What is that bird that plunges into Lake Washington feet first and comes up with a live fish with nearly every dive?
It's the osprey. The osprey is a highly successful species with a nearly worldwide distribution.
We are fortunate to have osprey breed in the Pacific Northwest, spending nearly six months in our area before returning to their wintering grounds. A significant number of nesting osprey reside along the Duwamish River and can be seen commuting over South Seattle to fish the waters of Lake Washington.
The osprey is easily observed. A vocal species, an osprey's loud, clear "keyew-keyew-keyew" calls will immediately draw your attention to the bird. In flight, you will see this large, narrow-winged hawk's distinct kink at the elbow accented with dark wrist marks. Perched birds are distinguished by a white cap, a dark brown eye-line that broadens behind the eye and white chin, throat, breast and belly.
With live fish accounting for nearly 99 percent of their diet, the ospreys are uniquely adapted for catching fish. The talons have a reversible front talon and barbed pads (tiny impaling spines) on the soles of the feet to help grip slippery fish.
And fishing is what this bird does most successfully. It hunts on the wing between 30 to 120 feet above the water. When spotting a fish, it often hovers prior to diving, then plummets, legs extended forward just before plunging feet-first into water. Amazingly, osprey can be submerged up to 3 feet during a dive.
Powerful wing strokes are needed for take off while partially submerged in water with a heavy load: prey typically represents about 10-30 percent, but may be greater than 50 percent, of the bird's body mass.
Once out of the water, the osprey shakes off vigorously and maneuvers the fish in the talons to be aimed forward, head first and belly down, using the fish's streamlining to reduce aerodynamic drag.
We can observe their fishing behavior in the spring when osprey return to the Northwest between March 20 and April 15 until they depart for their wintering grounds to the south between August 20 and September 25.
There are a couple important aspects about the osprey that have been instrumental in their population recovery from the impacts of DDT and habitat loss. First, they have been able to adapt and habituate quickly and easily to nearby human activity.
They are also able to build their nests on manmade structures, such as telephone poles, cell phone towers, building roofs, channel markers, and nest platforms designed especially for osprey nests. Due to the loss of natural nest sites, such as large mature trees with broken tops, manmade structures have become an important tool in reestablishing ospreys in areas where they have disappeared. In the Puget Sound area, nests are placed almost exclusively on artificial structures.
Pair bonds are strong in osprey and the same pair will return to the same nest site year after year. The female will lay one to four eggs, usually three, with one egg laid every two to three days. Both parents incubate, with the female always incubating at night. The male usually provides the female with all food during this period.
The eggs hatch in about 38 days sequentially between May 21 and June 27. Osprey eggs do not hatch all at once, and the first chick hatches up to five days before the last one.
The older chick dominates its younger siblings, and can monopolize the food brought by the parents. If food is abundant, little aggression is seen amongst the chicks, but if food is limited, the younger chicks often starve.
We should be seeing family groups of osprey at this time of the year. The first flight of young generally occurs between July 15 and August 21 when the young are 50 to 55 days old. They are dependent upon parental feeding for at least 10to 20 days. Young might catch prey as early as five days to 11 days after fledging.
Observations of young osprey that humans have released into the wild indicate that fishing behavior appears to be innate, because the young learned to fish on their own, without parents. When it's time to migrate to wintering grounds, young migrate on their own, lagging behind adults. Once in their wintering grounds, the young may remain until their third calendar year (age 29-32 months). Osprey do not reach breeding age until they are at least 3 years old, with 50 percent not breeding until their fourth or fifth year.
In the future we should be seeing more and more osprey in the Pacific Northwest due to their amazing adaptations to humans and hopefully our ability to protect our waterways, which will result in an abundant fish supply.
Sandra Wood and Ed Newbold may be reached at editor@sdistrictjournal.com.
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