Living Sanibel: Osprey’s diet 99 percent fish
In the classic work, “The Nature of Things on Sanibel,” Sanibel author and naturalist George Campbell noted that during the 1974-75 nesting season, 24 osprey nests produced 10 offspring on Sanibel and Captiva islands. Two years later, during the 1976-77 nesting season, 37 nests produced 12 young. In the 2007-08 nesting season, the International Osprey Foundation recorded 109 nests producing 79 healthy chicks. Most of this impressive rebound is a result of the elimination of DDT and related chlorinated hydrocarbon pesticides, which caused the osprey’s eggshells to thin and fail long before hatching. Although the osprey population is slowly recovering, the Florida Fish and Wildlife Conservation Commission has kept this beautiful raptor on its list as a species of special concern.
Like most birds of prey, the osprey tends to return to the same nest year after year, and it is especially fond of nesting on power poles. Taking a cue from this behavior, Mark “Bird” Westall, founder of the International Osprey Foundation, started constructing special nesting platforms on Sanibel in the mid-1970s to see if the osprey would take to them. Today you can see many of these nesting sites all across Florida, the most common design being a single pole with a sturdy square platform on top, approximately 30-40 feet above the ground. The platforms have proved popular with ospreys, though it doesn’t keep them from building nests in unlikely places, such as atop the buoys marking the Intracoastal Waterway, overhead signs, or high-tension power lines.
The osprey is learning to live with humans. It is one of the most widespread raptors in the world, found on all continents except Antarctica. It is sometimes mistaken for a bald eagle, though it is considerably smaller and has a mottled white head.
It can often be observed soaring along the Sanibel causeway searching for prey. With a diet that is 99 percent fish (it has been known to eat snakes and small reptiles, though rarely), the osprey is commonly found hovering over almost any good-size body of water, from inland ponds to open tidal flats. It strikes the water with incredible speed, sometimes completely submerging its body. Once the osprey grasps a suitable prey, be it a sheepshead, seatrout, mullet, or any other local fish, it quickly turns the fish to face forward into the wind, making it more aerodynamic to carry. The osprey has been known to die after sinking its powerful talons into a fish too large for the bird to lift. Unable to extricate itself in time, it drowns with a large redfish, snook, or large-mouth bass attached.
Bald eagles sometimes prey on osprey offspring, but by and large the biggest threats to the osprey come from manmade chemical pollutants and degraded water quality, which results in loss of fisheries.
This is an excerpt from Living Sanibel – A Nature Guide to Sanibel & Captiva Islands by Charles Sobczak. The book is available at all the Island bookstores, Baileys, Jerry’s and your favorite online sites.