Greater White-fronted Geese (GWFG): characteristics of Flavirostris and Gambelli - Part 3
This is a continuation of the earlier blog: http://gwfgmdde.blogspot.com/2017/10/greater-white-fronted-geese_11.htmlAll photos copyright Clive Harris unless otherwise stated.
As has been noted frequently, using bill color to assign GWFG to either flavirostris or gambelli is not straightforward because of variation in bill color, with some gambelli having peach-colored bills or with orange tones. Lighting conditions can change the apparent bill color. Finally there is observer bias to contend with based on our assumptions of what a bill color a bird should have.
The GWFG below has a pale pinkish-orange bill which contrasts strongly with the orange feet. This bird was photographed in Wexford, Ireland, and despite the bill color is certainly a flavirostris. It has the heavy wedge-shaped bill and blocky head typical of that species, uniformly brown appearance, narrow and indistinct upperpart fringes, a very narrow white flank line and black blotching extending well into the white vent.
North American birds can often show orange-toned bills and occur throughout the range of GWFG in the central flyway. The links below provide some examples.
https://ebird.org/ebird/canada/view/checklist?subID=S30570498
http://ebird.org/ebird/wi/view/checklist/S31583089
http://ebird.org/ebird/view/checklist/S34162251
https://www.flickr.com/photos/41782619@N00/16773436980/in/photolist-qrec9K-eaB3ns-rydfrj-eaB3N3
https://macaulaylibrary.org/asset/67052891#_ga=2.36105696.156608651.1504111059-1805810313.1497987670
https://macaulaylibrary.org/asset/67052891#_ga=2.36105696.156608651.1504111059-1805810313.1497987670http://ebird.org/ebird/view/checklist?subID=S40073716
https://ebird.org/ebird/view/checklist/S40287117
Lighting conditions can also affect our perception of bill color. In the left hand photo the GWFG has a bill with orange tones; in the right hand, with no sun, the bill is pale pink and very different in color to the legs.
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Finally our preconceived notions of what bill color should be may also impact our assessment of bill color in the field. When I visited Wexford, local birders informed me that non-birding visitors would tell them the local flavirostris had pink bills, whereas we birders "know" they have orange bills. Kaufmann (Birding, 1994) reports variations in the perception of bill color on specific birds amongst birders. The peach-colored bills or some gambelli might lend themselves easily to being called either pink or orange. The photo below compares GWFG from Korea (albifrons, although appearing more like North American than European birds). On the left hand photo, which is a cropped version of the right, the bills look quite pink. In the uncropped version a very pink-billed bird, top left is in the frame and the other birds suddenly look like they have more orange-toned bills.
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