Ian McLaren of Halifax Nova Scotia was coauthor of a paper "Probable Yellow-legged Gull in Nova Scotia", Birder's Journal 4 (1995): 302-304, describing a bird thought to be a Yellow-legged Gull (L. cachinnans michahellis). Since then, however, the record has been criticized and it now appears to be more likely a Herring Gull of the "omissus" type, i.e. a yellow-legged form of the northern European Herring Gull L. argentatus argentatus.
I thank Ian for sending me the photos below and the following opinion of Detlef Gruber:
1. Jizz very atypical for YLGU - which are normally more slender, etc.,
whereas argentatus (including "omissus") are of quite heavier build
than Herring Gulls of the subspecies smithsonianus and argenteus.
2. The head is too round, whereas YLGUs are more often flat crowned, not
"domed" as assumed in the article [above] by Cornell et al.
3. The bill is too short cf. YLGU which have long, thinner bills.
4. The color and extent of the red gonys spot and the light yellow legs
are atypical for Mediterranean YLGU in breeding plumage, which this bird
evidently has, from its lack of head streaking.
5. The subspecies argentatus, unlike argenteus or smithsonianus, has a red
orbital ring and often much darker upperparts, resembling YLGU. (The
Halifax bird, however, did not seem notably darker than accompanying
HEGUs.)
6. The large white tongue visible on the underside of p10 "is never shown"
on L. c. michahellis, "rarely" on L.c. cachinnans, "sometimes" on L.
a. argenteus, but "very often" on L. a. argentatus including omissus.
7. The wing extension beyond the tail is too short for YLGU.
8. The legs are too short. Compare the equal length of tarsus and middle
toe; in YLGU the tarsus is much longer.
