Larus cachinnans

(last update: February 16, 2013)

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1cy 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".

First part: INTRODUCTION & IDENTIFICATION

Below, we continue with "Juveniles (1CY birds in July–September)". "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.

Juveniles (1CY birds in July–September)

Moult and wear
This section deals with a period when both fully juvenile birds and individuals moulting into first-winter plumage may be encountered. On the right hand side of this page it shows a selection of birds photographed during this period; captions emphasise key identification features.

Caspian Gulls in fully juvenile plumage may be seen in July and early August, but by mid August many have commenced their post-juvenile moult (the partial moult into first-winter plumage). By early September it is rare to find a cachinnans with a full set of first-generation feathers – most have at least some new scapulars and some have a few new coverts and tertials.

Both cachinnans and michahellis hatch much earlier in the year than Herring Gulls and this contributes to their earlier postjuvenile moult. The stage of scapular moult seen in early to mid September among 1CY cachinnans is not reached until late October in many British Herring Gulls. The difference between cachinnans and northern argentatus is even greater, with many of the latter retaining some or all of their first-generation scapulars throughout the winter. The extent of wear and fading differs among the species, but is likely to be a function of environmental conditions in breeding areas as well as hatch timing. As with michahellis, it is not unusual to see cachinnans in early September with clear signs of wear on their first-generation feathers; at this time, young Herring Gulls are still in pristine condition. Moult timing and wear can thus be very useful in the identification of 1CY cachinnans (and michahellis) in a British context; before mid September, any 1CY large gull whose scapulars are mainly second-generation is well worth a closer look. In addition, it is extremely rare for Herring Gulls to include coverts or tertials in the post-juvenile moult (<1% of individuals; CG unpublished data from North-east Scotland). Consequently, any 1CY bird in western Europe with second-generation coverts or tertials and clear signs of wear on remaining first-generation feathers may well prove to be cachinnans or michahellis.

Larus cachinnans 1cy, August 2008, Riga, Latvia. Picture: Chris Gibbins.	Larus cachinnans 1cy, 12-20 September 2008, Mamaia, north of Constanta on the Black Sea coast of Romania. Picture: Chris Gibbins.
Larus cachinnans 1cy, 04-12 September 2009, Riga, Latvia. Picture: Chris Gibbins.	Larus argentatus arrgenteus 1cy, August 23 2008, IJmuiden, the Netherlands. Picture: Mars Muusse.

Plumage
Fully juvenile cachinnans (i.e. those with only first-generation feathers) are often quite different from the 1CY birds seen in western Europe in winter; although on average cleaner-looking than Herring Gulls, they are not as strikingly white as 1CYs in midwinter. Relative to Herring Gull, textbook juvenile cachinnans have fewer streaks and blotches on the head and body, and their upperparts have a rather washed-out, 'watercolour' look. The first-generation scapulars and wingcoverts are typically light grey-brown ('wet mud') in colour, with narrow, simple, pale fringes which tend to lack the large pale notches and indentations found on Herring Gull and many michahellis. Rusty tones are sometimes present on the lower rear neck, but otherwise the overall colour is a rather greyish 'mouse brown', lacking sharp contrasts. The generally soft tones and featureless pattern can sometimes be more reminiscent of juvenile Common Gull than Herring Gull. Juvenile michahellis are distinctly darker, more chocolatey brown and often have a dark eye-patch that contrasts with an otherwise white head.

The most striking cachinnans have greater coverts that completely lack pale notches; instead, each feather has a dark basal section and a diffuse pale tip that, at a distance, forms a striking pale wing-bar shaped rather like the Nike 'swoosh'. The exact pattern on the greater coverts varies subtly among individuals (e.g. plates 50, 51, 52), but the most typical birds have only weak, diffuse and irregular notches on the inner greater coverts, much less obvious than those of Herring Gull and michahellis. Normally, the pattern on the inner greater coverts appears to be more vermiculation than notching. A bird with strongly notched greater coverts should be checked carefully for other anomalous features. Caution is needed with michahellis, as some lack notches on their greater coverts (instead, some simply have sharp pale fringes). An oft-quoted feature of cachinnans during their first winter (1CY/2CY birds) is the presence of a second pale wing-bar, on the lowest row of median coverts. This, however, is rarely evident on fresh juveniles in July and August.

