Larus cachinnans

(last update: February 16, 2013)

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adult cachinnans: September

In 2010, Chris Gibbins, Brian J. Small and John Sweeney published two extensive papers in Britsih Birds, dealing with Caspian Gull. Below, you will find the content of the first paper "Part 1: typical birds".

Part 1: INTRODUCTION & IDENTIFICATION

Part 2: JUVENILES (1CY birds in July–September)

Part 3: BIRDS IN THEIR FIRST WINTER (1CY/2CY birds in October–April)

Part 4: BIRDS IN THEIR FIRST SUMMER (2CY birds in May-September)

Part 5: BIRDS IN THEIR SECOND WINTER (2CY/3CY birds during October-April)

Part 6: OLDER IMMATURE PLUMAGES (3CY–5CY birds)

Below, we continue with PART 7: ADULTS. "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.

Adults

Adult Caspian Gulls are best located in gull flocks by a combination of their peculiar jizz, and relatively dark, small-looking eyes that contrast with the white head (plate 86). Identification can then be confirmed by detailed study of bill proportions, primary pattern, bare-part colours and upperpart tone. The following sections deal with these features in turn; plates 87–96 show a selection of adult cachinnans, michahellis and Herring Gulls.

Fig. 2. Upperpart grey tones as represented on the Kodak Grey Scale for cachinnans and similar taxa. Common Gull Larus canus is included as a good tonal match for cachinnans; values are for nominate canus. The michahellis values exclude the Atlantic island populations (atlantis), which have darker grey tones (from 7–7.5) than Iberian and Mediterranean birds. Values are based on Malling Olsen & Larsson (2003) and Jonsson (1998).

Plumage
Fig. 2 shows the range of adult upperpart tones for cachinnans and similar taxa, at least in a British context. The figure uses the Kodak Grey Scale, a scale that has numbered increments from 0 (white) to 20 (black). The scale itself is not reproduced here and most gull-watchers will not go into the field armed with a copy of it; fig. 2 simply compares the upperpart tones among the various taxa and shows the degree of overlap between them. For grey-tone comparisons to be reliable, other taxa should be directly alongside or nearby. Observers also need to be aware of the effects of light and viewing angle on the perception of tone. Diffuse sunlight or overcast conditions are best: strong direct sunlight tends to bleach out subtle differences.

Another problem is that the grey tone may appear to change on the same individual as it faces in different directions relative to the observer; upperparts tend to look darkest when the bird is facing obliquely towards or away from the observer. Thus, a slightly darker-backed gull in a flock might just be facing in a different direction from the others. Any apparent difference should be confirmed by seeing the bird in a variety of
positions.

The tone (darkness) of the pure grey upperpart feathers of adult and near-adult gulls is of quite limited value in cachinnans identification, because it overlaps extensively with that of other species. Nonetheless, it can be useful when looking for the species among paler-mantled argenteus in Britain (although most darker birds will turn out to be argentatus or michahellis, depending on location and season). To the practised eye, cachinnans can be located in flocks of michahellis by their subtly paler upperpart tone. Common Gull is usually a close match for cachinnans and, when alongside, can be used as a tonal marker.

Regardless of tone, there is a subtle difference in colour hue between the upperparts of cachinnans and Herring Gull, when seen in good light and in direct comparison. That of cachinnans is a more neutral, silky grey, with less of a bluish hue than either argentatus or argenteus. The upperparts of michahellis are more of a slate-grey. The human eye is a per perceptive tool and it is certainly possible to see the differences in colour hue between these species in direct comparison. However, because of differences between how observers perceive and describe colour, it is difficult to articulate the differences here, in words.

Larus cachinnans sub-adult, 04-12 September 2009, Preila, Lithuania. Picture: Chris Gibbins. The extensive dark areas on the primary coverts, dark grey wash on the outer webs of P5–P7 and the black band across the tip of P10 suggest that this is not a fully adult bird.	Larus cachinnans adult, 08-13 April 2009, Riga, Latvia. Picture: Chris Gibbins.
Larus cachinnans adult, August 2008, Riga, Latvia. Picture: Chris Gibbins.	Larus cachinnans adult, 08-13 April 2009, Riga, Latvia. Picture: Chris Gibbins.

Wing-tip pattern
Adult cachinnans have a characteristic wingtip pattern and, particularly when multiple features in the wing-tip are used simultaneously, this can be a good means of identification (fig. 1 and plate 49). However, the
wing-tip pattern is not truly diagnostic, because of a degree of overlap with argentatus Herring Gull.

