English and Scientific names:

Slaty-backed Gull (Larus schistisagus)

Number of individuals: 

One, probably 2nd cycle

Locality: LOUISIANA: 

Cameron

Specific Locality:

Holly Beach - west end (1.5 miles east of where road leaves the beach)

Date(s) when observed:

2 May, 2009

Time(s) of day when observed:  

10:30-10:40 a.m.

Reporting observer and address:

Phillip Wallace

New Orleans, LA

Other observers accompanying reporter who also identified the bird(s):

Paul Conover and Curt Sorrells; all of us ID'd it as an odd Great Black-backed Gull. We noted the small size for Great Black-backed and the odd structural features such as bill size, but just assumed it was a runt Great Black-backed. We may have discussed the fact that the mantle color was not as dark as GBGU, but I don't have that in my notes written the evening of the observation.

Other observers who independently identified the bird(s)

None

Light conditions (position of bird in relation to shade and to direction and amount of light):

Good; sun to the left of the line of sight.

Optical equipment: 

Kowa 20x60 scope

Distance to bird(s): 

40-70 m

Duration of observation:

2-3 minutes

Habitat: 

Sandy beach at edge of the gulf

Behavior of bird: 

Resting on the beach; hanging around a dead fish; interacting with 2 Herring Gulls; flying.

Description:

Size - The bird was essentially the same size as the adjacent near-adult and 1st cycle Herring Gulls.

Bill - the bill was fairly long and narrow without a strongly pronounced gonydeal angle. It was bicolored, horn colored on the basal 2/3 and black on the tip. The bill appears to have a dark streak along the cutting edge of the lower mandible.

Legs - The legs were bright pink in color. They show in the photos and video as relatively thin and short, certainly thinner than is typical for Great Black-backed.

Eye - The eyes were clear whitish-yellow and appear to show no dark flecking in the photos.

Head and Face Pattern - At certain angles in the photos and video the forehead seems to approach the bill at a slightly steeper angle than the adjacent Herring Gull. There is dark feathering around the eye and a dark eyeline caused by the feathering. In some shots the nape seems to show the terra cotta flecking characteristic of Slaty-backed Gulls in basic plumage.

Mantle - The mantle color shows as slate gray, clearly lighter than is typical for Great Black-backed.

Spread Wings
A. Dorsal side - The upper side of the spread wings shows as primarily dark brown with some slate gray coloring like the mantle color. The broad white trailing edge of the wing, especially in the secondaries, is conspicuous in the photos and video. Although feather wear and the age of the feathers make it difficult to be sure, it appears in some of Conover's photos that P8 (maybe P7) has the pale gray tongue and white tip that is reputed to be diagnostic for Slaty-backed. Also in some of the video, the upper wing appears to show the string of pearls characteristic of later cyles for Slaty-backed.
B. Under side - The underwing is basically white with some brownish flecking in the wing linings. The dark coloration of the primaries on the upper wing is muted on the under side.

Folded Wing - On the folded wing, the coverts appear brown and very worn with some newer gray feathers showing. The broad white skirt (trailing edge of the secondaries) is apparent. The folded primaries are dark brown with no apparent apical spots, indicating a 2nd cycle bird.

Underparts - The breast and belly are basically white with a hint of pale brown or terra cotta flecking.

Tail - The basal portion of the tail, along with the uppertail coverts and rump, is white. The distal part of the tail is dark brown or black, becoming paler as it blends into the white proximal part of the tail.

Voice:

None

Similar species:

Great Black-backed Gull - Although we intially thought it was an aberrant or runt Great Black-backed until Conover analyzed his photos and raised the possibility of Slaty-backed, the mantle color is not dark enough for a Great Black-backed. Moreover, it's too small for a Great Black-backed and the bill size and shape are wrong for that species.

 

Western Gull - Facial pattern, especially around the eye favors Slaty-backed over Western. The mantle color favors Slaty-backed, but I'm not sure one could eliminate L.o. wymani on mantle color alone. Bill shape is better for Slaty-backed.

 

Great Black-backed x Herring Gull - I'm not sure how to eliminate this hybrid on plumage features, but I would assume that a hybrid with this parentage would be larger, with a more massive bill.

Photographs or tape recordings obtained?

Outstanding photos by Conover have already been submitted. Stills from video by Wallace accompany this report. Video by Wallace submitted to LBRC.

Previous experience with this species: 

I've seen once on a trip to Alaska with Sorrells, but that experience didn't help a great deal with this report.

Identification aids:

GULLS, Howell and Dunn;
"Slaty-backed Gull Winters on the Mississipi River," Goetz, Rudden, Snetsinger. American Birds, Vol. 40, No. 2 (1986);
"Adult Slaty-backed Gulls: Variability in Mantle Color and Comments on Identification," Gustafson and Peterjohn. Birding, Vol. XXVI, No. 4 (1994);
Various photos with discussion on the internet, especiallyhttp://www.coastside.net/chucao/gulls/Slatyback.htm

This description is written from: 

Notes made the evening of the observation and primarily from Conover's photos and my video.

Are you positive of your identification? If not, explain: 

 

I'm as positive as I can be about a Slaty-backed Gull in this plumage. I'm convinced that it's not a Great Black-backed or any other likely species in Louisiana. I will defer to the gull experts on the possibility of a hybrid or something more exotic.

Date and time: 

11:00 a.m. 21 June, 2009