You might ask, "Where are the photos of females?" (and immature, and fall indivduals). The answer is, a LibGuide is not the equivalent of a good field guide or comprehensive website. This is meant to assist and encourage beginning birders and can't cover everything.
In the bird world, individuals of a species may vary in appearance by age, sex, time of year, etc. In some species, adult males and females look alike to human eyes. In other species, the males and females will look quite different, usually the male being much flashier than the female. This is known as gender dimorphism. Also, immature/juvenile birds may resemble an adult female. Males may become drab in fall and winter when survival is more important than looking good. And there are many other variations: regional, hybridization, diet.
Beginning birders should concentrate on the easier birds, which tend to be either the non-gender-dimorphic type, or adult males in breeding plumage. For images of females, juveniles, fall/winter plumage, regional variants, hybrids, etc., consult All About Birds or a Sibley guide.
This guide is based on a PowerPoint Presentation I gave in 2014 on birding in the Colorado Springs area. The goal is to help CC'ers identify birds they see around town and to get them more interested in the natural world that is all around us, even in the city.
Images: I've used photographic images marked as being reusable via a Creative Commons license or being in the Public Domain. A huge thank-you to all the photographers out there who share their images on the Internet. If you are an image author and want your image removed, please email me at email@example.com