Awaiting the return of the osprey


Mid-February is a little early to begin seeing osprey here in the Chesapeake Bay, but they should be returning in the next few weeks from their winter vacations in South America.


The Chesapeake Bay region happens to be home to the largest breeding population of osprey in the World, so our area is an amazing place to experience these birds firsthand. They can frequently be found nesting above the waters of the Bay, diving for fish, or soaring gracefully overhead.


St. Patrick’s Day is roughly when osprey return, though some may return earlier and some later. Osprey return to the same area where they hatched, so we are likely seeing many of the same osprey and their offspring year after year. When you see them, great them like old friends.


According to the Chesapeake Bay Program, osprey mate for life and these mated pairs arrive earlier than those who will spend the first several weeks after they arrive looking for a mate and a nesting site. During these early weeks, you will frequently see osprey carrying sticks and other materials as they work to build a new nest or rebuild a previous nest. You may even see some fights break out (or at least hear some angry chirping) as osprey return to find their nests occupied by other birds such as resident Canada geese or bald eagles.


The increase in osprey population since the 1970’s is actually a bit of a success story in the conservation world. Like bald eagles, osprey were negatively affected by the use of the pesticide, DDT (Dichlorodiphenyltrichloroethane). This chemical ended up in waterways, where it was absorbed in small amounts by insects and other organisms. As those smaller organisms were eaten, DDT concentrations were amplified up the food web; this process is known as bioaccumulation. When osprey and other fish eating birds would eat a meal, they were getting dosed with large amounts of this chemical. Exposure to DDT made the eggshells of these birds extremely thin, so when it came time to sit on the eggs and keep them warm, they would break. This meant that prior to 1972, when DDT was banned, very few osprey and bald eagle eggs hatched successfully.


In the early 1970's there were only an estimated 1,450 breeding pairs in the Chesapeake Bay area, which increased to an estimated 3,500 by the 1990's. More recent studies have estimated at least 10,000 breeding pairs in this area, which is approximately 10% of the global population. However, that estimate is likely lower today as researchers have begun to see another decline in populations in the last several years. This decline is attributed to many different factors, including great horned owls eating osprey chicks, cold weather in May which is crucial egg incubation time, and a decline in food such as menhaden.


As a member of a natural ecosystem, it is normal to see ebb and flow in a population, including that of osprey. However, it will be important to keep an eye on the population to make sure it doesn’t dip too low, otherwise we may no longer have our majestic herald of spring.


Photo credit: Kellen McCluskey.
You can reach Kellen at [email protected]org if you are interested in her work.