We stopped at the West Horseshoe Park overlook in Rocky Mountain National Park to look at the breathtaking scenery. We saw several Red Crossbills perched in a conifer tree. Upon closer examination, we located where they were nesting in rocks near the side of the bridge walkway. It is currently thought that there are nine discrete populations of Red Crossbill (which may each be a separate species). Bill size varies with population and within population (depending on wear). See the Living Bird (Cornell Lab of Ornithology, Spring, 2009) article "An enigma, wrapped in a riddle, inside a pine cone?" by Jack Connor for further information. It was a partly cloudy morning with temperatures in the mid-60's.