Larus cachinnans

(last update: February 16, 2013)

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sub-adult cachinnans: August

In 2011, Chris Gibbins, Grzegorz Neubauer and Brian Small published two extensive papers in Britsih Birds, dealing with Caspian Gull. Below, you will find the content of the second paper "phenotypic variability and the field characteristics of hybrids".

The full title reads: From the Rarities Committee's files - Identification of Caspian Gull. Part 2: phenotypic variability and the field characteristics of hybrids, by Chris Gibbins, Grzegorz Neubauer and Brian Small, IN: BB 104/2011. ORDER PAPER COPY!

"we" in the text below refers to the original authors. If any errors occur in this text, please let me know and mail to marsmuusseatgmaildotcom.

PART 1: ABSTRACT & INTRODUCTION
PART 2: APPROACH
PART 3: ADULT BIRDS AND FIRST WINTER BIRDS
PART 4: DATA ANALYSIS
PART 5: VARIABILITY IN PLUMAGE (OF ADULTS)
PART 6: IDENTIFICATION OF FIRST WINTER BIRDS
PART 7: VARIABILITY IN EXTENT OF POST-JUVENILE MOULT

BELOW: PART 8 OF THE PAPER: UNDERWING PATTERN

Identification of Caspian Gull. Part 2: phenotypic variability and the field characteristics of hybrids

Larus cachinnans 1CY PDNZ July 25 2010, Simrishamn, Sweden. Picture: Jörgen Bernsmo.	Larus cachinnans 1CY PKTE Augustus 17 2012, Simrishamn, Sweden. Picture: Jörgen Bernsmo.
Larus cachinnans 1CY PUKZ August 18 2010, Lubna, Poland. Picture: Michal Rycak.	Larus cachinnans 1CY P521 September 21 2012, Simrishamn, Sweden. Picture: Jörgen Bernsmo.

Underwing pattern

Plate 432 (p. 734 in BB article) shows the underwing of a selection of Caspian Gulls. The birds were all photographed in either September or October of their first calendar-year and were selected to illustrate the continuum of underwing markings. The page on this website shows underwings of ringed birds.

The most typical impression of Caspian is an underwing which is paler overall than that of Herring (or Yellow-legged) Gull. The ground colour is silvery-white, and this is overlain with a degree of brown barring and mottling. In many birds, the median underwing-coverts are paler (less well marked) than the rest, and this gives rise to a pale band across the underwing; on some birds there is also a similar band across the lesser underwing-coverts. Consequently, on the medium and darker Caspian Gulls, the pattern is rather contrasting and so can be similar to the banding seen on some Yellow-legged Gulls. While the underwing of Herring Gull varies in overall darkness, the key point is that it is much more uniform, with little contrast between the darker and paler feathers. On Caspian Gull the long rear axillaries are often (but not always) the most strongly marked part of the underwing, although the actual pattern varies: some birds have heart-shaped spots, others coarse barring and some fine barring on the axillaries. The wing fold line along the upper flank is often contrastingly pale.

PUSZ is the darkest example we have of a proven Caspian Gull (it was ringed as a chick in Ukraine). The brown on the underwing of such birds is very cold and dark in tone and the barring is very dense, producing an underwing that is at least as dark as typically seen on Yellow-legged Gull. If seen in Britain, such birds would most likely cause considerable debate. Notice that on some birds the dark markings are coarse and sit over a pale ground colour, while on others the feathers have a buffy-brown ground tone with paler stippling over this (i.e. the reverse pattern). Thus, while the paler Caspian Gulls separate clearly from Herring and Yellow-legged Gulls, there are no simple character traits that separate the darker birds. An important point is that there is a strong correlation between the underwing markings and the extent of streaking on the head and body. Heavily streaked birds are likely also to have relatively dark underwings, as shown by PUSZ.

Larus michahellis 1CY 70Y October 21 2008, Westkapelle, the Netherlands. Picture: Ies Meulmeester.	Larus michahellis 1CY CH6258 September 02 2009, Westkapelle, the Netherlands. Picture: Ies Meulmeester.
Larus argentatus 2CY HL75 February 22 2012, Den Oever, the Netherlands. Picture: Herman Bouman.	Larus argentatus 2CY H16L January 24 2012, Katwijk, the Netherlands. Picture: Theo Muusse.

Identification of 1CY birds in August and September

First-calendar-year Caspian Gulls are now turning up regularly in Britain in July and August. On such early dates the post-juvenile moult has either not begun or barely started and so these birds retain a more or less full set of relatively fresh, first-generation feathers. At this time they can look extremely different from how they appear later in the autumn and winter, when moult and wear have turned them into much more distinctive birds. Some fully juvenile Caspian Gulls can easily be overlooked by the unwary, and so are worth discussing here, even though we have not scored them quantitatively.

An extremely dark-looking, well-streaked juvenile, especially if it has heavily marked wing-coverts, may not immediately strike observers as a Caspian Gull. However, this combination of traits does occur in pure Caspian Gull, as indicated by the Ukrainian birds PUHP and PUNP. PUHP is unusual in its overall darkness (trait score 4) and heavily notched greater coverts (score 3) as well as in having a tertial pattern more like that of a Yellow-legged Gull (score 1). In fully juvenile plumage, PUHP looks rather like some Lesser Black-backed Gulls L. fuscus and in Britain may be passed off as such. However, later in the autumn such birds can become more typical-looking. PUNP also looks dark but actually is rather typical of how many fresh 1CY Caspian Gulls look. Once we accept that such Caspian Gulls occur, the identification of unringed dark individuals as this species becomes more palatable.

Larus cachinnans 1CY PUHP Poland, July 16 2010. Picture: E. M. Sowa. Ringed as pullus on June 05 2010, at Cherkasy Kreminchuk reservoir, Ukraine (49,4 32,15).	Larus cachinnans 1CY PUNP August 09 2010, Lubna, Poland. Picture: Michal Rycak. Ringed as pullus on June 05 2010, at Cherkasy Kreminchuk reservoir, Ukraine (49,4 32,15).
Larus cachinnans 1CY PUTH August 09 2010, Rødvig-Stevns, Denmark. Picture: Lars Krogh. Ringed as pullus on June 05 2010, at Cherkasy Kreminchuk reservoir, Ukraine (49,4 32,15).	Larus fuscus 1CY YAFD August 22 2008, IJmuiden, the Netherlands. Picture: Mars Muusse. Ringed as pullus on June 30 2008, at IJmuiden, the Netherlands (52,27 04,34).

END OF PART 8

CONTINUE PART 9: DISCUSSION