Dec 2, 2020 | Featured in: Watching Backyard Birds, December 2020

Watch for Subtle Dimorphism

Dimorphism means “two forms.” Cardinals are a great example: Adult male cardinals are bright red; females are a warm brown. Photo by Shutterstock.

Don't worry: Sexual dimorphism is G-rated. It means that males and females of a species look different. Dimorphism means "two forms." Cardinals are a great example: Adult male cardinals are bright red; females are a warm brown. Similarly, in house finches and purple finches: Males are various shades of streaky red, raspberry, or orange, while females are streaky brown. Male bluebirds are brighter than their mates, too. Male downy and hairy woodpeckers have red on the back of their head, while their female counterparts do not. Not all birds exhibit sexual dimorphism; the sexes of wrens, jays, chickadees, and titmice, for example, might be obvious to each other, but are not distinguishable to humans.

A pair of eastern bluebirds, female (left) and male (right).

In some birds that visit your feeders, sexual dimorphism is subtle. Male and female nuthatches, for example, aren’t identical. Males are brighter; females duller. The summertime plumage of both male and female American goldfinches is quite distinctive, but in winter, both grow into dull feathers. Still, the male is dull yellowish, while the female is gray. Look closely at robins: Males are a brighter orange on the breast, and the black head contrasts with a gray back. The head and back of female robins are uniformly gray. Just for the record, in a few species of birds, most notably belted kingfisher and the phalaropes—unlikely to visit bird feeders—the females are more colorful than the males!

A female white-breasted nuthatch (left) and male (right). Note the gray cap on the female and the darker cap on the male.

What do you think? Tell us!

comments powered by Disqus

New On This Site

The Latest Comments

  • Thank you for sharing some things to take into consideration when it comes to backyard renovation, this is very timely as I'm planning to turn a portion of my backyard into some sort of patio while maintaining a nice open lawn area as well. I saw some outdoor furniture and outdoor decor on this website and after reading this article, I checked them out again and I found more stuff that I would love to buy for my new patio.
    by Eleonor Baker, Thu, 15 Apr 2021
  • Something is wrong with the Goldfinches in April 2021. I had to stop putting seed in our feeder because the birds seem to have a hard time flying. That attracts our cats, and I do not want to feed the cats. I have actually picked up two birds that seemed to be struggling to fly and tossed one into the air and another on a large pile of leaves. They took off, but they are very lethargic.
    by Beasleyhillman, Sat, 03 Apr 2021
  • How does one attract Calif Scrub Jays?? Due to neighbors outdoor cats most of birds are gone except a fee hummingbirds.
    by Dee Opde, Sun, 21 Mar 2021
  • You are talking about "black oil sunflower seeds" but showing regular striped sunflower seeds. There is a BIG difference! There is MUCH less waste with the black oil seeds. Plus they are easier for small birds to eat. They are both shown here: https://www.horsefeedblog.c...
    by Carolyn King, Sat, 20 Mar 2021
  • How long do other seeds stay fresk? Sunflower seeds? Millet? Safflower?
    by Sue, Sat, 06 Feb 2021