Larus cachinnans

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1cy cachinnans: August

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".

The full title reads: From the Rarities Committee's files - Identification of Caspian Gull. Part 1: typical birds, by Chris Gibbins, Brian J. Small and John Sweeney, IN: BB 103/2010. 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.

Identification of Caspian Gull. Part 1: typical birds

Abstract
This paper deals with the identification of the Caspian Gull Larus cachinnans. The aim is to synthesise what is currently known about the identification of this species and discuss the appearance of proven and suspected hybrids. The paper is split into two parts. Part 1 deals with the identification of typical cachinnans and their separation from Herring L. argentatus and Yellow-legged L. michahellis Gulls. It is targeted at non-specialists who remain unsure of the most reliable identification criteria, and at local records committees who need a structured basis for assessing claims. The paper covers all age groups, but concentrates particularly on those treated in less detail in the published literature. It includes a summary table that distils key information and ranks criteria according to their value in field identification. Part 2, to be published in a future issue, will deal with the identification of less typical individuals and hybrids.

Introduction

A lone Caspian Gull rests with a group of Herring Gulls in the Netherlands (January 09 2012, Utrecht, picture: Herman Bouman). Can you see it? It is white-headed, dark-eyed and is holding its bill distinctly downwards.
Below: Larus cachinnans adult, 29 December 2011, Boulogne-sur-Mer, NW France, Picture: Jean-Michel Sauvage. White-headed bird in the centre.

Rationale and aim
Our perception of the Caspian Gull Larus cachinnans as a British bird has changed dramatically in the past 20 years. It has gone from being a poorly known, southeastern race of Herring Gull L. argentatus (Grant 1986) to being recognised as a valid species (Leibers et al. 2001; Collinson et al. 2008) that regularly occurs in Britain. This transformation has been due, in no small part, to the groundbreaking identification studies of Klein (1994), Gruber (1995), Garner (1997), Garner & Quinn (1997) and Jonsson (1998). Subsequent contributions (e.g. Bakker et al. 2000, Small 2000, Gibbins 2003) built on this pioneering work. Along with that of Malling Olsen & Larsson (2003), these studies have demystified this gull to the extent that its identification may now be considered rather passé by some birders. But can we really close the book on the identification of cachinnans?
An identification review is timely, given that BBRC has now passed assessment of post-1999 claims to local committees. Moreover, there is anecdotal evidence that many observers are still struggling with the identification of Caspian Gull. Understandably, this is chiefly the case in areas where cachinnans remains truly rare and where observers have had little chance to gain first-hand experience. The key problems are confusion over the most reliable identification features and a failure to appreciate fully the normal variability shown by cachinnans and similar taxa. Some identification problems merely reflect the extremes of variation shown by cachinnans; others stem from hybrids, originating from the mixed-species colonies in central Europe (Neubauer et al. 2009); and some problems may occur with birds that have no cachinnans genes but which represent the extremes of variation in other species. We have arrived at a point where we should take stock of what we know of the identification of typical cachinnans and begin to look more closely at the identification of less typical individuals and their separation from hybrids. Are there clear dividing lines, and if so where are they?
The aim of this paper is to provide a distillation of known criteria, assess their merits and, for the first time, discuss the identification of less typical and hybrid individuals. We hope that it will be of value to both birders and local records committees. Part 1 deals with typical individuals. We describe in detail the plumage and structure of typical birds, emphasising key average differences from Herring Gull and Yellow-legged Gull L. michahellis; we outline normal variation but leave the extremes aside. Appendix 1 summarises key distinctions between typical cachinnans, michahellis and Herring Gull and ranks criteria according to their relative importance. It should not be used in isolation, but as a convenient summary and as an entry point to the details in the text. Less typical and extreme individuals will be dealt with in part 2, where we shall also discuss the identification of hybrids; this will be published in a future issue.
To date, literature on cachinnans has tended to focus on one or two age groups– the first-winter and adult birds that are found most regularly in Britain. To redress this balance, we pay particular attention to other age groups. The paper is intended primarily for birders in Britain, so does not discuss Heuglin's Gull L. fuscus heuglini. This taxon can look remarkably cachinnans-like in structure and some immature plumages. However, serious confusion is unlikely: heuglini has a different call, dark inner firstgeneration primaries, and once adult-type grey feathers develop their tone is much darker than those of cachinnans.

