Fish Crow

by John Shackford

Central Oklahoma may be getting a new nesting species—the Fish Crow (Corvus ossifragus)—through expansion from the east.  Bent, in his life history of Fish Crows (Life Histories of North American Jays, Crows and Titmouse, 1964) says that the Fish Crow is quite similar to the American Crow in its nesting behavior:  they usually nest well above the ground in a wide variety of trees, and normally lay 4 or 5 eggs that are “exactly like other crows except in size”, being slightly smaller than the eggs of the American Crow.  Bent makes the point that Fish Crows are often found in the vicinity of heronries.  Perhaps the birds reported at Overholser will utilize the heronry off NW 10th St., less than a mile from Lake Overholser, when that heronry gets going strong.  So if you should go to check out the heronry this spring, listen also for the call of Fish Crows in the area.

I believe Fish Crows have been reported in Norman at Lake Thunderbird for several years.  On 6 March 2011 (and other dates) Matthew Jung reported hearing and seeing 1 or more Fish Crows at Stinchcomb Wildlife Refuge, and our president Bill Diffin has sent in a carefully worded, probable report of 5 birds he observed on 1 April 2011 on the mudflats at the north end of Lake Overholser:  he heard only Fish-Crow-like calls from the group of birds.  Bill is well aware of the difficulty of making an unqualified identification of Fish Crow; I know because after our last bird meeting he and I had a conversation specifically about the problems of identifying them.

Absolutely confirming the identity of a Fish Crow is, indeed, something of a problem.  First, they are not easily separated by size and other morphology from the American Crow.  According to many authorities, the best way to tell these 2 crow species apart in the field is by voice.  Ken Kaufman (Field Guide to Birds of North America, 2000) says that the Fish Crow is “[s]lightly smaller than American Crow, but recognized with certainty only by sound.”  He gives the voice as “high-pitched, nasal kah-kah, second note lower.”  He goes on to say that it makes other caws, and that “young American Crows also have high-pitched, nasal voices at first.”  It would seem that after a few months the young American Crow’s call would no longer so closely resemble Fish Crow calls; thus most “kah-kahs” heard early in the spring, before nesting American Crow young would have hatched—timing that agrees with Matt’s and Bill’s reports—should be Fish Crows.  But in my conversation with Bill Diffin, he pointed out an additional problem:  we don’t really know all the calls an American Crow can give.  The American Crow can be quite imitative of a wide variety of sounds (including human words), and it is hard to rule out, absolutely, the possibility of an American Crow imitating the call of a Fish Crow.  But the weight of the evidence clearly is tending toward Fish Crows being in central Oklahoma.

Dr. George Sutton, the artist/ornithologist who graced our state for many years, had a similar identification problem in Cimarron County of the Oklahoma Panhandle between the Common Raven and its slightly smaller relative the Chihuahuan Raven:  I believe it is fair to say that there are even more differences between the 2 ravens than between the 2 crows being discussed here.  Doc knew for many years that the Common Raven was in the Black Mesa area, but he never could prove it beyond doubt.  He even had a standing offer, I think of $10 or $20, for anyone in the area who collected a specimen.  Finally Doc collected one himself in 1962, thereby lying to rest what was, no doubt, years of frustration for him in trying to prove absolutely that the Common Raven was indeed an Oklahoma species.  Today proving the identity of a Fish Crow could likely be done through genetic material gathered from a feather, rather than collecting a bird.  In summary, sometimes everybody is right—it just might be hard to prove absolutely!