Osprey – Pandion haliaetus. The size of this bird is closer to the eagle, reaching in the spread of its wings up to 1,8 meters. It has a white sinciput, neck, belly, stomach, and feet.
It has a white with black strokes tail, with black tips at the end of the wings. When flying its wings are bent forward in the form of shallow capital letter M, and the flywheel feathers of the first order are widely and seemingly thinned out.
The eyes of the ospreys are bright yellow, and it has a black beak. Ospreys are one of the most usual predatory birds in the world; it dwells on all continents besides Antarctica. It is possible to notice Ospreys everywhere close to open water, where it hunts for fish.
Comparing to males, the Osprey females are twenty percent heavier and the range of their wings is five to ten percent longer. In North America the weight of males varies in the limits of 1200-1600 g, the weight of females – 1600-2000 g. in females painting darker, and spotted necklace around the neck is more clearly expressed.
They nest everywhere, where there are safe places and shallow water areas with an abundance of fish.
Nests usually are built three to five kilometers from the water: swamps, lakes, reservoirs, or rivers, but they also can be arranged in a good place above the water. Places are selected in such a way, where it is possible to construct the large nest, almost inaccessible for the ground-based predators – sometimes above the water or on the small islet.
The following places can serve as a nest: dried tree, buoy, or other artificial construction.
The Ospreys that hatch nestlings travel up to 14 km from the nest in search of food, whereas in the remaining time they can fly up to 10 km.
In contrast to other predatory birds, the ratio of the Ospreys almost completely (more than 99%) consists of fish.
In the selection of concrete types, the birds are indiscriminate and feed by all, which can catch on the water surface. However, in a particular territory, two or three forms of fish can prevail as victim selection.
The birds living in northern areas migrate to the south in the winter, southern populations conduct a settled way of life. At the same time settled birds, when they do not nest, can travel several hours from the place of nesting in search of food. The marriage period begins in December – March, in the migrating birds in northern areas in April or May.
The migrating Ospreys prefer to nest, where winter is sufficiently cold and fish in wintertime go deep into the water.
The migrating females and males arrive at the place of nesting separately, generally, the male arrives flying by several days earlier.
Sometimes around the nest area, the male carries out noticeable air pirouettes, which considers as an early sign of attracting the female’s attention or deterrence of competitors.
Although both the male and the female gather material for the nest, mostly the female builds it.
The nest is built from twigs and then it is twined by algae or grass. The Ospreys use the same nest for several years, but each they continue building bringing it to order.
As soon as the nest is built, the male begins to gather food for the female, and this process continues until the nestlings are feathered or if laying eggs for any reason did not take place.
As a rule, the female, to which the males bring more food, are more receptive to coupling. They request food from their pair, but if the male is not capable to feed, then from other near located males.
The male guards the female against other newcomers and at the same time he tries to feed her. As a rule, falcons are monogamists. Polygamy is possible in rare cases when nests are located close to each other, and the male is capable to protect both nests. In such cases, the first nest has the larger reproductive advantage, since the male brings the food there.
The female lays 2-4 eggs one by one with the interval of one-two day each.
The eggs are white with red and reddish-brown speckles. Both parents participate in hatching, the incubating period lasts about 40 days.
The nestlings appear in the same order, that the eggs were laid one each a day or two. The first nestlings grow earlier and have an advantage over those following. If food is insufficient, then the late nestlings do not manage to obtain it and often they perish. As a result, the remained nestlings have more food and the percentage of survival is higher.
At first, the nestlings are not capable of supporting the normal temperature of the body, and the female almost always warms them the first two weeks. Further, she continues to handle them in the case of too cold or hot weather, until approximately 4 weeks.
Ospreys are relatively long-life birds. The oldest Osprey known in North America proved to be a male, whose age was evaluated as 25 years. The oldest known female lived 23 years.
However, the majority of Ospreys do not live until this age. The viability of Ospreys after one year varies in different populations but approximately estimated 60% for the young individuals up to 2-year-olds and 80- 90% for the adult birds.
Ospreys are subject to attacks of air predators, in particular, owls and eagles.
In North America as enemies of Ospreys could be considered Bald Eagle (Haliaeetus leucocephalus) and Great Horned Owl (Bubo virginianus), who hunt for the nestlings and in rare cases adult birds.
Among the ground-based predators, that hunt for the Ospreys’ nests it is possible to name raccoons, snakes, and other climbing species.
The birds located in the winter can be hunted by crocodiles – for example, Nile crocodile (Crocodylus niloticus) can lie in wait for the Osprey that dives after the fish. Despite that, that is not the most dangerous threat to Ospreys.
Similar to all birds, Ospreys have faced massive threats with the coming of industrialization in the last two to three centuries, but even before that, they were subject to victimization.
There are known facts from the Middle Ages of Ospreys being killed when they were considered as a threat to fish ponds. But the most dangerous threat was yet to follow, the widespread use of pesticides that caused the most substantial decline in numbers of the Ospreys.
DDT is a pesticide, used against gnats, cotton, soybean, and peanut pests. It is one of few means which were effective against the locust.
Paul Hermann Muller – a Swiss chemist and the laboratory head of the firm “Geygi” was awarded the Nobel Prize for Physiology or Medicine for the detection of the striking insecticidal properties in DDT. But it was later that various negative effects have arisen from the usage of those pesticides. The most important negative aspect of the application of pesticides – is the negative effect on the environment and human health. This problem disturbs the community most of all.
In the years 1950-1960 ornithologists (specialists who study birds) noticed catastrophic declines in populations of many species of birds, which correspond to the top of the food chains.
