Unless the bird is actually seen swallowing an item, it is hard to know if what they carry is prey, or just decoration. But there have been observations of them feeding with Turkey Vultures on carrion, and a bullfrog has been seen going down the hatch. They have been known to catch squid, and even eels have been found at the foot of a pole, but there is no real way to know if one was eaten.
It is at fishing that the Osprey excels. Thirty, 40, 60 feet up it hovers, its parallax vision able to locate a fish within a couple of feet of the surface. Its dive is graceful. It drops and drops, its wings fold back and at the last second the splashdown, feet first, sends water cascading in every direction.
It is a learned skill. At first young Ospreys often come up empty-footed. But canny older birds can be seen, talons hooked, lugging their catch home. Specially-adapted toes adjust to position the fish in the most aerodynamically efficient way. And spring, an uncertain season weather-wise, is confirmed. ///
Virginia Andrews writes the weekly “Island Bird Sightings” column for The Inquirer and Mirror and is a regular feature writer for Nantucket Today.