Circularity and the empirical basis of this paper
Circular reasoning (bird A is a Caspian Gull, it shows features X, Y and Z, therefore X, Y and Z are features of Caspian Gull) may undermine attempts to develop identification criteria. Circularity can be avoided if:
(a) the species is studied in the core of its accepted breeding range, where potential confusion species are absent and hybridisation is not a significant issue; or
(b) the sample consists only of individuals of known provenance (ringed birds). Much of our knowledge of cachinnans is actually based on unringed birds observed in western Europe in winter, well away from core breeding areas and on the edge of the wintering range.
Circularity is thus a potential problem, especially because of the risk of incorporating an unknown number of hybrids into the 'cachinnans' sample. Moreover, as we may be picking up only the most striking birds in Europe, there is a danger of developing criteria based on an unrepresentative sample. Studies of cachinnans wintering in the Middle East suffer similar problems, owing to the presence of extremely similar taxa whose identification has yet to be fully resolved (notably barabensis). Access to the heart of the breeding range of cachinnans, where both Herring and Yellow-legged Gulls are absent, is difficult and few western ornithologists have studied the species there. Consequently, we are largely constrained to studying cachinnans in wintering areas and must be aware of the problem of circular reasoning.
Circularity is most problematic with less typical individuals. In part 2 we therefore use ringed individuals of known provenance to help to develop criteria for the separation of hybrid from pure individuals. Circularity is less of an issue with the 'classic' birds that are the focus of part 1. Nonetheless, to study cachinnans we have travelled to parts of the breeding range (e.g. several trips to the Danube Delta, Romania) and areas of the southern Baltic where cachinnans occurs in large numbers in the immediate postbreeding period and can be the most abundant large gull at some localities (e.g. on the Curonian Spit in Lithuania). The majority of plates show birds from these areas. Since the paper is aimed at British birders, it may seem that examples of cachinnans photographed in Britain are under-represented in the plates; this is a product of the need to limit the problems of circularity.
'Herring Gull' is used here to refer collectively to both races; 'argentatus' is used when referring specifically to the Scandinavian/ Baltic race and 'argenteus' when referring to the British/west European race. Yellow-legged Gull is referred to as 'michahellis' and relates only to Mediterranean birds. The Atlantic Island populations of Yellow-legged Gull represent a taxon whose status is still debatable and which, in any case, have rather dark immature plumages and structural traits that make them unlikely to be confused with cachinnans. We treat cachinnans as monotypic, as the extent and nature of geographic plumage variation has yet to be firmly established. Nonetheless, future work may reveal consistent differences between eastern and western birds (see section on adults).

Patterns of occurrence in Britain

It is difficult to assess the number of cachinnans currently occurring in Britain each year. This relates chiefly
to the fact that the species is now so abundant in some areas that observers do not necessarily report all sightings. Nonetheless, it is clear that cachinnans is recorded more frequently now than in the past and that there are strong seasonal and geographic patterns to its occurrence. Caspian Gulls are most frequent in southern England, particularly the southeast. The first birds arrive in late summer and early autumn, when the majority of records come from the coastline between Kent and Suffolk. Juvenile cachinnans now occur regularly in early August, when many young British Herring Gulls are not even fully independent. These cachinnans are not necessarily from the nearest breeding areas, since juveniles may disperse far from their natal colony soon after reaching independence. For example, a bird at Espoo, Finland, on 26th July 2004 had been ringed as a pullus on 27th May on the River Dnper in southern Ukraine (49°46'N 31°28'E). Consequently, observers should be looking out for first-calendar-year (1CY) cachinnans from late July onwards. Post-breeding adults tend not to be seen in Britain until later in the autumn; this delayed arrival may be linked to the progression of primary moult.
Following their arrival, many birds move inland and disperse northwards as the autumn and winter progress. They are supplemented by new arrivals, perhaps linked to cold weather on the Continent. For example, hundreds of cachinnans are present at lagoons along the coast of Lithuania in autumn but these disappear in midwinter, once the water freezes (Vytautas Pareigis pers. comm.). The largest numbers of cachinnans in Britain are recorded in winter, with birds seen regularly on favoured landfill sites and in reservoir roosts in southern and central England. However, they remain distinctly scarce in north and northwest Britain; there are few records north of the River Tees and the species remains extremely rare in Scotland (fewer than five records) and Ireland. Very few are recorded in the summer months. This probably reflects the movement of birds back to the Continent, but perhaps also the relative difficulty of identifying moulting immatures in summer and the fact that gull-watching in Britain tends to be a winter pursuit.

Identification

Classic structure: long exposed tibia, high breasted, elongated rear end, snouty head.

