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Identification of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids.

Identication of juvenile Greater
Spotted Eagle, Lesser Spotted Eagle
and hybrids
Jan Lontkowski & Grzegorz Maciorowski
The identication of Greater Spotted Eagle
Aquila clanga (hereafter clanga) and Lesser
Spotted Eagle A pomarina (hereafter pomarina) is
a well-studied and often difcult issue. Several
good papers on identication of spotted eagles
have been published. Their eld characters are
rather well known and especially birds in juvenile
plumage are relatively easy to tell apart. The spe-
cic characters are visible already in nestlings,
with their feathers only partly grown. There is a
wide individual variation in the identication fea-
tures which, however, show almost no overlap
between the two species. Identication problems
arise in the zone where both species occur in
sympatry, from eastern Poland, Lithuania, Latvia
and Estonia east to western Russia and south to
the Black Sea in central Ukraine, because, in this
zone, hybrids between the two species are quite
common (Lõhmus & Väli 2001, Helbig et al 2005,
pers obs), showing mixed or intermediate plum-
age features.
Identication of hybrids based on the indices
proposed by Väli & Lõhmus (2004) is of little, if
any, use in the eld. Dombrovsky (2009), dealing
with these hybrids based on much more extensive
data than we used, does not specify any features
enabling eld identication.
The aim of this paper is to present diagnostic
characters of the European spotted eagle species
and their hybrids in juvenile plumage. Although
working from a eld identication perspective,
we acknowledge that birds appearing like pure
clanga or pomarina may still show genetic traces
of hybrid ancestry. The set of characters described
here allows to identify birds in the hand, well seen
in the eld or well photographed.
Our analysis is based mainly on photographs
and feathers taken from nestlings during ringing in
1994-2010. We examined more than 65 nestlings
of clanga, 160 of pomarina and 35 hybrid nest-
lings. The identity of hybrids was conrmed by
observation of their parents on the nest. The char-
acters taken into consideration were general col-
oration, especially of head and upper wing; eye
colour; size; silhouette; and wing formula (cf
Forsman 1999). We have used also results of 62
DNA samples which allow us to learn more about
the plumage of conrmed pure species and hy-
brids (Väli et al 2010). All nestlings of clanga and
their hybrids, except two, came from Biebrza val-
ley (north-eastern Poland), the only breeding
place of the species in this country with 18 pairs.
Some pomarina data were also collected at
Biebrza valley. Besides, we collected data on
pomarina from Lublin area (eastern Poland), c 350
km south of Biebrza valley, and also from Silesia
(western Poland), 500 km to the west, where clan-
ga does not occur. In 2006-10, we examined more
than 80 nestlings from these areas.
Identication of juvenile spotted eagles
The species characters of clanga and pomarina
presented by Svensson (1975) and Forsman (1991,
1999) are still applicable, especially for birds in
the eld. However, considering the possibility of
encountering hybrids, the descriptions must be
very precise and include a complete set of details
not all mentioned by these authors. The most im-
portant diagnostic characters to distinguish juve-
nile spotted eagles and their hybrids are the pat-
tern of the uppertail-coverts, ight- and tail-feath-
ers and rump and the nape patch coloration.
The pattern on these feathers has never been ana-
lysed for identication purposes. The size and
shape of the pale tip and the colour of the basal
part of the feather are important.
Svensson (1987) was the rst to notice the impor-
tance of the barred pattern on the underside of the
secondaries in spotted eagles (and Steppe Eagle
A nipalensis). That information will not be repeat-
ed here. It is important to note whether the bars
are even across the entire length of the feather and
how far from the tip they disappear or fade away.