The outermost primary (P10) of cachinnans is black, except for a long, pale 'tongue' on the inner web (grey on the upperside of the feather, white on the underside) and a long white tip. The black separating the tongue from the white tip is narrower than the length of white tip. This pattern is never seen in michahellis and is very rare in argenteus; however, it is common in argentatus. The details of the P10 pattern may be difficult to see well on flying birds (except, of course, in photographs) but can often be seen on a standing or swimming bird by viewing the underside of the folded wing. Occasional variations in the P10 pattern of cachinnans include cases where the pale tongue breaks through the black to merge with the white tip – a pattern typical of Thayer's Gull L. (glaucoides) thayeri.

An example of this from Ukraine is shown by Liebers & Dierschke (1997, plate 289), while CG has seen such birds in Romania (Lake Histria, September 2006). These locations suggest that the 'thayeri pattern' occurs occasionally in pure cachinnans, rather than being indicative of introgression with Herring Gull. Some birds show a small amount of black within the long white tip of P10: of 31 adult cachinnans examined in the hand by Liebers & Dierschke (1997), 11 showed a subterminal black band (complete or incomplete) across the tip of P10. There is also variation and overlap among the taxa with respect to the exact shape of the pale tongue, especially between cachinnans and argentatus (Gibbins 2003). To reiterate, the P10 pattern is not
diagnostic.

Long, pale grey tongues are also present on the inner webs of P7–P9 of cachinnans and, collectively, these give the impression of pale wedges eating into an otherwise black wing-tip. This pattern is very different from that of michahellis (which has a solid black wing-tip) but is seen on many argentatus. Black extends
inward as far as P5 on cachinnans and on some (16%; Jonsson 1998) also to P4. Ideally, a candidate cachinnans should have a black band extending unbroken across both webs of P5, typically slightly less deep than that of michahellis. However, there is considerable variation in the pattern of black on P5 of all the taxa. Around 10% of cachinnans lack a complete black band on P5 (Jonsson 1998): such birds may have isolated marks on both the inner and outer webs of the feather (plate 49) or have black restricted to the outer web. Herring Gulls may lack black on P5 altogether (e.g. many Norwegian argentatus), have black only on the outer web (frequent in argenteus) or have black on both webs. When black is present on both webs of P5 in Herring Gull, it may be as an isolated black spot on each (usually larger on the outer web), or as a complete band (plate 90). When present, the band is usually much narrower than on michahellis, but it
matches many cachinnans. Black on both webs of P5 is a surprisingly common feature in eastern Baltic populations of Herring Gull (Malling Olsen & Larsson give a value of 30%), so these birds are a real cause of confusion. Overall, the variability in P5 pattern means that it is difficult to give definitive criteria regarding its value in identification. Like cachinnans, Herring Gulls can have black extending inwards as far as P4, though this is rare.

Some have argued that eastern and western populations of cachinnans differ with respect to primary pattern (e.g. Stegmann 1934). Adults from eastern populations normally have a less extreme wing-tip pattern, where the long white tip of P10 is regularly interrupted by small black spots on each web, sometimes merging to form a subterminal band. A significant proportion show black on P4 (50%; Jonsson 1998). Compared with western birds, eastern cachinnans may also show shorter pale tongues invading the black of the upperwing, but these still break up the black of the outer primaries in a way that michahellis never shows. More research is needed to determine whether eastern and western cachinnans deserve formal subspecies status.

Larus cachinnans 8CY 671P 11 September 2010, Boulogne-sur-Mer, NW France, Picture: Jean-Michel Sauvage. Ringed in Poland.	Larus argentatus argenteus 10CY H-132951December 13 2012, Boulogne-sur-Mer, NW France. Picture: Jean-Michel Sauvage. Bird from Belgium. As well as the compact jizz, note the extensive soft streaks across the head, neck and upper breast, the pale eye and yellowy-orange eyering.
Larus cachinnans adult, 25 November 2010, Boulogne-sur-Mer, NW France, Picture: Jean-Michel Sauvage. Probably female; it looks rather compact, the bill is not noticeably long and the head is high and rather peaked. Because of the dark eye, many such presumed female cachinnans are surprisingly reminiscent of a Common Gull. The broad black band across P5 is visible below the tertials.	Larus argentatus argentatus 7CY C266U April 12 2008, Tara dump - Tampere, Finalnd. Foto: Hannu Koskinen. Bird with yellow legs. This represents a potential cachinnans-trap for the unwary. Baltic Herrings commonly have a complete black band across P5, a long white tip to P10, yellowy legs and a reddish orbital ring; its bill is rather slender-based and its upperparts are a good match for cachinnans. However, the head retains the typical bulk of Herring Gull, its iris is unmarked yellow, and the bill has a rather sharply curved culmen and a marked gonydeal angle.
Larus cachinnans adult, 10 November 2010, Boulogne-sur-Mer, NW France, Picture: Jean-Michel Sauvage. Probably male. The eye of Caspian Gull is normally described as being dark, but rather few have truly dark eyes. Most have a speckled iris, which in the field varies in colour from pale amber to brown, depending on the density of speckling. The eye of this bird is medium amber.	Larus argentatus argentatus 8CY CE950 April 12 2008, Tara dump - Tampere, Finalnd. Foto: Hannu Koskinen. Another yellow-legged Herring Gull from Finland. 8CY argentatus, ringed white CE942 as pullus on July 04 2001 in Vilppu, Finland (62.15N 24.05E).

