Amir Ben Dov (Israel)
Chris Gibbins (Scotland)
Hannu Koskinen (Finland)
Mars Muusse (the Netherlands)
adult heuglini: May
Is it possible to identify Baltic and Heuglin's Gulls?
By Chris Gibbins, IN: Birding Scotland 7(4), December 2004.
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Field discussions with delegates at the International Gull Meeting held in Finland in August
2002 considered the possibility that heuglini might show a tendency to have the red gonys spot restricted to the lower mandible, in contrast to graellsii and intermedius in which the
red frequently extends onto the upper mandible. Analysis of photographs of heuglini taken
either on the breeding grounds or in the Middle-East (n = 31) indicated that 71% lack red
on the upper mandible. Analysis of data supplied by Mars Muusse, together with
assessment of published photographs (n = 310) indicated that 56% of graellsii/intermedius lack red on the upper mandible. The data for graellsii/intermedius suggest that the presence of red on the upper mandible is season specific, being much
more frequent in mid-summer when birds are feeding young than it is in winter (Figure 2).
Because of the relatively small sample size, it was not possible to disaggregate the heuglini
data in the way necessary to conduct this seasonal analysis. However, THIS BIRD indicates
that heuglini can have red on the upper mandible in mid-summer. While these analyses
suggest that there may be average or population-level differences in the frequency of red
on the upper mandible (less frequent in heuglini), they also indicate that because of
overlap this feature is not particularly useful for identifying individual birds. Buzun (2002)
argued that red on the upper mandible of heuglini is a feature of young adults, being
present on a part of the bill that was previously black. However, this is not the case in
graellsii: for example, studies by Mars Muusse and colleagues in the Netherlands have
shown that birds in their 19th calendar year can have red on the upper mandible, while
birds in their 15th calendar year can have both red and black on the upper mandible.
The timing of the primary moult of adult birds is frequently cited as one of the key differences between heuglini and graellsii/intermedius. The primary moult of graellsii and intermedius usually commences in May and continues until November/December. The
moult of heuglini is later, commencing in June/July and often not being completed until
January/February. Two birds from around 100 heuglini seen in UAE in the period 28
February–16 March 2004 still had P10 regrowing, illustrating how late the completion of
primary moult can be in this bird. The primary moult of heuglini is usually suspended prior
to southward migration in the autumn whereas in graellsii it is usually continuous. At the
population level, the difference in moult between heuglini and graellsii is illustrated nicely
in data given by Rauste (1999) and Stewart (in press). These data have been used to
produce Figure 3. Plate 169 shows a heuglini photographed on 1 September; it is very
typical, with seven retained old primaries and only one fully grown new one (P2 is not yet
fully grown and P 3 is missing). On this date, the majority (77%) of graellsii have three or
more fully grown new primaries (as per pages 166–167).
The relatively late primary moult of heuglini has been used in the search for out or range
individuals. For example, a dark-backed gull on Shetland on 28 November 1999 was
initially mooted as a possible heuglini for this reason. The value of population-level
differences in primary moult for the identification of individual birds is discussed with
respect to the first case study bird (see part iv below).
(iii) Field characters of immature heuglini
Like fuscus, a proportion of immature heuglini return to northern areas during the summer.
Such birds may wander or be displaced while on passage and so are possible vagrants to
Western Europe. It is therefore useful to consider their identification. Some examples of 2
cy and 3 cy heuglini are shown in on thi ssite as well.
The post-juvenile moult of heuglini is rather variable. The first generation (juvenile)
scapulars are usually all replaced on the wintering grounds. The pattern on the second
generation scapulars is typically rather simple, with a brownish-grey feather centre and a
diffuse paler fringe and tip; darker patterning usually comprises a simple shaft streak,
although some can have a prominent anchor pattern. Anything from 0-100% of the first
generation wing coverts and tertials may be moulted out on the wintering grounds, so
birds can arrive back in the spring of their second calendar year with either first or second
generation feathers; usually there is a mixture of both. In the UAE it was not possible to
determine the dominant pattern of covert moult in heuglini because of the difficulty of
separating heuglini from barabensis in their first winter (personal observations, March
2004). Like the scapulars, the pattern on the second generation coverts of heuglini
tends to be simple, although again there is individual variation. Many heuglini in the
summer of their second calendar year have some silvery-grey scapulars and coverts
which appear paler than adult feathers. It is difficult to know whether these are second
or third generation feathers. It may be that like some other gulls, feathers of the same
generation can have a different pattern, depending on when they are moulted in. Thus,
the grey feathers may be third generation (perhaps most likely), or they may be late moulted
second generation feathers that contrast with the earlier-moulted, brown ones
(this is discussed in the caption to Plate 173). Birds usually return north with a complete
set of first generation primaries and start moulting them in May or June (Rauste, 1999).
However, 5-10% of birds undergo some primary moult during their first winter (HERE, HERE, HERE, HERE). In June 2002 Visa Rauste observed two 2 cy birds in Komi, Russia, each with a full set of second
generation primaries (Rauste, pers. comm.). In other respects they were typical heuglini.
These two birds suggest that heuglini can undergo a complete primary moult during
their first winter and so, in this respect, overlap with fuscus.
Overall, heuglini appear white-headed and white-bodied in the summer of their second
calendar year, with dark streaking usually restricted to the hind neck and, to a lesser extent, the
head. The bill usually has a pinkish base and dark tip. Sometimes the dark tip is rather diffuse,
sometimes it is rather sharp and Glaucous Gull-like. Some individuals can have yellow pigment
beginning to develop in their bill and even some red around the gonys. As with fuscus, the
underwing is usually rather white compared to graellsii and intermedius. Nonetheless, some
second generation underwing coverts can show quite strong marks or barring; set against the
white feathers, this can produce a rather contrasting underwing (HERE).
For UK birders used to dealing with graellsii, heuglini in the summer of their third calendar
year tend to look old for their age. Typically they have many grey, adult-like coverts and so
sometimes look more reminiscent of 4 cy graellsii. This greyer wing is shared
by many 3 cy intermedius (Mars Muusse, pers. comm., from observations of ringed birds).
As with other large gulls, the bare parts of this age group are rather variable. In some the
legs have already developed strong yellow tones, in others they are pinkish. The bill usually
has yellow tones, with a variable combination of black around the tip and signs of the red
gonys spot developing. Note also the dark eyes of the bird in Plate 174. The tail pattern of
3 cy heuglini is rather variable: usually there is some blackish or dark brown patterning on
the feathers but some have a wholly white tail.
END OF PART 3
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|Heuglini adult, May 01 2006, Tampere, Finland. Picture: Hannu Koskinen.