The first-generation tertials of cachinnans typically have a muddy-brown base and a diffuse pale fringe around the distal portion of the feather. The pale fringe sometimes coalesces with pale oval patches in the central part of the feather to form an extensive pale tip, reminiscent of the pattern on a juvenile Common Gull (e.g. plate 50). The exact pattern varies subtly but the key point is that the pale fringe lacks the notches of Herring Gull (plate 53) and is generally broader and less sharply defined than shown by typical michahellis (plate 54).

Most juvenile cachinnans are as striking in flight as they are on the ground (plates 55 & 56). From above and below, the general impression is clearly different from Herring Gull (plate 57), and while they look similar to michahellis from above, their underside is quite different. The relatively white underwing is perhaps the most obvious in-flight feature of cachinnans. This is created by the off-white ground colour to the underwingcoverts; the secondaries and primaries are also paler (silvery to off-white) than those of Herring and michahellis. Most cachinnans have a degree of soft, grey-brown barring on the axillaries and underwing-coverts, so the underwing is not wholly white (e.g. plate 56). The underwing-coverts of Herring Gull are much more extensively and strongly marked with brown and the general impression is therefore of a much darker and rather uniform underwing. In michahellis (plate 58) the underwing-coverts are heavily marked with dark, chocolate brown over a pale base colour, often creating a contrasting pattern of light and dark bands. However, some michahellis lack such extensive dark marks so from a distance their underwings can look surprisingly pale. The incidence of pale underwings may be more prevalent in eastern populations of michahellis.

The underwing of some cachinnans is strikingly white, and photographs suggest that some birds drop some underwingcoverts and axillaries during their first winter; this exposes the paler bases to remaining feathers and heightens the appearance of a white underwing. Conversely, observations on breeding lakes in Romania (i.e. birds with known provenance) indicate that some 1CY cachinnans can have quite well-marked underwings, with dark brown barring and spotting across many feathers, especially the lesser underwing-coverts and axillaries. Such dark birds tend to have more contrasting underwings than Herring Gulls, as the brown barring sits on an otherwise rather pale ground colour. This creates a degree of overlap with michahellis.

The contrasting black-and-white pattern of the rump and tail of cachinnans is striking in flight and often likened to that of a Roughlegged Buzzard Buteo lagopus. The general pattern is more like that of michahellis than Herring Gull. Juvenile Herring Gulls show a variable but usually extensive scatter of dark bars and spots on the rump, uppertailcoverts and tail base. This reduces the contrast between these areas and the broader, more diffuse tail band, which averages a little browner than that of cachinnans and michahellis. Both cachinnans and michahellis have a very dark (black-looking) tail band that contrasts strongly with the white rump and tail base. Malling Olsen & Larsson (2003) stated that the tail band of cachinnans is 'fuller and more even' than that of michahellis. Certainly, the tail band of many michahellis is uneven, being noticeably deeper on the central tail feathers. In general, the tail band of cachinnans is more even in width but on some it is clearly deepest in the middle, and hence uneven. While many cachinnans the tail band is deep across its whole width, on some it is no fuller than for michahellis. In short, the depth and evenness of the dark tail band are thus of no real value for the separation of cachinnans and michahellis. There is a greater tendency for the dark tail band of cachinnans to break into a series of narrow, regular bars along its basal edge (e.g. plate 55) while the white tips to the tail feathers are deeper in michahellis than cachinnans, forming a more striking terminal band (Jonsson 1998).

The pale 'window' on the inner 4–5 primaries is generally less prominent in cachinnans than Herring Gull. The (ranked) order of window prominence runs from Herring to cachinnans to michahellis to Lesser Blackbacked Gull (virtually no window). In Herring Gull, the inner primaries (both inner and outer webs) are much paler brown than the outer primaries, creating an obvious panel; in michahellis, the outer webs of all the primaries are much more similar in tone and only the inner webs of the inner primaries are slightly paler, giving a much less obvious window. In cachinnans the pattern is rather variable but overall intermediate between Herring and michahellis: on many, the inner webs of the inner primaries are distinctly paler than the outer webs, while the outer webs of these feathers are almost as dark as
the outer primaries. This produces a more contrasting, 'Venetian-blind' pattern than seen on Herring Gull and michahellis. However, darker cachinnans are very similar to michahellis, with only slightly paler inner webs to the inner primaries. Occasionally, the outer webs of the inner primaries of cachinnans are also paler than the outer wing, so rather than a Venetian-blind pattern the impression is of a subtle, pale panel.

