Great Black Hawk vs. Common Black Hawk (1 Viewer)

[rdavis]

Niels has suggested to me that the "Great Black Hawk" (GBH) I recently posted on the Bird Forum Gallery is probably a Common Black Hawk (CBH). As I do not have a good estimate of the size of the bird (it was roughly between ~1/3 and ~1/2 m), I lack the information for making the distinction based on size. A local and well respected bird guide in the Cabo Matapalo area of the Osa Peninsula in Costa Rica where I took the photo called the bird a GBH, but he could have been mistaken. Subsequently, I tried to confirm the ID. It lacks the dark slaty lores included in ID info in the Garrigues & Dean(G&D) "The Birds of Costa Rica," but does have lightly barred thighs (pointed out for GBH by G&D). There may be considerable variation in the lores color, either related to bird age and/or geographic variation. Please see my posting, and give me your opinion on the ID of this bird. You can find the posting by using the search function of the Bird Forum Gallery, and searching under my user name, rdavis.

Thanks,

Ron

 

[rockfowl]

This one - http://www.birdforum.net/gallery/showphoto.php/photo/306431/ppuser/83570

I also think Common Black Hawk, leg length seems short, very bright yellow bare skin, long primary/wing length compared with GBH. Great image though!

 

[njlarsen]

I better come with the arguments that I made, and then leave it up to the experts!

I am mainly going by the info in Ridgely and Gwynne on this one, according to which Great BH from western Panama and north of there (subspecies ridgwayi) should:
Have lores slaty
Have two black bands in tail, and the distal one therefore narrower than in Common BH; if the drawing in the book is correct, then the width of this black band fits better with CBH.
Please notice that these characters all differ from the Great Black Hawk I know from Tobago, but it did fit with one bird I saw in Panama when I visited there, and ridgwayi should be the form in Costa Rica.

Counter to this should be white feather rims on the thighs. I have been convinced by Dave B Smith that this is not a good character due to a bird showing those, that we saw in Trinidad, being id'ed as a Common BH (and I hope that the common BH has less geographic variation; no subspecies are recognized).

Niels

 

[Birdingcraft]

For me, this is a Common Black Hawk. Although this bird shows faint barring on the thighs, the barring shown Great Black Hawk is much more prominent.

As was mentioned by Rockfowl and Niels, Great Black Hawk also has a longer tail (wings don't reach the tip like this bird shows) and two black bands on the tail. Although the slaty lores of GBH arent always obvious, this bird appears to show yellowish lores.

Another point for Common BH is if you took this picture on or close to the beach. Common Black Hawks in Costa Rica are almost always found near the coast while Great BH is a forest bird (and has become much less frequent in CR IMO).

 

[rdavis]

I'm changing ID on the hawk posting in gallery

Much thanks for all your comments. You've convinced me that I was mistaken in posting the photo as a Great Black Hawk. A soon as I send this, I'm going to the Gallery to change the ID to a Common Black Hawk.

I trust that with this decision the Forum "thread" on this issue comes to an end.

Ron