Updated: Sep 10, 2020
Do you hate identifying gulls? Join the flock...
I would not enjoy the results of surveying how birders deal with identifying gulls. I would bet a life bird or two, that many birders guess, skip, or lump a majority of the Larus gulls they see. If you do not know what a Larus gull is, do not fret. Not everyone can be a "Larophile..."
Larus, Larus, Leucophaeus
Larus is the genus of the majority of the larger, white-head gulls. The failed attempt at a "duck, duck, goose" joke in the title of this section includes a second genus from another common gull in much of North America, the Franklin's Gull. While I will not use Larus extensively in this post, you should expect to see me refer to white-headed gulls with the colloquial "Larry's". I get so much joy from shouting, "Whoa! That is one giant flocking group of Larry's!"
We have two main species of Larry in the Rockies, the Ring-billed Gull (the dumpster Larry) and the California Gull (the hipster Larry). Now, sit back and enjoy my ramblings, as I attempt to focus my energies on providing identification tips on these two common interior Larry's.
Identification of Ring-billed Gull vs California Gull
There are 5 "obvious" keys to look for when separating the Ring-billed Gull (RBGU) from the California Gull (CAGU):
These 5 areas can lead to an "easy" Larry identification, but only for adult birds. Do not cuss me yet, I will get into the younger birds (aka Dirty Larry's) in a later post. Let's get started.
The eyes of an adult RBGU have a light-colored iris, year-round. This contrasts greatly with the dark iris of the CAGU. This rule is usually steadfast for older birds, though there are always exceptions...
Color can be a tough identification key for some folks. What I call yellow-green and what you call yellow-green can be two very different colors. However, I cannot help if you have a refined color-pallette. Get down to my level. The Larry level. Let's talk legs, Larry's legs:
Basic Plumage (nonbreeding)
RBGU - yellow to yellowish
CAGU - greenish blue to blueish
Alternate Plumage (breeding)
RBGU - yellowish orange to yellow
CAGU - yellowish
The leg color of a CAGU is almost always "off." The legs are never quite an obvious color, with an almost greenish hue, all year. The leg color of the RBGU is what most would describe as yellow. During the breeding season, they can have a bit of orangey to them, but they are still vibrantly yellow.
This is a tougher tip to teach. Unless you have wonderful lighting, close views, and an eye for subtle contrasts, the color of the "back" feathers on Larry's is no easy tell-tale. However, if the planets align, you might notice the RBGU has a paler mantle color than the CAGU. How much is that difference? Well, if you were to use Munsell Values, where black=1 and white=10, the RBGU is about a 6.5, and the CAGU is closer to a 5. Helpful, right? Next time you are in the field, just whip out your Munsell grayscale fan deck and hold it right up to the bird... You get the point, RBGU=lighter Larry and CAGU=darker Larry.
The CAGU has a larger bill than the RBGU, but that is not helpful unless you can directly compare the two! Or perhaps you have spent countless hours gazing into the gonydeal spot of these lovely Larry's and have their bill sizes memorized. You CAN, however, use the coloration on the bill to separate these grayish ghouls. The RBGU and CAGU both have black markings near the tip of the bill, but... the adult CAGU also has an obvious RED mark proximal to the black mark. Woo hoo! Bingo! But, you have to be close enough to see this mark, and you can forget using it if we are looking at young birds.
There is one more tip I can provide for this feathery puzzle. When these birds have "fresh" or "new" flight feathers, the CAGU often shows far more white at the tips of its primaries. While not always reliable (depending on the progression of molt), this feature can be useful when the birds return to mall parking lots across the Rocky Mountains, at the beginning of spring.
Let's Practice with our Larry's!
Quiz answers are at the bottom of the post.
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1) Eleven RBGU (the 11th is on the far right), 2) RBGU, 3) RBGU in the front, CAGU in the rear 4) Front to back: CAGU, CAGU, RBGU, CAGU