Bald eagle at Valmont Reservoir

Winter Raptor Surveys: 1983 - present

Since 1983 Boulder County Nature Association (BCNA) volunteers have counted wintering raptors along survey routes scattered throughout the plains of Boulder County, Colorado. We initiated the surveys during a time when intensified poisoning efforts by private landowners and government agencies appeared to threaten prairie dog populations in parts of Boulder County. Some of these poisonings were occurring in the Boulder Reservoir area, where Ferruginous Hawks, Red-Tailed Hawks, and Bald Eagles gathered each winter. We wanted to observe the effects of fluctuating prairie dog populations on these and other species. We also hoped to locate wintering raptor concentration areas, such as Bald Eagle roosts, Northern Harrier roosts and large prairie dog colonies, so that these areas could be protected.

Raptor Survey Maps and Forms

Maps and transect report forms are available here for volunteers participating in BCNA's wintering raptor survey.  They can be printed using the free Adobe Acrobat Reader. If you are unable to print your own and would like us to mail a map or form to you, contact us.

Raptor Survey Report Form - Fill out one form for each trip.

Maps are portions of the actual USGS quads.

New maps for 2014 are all high-resolution PDFs, with one page for the map and a second with a 500-m grid with numeric label.

Research data and reports

Wintering Raptor Survey Protocol

1. In teams of 2 to 4 observers per vehicle, drive your assigned route five times (once each month for the five (5) month season) between 15 October and 15 March on calm (constant wind velocity less than 25 km/hr or 15 mph) mornings or afternoons. You are within your rights to monitor from the public right of way. If you are approached by a property owner in a confrontational manner, politely state your right to monitor from the public right of way and withdraw. If you feel threatened, call the Boulder County Sherriff's dispatcher at 303-441-4444.

2. Drive at a constant rate of 40 km/hr (25 mph), stopping only when you see a perched or flying raptor with your naked eye. Maintain 25 mph speed and stop or pull over only when it is safe to do so. If your route has an out-and-back or in-and-out section (Stearns Lake, Boulder Reservoir, North Rabbit Mountain), enter raptors seen driving only in one direction.

3. Stop to identify the raptor and any other raptors you can see from that point with your naked eye. Do not scan trees with binoculars or scopes.

4. Mark initial sighting location (where the raptor was when you first saw it) of each raptor on a topographic map (500m grid) of the route you are surveying. Use the raptor codes on the BCNA Wintering Raptor Survey Report Form to indicate the species. If you are not sure of a species' identification, use the UNEA, UNFA, UNBU, or UNRA codes.

5. Complete a survey report form, including the total number of all species observed and the name of each participating monitor, and attach it to the map. Use a separate map and survey report form for each trip and each route. Enter the survey date on the margin of the map. Retain the paper maps and report forms until the end of the season or you are advised to do otherwise.

6. Promptly after each survey, enter your data electronically at: If you have questions or concerns contact Sue Cass,, 720-684-6922 (home) or 303-641-4809 (cell).

Additional maps and report forms are available at the BCNA website:

Revised, September, 2014