Koshelev
V.I.1, Zagalska M.2
1 – Melitopol Pedagogical University, Melitopol,
Ukraine
2 – Dept. of
Genetics and Animals Breeding, University of Agricultural, Poznań, Poland
SEX
DIMORPHISM IN ADULT AZOV CASPIAN GULL LARUS
CACHINNANS CACHINNANS PALLAS, 1780
Introduction
The taxonomic
status of the gulls from cachinnans group
is not clear and still discussed (Johnson 1985; Filchagov, 1992, Wink et al.,
1994; Helbig, 1994; Heidrich et al., 1996; de Knijff et al., 2001). Many
authors described field features of this forms (Klein, 1994; Gruber, 1995;
Garner & Quinn, 1997; Garner et al., 1997; Jonsson, 1998). Still heated
discussions under cachinnans could be
caused among other things by poorly known populational variability within of
the Caspian Gull. There are only two papers describing just some aspects of the
morphometric problems (Mierauskas et al., 1991; Liebers & Dierschke, 1997).
In this paper we show morphological variability within analyzed group and
features to recognize sexes.
Material and
methods
Gulls were trapped
in the breeding colony at Molochnyy Lyman in 2000-2001, 2005-2011. This is salt
reservoir near the north Azov seashore (20 km southeast from the Melitopol
city). Natural formations around the Lyman are the salina and steppe. Total
number of Caspian Gulls on the Lyman varies between 5,0 and 6,5 thousands of
breeding pairs (Koshelev, 2000; Chernichko et al., 2000). All gulls were
trapped on the nests on the Podkova Island, located near the Verchnya Girsovka village.
About 2,000 pairs were breeding here at this time. The Podkova Is. is located
about 100 m from the tip of narrow peninsula, and about 1 km from the eastern
bank of Lyman. This is a lagoon-type islet, with diameter of about 700 m, and
the lake of stagnant water in the central part. Most of area is open and flat
only partially grown by reeds Phragmites
communis. Birds nests are usually
located on the ground, in low, dense vegetation (Salicornia sp.) or at the edge of reeds. Some nests were found in old
Cormorant’s nests (to 0,5 m above ground) or just on the open ground with no
vegetation.
Some dead gulls
found in the breeding colony and specimens collected in the INFS (Bologna,
Italy) from Sivash Lake and Danube Delta were measured. The total of measured cachinnans is 80 birds.
Measurements description
For trapped birds
was taken 28 parameters (14 metrical and 14 colour features), based on the
instruction by P. Chylarecki, W. Meissner and A. Sikora with our corrections.
Among standard measurements were: total head length (HE), bill length (BI),
tarsus length (TR), wing length (WI). Additional were measured: bill height at
gonydeal angle (HBIG), minimum bill height between gonydeal angle and skull
(HBIN), middle toe length (MT), and “hand” – the distance between tip of 1st
and 10th primary (DL) on maximum spread wing, not measured in
moulting birds. Colours were determined for following parts of the gull body:
iris (IR), scale 1 to 4, where (1) was pure pale with no dark pigmentation, (2)
– a few and tiny dark spots, (3) – many, tiny or big dark spots (at the
distance usually seems to be dark iris) and (4) – lots of dark pigmentation,
covering all or almost all of the iris surface - at distance looked as totally
dark eye. Eye-ring (ER) colour was determined in following scale: (1) – yellow
or yellowish, (2) – pale orange, (3) – dark orange and (4) – reddish/red. Legs
colour was determined separately for tarsus, toes and the swimming web with the
same scale: (1) – “cadaverous” (pale grey, greyish, green-grey), (2) – pinkish
to flesh pink, with no yellow tone admixed, (3) – pinkish with slight yellowish
tinge, (4) – yellowish or pale yellow and (5) – deep yellow. It is need to
notice, that all the colours were determined just after the bird was trapped (colours
may bleed after few minutes because of bird’s stress!). Mantle colour (M) was
determined on alive, captured gulls or later, on the feathers taken from the
mantle with the use of Kodak Gray Scale (Small) CAT 152 7654 1995 where 0 is
white and 20 is black. The colour of tongue on P10 (Z) was determined in three
categories: (1) white/whitish, (2) grey, but lighter than mantle and (3) grey,
as dark as mantle.
