Ospreys require nest sites in open surroundings for easy approach, with a wide, sturdy base and safety from ground predators (such as raccoons). Nests are usually built on snags, treetops, or crotches between large branches and trunks; on cliffs or human-built platforms. Usually the male finds the site before the female arrives.
Osprey nests are built of sticks and lined with bark, sod, grasses, vines, algae, or flotsam and jetsam. The male usually fetches most of the nesting material—sometimes breaking dead sticks off nearby trees as he flies past—and the female arranges it. Nests on artificial platforms, especially in a pair’s first season, are relatively small—less than 2.5 feet in diameter and 3–6 inches deep. After generations of adding to the nest year after year, Ospreys can end up with nests 10–13 feet deep and 3–6 feet in diameter—easily big enough for a human to sit in.
Cream to pinkish cinnamon; wreathed and spotted with reddish brown.
Condition at Hatching
Capable of limited motion. Covered with down and with eyes open.
The Osprey is the only hawk on the continent that eats almost exclusively live fish. In North America, more than 80 species of live fresh- and saltwater fish account for 99 percent of the Osprey’s diet. Captured fish usually measure about 6–13 inches in length and weigh one-third to two-thirds of a pound. The largest catch on record weighed about 2.5 pounds. On very rare occasions, Ospreys have been observed feeding on fish carcasses or on birds, snakes, voles, squirrels, muskrats, and salamanders. Ospreys probably get most of the water they need from the flesh of their prey, although there are reports of adults drinking on hot days.
Ospreys have high-pitched, whistling voices. Their calls can be given as a slow succession of chirps during flight or as an alarm call—or strung together into a series that rises in intensity and then falls away, similar to the sound of a whistling kettle taken rapidly off a stove. This second type of call is most often given as an unfamiliar Osprey approaches the nest. As the perceived threat increases, the call can build in intensity to a wavering squeal.
About the Hellgate Canyon Ospreys
This Osprey nest is at the mouth of the spectacular Hellgate Canyon at the edge of Missoula, Montana. It’s in a very busy location, right outside the Riverside Health Care Center and next to busy parking lots, a construction site, a busy highway, and a railroad. However, it’s also an ideal location in many ways, since these Ospreys have riverfront property only about 50 feet from the Clark Fork River. Being so close to people does not bother them, and hundreds of people enjoy watching them every day.
The female Osprey at this nest is called Iris because she has very distinctive spots on her iris, especially in her left eye. These iris patterns serve as individual barcodes and allow us to identify her. She has nested at this site for many years.
Ospreys are consummate fishing birds, and this pair fishes primarily from the Clark Fork River and nearby Rattlesnake Creek. They use their 6–7 foot wingspans to soar above the water, looking for fish, then diving as deep as 3 feet for shallow-swimming prey. Adult Ospreys usually weigh 3–4 pounds, and they can carry prey up to 50 percent of their own weight. Ospreys can live up to 25 years, and they typically lay 1–4 eggs in a clutch.
Most Osprey pairs are monogamous, staying paired across seasons and beginning nesting soon after each returns from a long migration. Both sexes incubate the eggs. The female sits for the majority of the time (including throughout the night) while the male provisions her with fish. After the eggs hatch, the male continues to bring fish to the nest; the female exclusively broods the young and dissects their meals for about a month after hatching. Later on, when the chicks no longer require her protection and their appetite for fish increases, she will leave the nest and go fishing.
The nest used to be on a power pole about 200 feet west of where it is now. This was dangerous, since the Ospreys could have been electrocuted, causing fires and power blackouts. In 2007, the current nest platform was erected to provide a safer place for the Ospreys to nest. They took to it immediately. Getting the new nest platform set up, and installing and running to high resolution camera for this feed for you to enjoy has been a large effort involving many groups: Riverside Health Care Center, Karen Wagner, Kate Davis and Raptors of the Rockies, Northwestern Energy, Dave Taylor Roofing Company, and Drs. Heiko Langner and Erick Greene of the University of Montana.
2012 Breeding Details
Iris showed back up at this nest in early April 2012, and her mate of many years showed up a short time later. However, he was only around for a day or so and we never saw him again. Iris was alone for about three weeks, and spent much of her time bringing in sticks and calling from the nest. Eventually a new male showed up, much to the apparent delight of Iris. At first the new male was extremely submissive, but within a few days they appeared to be solidly paired. Eventually they fledged three chicks from the nest in 2012 (see Timeline Tab for details)
About Project Osprey
These Ospreys are an important part of a much larger project focusing on the health of aquatic systems and Osprey populations in western Montana. In collaboration with Rob Domenech (Director of the Raptor View Research Institute), Dr. Heiko Langner and Dr. Erick Greene started Project Osprey in 2007. They have been monitoring about 200 Osprey nests in western Montana.
Because of their top position in the food web, Ospreys are useful indicators of local environmental conditions. Young Ospreys eat only fish their parents catch within a few miles of the nest, so these young birds reflect the condition of the local fish population. And although many hawk species can be touchy—even dangerous—to work with, Ospreys make good subjects: they tolerate human activity well and they actually seek out human-made structures to use as nest platforms.
Osprey populations declined to near-extinction in the Lower 48 states after World War II as a consequence of exposure to DDT-based pesticides. The dwindling Osprey population helped trigger research into problems with DDT, resulting in its ban in the United States in 1972. Since then, Ospreys have returned to many large water bodies. Studies such as this one help scientists keep a watchful eye on how Ospreys—and the water bodies they depend on—are doing.
Since young Ospreys eat fish that their parents catch usually within a few miles of the nest, the young birds reflect the condition of the local water quality and fish. When the chicks are large enough to band, the researchers use a large bucket truck to get up to the nests. They take very small blood and feather samples from the chicks and put them quickly back in their nest. These samples are analyzed in Dr. Langner’s state-of-the-art environmental chemistry lab. The good news is that levels of some of the heavy metals of particular concern in western Montana (arsenic, lead, cadmium, zinc, and copper) occur at very low levels in the Osprey chicks. The bad news is that levels of mercury, a powerful neurotoxin, occurs in very high levels in Osprey chicks in some places. Project Osprey is now focusing on this serious environmental problem.