Unidentifiable Females

Don't worry, I'm talking about birds, not humans!  Twice in the last couple of weeks I've seen a bird by the feeder that I wasn't able to identify - until I saw the male bird and then was able to put two and two together.  Two great examples of sexual dimorphism (the systematic difference in form between individuals of different sex in the same species).  The first instance was when I saw a bird that looked like a mutant song sparrow, but a lot darker in color and no central spot on the breast.

At first I thought it was another type of sparrow, but couldn't find a picture of one that looked similar.  I saw it several times at the feeder before I saw the male bird - a red-winged blackbird!  Then I was able to make a positive ID.  Here are better pictures of both birds courtesy of Wikipedia.

Male red-winged blackbird  by Walter Siegmund

Female red-winged blackbird

In the second case, I kept seeing a rather nondescript grayish, brownish bird with no distinguishable markings.  I saw it several times as well before I saw the male - a brown-headed cowbird.

Female brown-headed cowbird By Lee Karney

Male brown-headed cowbird

Cardinals are also examples of sexual dimorphism, although to me it's not quite as extreme and the above illustrations.

Female Northern Cardinal by Geoff Clarke

Male Northern Cardinal by Whaledad

Identifying birds is hard enough without having to remember that the male and female look totally different!