Larus cachinnans

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adult cachinnans: April

Mixed colonies of large white-headed gulls in southern Poland

BY: Marcin Faber, Jacek Betleja, Robert Gwiazda and Pawel Malczyk
IN: British Birds 94: 529-534, November 2001

In the early part of 1999, we discovered a small colony of large white-headed gulls Larus at a gravel-pit near Jankowice, on the banks of the Vistula river in southern Poland, about 50 km from Krakow. On 28th February, we observed six pairs of gulls there which showed characteristics of the nominate race of Yellow-legged Gull L. cachinnans cachinnans ('Caspian Gull', hereafter referred to simply as cachinnans). When engaged in the characteristic long-call display, they adopted the 'albatross posture', with head raised vertically, and wings raised above and behind the body with the hand unbent, which is characteristic of cachinnans (Mierauskas et al. 1991; Jonsson 1998), while the calls were also lower-pitched than those of 'Northern' Herring Gulls L. argentatus argentatus (hereafter referred to simply as argentatus). During a subsequent visit to the colony, on 17th April, when the gulls were nesting, we also observed two individuals of the Mediterranean race of Yellow-legged Gull L. c. michahellis (hereafter referred to simply as michahellis).
At the Jankowice colony, there were 11 occupied nests in May 1999, while some 40 nests were found in both 2000 and 2001. We visited colonies of large gulls elsewhere in southern Poland, including one of about 120 nests (at Tarnow) and two each of about ten nests (at Goczalkowice reservoir and Czorsztyn reservoir), and we estimate the current breeding population of cachinnans in southern Poland to be approximately 180
pairs.
During three years of study at Jankowice, Tarnow and Goczalkowice reservoir, we managed to capture 85 gulls, which we ringed, measured and photographed (see plates 287-297), and of which we compiled detailed descriptions. Most (77.6%) showed characters of adult or subadult cachinnans (plates 287-289), while five individuals (5.9%) were identified as michahellis (plates 290 & 291). We did not find typical argentatus in these breeding colonies, but 16.5% of the gulls which we examined in the hand showed features consistent with their being hybrids. Most of those which we believe to have been hybrids exhibited characters that were intermediate between those of argentatus and those of cachinnans (plates 294 &
295). In addition, two individuals showed features intermediate between cachinnans and michahellis (plates 292, 293, 296 & 297).

287. Subadult Yellow-legged Gull Larus cachinnans of nominate subspecies cachinnans, Jankowice, southern Poland, 2nd May 1999. Note the very long and comparatively slender bill, and flat forehead. Orbital ring orange-red, while the iris appears dark at distance (but is yellowish with dense brown spotting at close range). Picture: Jacek Betleja.	288. Wing of adult Yellow-legged Gull Larus cachinnans of nominate subspecies cachinnans, Jankowice, southern Poland, 2nd May 1999. This individual has a typical 'ponticus' (Black Sea-type) wing pattern, with a white tip to P10 and extensive white 'tongues' extending into the black wingtip. Picture: Marcin Faber.
289. Wing of subadult Yellow-legged Gull Larus cachinnans of nominate subspecies cachinnans, Jankowice, southern Poland, 1st May 1999. Like the individual in plate 288, this has a typical 'ponticus' wing pattern. On the primary coverts, traces of brown confirm that this bird is not yet fully mature. Picture: Marcin Faber.	290. Adult 'Mediterranean'Yellow-legged Gull Larus cachinnans michahellis, Jankowice, southern Poland, 1st May 1999. Note the dark grey mantle, deep yellow legs and plain, pale yellow iris. Picture: Jacek Betleja.

