THE SEA HAWK
By Jim Foster
Just to clear the air so to speak the title of this article is not about a professional sports team in Washington State – it is about one of the most interesting of raptors, the osprey.
Known by several names including Sea Hawk and Fish Hawk the osprey is a large bird sporting a wingspan of around six feet and being one of the most successful hunters of raptor species.
The Osprey tolerates a wide variety of habitats, nesting in any location near a body of water providing an adequate food supply. It is found on all continents except Antarctica although in South America it occurs only as a non-breeding migrant.
The Osprey differs in several respects from other diurnal birds of prey. Its toes are of equal length, its tarsi are reticulate, and its talons are rounded, rather than grooved. The Osprey is the only raptor whose outer toe is reversible, allowing it to grasp its prey with two toes in front and two behind.
The sexes appear fairly similar, but the adult male can be distinguished from the female by its slimmer body and narrower wings. The breast band of the male is also weaker than that of the female, or is non-existent, and the underwing coverts of the male are more uniformly pale. It is straightforward to determine the sex in a breeding pair, but harder with individual birds. Looking at the photographs try to tell the male from the female.
Fish make up 99 percent of the Osprey's diet. It typically takes fish weighing 5–10 ounces and 10–14 inches in length. However, the weight can range from 2 up to 68 ounces. I have seen a large osprey try to tackle a fish bigger than it can lift in the Lower Laguna Madre of Texas and a 15-inch rainbow trout on the Salmon River in Idaho.
Prey is sometimes spotted when the Osprey is up to 130 feet above the water. It will then it will plunge feet first into the water at times to a depth of three feet. The angle of entry into the water varies with the nature of the prey; steeper, slower dives are used when pursuing deeper, slow-moving fish, while long, quick dives are used for faster surface fish. After catching the fish considerable effort is needed to get airborne again. As it rises back into flight the fish is turned head-forward to reduce drag. When returning to the nest the osprey will hold the fish with one foot while acquiring the nest with the other.
The Osprey breeds by freshwater lakes, coastal brackish waters, and saltwater bays. Ospreys reach sexual maturity and begin breeding around the age of three to four years old. The nest is a large heap of sticks, driftwood and seaweed built in forks of trees, rocky outcrops, utility poles, artificial platforms.
The female lays two to four eggs within a month, and relies on the size of the nest to conserve heat. The eggs are incubated for about 5 weeks to hatching. The newly hatched chicks weigh around 2 ounces, but fledge in 8–10 weeks. A study on Kangaroo Island, South Australia, had an average time between hatching and fledging of 69 days.
Some owls and hawks will prey on the chicks but this is somewhat rare here in the Lower 48. Due to the ospreys hunting ability most chicks are fledged but then may be lost for one reason or another after leaving the nest and protection of their parents.
An observed behavior surprised me – that behavior by the female was to spread her wings providing shade and a cooler environment for her young.
The osprey is an interesting bird and the more I watch and photograph the family in the nest the more interesting they are.
If you have comments or news for Jim Foster please email him at: jim@jimfosteroutdoors.com