To characterize
black and white pattern on the outer primaries, following measurements were
taken: maximal length of the white on P10 tip (W10); length of the white on P9,
measured as the distance between the beginning of the white spot and the tip of
the feather (W9); minimal length of the black bar on P10 (B10), length of the
black on P9, measured from the distal end of grey/white tongue to the end of
black bar (B9), in the same way length of black bar on P7-8 was measured (B7,
B8). All the measurements were taken along the shaft. For two outermost
primaries (P9-10) the types of black-white pattern were noted, in scales from 1
to 5. On P10 following types were recognized (T10): (1) - “thayeri-pattern” – grey or white tongue connected with the white
primary tip, regardless of presence or absence of black bar (2) all white tip
of the primary, no black markings, (3) – traces of black near the tip, (4) –
incomplete subterminal black bar and (5) – complete subterminal black bar. For
P9 the types were (T9): (1) – “thayeri
pattern”, grey/white tongue connected with the white tip, regardless of
presence or absence of subterminal black bar, (2) – huge white spot, reaching
both feather’s edges, (3) – white spot do not reaching one of the feather edge,
but reach the second one, (4) – small white spot on one web only, not reaching
any edges of the feather and (5) – no white spot. Also the number of
black-tipped primaries was noted (NB), and the type of black pattern on the
innermost primary with dark (TI) in three
categories: (1) – only dark spots, (2) – incomplete black bar and (3) –
complete black bar.
Blood samples were obtained from the most of the
captured birds. Blood was conserved with EDTA buffor. Sex of gulls was
determined with use of molecular methods (Polymerase Chain Reaction; Griffiths
et al., 1998; Griffiths 2000; Kahn et al., 1998).
Standard measurements. In wing length obvious sexual
dimorphism is shown, with only a small overlap. The total head length is
distinctly higher for males (mean 137.1 mm) than for females (mean 122.9 mm).
Combination of wing length and total head length is very good character
distinguishing sexes. Bill is longer and higher (at gonydeal angle) within
males. Both sexes have the same bill proportions, so the bill ratio is the
same. Longer bill with less prominent gonydeal angle in cachinnans results in general bill ‘jizz’ – it seem to be thinner
and more elongated, what is useful in field identification. Note however, that
some cachinnans males can look very
heavy-billed, in both hand- and field-appearance and some females surprisingly
delicate- and thin-billed. Both tarsus and middle toe are longer in males, although
covering of dimensions between the sexes was found.
Iris & Eye-ring. Strong variability was noted
in the eye-colouration within examined gulls. No birds with pure pale iris,
without any dark spots were trapped. Out of 58 gulls, 26 have pale iris with a
few dark spots admixed. Next 11 birds have a lot of dark pigmentation, covering
most of iris, what from a distance looked as a completely dark eye. At the end
of the scale (4) – completely dark iris – were 21 gulls. Background variability
of iris is also observed, from very pale yellowish to khaki with greenish
shade. Within birds no yellow eye-ring was found. Most of gulls (n=56) have
eye-ring pale- (24) or dark-orange (30) and only two individuals have it reddish.
Correlation between colours of iris and eye-ring was weak (Pearson r = 0,31).
Bill. Was usually pale yellow. It is worth to notice,
that only females (5 of 32) have an amount of reddish tinge on upper mandible,
in all males the reddish spot was restricted to the lower one. Out of 55
otherwise fully adults, 24 had various dark signs on the bill, which varied
from single dark grey spot to black bill band. Recorded in the same proportion in both sexes, it was present also in 11-
and 12-years old birds.
Legs.
Legs colour varied strongly.
Most of trapped gulls (n=56) had legs with “cadaverous” colour (such a colour
could have been greyish, grey-green or pale pinkish “washed out” – 68% of trapped birds). The second big group
are birds with some yellow on the legs (32%), the most numerous were pale
yellow- or yellowish-legged birds. No birds with intensive, deep yellow legs
were trapped. There are no difference in colour between tarsus, toes and
swimming web in general. The only one
bird (male) with very intensively coloured tarsus and toes (pale yellow, 4 on
the scale), had swimming web flesh yellow (5 on the scale, the same as in michahellis). Two next birds (female and
male) had also more intensive colour on the swimming web (pinkish) than on the
rest of leg (cadaverous).
To check how the
colour depends on the light, we took a sample of birds seen from the distance.
In the group of 104 adults, 58 had “cadaverous” legs and 46 had more or less
yellowish tinge, sometimes very deep yellow. It is need to notice, that in
strong sunlight “cadaverous”, wet legs (with a slight yellowish tone) seen from
a distance can look very yellow.
Mantle colour. The grey mantle
colour varies strongly within cachinnans gulls.
The lightest individuals were about 5.0 on the Kodak scale, while the darkest
at about 7.0 (medium neutral grey), with the mean for all examined birds (n=56)
placed at 6.22. There were no differences between males and females.