Details of captured gulls

In order to assign individuals to a particular taxon, we used the following key texts: Bakker et al. (2000), Garner & Quinn (1997), Garner et al. (1997), Jonsson (1996, 1998), Klein & Gruber (1997) and Neubauer &
Millington (2000). We also discussed the putative hybrid individuals with a number of gull experts, in particular Detlef Gruber, Ronald Klein, Gregory Neubauer and Rik Winters.
L. c. cachinnans The upperwing pattern was typical of the western, or Black Sea, type, often referred to as
L. c. ponticus. Biometrics also supported our identification of these birds as cachinnans. Key identification features were as follows. Long, obvious, whitish 'tongue' projecting towards the tip of the inner web of the outermost primaries, forming a clear contrast with the darker mantle. Typically, a wide, complete black band across both webs of P5 (primaries numbered descendently, with the outermost being P10), sometimes with a black spot on P4, too (plate 288). Only a narrow black band on P10, this lacking altogether in many cases. Mantle paler than michahellis, and a similar shade of grey to argentatus. Forehead comparatively long and flat, bill slender. Legs pale yellow or greyish-pink. Orbital ring orange-red. Iris generally brown or light brown, but often yellowish with dense, darker brown spotting, causing it to appear dark at a distance (plate 287).
L. c. michahellis Mantle colour dark grey, darker than any other form discussed here, with deep yellow legs and clean, pale yellow iris (plate 290). Primaries with extensive black, covering almost one-third of the hand. Pale tongues on the outer primaries, not showing marked contrast with mantle (plate 291).
'argentatus × cachinnans hybrids' 12 individuals showed features intermediate between these two forms, although we cannot be absolutely certain that they are true hybrids, rather than simply less typical cachinnans. These birds typically showed the following features: In general, biometrics not typical of argentatus or cachinnans (BWP; Mierauskas et al. 1991; see Appendix 1 on page 534). Rounded head shape, with high forehead, favouring argentatus, as did the iris colour (very pale, yellow, finely spotted brown; appeared pale at a distance). Leg colour intermediate between the two, greyer than typical flesh-pink of argentatus. Upperwing primaries showed a typical pattern for western cachinnans, with very obvious whitish tongues on the outermost primaries, showing a marked contrast with the darker mantle. Mantle colour of similar shade of grey to cachinnans. One individual is shown in plates 294 & 295. The biometrics of this individual are typical for argentatus (BWP; Mierauskas et al. 1991), with the exception of the bill, which was comparatively long and slender. Wings relatively short, and tarsi relatively short and wide, similar to argentatus. In addition, this individual, when examined on 1st May 1999, differed from all the cachinnans
handled on that date in that it was the only one which had not yet begun primary moult. All the gulls diagnosed as pure cachinnans had commenced moult, having lost two or three innermost primaries.
'michahellis × cachinnans hybrids' Two adult males showed features intermediate between these two forms. They were characterised by a comparatively dark mantle, darker than that of a typical cachinnans, with a broad black band on P5. One of them had dark grey longitudinal spots on P4 and P3, while the primaries had very small apical spots. A large extent of black on the primaries covered approximately one-third of the hand (plates 292 & 297). Both had a relatively steep forehead, and the bill was long and, particularly, deep. Leg colour of one individual was pale yellow, and that of the other pale pink. The irides were yellow with some brown spotting (plates 293 & 296). These two individuals had biometrics closer to cachinnans than to michahellis, the only marked difference (from cachinnans) being in bill depth (see Appendix 2).

291. Wing of adult 'Mediterranean'Yellow-legged Gull Larus cachinnans michahellis, Jankowice, southern Poland, 1st May 1999. This form shows a great deal of black on the primaries, extending across about one-third of the hand. The grey 'tongues' on the outer primaries do not differ sharply in colour from the mantle. Picture: Jacek Betleja.	292. Wing of adult gull thought to be hybrid between nominate and Mediterranean forms of Yellow-legged Gulls Larus cachinnans cachinnans and L.c.michahellis, Jankowice, southern Poland, 1st May 1999. The grey 'tongues'do not contrast with the dark mantle;there is a broad black band on P5 and dark grey longitudinal spots on P4 and P3, while there are just very small apical spots on the primaries. See text for further discussion. Picture: Marcin Faber.
293. Head of putative hybrid between nominate and Mediterranean forms of Yellow-legged Gulls Larus cachinnans cachinnans and L. c. michahellis, Jankowice, southern Poland, 1st May 1999. Note the long bill (more similar to cachinnans), but which is also deep, and the steep forehead (both more similar to michahellis).The iris is yellow but with plenty of brown spots, intermediate between the two forms. Picture: Jacek Betleja.	294. Adult gull thought to be hybrid between nominate Yellow-legged Gull Larus cachinnans cachinnans and 'Northern' Herring Gull L. argentatus argentatus, Jankowice, southern Poland, 1st May 1999. The head shape is rounded, with a high forehead, while the tarsus is short and quite thick (favouring argentatus). The bill is long and comparatively slender, favouring cachinnans.The legs are pale, greyish-flesh, while the iris colour is pale, yellow, but spotted brown, both features which are intermediate between typical examples of the two forms. Picture: Marcin Faber.
295. Wing of putative hybrid between nominate Yellow-legged Gull Larus cachinnans cachinnans and 'Northern' Herring Gull L. argentatus argentatus, Jankowice, southern Poland, 1st May 1999. The mantle is very pale grey, with a typical 'ponticus' wing pattern showing a very long white 'tongue' on P10. All biometric features are, however, typical of argentatus. Picture: Marcin Faber.

