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Osprey

By Mary Nelesen

The osprey, like several of my friends and neighbors, has gone south for the winter seeking a warmer climate. And like my snow-bird friends, I know the osprey will return in the spring.

I became interested in ospreys while watching the webcam at St. Mary’s in Glacier National Park last summer. For those of you who may not be familiar with this webcam, it is located on the St. Mary’s Visitor Center just inside the east entrance of Glacier National Park on the Going to the Sun Road. The webcam is focused on a pole with a nesting platform. The webcams can be viewed on the park website, https://www.nps.gov/glac/index.htm.

According to Bill Hayden, the park’s Interpretive Specialist, a pair of osprey returned to the platform in early spring, on approximately April 17 or 18, 2011. The pair was frequently seen by park staff and was observed mating on May 15. On May 19, the male was found dead. He apparently flew into some nearby power lines. The female stayed close by the nest for about a week before leaving the platform. A new pair of ospreys was observed on the nest, but it was thought to be too late in the season for them to raise young. Throughout the rest of the summer, I would occasionally catch sight of a variety of birds perched on the platform but, alas, no osprey chicks.

Ospreys (Pandion haliaetus), sometimes known as sea hawks or fish eagles, are diurnal fish-eating birds of prey. They can be confused with bald eagles but can be identified by their white underparts. Their white heads have a distinctive black eye stripe that goes down the side of their face. Eagles and ospreys share similar habitats and sometimes battle for food. Eagles often force osprey to drop fish that they have caught and sometimes steal them in midair.

Ospreys are superb fishers and eat little else – fish make up 99% of their diet. They have barbed pads on the soles of their feet, which helps them grip slippery fish. When carrying a large fish, they carry the fish head-first, to be as aerodynamic as possible. Because of their diet, they can be found near ponds, rivers, lakes and coastal waterways around the world. Ospreys are found on every continent, with the exception of Antarctica.The sexes appear fairly similar, but the adult male can be distinguished from the female by a slimmer body and narrower wings. In addition, 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. Their call is a strong, clear “cheep,” given in a slow, regular cadence, or a faster piping “peep-peep-peep.”

Most ospreys are migratory birds that breed in the north and migrate south for the winter. They usually lay 2 to 4 eggs, which both parents help incubate. According to Cornell’s Lab of Ornithology, osprey eggs do not hatch all at once, but instead 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 among the chicks, but if food is limited, the younger chicks often starve.

The platform/pole outside the St. Mary’s Visitor Center in GNP was placed there by Glacier Electric. Artificial nesting platforms are common in areas such as St. Mary’s, where preservationists are working to reestablish the osprey. Despite its population rebound, the osprey’s survival still depends upon the kindness of strangers who place poles and platforms along our waterways. So until next spring, I’ll look forward to the ospreys’ return, with the hope of watching a new family take up residence at St. Mary’s in Glacier National Park.

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