Piscivorous birds, such as Ospreys, were so affected that there was danger of their complete disappearance. Studies have demonstrated that the problem is related to reproduction: eggs were broken in the nest before hatching nestlings.
The reason for this has proved to be the accumulation of high concentrations of DDT in eggs. The scientists found that DDT affects the exchange of calcium, resulting in laying eggs with a thin shell. According to further research, birds received high doses of DDT in the process of bio-concentration in the food chain.
Despite the possibility that other chemicals may have caused biochemical and physiological stress to Ospreys at that time, their sub-lethal effects are less clearly understood than for DDT.
The process of the thinning of eggshells is considered the first reproductive problem related to contaminants found in fish-eating birds.
Eggshell thinning is caused by the presence of DDE in female birds. Eggshells consist of calcium carbonate, which is synthesized from calcium and carbon dioxide in the bird’s body.
This chemical reaction is assisted by the activity of an enzyme, and DDT prevents the process of this enzyme. The result of this is that the eggshell becomes thinner than it normally should be and the possibility that the egg could be broken increases.
The concentrations of toxic chemicals in the environment are often expressed in parts per million (ppm).
When dealing with bird eggs, the concentrations are usually given relative to the weight of the liquid part of the egg – its ‘wet weight’. Therefore, ppm (wet weight) is the number of grams of contaminant per one million grams of egg contents. To help you picture how small some of these concentrations are, one part per million is equivalent to a cube of ice (5 g) in a five tones block of ice. Unfortunately, some chemicals are harmful to wildlife even at these very low levels.
Other contaminants can be considered dangerous to the environment. Here are some examples of these contaminants:
- PCBs: Polychlorinated biphenyls (PCBs) have been in use since 1929. A small number of these isomers are particularly toxic and are thought to account for the bulk of PCB-induced toxicity in animals. PCBs have not been manufactured in North America since 1978.
- 2,3,7,8-TCDD: Dioxin is the popular name for a class of chlorinated hydrocarbon.The most toxic dioxin is 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Animal species vary considerably in their sensitivity to this chemical.
- Mercury: At higher concentrations, mercury is extremely toxic to animals, and concentrations of only 0.5 ppm in eggs of birds of prey can kill the developing embryo.
But fortunately, Mercury is usually found within the natural environment in very small concentrations.
The mid-1970s represent a turning point for Ospreys in the Great Lakes Basin, and in other parts of North America. Since 1972, DDT use had been severely restricted, and Ospreys have been able to increase their reproductive output.
In addition to the restriction to the use of DDT and other toxic chemicals, human activities also helped the increase in the Osprey populations.
These activities may include: Constructing artificial platforms for the Ospreys to build their nests; the assistance of Government programs along with individuals and local conservation groups in installing different customized nesting platforms in an attempt to improve wildlife habitat (these Osprey platforms became so successful that in some places it required to be on a waiting list before installing within a view of the house).
As a result of such activities, it can be seen that building artificial platforms compensates for the shortage of natural habitat and nesting sites, in addition to the stability of such platforms they are less accessible to ground predators.
A top food chain species such as Ospreys can inform us many things about the environment it lives in. It shows the side effects of particular activities humans could not recognize at first.
The Ospreys’ tolerance to humans makes them perfect indicators, in contrast to other predatory birds such as Bald Eagles and River otters Ospreys usually build their nests near houses. These days, Ospreys are considered by many as a symbol of a healthy and productive ecosystem. It is Osprey’s long life expectancy that enabled it to survive through those years of heavy pollution, despite low productivity.
In addition to being an excellent model of North American wildlife, the Osprey serves as a biological indicator of environmental problems. And as long as people continue to react to those signals that this and other indicator species are sending out about the condition of the environment, populations of Ospreys and many other species will remain.
Other factors that affected the Ospreys population might be less important compared to the previously mentioned, but the most important is the change in the relations of people toward nature and the environment. The people’s desire to watch and protect Ospreys has helped in forming clubs and communities that made their goal in protecting the Ospreys. For example by the early 1970s, there were as few as 10 nesting pairs of ospreys in Cape Cod, state Massachusetts.
Today, there are approximately 400 pairs of Ospreys nesting in Massachusetts, with 50 pairs on the Cape for part of the year. A lot of these people simply enjoy the view of Osprey fishing, tending its nest, or flying around high in the sky. As the Osprey becomes more common in the areas such as Cape Cod, some people especially tourists come to witness this amazing bird, diving from great heights into the water, for the very first time. The community and naturalists groups and clubs have worked together with government agencies and programs in various parts of the US to help to protect the Ospreys. These efforts are promoting the successful recovery of Osprey populations, particularly in areas where there seems to be a shortage of natural nest sites. These cooperative partnerships are a positive way of bringing the community together, working towards improving the overall quality of the environment which we share with a wealth of wildlife species.
Works Cited
Poole, A.F.Ospreys: a natural and unnatural history. Cambridge University Press, Cambridge, U.K. 1989.
Poole, Alan F., Rob O. Bierregaard and Mark S. Martell. Osprey (Pandion haliaetus), The Birds of North America Online (A. Poole, Ed.) 2002. Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America. Web.
Cassidy P. “Fire causes relocation of osprey chicks” Cape Cod. Web.
Clark, W. S. & B. K. Wheeler. A field guide to Hawks of North America. Houghton Mifflin, Boston. 1987.
Grier, J.W., C.R. Sindelar and D.L. Evans. Reproduction and toxicants in Lake of the Woods Ospreys. 1977.
Poole, A.F. Ospreys: a natural and unnatural history. Cambridge University Press, Cambridge, U.K. 1989.