Size and structure
Caspian Gulls can be strikingly large, tall birds, but most individuals are similar in length and weight to Herring Gull and so do not stand out on size alone. However, cachinnans is structurally distinctive at all ages, often described as 'lanky' or 'gangly'. It has relatively long, thin-looking legs (the extra length is particularly noticeable in the tibia) and often seems to stand taller than Herring Gull. Next to michahellis, its legs tend to look longer and less robust. However, some michahellis are long-legged compared with Herring Gulls, so observers should be mindful of this when confronted with an apparently lanky bird. There are marked differences in size and structure between male and female cachinnans (see Malling Olsen &
Larsson 2003) and these differences may be more marked than for other large gulls (Gibbins 2003). Some, presumably males, can look incredibly long-legged, yet others, presumably females, can actually look rather short-legged. Consequently, birders and committees should not automatically dismiss a bird that lacks the textbook long-legged look.

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TARSUS	range	average	n:
L.a. argentatus
adult male	62.0-75.2	67.1	131
adult female	55.1-69.8	62.4	142
first-year male	59.4-70.3	66.7	48
first-year female	55.8-68.0	60.9	43
L.a. argenteus
adult male	56.4-70.3	64.1	52
adult female	53.3-68.6	59.6	63
first-year male	54.5-66.7	62.6	22
first-year female	52.9-64.2	58.5	22
TARSUS (N Norway)
adult male	62.5-75.0	67.5	25
adult female	57.1-68.1	62.2	21
TARSUS (Finland. Estonia)
adult male	67.0-72.0	69.2	6
adult female	57.3-66.8	60.6	7
TARSUS (Denmark)
adult male	61.6-73.6	66.7	52
adult female	53.6-70.4	62.8	55
TARSUS (W Germany)
adult male	57.0-72.0	65.9	80
adult female	52.5-67.0	61.2	80
TARSUS (Sobortsk, White Sea)
-	58.8-75.0 (rarely <70mm)
L.c. cachinnans
adult male	65.8-77.0	69.9	30
adult female	58.7-73.8	64.0	26
first-year male	65.7-69.9	67.5	4
first-year female	57.2-66.1	61.1	4

The head can appear oddly small for the body, generally looks pear-shaped, and normally lacks the bulky feel of the head of Herring Gull and (especially) michahellis. The head often looks 'anorexic', as though
there is little flesh covering the skull; this means that head shape equates more closely to skull shape than for other large gulls. The often-quoted, but perhaps over-emphasised, 'snouty' look is due to a combination of the long sloping forehead and the relatively long, slim bill, which gives the front of the head a tapering, 'pulled-out' appearance. This snouty look can be a striking and defining feature, but it is important to note that not all cachinnans show it. For a significant proportion of (presumed) females, the bill length is unremarkable, and, because of their higher, more rounded heads, they may recall Common Gull L. canus. Conversely, some larger males can have a robust bill and a solid, more angular head that overlaps in appearance with both Herring and Yellow-legged Gulls. Yellow-legged Gulls typically have a deeper, blunter bill and a larger, more angular head, yet, as with other gulls, males and females can be rather different, and the1 slighter individuals overlap with Herring and even Lesser Black-backed Gulls L. fuscus. Furthermore, michahellis from the Atlantic coast of the Iberian Peninsula tend to be smaller, less robust and less rangy than Mediterranean birds.
Most Caspian Gulls appear longer-billed than Herring Gull and michahellis. They have a more gentle, even curve to the culmen and a less obvious gonydeal angle; unlike Herring Gull and michahellis there is little or no bulging at the gonys and the general impression is of a gently tapering bill. Data in Malling Olsen & Larsson (2003) indicate that there is actually much overlap in the bill length of cachinnans and Herring Gull
(males: Herring 46.4–64.9 mm, mean 54.6, cachinnans 50.7–63.5 mm, mean 56.3; females: Herring 44.9–59.0 mm, mean 49.7, cachinnans 48.0–59.5 mm, mean 51.9). Thus, the longer-billed impression given by cachinnans results from the interaction of its shape, depth and length, accentuated in some birds by the pear-shaped head and long neck.
Gibbins (2003) assessed the ratio between bill length and gonys depth (measured from photographs; length and depth as indicated in fig. 1) in a sample of Herring and Caspian Gulls (n = 68). Most Herring Gulls were scored as having a ratio of 1.75–2.00 whereas most cachinnans were scored as 2.25–2.50. Thus for cachinnans the bill is most often more than twice as long as its maximum depth, while for Herring it is most frequently a little less than twice its maximum depth. Some cachinnans can be extremely long- and
slim-billed, with ratios up to 3.25, compared with a maximum of 2.5 in Herring. Note that bill deformity is not uncommon among gulls (especially first-years), so a long, slim bill is not, in itself, sufficient for identification or record acceptance.
The body shape of cachinnans is subtly distinctive. One of the most noticeable features is the attenuated rear end; this is a consequence of a flat back, limited or absent tertial step and relatively long wings. The tip of the tail falls one-third to halfway along the exposed primaries, while on Herring Gull it usually reaches halfway or slightly further (this comparison holds good only for birds that are not moulting their outer primaries). Herring Gulls and michahellis are generally less attenuated and have a more prominent tertial step although, especially in hot weather, michahellis can appear to have a very long rear end. The belly profile of cachinnans often continues behind the legs as a ventral bulge that sags below the wings, making the underbody resemble a boat keel in shape. This may be obvious for some birds yet not apparent for others. At rest, compared with Herring Gull and most michahellis, cachinnans has a higher chest, with a slightly 'bosomed' effect, as if holding its breath. This stance is exaggerated by the long wings and ventral bulge, which, along with the head and bill shape, give the most typical birds an instantly recognisable jizz.
In flight, the long- and broad-winged appearance of cachinnans may catch the eye of regular gull-watchers. Compared with Herring Gull and michahellis, the greater length of the head, bill and neck extension in front of the wings is also noticeable.
To summarise, the most typical cachinnans have a striking jizz, much more eyecatching than that of michahellis. They can be a large yet elegant gull, easily located in mixed flocks. However, some lack the rangy/gangly/snouty character usually associated with the species and so are much less distinctive. Weather conditions and posture influence appearance, and in hot conditions, when their feathers are sleeked down, cachinnans may look very slim, long-legged and lanky. On cold winter days they look quite different, and experience from birding holidays in the Middle East may not translate well to Britain.

