There are many variations in birds and even some significant variations within the same species. Males can look much different than females. Immature birds can look different from adults, and some birds can look much different in winter than in summer.
In some species, such as buntings, the male and female look very different. This is called sexual dimorphism. Recent studies have shown that these differences have evolved with migration, in which bird species leave their winter territory and travel varied distances to establish a summer nesting territory. Some bird migrations can be thousands of miles. The majority of migratory bird species have significant coloration differences between males and females, while the majority of nonmigratory birds, or birds that stay together in a small territory year round, do not. Male feather coloration is vital in attracting a mate in many migratory species. Migratory males usually arrive before the females to set up a nesting territory. When the female arrives, she chooses a mate with the brightest plumage. The female’s drab plumage allows her to spend valuable energy on egg development and raising the young instead of on growing more colorful feathers like her male counterpart.
In most species, males and females are close in size, with the male being a bit larger. Hawks, owls and hummingbirds are the exception, with the female being significantly larger. It is not known why the female is larger in these particular species. One guess is that it’s because the female does most of the incubating of the eggs and the larger body size helps keep the eggs covered and warm.
The European starling’s winter plumage can be quite different from breeding plumage. The adult winter plumage is blackish overall, with small white spots on the body and a dark bill. In spring, the adult breeding plumage changes to a shiny greenish-black appearance overall with a yellow bill.
Some male and female bird species are identical in appearance. In this instance, behaviors may be the best way to distinguish the sexes. The Canada goose male and female look identical, but the slightly larger male tends to stand taller, at the ready to defend the nesting territory and young. Behavior also helps to identify young birds. Young birds often reach adult size a few weeks after hatching. Their slightly uncoordinated behaviors and disheveled appearance more give them away.
Now is the time in New Mexico to watch for fall migrants moving through your backyard.
Mary Schmauss is the owner of Wild Birds Unlimited in Albuquerque. A lifelong birder and author of “For the Birds: A Month-by-Month Guide to Attracting Birds to our Backyard.”