by: Erick Greene
June 1982

It was a strange place to be bird watching. from my observation point on the end of a pier I had a good view of busy Halifax Harbour. boats of all sizes, from Cape Islanders to container ships, went about their work. A large tanker laden with Hondas towered over me, and was nudged to its dock by tugs. Its cargo was destined for the vast parking lot which stretched out of sight behind me. The oil refinery to my right belched out its bitter-sweet fumes. A continuous stream of helicopters and jets roared overhead from the Canadian Forces Base Shearwater behind me.

Yet, if you carefully search high above the commotion, you are sure to see a large bird oblivious to the hustle and bustle of the harbour. The bird hovers high overhead, gazing intently into the waters below. Suddenly the wings are folded and the bird plummets out of the sky. An instant before it plunges into the water, the bird shoots its feet downwards. The bird disappears in a plume of spray, but a few seconds later, more often than not, it lifts off the water grasping a wiggling fish in its powerful claws.

This spectacular bird is an Osprey, or Fish Hawk. We in Nova Scotia are fortunate that these magnificent birds are a common sight, especially along the Eastern, Southern, and Northumberland shores. In fact, many Nova Scotians take Ospreys for granted, without realizing that in many other places in the world Ospreys are very scarce. It helps to put this into perspective by considering that there are more Ospreys nesting on McNab's and Lawlor's Islands at the mouth of Halifax Harbour than there are in the entire British Isles! In Scotland, Osprey nests are surrounded with barbed wire to deter unscrupulous people from taking the eggs.

IMAGE:  Tree covered McNabs Island at the entrance to Halifax Harbour shelters a large population of Osprey's in the center of Nova Scotia's largest urban area.

Wardens are stationed by the nests throughout the breeding season. One Osprey nest even has a tourist shop associated with it, where one can buy Osprey T-shirts, teacups, and other assorted Osprey knick-knack!

Two adult ospreys crowd the nest with two 45 day old chicks

Although Ospreys are related to eagles and hawks, they do not have any close cousins. For this reason biologists place them in a separate taxonomic family by themselves. Ospreys are chocolately-brown above on the wings, back, and tail, creamy-white below. A distinctive brown stripe runs across the head through the fierce yellow eye. A spotted "necklace" adorns the breast. In females this necklace tends to be wider and more conspicuous than in the males. The female Osprey is a third larger in size than the male, this phenomenon is true in general for almost all birds of prey. In flight Ospreys hold their wings with a bend at the "elbow". This is a good field mark for distinguishing Bald Eagles from Ospreys at a distance: Bald Eagles hold their wings flat while Ospreys have a noticeable crook in their wings.

Ospreys are well equipped for their fishing livelihood. Their keen eyes are far more sensitive than ours, allowing them to detect fish in the water from great heights. They have long powerful legs, and feet armed with inch-long talons. The pads of their feet are covered with hundreds of sharp spines. Perfect for grasping slippery fish!

Ospreys eat a wide variety of fish. Gaspereau and smelt are heavily preyed upon during their spawning runs in April and May. Pollock, cod, tomcod, and winter flounder are fished later in the summer in the coastal estuaries. On inland lakes and rivers yellow perch and suckers are favorites.

Ospreys return to Nova Scotia from their wintering grounds in South America and the Caribbean by mid-April. They usually mate for life, and return to the same nesting area year after year. Early in the breeding season the reunited Osprey pair performs and exciting aerial courtship display. The male flies high over the nest with a fish in his talons, emitting high-pitched slurred whistles. He then performs a series of spectacular dives over the female on the nest. eventually he flies down to the nest and presents the fish to the female. These displays culminate in mating on the nest.

A female osprey stands guard over a young chick. These fish hawks are a common sight along Nova Scotia's Southern, Eastern and Northumberland shores.

