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David Sibley takes a close look at American Avocets

These illustrations show the differences between male and female American Avocets. Art by David Sibley
These illustrations show the differences between male and female American Avocets. The male (left) has a straighter bill, lower forehead, and longer, flatter rear crown; the female has a more curved bill, bulging forehead, and steeper rear crown. Art by David Sibley

I often say that I learn new things every time I go birding and that the opportunities for learning will never end. One of the keys to that is being an “active” observer and asking questions, and for this column, I thought it would be worthwhile to describe my approach and a recent experience. 

On a recent April day in Texas, I was happy to see a close flock of resting American Avocets. I took advantage of the opportunity to think of questions I could ask about American Avocet. The first thing that came to mind was: “What’s up with the few gray-headed birds (non-breeding color) among the many with orange heads (breeding color)?” I have wondered about this variation in the past, and with such close views, now I could confirm that all the gray-headed birds were immatures, less than a year old, while all of the older birds had orange heads. (New info number 1!)

Now that I had identified these few birds as immatures, I wondered, “Does the sexual difference in bill shape apply to all ages equally?” (A female’s bill is more curved, the male’s straighter.) A little scanning and comparison confirmed that even immatures show the distinctive differences in bill shape, just like older birds. (New info number 2!)

While comparing the bill shapes, I came up with another question: “Do adult males and females show differences other than bill shape?” After identifying several males and females by bill shape and then comparing details between them, I concluded that there was no consistent difference in plumage color, size, leg color, and more. (New info number 3!) 

But there was something about the head. Females seemed to have a more bulbous forehead, males more sloped. This was variable and hard to pin down, and I left it at that. Later that evening, I looked at my photos and worked on some drawings, and this process revealed some other differences and a few specific things to look for on my next encounter.

A return visit the next day was more conclusive: Males and females do seem to have different head shapes! The feathers can be raised or lowered, reducing the differences when you’re watching them in the field, but I think there is a real difference. (New info number 4, and an exciting question to ask the next time I see avocets.)

Admittedly, these are all minutiae, but big discoveries happen the same way. Simply asking questions, looking for patterns, and watching carefully can lead to revelations, even in your own backyard. 

This column was published in the July/August 2022 issue of BirdWatching magazine.

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David Sibley

David Sibley

David Sibley writes the column “ID Toolkit” in every issue of BirdWatching. He published the Sibley Guide to Birds in 2000, the Sibley Guide to Bird Life and Behavior in 2001, and Sibley’s Birding Basics in 2002. He is also the author of the Sibley Guide to Trees (2009), the Sibley Guide to Birds-Second Edition (2014), guides to birds of eastern and western North America (2016), and What It’s Like to Be a Bird (2020). He is the recipient of the American Birding Association’s Roger Tory Peterson Award for lifetime achievement in promoting the cause of birding and a recognition award from the National Wildlife Refuge System for his support of bird conservation.

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