Outermost primary (P10). On P10 connection of grey
tongue and white primary tip and the extension of subterminal black bar developing
were noted (see Material and methods). The one extreme is the lightest variant
- a “thayeri”-pattern (very pale,
usually white tongue connected with white primary tip, regardless of developing
extension of subterminal black bar), the darkest one – fully developed
subterminal bar, crossing the feather transversally (with the black bar
separating pale tongue from the white primary tip).
Variability was
found within population. Most
numerous, together giving over 70% were types 2 and 3 (all-white P10 tip or
white with traces of black). “Thayeri”-pattern
was present with about 8% of birds, and all of them were females. P10 patterns
of females differs from that of males, being moved to have more white in
general (highly significant, χ2 test, p<0.001). Black bar
(B10), separating end of the inner web tongue from the white primary tip was
narrow. Very pale, white or whitish inner web tongue strongly contrasts with
black, and only in 4 of 55 individuals the border between white and black was
little diffused. All of them were males, with significantly more black on P10
(41.2 mm) than mean for males (31 mm). The white tongue is deepest from all
European gulls, ending 58-115 mm from the primary tip, and often has specific
shape. White primary tip (W10) is long, with mean of 65 mm.
Second outermost primary (P9). The P9 pattern was
very stable (the reverse of P10 patterns). Huge white mirror, reaching both
feather’s edges was present in all males and in the most females. Only 5
females have it reduced to reach one of primary edges, but it still was present
on both webs. One bird, a female, had “thayeri”-pattern.
The black bar is strongly broader than on outermost primary. The white was shorter than on P10. Inner web tongue was
still very pale, although can be darker grey than on P10; the typical shape and
sharp delineation from black was present in almost all cases.
Discussion
Idetification of
large gulls require a combination of multiple field marks (Klein & Gruber
1997; Jonsson, 1998 among others).
Variability within
analyzed population seems to be more pointed for females. Also there are some
features, mainly in basic measurements (Cramp & Simmons, 1983), let to
distinguish sexes. Of course sexual dimorphism is evident from measurements,
the males are larger then females (Harris & Hope Jones, 1969).
The difference
between minimal and maximal (at gonydeal angle) bill height is obviously small
within cachinnans gulls (0.4-2.1,
mean 1.3 mm), smaller than in the two other european populations (michahellis and argentatus, t-test, p=0.001). Presence of dark sings on the bill
were in the same proportioin as presented by Liebers & Dierschke (1997), c
50%. It seems to be specific for part of population. There is no evidence to
judge age of the birds because of the presence a dark sings on the bill.
Iris in cachinnans
group is variable but often more or less dark coloured (Garner & Quinn, 1997; Klein & Gruber, 1997), and it is a good feature
distinguishing cachinnans from other
european populations, among which dark-eyed gulls are extremely rare. No pale irises without any dark spots were
noted in examined birds. Gulls observed from the distance seems to be
“pale-eyed” but in hand iris in most cases has dark spots with different
intensity. Liebers & Dierschke (1997) suggest that over 60% of birds have pale iris. It is very possible
that to this group were joined birds with iris signed in our classification as
a type 2 and probably sometimes type 3. Classification suggested by this
authors basis on the impression which could depend on intensity of the light
and can not be treated as given the factual view. Furthermore very weak
correlation was found between colour of iris and eye-ring, in opposite to
Liebers & Dierschke (1997).
We agree that from
the distance legs in many birds are deep yellow (Liebers & Dierschke, 1997)
especially under specific light condition (e.g. sun set). In-hand all birds
never had deep yellow legs (such as michahellis),
only admixed yellow or yellowish tones.
Females evidently tend to have more white on the
primaries, what results also in having more restricted black parts of the
feathers in all examined features (P9 & P10 patterns, black and white
dimensions, number of primaries with black). According to Mierauskas et al.
(1991) the number of the black-tipped primaries was 6 or 7, but in our analysis
we found differences between sexes to be significant. While comparing our data
referring types of black on P10 and P9 and data by Mierauskas et al. (1991) we
find some new aspects. Interesting is that “thayeri” type appeared on the P10
(not recorded by Mierauskas et al., 1991) and/or on the P9 and only in females.
Additionally on the P9 in males only type 2 were noticed. It seems to be very
stable feature although there no statistically significant differences between sexes.
In summary, the morphometric
variation of cachinnans could be very wide, but knowing the biometrical space it
is possible to distinguish sexes on alive birds. Within defined variation exist
typical and unique characters for cachinnans.
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