Northern Mockingbird by Christian Goers

What makes a rare bird rare?

(published 4-12-17)

Sharing good news is a natural human instinct. When I’m excited about a bird sighting, I’ll sometimes tell the nearest bystander, birder or not. The reactions I get are interesting.

Strange looks and quick walkaways are normal. But another common response is the person asking, “Was it rare?” And sometimes that’s an excellent question.

Like the colorful spring warblers now upon us, the notion of avian rarity deserves a closer look.

Defining “rare” seems simple on paper. The American Birding Association (ABA) assigns a number to every North American species. Every bird is rated from 1 (easily observed in its normal geographic range) to 6 (no chance). Some Code 1 examples are blue jay, cardinal, chickadee and robin, along with less common visitors like yellow-throated vireo, prairie warbler and Lincoln’s sparrow.  

Species rated “6” are presumed extinct, exist only in captivity or have no self-sustaining population in the wild. Want a Code 6 for your life list? You’ll need to find that ivory-billed woodpecker.

Most birds are Code 1 or Code 2: “Regularly occurring North American avifauna.” Code 3 species are officially “Rare,” since they occur in very low numbers—spotted just a handful of times in a year.

Code 4 is “Casual” and Code 5 is “Accidental.” Avid birders sometimes use the term “mega” for these ones, as in mega-rarity. Some lucky Illinois watchers scored a mega in 2016 when a black-tailed gull (Code 4) visited downstate Carlyle Lake.  

The ABA system doesn’t measure rarity, per se. It rates difficulty of observation within the defined ABA listing area. There is a difference.

Everyone agrees that the whooping crane is a rare species; fewer than 500 exist in the wild. But it’s a Code 2 bird because seeing a whooper is easy if you visit the right place at the right time.

Likewise, Kirtland’s warbler, “America’s rarest warbler,” is ABA Code 2 since you can readily find one with a good map. (Hint: Go Blue!)

Almost every bird we encounter locally is Code 1. “Rare” birds just don’t come around much. That’s what makes them rare! But rare sightings happen all the time, and usually they involve common birds gone astray.

A northern mockingbird in DuPage County is notable, and many birders (including me) would jump at the chance to witness one. Triple that jump for a scissor-tailed flycatcher. In the South, these birds are as common as cotton. Here they are rock stars.

Vagrant birds are always cause for excitement. Anybody recall the sage thrasher at Montrose? The nine black-bellied whistling ducks in Yorkville? Or the varied thrush at Morton Arboretum? I dare you not to call them rare.

Common but out-of-season birds can be rarities too, such as a “winter bird” that appears in the dog days of summer. In August 2014, a dark-eyed junco turned up in downtown Chicago! That’s rare.

The DuPage Birding Club offers a handy checklist showing the relative abundance of our local birds, season by season. It’s an excellent reference for knowing what birds to expect and when. For example, the line on Killdeer is F in early spring (meaning fairly common), C (common) in late spring through early fall, U (uncommon) in late fall and X (extremely rare) in winter.

X-rated birds are a lot of fun. We had one on the Christmas Bird Count in 2015, a Nashville warbler. The chances of it being here in December, let alone our stumbling upon it, were thinner than a rail on a crash diet.

But here’s the real skinny: You decide what’s rare. The rarity is in the experience, and it’s personal. What’s “rare” may depend on who you are, the time of year and where you happen to be standing.

Oh, it’s personal all right. Until I see one, worm-eating warbler is absolutely the rarest bird on earth.      

Lastly, a travel note: I’m off to the Indiana Dunes Birding Festival May 4-7 and promise to report back.  Maybe you should go, too: check out I don’t know if we’ll see any rare birds but the spring migration weekend is sure to be mega fun.  

Copyright 2017 by Jeff Reiter. All rights reserved.