Head pattern
The head of adult cachinnans normally appears unmarked (plate 87). Any streaks are extremely fine, often confined to the lower rear neck, and usually only apparent at close range for a limited period in autumn (plate 88). In michahellis, streaking is also usually apparent only in the autumn but is concentrated around the face and ear-coverts. On average, this streaking is clearer than shown by cachinnans at this time. Streaking disappears in late autumn, as feathers wear. From early autumn to mid/late winter, the vast majority of Herring Gulls show a variable but usually obvious degree of dusky streaking and/or blotching on the head and neck (plate 90). There are exceptions and it is possible (though uncommon) to find clean-headed argenteus and argentatus before January, just as it is possible to find the odd Black-headed Gull Chroicocephalus ridibundus with a full hood in mid-winter.

Bare parts
Outside the breeding season, the bill of cachinnans is normally a rather weak, greenish-yellow, fading to grey-green basally. There are frequently some dark marks (small spots or crescents) in the gonys, while the red is usually less bright than for either michahellis or Herring Gull. Thus, in general, the bill of cachinnans in winter stands out as being duller than that of the other species. However, as many argentatus have washed-out, greeny-yellow bills in winter, bill colour and pattern is merely a supportive feature.

The bill becomes a richer yellow in late spring and, during the breeding season the bill coloration of cachinnans overlaps with that of Herring Gull. Neubauer et al. (2009) argued that, unlike the orbital ring (see below), bill tones do not differ consistently between cachinnans and Herring Gull in breeding plumage. The bill of cachinnans is distinctly duller than the bright, orange-toned bill of michahellis; moreover, the red gonys spot of michahellis is extremely bright and regularly spreads extensively onto the upper mandible.

In the field, most adult cachinnans appear dark-eyed; in fact, the iris is not wholly dark, but peppered by dark brown spots. Depending on the density of these spots, the iris may appear dirty amber-yellow or uniformly dark brown, but never completely black. Eye colour varies enormously in cachinnans: Jonsson (1998) suggested that c. 75% of adult cachinnans appear 'medium- to dark-eyed' in the field, whereas Liebers& Dierschke (1997) found that 48% of birds in one Ukrainian colony and 62% in another were 'pale-eyed'. Much depends on how 'dark' is defined. Most birds do look darker-eyed in the field than typical Herring Gulls or michahellis and truly pale (clean yellow) eyes are rare in cachinnans (<10% Jonsson 1998;
2–5% Hannu Koskinen pers. comm.). Note also that some apparently adult Herring Gulls have dark peppering in the iris and some look genuinely dark-eyed in the field (plate 96); anyone checking large numbers of Herring Gulls should expect to find darkeyed birds with moderate regularity.

The orbital ring of cachinnans varies from pale orange to red (Liebers & Dierschke 1997; Neubauer et al. 2009). That of Herring Gull varies from yellow (typical argenteus), through pure orange to orangey red; that of some Baltic argentatus looks deep red and thus approaches michahellis. Orbital ring colour in Herring Gulls has been shown to differ among birds breeding in the same colony (Muusse et al. unpubl.). Thus, while
orbital-ring colour is a useful feature for cachinnans (orange to red is acceptable, yellow is a problem), it is merely one of a number of features that combine to make the species distinctive but which are not individually diagnostic. Liebers & Dierschke (1997) reported a correlation between iris and orbital ring colour – pale-eyed cachinnans having pale orange orbital rings and dark-eyed birds having redder orbitals – and this relationship is clearly worth further study.

The leg colour of adult cachinnans varies seasonally and individually. In winter, the legs are typically pale, greyish-flesh; some have a weak, greenish-yellow tint. In spring and early summer, the legs of many adults become distinctly brighter and yellowish. The proportion showing truly yellow legs during the breeding season is uncertain and may vary among populations and even from year to year (perhaps linked to diet). The leg colour of an individual bird can vary during the course of the breeding season, probably as a function of physiological condition (Neubauer et al. 2009). There is complete overlap in leg colour between cachinnans and the Herring Gulls of the eastern Baltic (from pure pink to lemon yellow) so this feature is of limited value. However, cachinnans rarely matches the rich yellow of the legs of michahellis.