Tail pattern
The barring on the tail-feathers is weaker than on
Let op: glyphs nodig
[Dutch Birding 32: 384-397, 2010]
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
FIGURE 1 Variability of nape patch in spotted eagles and their hybrids (Michał Skakuj). AQP = Lesser Spotted Eagle /
Schreeuwarend Aquila pomarina, AQX = hybrid, AQC = Greater Spotted Eagle / Bastaardarend A clanga.
the secondaries, as usually the tail-feathers are
darker. A very important feature is the pale tip of
the tail viewed from above, where differences oc-
cur in the shape and contrast of the pale terminal
band. On the underside, it can be similar in both
Presence or absence of a pattern of streaks on the
rump occurs in both species, and the variation
and overlap are considerable. Birds with the most
extreme pattern can be identied by this feature
alone but hybrids can have an equally strong pat-
tern. The shape of the pale streaks is also impor-
Nape patch
The presence or absence of a nape patch has been
regarded as a good identication feature. It is in-
deed good but only when considered in the con-
text of the whole characters set. It is one of the rst
clues of hybrid when such a nape patch occurs in
a ‘Greater Spotted Eagle’. The colour is also im-
Other features
The pattern on the inner primaries, shape and size
of pale tips on the upperwing-coverts and the un-
dertail-coverts have all been mentioned in the lit-
erature. However, variation in these characters is
wide, with considerable overlap, and such char-
acters will only support an identication.
Lesser Spotted Eagle
Juveniles are relatively easy to identify. They have
an ochre nape patch, brown upperwing coverts
paler than the blackish ight-feathers, and sec-
ondaries strongly and evenly barred over the en-
tire length. The general coloration is slightly vari-
able, with darker birds approaching clanga.
Hybrids have at least some of the features men-
tioned, so examination of all features is necessary.
It should be stressed that the important features of
pomarina vary more than those of clanga.
The feather pattern of a brown inner vane, paler
outer vane and pale, off-white tip, which is small
and oval, ‘nger nail-shaped’ (in clanga cut-off
straight and covering the entire distal part) are
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
FIGURE 2 Variability of main characters in spotted eagles and their hybrids from above (Michał Skakuj). AQP = Lesser
Spotted Eagle / Schreeuwarend Aquila pomarina, AQX = hybrid, AQC = Greater Spotted Eagle / Bastaardarend
A clanga.
FIGURE 3 Variability of main characters in spotted eagles and their hybrids from below (Michał Skakuj). AQP = Lesser
Spotted Eagle / Schreeuwarend Aquila pomarina, AQX = hybrid, AQC = Greater Spotted Eagle / Bastaardarend
A clanga.
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
characteristic for this species. The outer vane can
be much paler than the inner one, uniform or
barred, but can however also be almost as uni-
formly coloured as the inner vane. A signicant
difference is the small size of the tip and the rela-
tively pale brown colour of the basal part (black-
ish in clanga). This is a very useful character as
even a small difference in the size or shape of the
tip or coloration of the basal dark part are strong
indications of a hybrid. As a whole, the uppertail-
coverts are paler than the rump and clearly paler
than the blackish tail-feathers, forming a pale
brown or bufsh patch at the tail base, with a nar-
row whitish ‘U’ along the tip of the coverts.
Tail pattern
Seen from below, the pattern can sometimes be
very similar in clanga, pomarina and hybrids. The
diagnostic difference is found on the upperside. In
pomarina, the blackish tail ends with a whitish,
straight and sharply cut-off, relatively wide band.
Despite the wide variation in the intensity of the
rump pattern in both species, the shape and size
of the pale spots make a very useful character. In
just over half (53%) of juvenile pomarina, there is
no pattern on the rump at all (against 3%, ie, two
out of 60 individuals, of clanga). There are bufsh
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
533 Lesser Spotted Eagle / Schreeuwarend Aquila pomarina, juvenile, Biebrza marshes, Poland, 23 July 2008 (Jan
Lontkowski). Typical juvenile plumage. Note bright nape patch, narrow wedge-shaped spots on rump with straight
sides, uppertail-coverts paler than rump with oval tip. Tail with typically well-dened contrasting whitish tip. Note
also similar contrasting pattern on inner primary coverts.
