Ospreys are seemingly ubiquitous today since they are found in so many locations around the world. But that has not always been the case. From 1950 to 1970, ospreys suffered severe reductions in their populations. It was recognized that this was due to pesticide poisoning, which caused the thinning of the eggshells causing fewer eggs being strong enough to develop and hatch. It is estimated that 90% of the breeding pairs disappeared along the coast between New York and Boston.
After the pesticides were banned in the early 1970’s, there began a rapid recovery in the Osprey populations although not in all the places that they previously inhabited. Partners in Flight estimates a global breeding population of 500,000. In addition to the banning of pesticides, the recovery was assisted through the construction of artificial nesting sites. As natural nest sites succumbed to tree losses and land development, specially constructed nest platforms and other structures such as channel markers and utility poles have become vital to their recovery.
Usually the male finds the site before the female arrives. Osprey nests are built of sticks and lined with various materials that the male finds, such as bark, sod, grasses, vines, algae, and other items found floating on the water. The female arranges the nest. It has been observed that the male will break dead sticks off trees as he flies by. On artificial platforms, a breeding pair will return to their nest year after year continually adding to the nest and can end up with nests 10-13 feet deep. Artificial nests can outgrow their platforms after years of use and may need to be trimmed back by humans in the nonbreeding season. Because Ospreys utilize twine, fishing line, and other discarded lines in the nest, these have been known to wrap around a chick’s body and injure it or keep it from leaving the nest and ultimately causing its death. Humans routinely inspect the nests and try to remove those items from the nest materials.
Thus manmade structures have become an important tool in the growth of Osprey populations. In some areas nests are located almost exclusively on artificial structures. These structures were critical to attracting them back to areas that had been abandoned because of failing populations due to the pesticide use. The nests are specially designed for Ospreys recognizing, for example, that Ospreys require nest sites in open surroundings for easy approach, and safety from ground predators, such as raccoons.
So human activities were involved in the reduction of Osprey populations, but they now are actively helping with the recovery and maintenance of Osprey populations. Truly, the Osprey has become a conservation success symbol.