Just a short note to go with the guide below...
Osprey are often confused with Bald Eagle. Osprey are actually only about 2/3 of the size, but size is often difficult to gauge in the field. Osprey also have more brown on the head and tail than an adult Bald, and they have very white and skinny wings. These last field marks can be very helpful when Osprey fly over, especially when you aren't expecting them. I was up at Logan Pass and saw two raptors high overhead and tried to make them into several other species until I finally realized they had skinny wings with lots of white underneath: Osprey. One study looking at osprey diving success in Yellowstone found that they successfully catch a fish almost 50% of the time. Spend time watching Osprey fishing in one of Glacier’s larger lakes and you may witness Bald Eagle harassing osprey for their catch.
Osprey were greatly affected by the use of the pesticide DDT in the 50's and 60's. The link between Osprey nest success and DDT was what led to the creation of the Environmental Defense Fund who were integral in the push for a nationwide ban. The ban was finally established in 1972, and since that time, Osprey populations have increased steadily. Some years, the St. Mary Visitor Center has a webcam set up on an Osprey nest just outside of the center.
Top of page photo by Randy Patrick
David Benson Ph.D.
White-tailed Ptarmigan researcher and National Park Service Ranger Naturalist in GNP since 1995. "The Bird Ranger"