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.
Please visit www.DunrovinOsprey.net to view the live osprey cam at Dunrovin Guest Ranch and to learn more about the daily activities at the ranch.
About the Dunrovin Osprey Nest
These Ospreys are nesting amid the hustle and bustle of Dunrovin Guest Ranch in Lolo, Montana. During the past 10 years they have fledged 1–3 young per year, first on a telephone pole and now on a new platform and pole installed by Northwestern Energy in 2011. Neither of the adults is banded, but they are thought to be the same pair given their easy habituation to daily ranch activities. If you look carefully, you can probably tell the male from the female by her more heavily streaked chest. Ospreys are consummate fishing birds, and this pair fishes both from a nearby reservoir as well as the Bitterroot River. They use their 6-7 foot long wings 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.
About Project Osprey
For the past five years, Dr. Erick Greene and Dr. Heiko Langner from the University of Montana, and Rob Domenech from the Raptor View Research Institute, have studied Ospreys in western Montana, including these birds at Dunrovin Guest Ranch. They’re learning about the health of local rivers by studying what the Ospreys bring back to the nest and feed their chicks. For this research they are employing a number of video cameras on Osprey nests, two of which are viewable on the Bird Cams website. They recently received a grant from the Natural Resource Damage Program to continue public education and research involving the local Ospreys. 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. Researchers plan to band and collect small feather and blood samples from the nestlings before they fledge. 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. Every summer when the chicks are big enough, the researchers band the chicks, take very small blood and feather samples. These samples are analyzed for environmental toxins in Dr. Heiko Langner’s lab. The good news is that levels of some heavy metals of particular concern (lead, arsenic, cadmium, lead and zinc) occur at very low levels in Osprey chicks in western Montana. The bad news is that we have found that levels of mercury, a powerful neurotoxin, is at extremely high levels in Osprey chicks in some places. Fortunately, the chicks in this Dunrovin nest have had low levels of mercury for the past five years. We have discovered that about 20 miles away, Opsreys living along the Clark Fork River have unacceptably high levels of mercury. Their research is now focusing on this serious environmental problem.
About Dunrovin Guest Ranch
The mission of Dunrovin Guest Ranch is to enrich lives by providing unique and educational experiences which promote individual learning and cultivate a connection with nature through the lens of the outdoors, the arts, and partnership with the animal world—particularly horses. The owners, SuzAnne and Sterling Miller, consider the Ospreys an integral part of their ranch, engaging their family as well as the surrounding community. They hope that hosting this live cam will create an even greater community of people interested in learning about these incredible birds and further deepen that connection with the natural world.