|
English
and Scientific names: |
Great
Black-backed Gull (Larus marinus)
|
|
Number
of individuals: |
1 - 3rd cycle |
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Locality:
LOUISIANA: |
Jefferson Parish |
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Specific
Locality: |
Grand Isle State Park, at the pass between Grand Isle and Isle Grande Terre |
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Date(s)
when observed: |
6 April 2007 |
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Time(s)
of day when observed: |
1400 |
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Reporting
observer and address: |
Erik I. Johnson Louisiana State University |
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Other observers
accompanying reporter who also identified the bird(s): |
Ceci Johnson |
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Other observers who
independently identified the bird(s) |
none |
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Light conditions
(position of bird in relation to shade and to direction and amount of light): |
I was south/southwest of the bird the entire time observing it. I therefore had good light on the bird, as it was early afternoon and sunny. |
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Optical
equipment: |
Swarovski EL 10x42 |
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Distance
to bird(s): |
a couple hundred meters |
|
Duration
of observation: |
30 min, while observing other birds |
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Habitat:
|
coastal waters |
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Behavior
of bird: |
The bird was first observed flying mixed with Herring, Ring-billed, and Laughing Gulls, Northern Gannets, Brown Pelicans, Forster's, Royal, Caspian, and Sandwich Terns, and Double-crested Cormorants. It would occasionally alight on the water to grab food. Within the 30 minutes watching this foraging group, the GBBG was seen resting on the water with some of the other species mentioned. |
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Description: |
When flying, the dark back and white head made it stand out from the other gulls. After watching it a few minutes, it was clearly larger than the many Herring Gulls (adult and juvenile plumaged) with it. The shade of the back was charcoal gray - nearly black, but the wing tips were darker. The "consistency" of the black back was not uniform; there were slightly paler/browner areas, especially on the wing feathers. The windows in the primaries could not be seen from this distance. There was a distinct white border along tips of the secondaries and inner primaries. The tail was completely white. When it was resting, it was doing so next to an adult plumaged Herring Gull. Again, it was clearly larger, perhaps 25% larger in bulk. The bill was also more massive. I could make out that it was yellow with black near the tip, similar to a Ring-billed Gull. The upper mandible appeared to have a narrower band of black than the lower mandible. Eye color and leg color could not be determined from this distance |
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Voice: |
none heard |
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Similar species: |
Clearly not any of the lighter-backed gulls (i.e. Herring, Ring-billed, etc) by back color. Size alone, especially with long, deliberated looks comparing the size to other birds including Herring, Ring-billed and Laughing Gulls was sufficient to eliminate other dark-backed gulls including Lesser Black-backed, Western, and Kelp. Yellow-footed Gulls in subadult plumage should have a dark band at the tip of the tail...an adult YFGU, although lacking the tail band should not retain a dark tip to the bill. This species should be even less likely than GBBG, but was considered while watching the subject bird. |
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Photographs or tape
recordings obtained? |
none |
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Previous experience with
this species: |
Lived in Massachusetts and worked on a beach monitoring endangered nesting birds from 2001-2003, thus am very familiar with GBBG in various plumages. I have limited experience with things like LBBG and WEGU and no field experience with YFGU and Kelp Gull. |
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Identification
aids: |
at time of observation: Searching the internet for images and descriptions of Kelp
Gull and other dark backed gulls the next day (did not have internet access
until then). |
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This
description is written from: |
Notes from time of observation. |
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Are you positive of your
identification? If not, explain: |
Nearly. Gulls are not exactly an easy group to identify and I certainly struggle with juvenile plumages. However, most typical adult or near adult plumages are relatively straight-forward and a dark-backed bird has only a few possibilities. Given the size of this bird compared to others, I can't imagine what else it could be, so I am nearly certain of this identification. If I had seen this bird in Massachusetts, I would not hesitate with the ID. |
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Reporter:
|
Erik I. Johnson
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Date
and time: |
9 April 2007, 0900 |