There are chores to attend to before the Ospreys lay their eggs. The large stick nest, which has usually taken a beating during the winter gales, is in need of renovating. Branches, sticks and seaweed are brought in to refurbish the nest. A patriotic pair of Ospreys near Halifax lined their nest with a Canadian flag. A more practical pair I know of lined their nest with a pair of diapers! Osprey nests are usually built in tree tops near fishing areas. Not being fussy, however, Ospreys will readily build nests on artificial structures such as the cross bars of power poles. In areas where Ospreys are common, they can be attracted to breed on old wagon wheels mounted on the top of a tall upright post.

In early May, the female Osprey lays up to four buffy brown eggs, covered with cinnamon splotches. Unlike chickens and ducks which don't start incubating their eggs until all are laid, Ospreys begin incubating as soon as the first egg is laid. As a result, the first egg has a head start over the second egg, which has a head start over the third egg, and so on. When the chicks are born about 32 days after egg-laying, there is a noticeable difference in size between the oldest and the youngest chick. This is thought to be an adaptation to unpredictable food resources. In years of plenty all the chicks get enough fish to survive. In lean years, however, the oldest and strongest chick gets most of the food, and the others will likely starve. This may seem cruel, but it is nature's way of censuring that at least one strong and healthy chick has a good chance of fledging, even in difficult years.

Osprey chicks grow quickly on a steady diet of fish. At birth the chicks are covered with a fine grey down. Feathers begin pushing through the down when the young are about 28 days old. By 40 days of age, the Osprey chicks are fully feathered, and closely resemble their parents. At this stage, the chicks spend much time flapping their wings and developing their flight muscles. By early August the young Ospreys have made their first flights, although they often return to the nest.

The first task facing the young Ospreys is to learn the difficult skill of fishing. Those that don't learn quickly perish. Fishing is learned by watching adults dive for fish, and by many trial and error dives. It is estimated that only about 60% of Ospreys that fledge survive the first year of life on their own.

With the onset of fall, Ospreys make their way south to their wintering grounds. The young birds tend to remain south for two years honing their fishing skills. The three-year old birds tend to return close to the areas where they were hatched, and a suitable nesting site is chosen and a mate sought. Breeding starts between the ages of three and five years. Ospreys are quite long lived; a ten-year old Osprey is not unusual, and a bird twenty five years old has been recorded.

We have not always been fortunate enough to have Ospreys so common along our coast. Twenty years ago, an Osprey in Nova Scotia was a rare sight indeed! Ospreys, like many other predatory and fish-eating birds in North America (such as Bald Eagles, Peregrine Falcons, and Pelicans) experienced drastic population declines starting in the late 1940's. A common symptom among these birds was that the eggshells were getting so thin that they could not support the weight of an incubating adult. It was discovered that the cause of this eggshell-thinning was contamination by a group of pesticides known as organochlorines (DDT is the most notorious of this group of pesticides). In healthy birds, an enzyme called carbonic anhydrase takes calcium from the blood stream and deposits it on the developing egg, resulting in a normal, sturdy eggshell. In pesticide-contaminated birds, however, the DDT interferes with this enzyme, so that little calcium is deposited on the egg. The result is an easily breakable egg.

Many biologists in the 1960's feared that Ospreys in North America were on the road to extinction. The severity of the plight facing the Osprey is well illustrated by the decline of the Gardiner's Islands Osprey colony. Gardiner's Island, off Long Island, New York, was among the most famous Osprey breeding area in the world. In 1945, Gardiner's Island supported over 300 pairs of Ospreys. Over 600chicks were raised in the course of that summer. A mere 20 years later there were only 55 active Osprey nests, and only 4 chicks were fledged from those nests.

Fortunately we do not have to write an epitaph to the Osprey. When it was realized that DDT was implicated in eggshell thinning, its use was severely restricted in North America. Over the last decade, DDT has dissipated from aquatic and estuarine ecosystems. As DDT levels in Ospreys diminished, they once again laid eggs with thicker shells. Reproductive success has improved and slowly Ospreys are return to their old haunts in former numbers. Nova Scotia is a lucky province since it can boast of such a healthy Osprey.