It’s a Bird, It’s a Plane…

Red-tailed Hawk_ElPasoCo_LAH_9836r

I thumbed through the field guide. Let’s see… a Red-tailed Hawk is 19 inches, head to tail, with a wingspan of 49 inches. A Rough-legged Hawk is a couple of inches longer, 21 inches tall with a 53 inch wingspan. And a Ferruginous Hawk is larger still, 23 inches tall and 56 inches across.  Or, it could be a Northern Harrier, checking in at 18 inches by 43 inches. So which hawk was it sitting on that pole, silhouetted against the sky? I was glad that there were only a few real options in eastern Colorado at this time of year.  I flipped the page to a Golden Eagle, 30 inches in height, wingspan of 79 inches. No, surely I’d be able to tell if the bird was that large! It had to be a hawk.

The problem is that I couldn’t see any markings, with the bird backlit by the sun rising  in front of me. Looking for other clues, I considered the shape of the head—not an owl-like harrier. I could barely make out the legs—not  feathered, plus the feet were pretty large—so it wasn’t a “Roughie” either.  That left the smaller Red-tail and the substantially larger Ferruginous. And there I got stuck. I just couldn’t estimate the size of the bird.

I have a terrible time trying to figure out the size of the birds I see. I know part of the problem is that I’m bad at estimating sizes in general, but it’s not all me. There’s an issue with the way our brains are programmed.  Have you ever been out birding, ready to call a sighting of a soaring bird, only to suddenly realize that it’s an airplane, much farther—and much bigger—than you’d initially assumed? The fact is, with no frame of reference, we really can’t tell the difference between near small, and far and big.

Later that day, I viewed the morning’s photos and realized that maybe it wasn’t too late to identify the hawk. I just had to apply some helpful tips I’d heard over the years.

Red-tailed Hawk on windmill

First, and most useful in this case, I could compare the size of the bird to the size of a nearby object. The hawk was perched on a utility pole. These poles vary in sizes, depending on what type of wire they support. Typically, a telephone pole, the kind made from a tall, straight (often cedar) log, runs about eight to nine inches in diameter. (Anyone know how large these windmill blades are?)

Red-Tailed Hawk with prey_E of I-25 - CO_LAH_0064You can also compare your bird to a fence post, which is easily measured in the field, or perhaps your backyard bird feeders. Typically, though, it’s the distant birds that cause us the most difficulty.

If you’re looking at more than one bird, you can compare their respective sizes with one another. This approach is extra helpful when viewing flocks of gulls and terns, ducks, sandpipers, or even mixed flocks of sparrows. In these examples, the the Willets are larger than the sandpiper in the middle, the Hooded Merganser on the left is much smaller than the Common Mergansers, and the Heerman’s Gulls are significantly smaller than the Western Gulls on their right:

If you can identify one of the birds, you can easily look up how big it is, and get a good guess on the size of the other birds.

It’s also helpful to estimate size based on a comparison to a bird that is very familiar. The American Robin, at ten inches in length, is probably the most common choice. When it comes to waterfowl, a mallard provides a good standard. While many ducks are a few inches shorter in length, teals, Buffleheads, and Ruddy Ducks are much shorter. On the other hand, Common Mergansers run a tad longer. Even I can see the difference.

Estimating the size of birds takes patience and practice. In the meantime, don’t feel bad if you mis-identify that Southwest Airlines plane as a Red-tailed Hawk. We’ve all done it.


The answer to last week’s quiz is American Tree Sparrow.

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