Larus argentatus argenteus adult, February 07 2013, Katwijk, the Netherlands. Picture: Mars Muusse. Much black in wingtip. P10 full black band, P9 small mirror, P5 full black band. This is a typically compact and short-billed argenteus.

Larus michahellis adult, November 25 2006, Etaples, France (50.44N,01.35E). Picture: Mars Muusse. A typically large, robust and long-winged bird. Note the broad black band across P5 and the small mirror on P9.

Larus michahellis, April 04 2009, Rosas, Spain. Pictures: Antonio de la Cruz. The underside of P10 is visible here and shows a triangular wedge (not a square tongue) extending only 1/4 down the exposed feather.The huge bill suggests this is a male. The gape is bright red, similar in tone to the orbital ring. Note red on the bill and saturated yellow bare parts.

Larus argentatus argentatus adult, January 23 2013, Katwijk, the Netherlands. Picture: Mars Muusse. The P10 pattern of this bird is similar to that of cachinnans – it has a long grey tongue, visible here on the underside, and a long white tip to the feather. Its bill, however, is robust and it has very limited black on P5. This bird illustrates the problems posed by some argentatus; careful assessment of the full range of features is needed for correct identification.

Pitfalls
The most likely problem is confusion with a Herring Gull from the eastern Baltic. These are quite unlike the Norwegian argentatus that we are familiar with in the UK and can have upperpart tones, bare-part colours and wing-tip patterns that are virtually identical to those of cachinnans. The potential for confusion is increased by the fact that these argentatus may look slightly longer-winged, longer-legged and longer-billed than argenteus (although less obviously so than cachinnans). The occasional dark-eyed bird can create real problems.

Concluding remarks
The aim of part 1 of this paper has been to describe the appearance of typical Caspian Gulls. The birds featured in the plates are all rather typical and should not pose any identification problems. Variability is a feature of large gulls, however, and observers should not expect all cachinnans to look identical. Nonetheless, there is what might be regarded as normal or typical variation (that outlined above) and that which is extreme or atypical. In part 2 we shall deal with the extremes and discuss birds that sit in the overlap zones between the species. We shall also consider hybrids; this is a very real problem given that hybridisation is occurring in Poland, for example, and that hybrids originating there have been recorded in Britain. Before becoming embroiled in debates about the more difficult individuals, it is important that birders are familiar with the identification of typical birds. We hope that part 1 has provided this familiarisation.

Acknowledgments
The authors would like to thank Nic Hallam, Hannu Koskinen, Ian Lewington and four anonymous reviewers, whose insightful comments greatly improved this manuscript. We are also grateful to Ruud Altenburg, Steve Arlow, Hannu Koskinen, Mike Langman and Pim Wolf for sharing and allowing us to use their photographs. A number of birders shared their knowledge and experience of cachinnans during the preparation of this paper; we especially thank Ruud Altenburg, Hannu Koskinen, Mars and Theo Muusse and Visa Rauste in this regard. Dmitri Mauquoy kindly produced fig. 1.

References
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— & Quinn, D. 1997. Identification of Yellow-legged Gulls in Britain. Brit. Birds 90: 25–62.
Gibbins, C. N. 2003. Phenotypic variability of Caspian Gull. Birding Scotland 6: 59–72.
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Limicola 19: 121–127.
Howell, S. 2001. A new look at moult in gulls. Alula 7: 2–11.
Jonsson, L. 1998.Yellow-legged Gulls and yellow-legged Herring Gulls in the Baltic. Alula 4: 74–100.
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in Mecklenburg – erste Ergebnisse einer Ringfundanalyse. Vogelwelt 115: 267–285.
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—, Helbig, A. J., & de Knifff, P. 2001. Genetic differentiation and phylogeography of gulls in the Larus cachinnans-fuscus group (Aves: Charadriiformes). Molecular Ecology 10: 477–2462.
Malling Olsen, K., & Larsson, H. 2003. Gulls of Europe, Asia and North America. Helm, London.
Neubauer, G., Zagalska-Neubauer, M. M., Pons, J-M., Crochet, P-A., Chylarecki, P., Przystalski, A., & Gay, L. 2009. Assortative mating without complete reproductive isolation in a zone of recent secondary contact between Herring Gulls (Larus argentatus) and Caspian Gulls (L. cachinnans). The Auk 126: 409–419.
Small, B. 2000. Caspian Gull Larus cachinnans in Suffolk – identification and status. Suffolk Birds 49: 12–21.
Stegmann, B. K. 1934. Ueber die Formen der Großen Möwen ('subgenus Larus') und ihre gegenseitigen Beziehungen. J. Orn. 82: 340–380.