Adult Caspian Gull, Latvia, 11 Apr 2009.This large male was typically aggressive and, as pictured here, incessantly gave the rapid, laughing call which is diagnostic of Caspian Gull. Unlike Yellow-legged and Herring, Caspian Gulls hold their wings open when giving the long call – the so-called 'albatross posture'.The characteristic primary pattern is visible here: note the grey tongues eating into the black wing-tip on the upperside of P7–10 and the long silvery tongue on the underside of P10. Like Yellow-legged Gull, Caspian usually has a broad, black subterminal band extending unbroken across P5, but there is much individual variation and this bird has only isolated black marks on the outer and inner webs.

Behaviour and voice
Caspian Gulls mix freely with other large gulls in both feeding and resting areas (plate 48). When feeding on
rubbish dumps, large individuals are often extremely aggressive (more so than Herring and michahellis) and
dominate favoured patches. Caspian Gulls habitually raise their wings, especially in aggressive encounters, and this can be an easy way to locate them in groups of feeding gulls.
Their calls (appendix 1) also attract attention and can be heard clearly even above the noise created by large numbers of squabbling Herring Gulls. The importance of the long call and long-call posture in separating cachinnans from other large gulls has been rather underplayed in the literature and it is clear that not all birders are aware of their value. Calls are always difficult to capture in words and the long call of cachinnans has been described in various ways. The full long call is a loud, rapid 'haaa-haaa-haa-ha-ha-haha- ha-ha-ha', with a characteristic nasal, laughing quality, very different from Herring Gull's. Once heard it is easily recognised. Adults frequently give shorter versions of this call (the last six or seven notes) during aggressive encounters. Evidence suggests that the full long call takes time to develop: in August and September, 1CY birds give a much more subdued version (Hannu Koskinen, pers. comm., CG pers. obs.). Juveniles often also give screeching calls, especially when coming in to land to join a feeding melee. These calls are very high-pitched (they have a clear squealing quality) and, once heard, are distinct from the whine of juvenile Herring Gulls.
The full long call is frequently accompanied by the 'albatross posture', with wings open and held back and the head raised progressively as the notes are delivered (plate 49). Herring Gulls and michahellis keep their wings closed when long-calling, so this is a key distinction. Herring Gulls raise their heads only to approximately 45° when longcalling, while both cachinnans and michahellis often (but not always) raise them to 90°.

Urszulin (near Zabrodzie), Włodawa County, Lublin Voivodeship (51.4342N 23.2285E). Recorded on 2012-03-12 by: Jarek Matusiak. Colony about 32 Pairs; some birds can be hybrids among L. cachinans and L. michahellis.
Góra Kalwaria (near Podłęcze), Piaseczno County, Masovian Voivodeship (52.0312N 21.2262E). Recorded on 2013-02-26 by: Jarek Matusiak. Response on White-tailed Eagle; colony of about 83 pairs; some birds can be hybrids among L. cachinnans and L. michahellis. At least 3 L. michahellis were present, and one L. f. intermedius (but silent).
Rødvig havn (55.2528N 12.3737E). Recorded on 2009-10-31 by: Lars Krogh. Begging 1st winter bird. Background gulls are some L. argentatus and L. fuscus.

END OF PART 1

CONTINUE PART 2: JUVENILES (1CY BIRDS JULY-SEPTEMBER)