There are also some differences among the species in the markings at the tip of the inner 4–5 primaries. Herring Gulls normally have a complex pattern: individual feathers have a mixture of subtle, diffuse pale areas on both webs, a dark shaft streak and arrowhead, often with a crossbar (plate 57). The precise pattern varies individually, but the key point is the complexity. There is no such complex patterning to the inner primaries of michahellis, which simply have a uniform dark outer and a fractionally paler inner web (plate 58). Occasionally, michahellis have a small and subtly paler oval patch on the outer and/or inner web of some of their inner primaries (P2–P4/5). Contrary to some literature (e.g. Garner & Quinn 1997), cachinnans frequently also show such pale patches. In fact, a large proportion have clear, sharply defined lozenge- or cigar-shaped patches on the outer web of the inner primaries (e.g. plate 55) which are more striking than those of michahellis. These are often accompanied by a more diffuse oval patch on the inner web.When present, these pale areas tend to break up the Venetian-blind pattern. However, darker cachinnans lack pale patches in their inner primaries and so resemble typical michahellis. In general, it seems that both cachinnans and michahellis have the outer web of P1 entirely dark, with pale patches present on only P2–P4/5, whereas Herring Gull has pale areas as well on P1.

Overall, the pattern on the inner primaries is useful for separating Herring Gull from michahellis. Typically, cachinnans sits somewhere between the two, but extremes overlap with darker Herring Gulls and lighter michahellis, so the pattern of the inner primaries is only a supportive feature. Assessment of the primary pattern requires good-quality flight photographs.

Larus michahellis 1cy, August 27 2012, Katwijk, the Netherlands. Picture: Mars Muusse. A typical, strongly marked michahellis. The tertials have simple, sharply defined narrow fringes that extend only around the distal part of the feather, and the greater coverts have extremely obvious notches. There is a dark mask around the eye.

Larus cachinnans 1cy, 04-12 September 2009, Klaipeda, Lithuania. Picture: Chris Gibbins. A striking bird, with a well-marked tail pattern. The 'window' in the inner primaries is paler and more distinct than on michahellis but less striking than on most Herring Gulls. Note the pale 'lozenges' on the outer webs of P2 and P3: these are less frequently present on the inner primaries of michahellis and, when they are, are typically smaller and less prominent than on this cachinnans.

Larus cachinnans 1cy, 04-12 September 2009, Klaipeda, Lithuania. Picture: Chris Gibbins.

Larus michahellis 1cy, July 25 2010, Roses, Spain. Picture Chris Gibbins. The underwing is much darker than on cachinnans, with a bold pattern of alternate dark and pale bands.The inner webs to the inner primaries of this individual are at the paler end of the scale, but note that it lacks pale lozenges on the outer webs of the inner primaries.

Bare parts
The bill of 1CY cachinnans usually appears largely black, with a pinkish base to the lower (and sometimes the upper) mandible visible at close range. In extreme cases, the bill of cachinnans (and michahellis) can be extensively pale in mid September. This seems to be a more common feature in these species than in Herring Gull. The legs of 1CY cachinnans are a pale, washed-out flesh colour, sometimes appearing greyish or bluish flesh. The iris is dark brown.

above: Larus cachinnans 1CY PLG DN-25866 August 06 2008, Minden, Germany (Armin Deutsch).

above: Larus cachinnans hybrid 1CY 21P3 August 14 2007, Oostende, Belgium (Francois Roland).

below: Larus argentatus argentatus 1CY HX09 August 13 2010, IJmuiden, the Netherlands (Mars Muusse).

END OF PART 2

CONTINUE AT PART 3: BIRDS IN THEIR FIRST WINTER (1CY/2CY BIRDS IN OCTOBER-APRIL)

Below:
Larus cachinnans 1cy in Azerbaijan.

first set:
Larus cachinnans 1cy in Azerbaijan
showing limited post-juvenile moult

third set:
Larus cachinnans 1cy in Azerbaijan
extensive wing & covert moult

flying birds