Discussion

In recent years, large white-headed gulls have shown an increase in numbers and an expansion of range in many parts of Europe (Snow & Perrins 1998). In Poland, argentatus began to nest in the early 1970s, since when a steady rise in numbers and an extension of the area occupied have been observed (Tomialojc 1990). Currently, this subspecies occurs mainly in northern Poland (Hagemeijer & Blair 1997). Large gulls with yellow legs were first recorded breeding in southern Poland in the 1980s, in the central part of the Vistula river basin (Dubois et al. 1990), where small numbers still breed. The subspecific identity of these gulls has caused a great deal of debate (Chylarecki & Sikora 1991; Dubois et al. 1990; Eigenhuis 1990;
Mierauskas & Greimas 1992; P. Chylarecki in litt.), although Jonsson (1998) claimed that all three forms (argentatus, cachinnans and michahellis) are present at this site. Away from this area, breeding by yellow-legged gulls was recorded in 1998 in Malopolska, near Przemysl (Walasz & Mielczarek 1992), and on the Mietkowski reservoir, in Silesia, where two pairs of michahellis nested within a colony of cachinnans in
2001 (T. Stawarczyk in litt). Until recently, this was the only confirmed Polish record of yellowlegged gulls which had been confidently identified to subspecies. Now, new colonies of nesting large gulls are discovered in southern Poland every year. At Jankowice, we have confirmed that individuals of the forms michahellis and cachinnans are nesting side by side. We cannot be absolutely certain that the two forms are mixing,
although the appearance of gulls with intermediate features would suggest that this is the case.
In conclusion, although the identification of adult michahellis is, in our opinion, relatively straightforward, our experience suggests that the positive identification of adult cachinnans in this part of Europe can be extremely tricky. The occurrence of putative hybrids, or of individuals which are intermediate in appearance
between cachinnans and argentatus, means that observers should be cautious in assigning individuals to this taxon in the field, at least without extremely detailed observations or an analysis of photographs.

296. Head of adult putative hybrid between nominate and Mediterranean forms of Yellow-legged Gulls Larus cachinnans cachinnans and L. c. michahellis, Jankowice, southern Poland, April 2000. Picture: Jacek Betleja.

297. Wing of adult putative hybrid between nominate and Mediterranean forms of Yellow-legged Gulls Larus cachinnans cachinnans and L. c. michahellis, Jankowice, southern Poland, April 2000. Picture: Jacek Betleja.

Acknowledgments

We are grateful to all those who offered useful discussion and comment, in particular Detlef Gruber, Ronald Klein, Gregory Neubauer and Rik Winters.

References

See PDF.

Appendix 1.
Biometrics of Larus cachinnans cachinnans from the Black Sea and of L. argentatus argentatus from the Baltic Sea (Mierauskas et al. 1991), together with biometrics of 12 Polish gulls showing intermediate characters between those two taxa. All measurements are in mm.

Appendix 2.
Biometrics of Larus cachinnans michahellis from the Mediterranean and of L.c. cachinnans from the Black Sea (G. Neubauer & M. Zagalska, unpublished data), together with biometrics of two Polish gulls showing intermediate characters between those two taxa. All measurements are in mm, and all refer to males.