Examining the Territory of Ospreys in the Wye River

Abstract

In this project I was trying to determine the average nesting territory size of Osprey. I went out on my neighbor’s boat and took GPS reading for every nest we could find on the Wye River and on Wye Island. I also made observations such as, if there were any young, did the nest look abandon, how high was the nest and what structure was the nest built on. I made a table in Arc View and then set it to a theme, making every point appear on and aerial view map of the Wye River/Wye Island area. I then gave each point a number and using the measuring tool on Arc View, found the distance to the nearest closest nest. I put all the distances on an Excel spreadsheet and found the average distance, .6 miles.

Background Information

The osprey, also called the “fish hawk” is very common in and around the Chesapeake Bay. The average person knows very little about osprey other than the fact that they are very protective of their large nests built on artificial posts, in tall, dead trees, on buoys, and occasionally duck blinds, how much do we really know about them???

The osprey’s scientific name is Pandion helianthus. It’s genus is padion, class is Pandionidae, order is Falconiformes, class is Aves, and Kingdom is Animalia. This means that the osprey is classified as an animal, a bird, a bird of prey, and finally an osprey. Osprey are brown, black and white. They have dark brown patches on the bend of each wing and through their face. They are 21-24 inches long and have a wingspan of 4 1/2 to 5 1/2 feet. Ospreys weigh from about 1.5 to 1.8 kg. Their wings are narrow and in the shape of a stretched out “M”. Females are about 12 to 20 percent bigger than males. Young Osprey get their adult feathers at about 18 months. The osprey is a bird of prey that prefers fish and because of this lives near water so it can hunt and eat fish. The Chesapeake Bay and it’s tributaries are perfect for this type of bird. Although decades ago the osprey population was decreasing, the cause was found to be a fertilizer known as DDT. DDT was banned in 1970 for causing egg failures in many birds of prey. With DDT eliminated, osprey are now thriving in the Chesapeake Bay Region.

An osprey nest can consist of anything they can find from shoestrings and grass to garbage. Unfortunately, young osprey can get tangled in or even die from garbage or fishing line in their own nest. This doesn’t mean that adult osprey have no problems, they also can die from fishing line. Osprey can starve if fishing line gets tangled around their beaks, talons, wings or neck, because they can not get or eat food.

Even though osprey can easily be killed by almost any human, they will nest very close to people and not bother anybody unless they are harassed. Most osprey nest offshore for two main reasons. First, they are away from all predators that are stuck on land. This keeps them safe from dogs, raccoons, squirrels and much more. The second reason is because they are then close to their food supply, fish.

Osprey have two main ways of hunting and fishing for the medium sized fish that they eat. One way they catch fish is to fly high and then fold their wings and drop feet first into the water. Using this technique, the osprey go all the way under the water to get the fish. The other way is to scoop the water until they get something either with their talons or sharp beak.

The abundance of fish was also found to determine their territory size. Where there is an abundance of fish, Osprey may nest as close as 66 feet apart in loose colonies. However, towards the north, where there are not many fish, Osprey may live as far apart as 75 square miles.

When osprey come back in March from their migration to the Caribbean, Central and South Americas for the winter, they either find a mate or their old mate. When osprey mate, they usually mate for life and come back to the same nest each year and usually just do a little “redecorating”. They build nests in shallow water estuaries, lakes and rivers. Males show off their strength by flying high after a successful hunt. After they mate the males search everywhere for food while the females stay close to the nest.

Territories are usually hard to keep and take a lot of energy to defend because of the food supply. The nest usually has a depressed center to help conserve heat. There are usually 3-4 cinnamon brown colored eggs in a nest. They look like jumbo chicken eggs and are incubated for 5 weeks. When the eggs hatch they are each about 2 ounces. If there is not enough good food, the first one to hatch will usually be the only one to survive. However, he/she may not give his /her bothers and sisters an equal chance to survive. In an environment with little food the first born usually pushes his/her siblings out of the nest.

At about 8 weeks, the young osprey start flying and at the end of August, they begin their southern migration. During the summer, the Tred Avon River in Easton, Maryland has lots of boat traffic although it supports over 30 nests. The river is 15 miles long which would mean that their would be about 2 nests per mile or 1 nest every half a mile. Nests can also be found in the Wye, South, Severn, Maggoty, Back and Potomac Rivers.

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