Cachinans Gull records

Published on 01 July 2000

BBRC is aware that this form is being reported with increasing frequency in Britain though as yet is has not been formally admitted to the British List. This would require a record or records to be accepted by both BBRC and BOURC. We are aware that various individuals have been well documented (e.g. Garner et al 1997) and some have now been formally submitted. The acceptance of some of these may be expected to follow shortly.

The species appears to be rare but regular in small numbers, especially in East Anglia and the Midlands, but its true status is clouded by a lack of thoroughly documented and reviewed records. While it may be overlooked, it is also true that its abundance could be exaggerated by optimistic claims. We are also aware that the identification of the form can be more complex and difficult to prove than some recent articles have implied. For example hybridisation with Herring Gulls (Larus argentatus) has been reported in Germany.

BBRC would like to receive well-documented sightings from before 1st Jan. 2000 to place it on the British List and establish a baseline of well-documented records. The following guidelines are intended to encourage observers to make the high quality submissions needed to prove the identification of this form:

General – Birds should have been well seen and watched over long periods, preferably by experienced observers who are regular gull watchers, familiar with their local ‘large white-headed gulls’ and with ‘Western Yellow-legged Gull’ Larus (cachinnans) michahellis and ‘Northern Herring Gull’ L. argentatus argentatus. Subtle elements of size and structure are important features, as with other large gulls, and these are best appreciated by those fully familiar with variation in the commoner species. Even for experienced observers these features may be difficult to adequately get down on paper though they may nonetheless produce a distinctive ‘feel’ to the bird. For this reason it would be preferable for good quality photographs or video footage to accompany submissions.

The exact stage of moult should be noted.

Records of birds at reservoir roosts are unlikely to be accepted as the full range of structural and bare parts features are rarely apparent under such circumstances. These are subtle birds, which need to be watched at close range if possible!

Adults – It must be clear that the bird is fully adult (primary patterns of sub-adults are not diagnostic). The precise pattern of the primaries needs to be clearly established including that of the underside of p10. This may be difficult to observe, even in bathing and preening birds, but can be captured on film or video.

When comparing mantle colour with other taxa be aware of the effects of strong light and the angle of the birds in relation to the light source and the observer. For a fuller discussion of generic problems of large gull identification see Garner (1997). Bill, leg eye and, ideally eye-ring (the latter usually very hard to see) colours should be established and the extent and nature of any head or neck streaking accurately described.

[If the bird is observed long-calling the posture adopted should be noted (this can also give a chance to observe the elusive p10 pattern). The call itself should be noted.]

Juveniles and first winters – As well as vital structural features it is important to note: the colour of the head and body including the precise pattern and distribution of any streaking or barring; the pattern of the scapulars (note any second generation feathers), coverts (paying particular attention to the greater coverts) and tertials, the pattern of the underwing and upperwing, rump and tail pattern.

Other ages, from first summers through to sub-adults, are the most problematic. The diagnostic plumage features shown by adults (notably the precise primary pattern) and juveniles/first-winter birds can not be used. Identification must be largely based on less solid features. Structural features are critical and in order to correctly judge these photographs or video footage would be almost essential (though an exceptionally good set of notes could suffice).
Only classic birds are likely to be accepted.