534 Hybrid Greater Spotted x Lesser Spotted Eagle / hybride Bastaard- x Schreeuwarend Aquila clanga x pomarina,
juvenile, Biebrza marshes, Poland, 21 July 2009 (Jan Lontkowski). Note brown nape patch and drop-shaped spots on
rump, both diagnostic for hybrid. Uppertail-coverts of clanga-type, blackish with wide and rectangular spot. Tail pat-
tern also of clanga-type with diffuse narrow pale tip. Note also purple and green sheen rather similar to clanga but
not pomarina. Parents: female clanga (identied by plumage), male pomarina (caught).
535 Greater Spotted Eagle / Bastaardarend Aquila clanga, juvenile, Biebrza marshes, Poland, 21 July 2009 (Jan
Lontkowski). Note diagnostic lack of nape patch. Typical big and oval rump patches, blackish uppertail-coverts with
extensive cream distal part. Pale tips to unbarred tail-feathers diffuse. Similar pattern to secondaries and primary
coverts. Note diagnostic inner primaries with no pattern. All upperparts uniform blackish.
536 Lesser Spotted Eagle / Schreeuwarend Aquila pomarina, juvenile, Długi Las, Lublin province, Poland, 19 July 2009 (Jan
Lontkowski). Pale bird with no pattern on rump. Note colour of nape patch and pattern and coloration of uppertail-coverts.
Characteristic contrastingly pale tip of tail.
537 Lesser Spotted Eagle / Schreeuwarend Aquila pomarina, juvenile, Zulice, Lublin province, Poland, 19 July 2009 (Jan
Lontkowski). Note uppertail-coverts paler than rump with characteristic rounded cream tip.
538 Lesser Spotted Eagle / Schreeuwarend Aquila pomarina, juvenile, Biebrza marshes, Poland, 25 July 2008 (Jan Lontkowski).
Darker individual. Note very small nape patch, typical patterned uppertail-coverts with small ‘nger-nail’ tip. Tail tip and tips of
primary coverts contrasting and clearly dened.
539 Lesser Spotted Eagle / Schreeuwarend Aquila pomarina, juvenile, Biebrza marshes, Poland, 22 July 2009 (Jan Lontkowski).
Typical individual with heavy barring on remiges. Note bright nape patch and similarly coloured sharp streaks on breast.
540 Lesser Spotted Eagle / Schreeuwarend Aquila pomarina, juvenile (same as plate 538), Biebrza marshes, Poland, 25 July 2008
(Jan Lontkowski). Very dark individual. Note dark undertail-coverts and distinctly demarcated tail and ight-feather tips.
541 Lesser Spotted Eagle / Schreeuwarend Aquila pomarina, juvenile (same as plate 537), Zulice, Lublin province, Poland, 19 July
2009 (Jan Lontkowski). Note narrow bars on tail-fathers similar to clanga but same width along entire length of feather.
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
or whitish shaft-streaks with a characteristic nar-
row wedge shape and the sharp point directed to
the feather base, with straight sides and ‘opened’
at the tip. Unlike clanga, they are never oval or
rounded at the tip.
Secondary pattern
The secondaries are always clearly barred, and –
characteristically – the bars are of the same width
across the entire length of the feather, almost
reaching the tip, leaving just a narrow pale un-
barred terminal band. The barring is best visible
on the underwing and may be hard to discern on
the upperwing. In most of the birds the dark bars
are wider than the pale ones, although in c 30%
of the birds they are narrower than the pale ones,
but still of the same width over the whole feather,
and with the last bar not broken nor narrower. The
faded barring typical for clanga is never shown by
Nape patch
All the nestlings we examined had a bright ochre
nape patch. In most of them, it was medium sized
and oval, whereas in c 30% the patch was much
larger and reaching high up to the crown, some-
542 543
542 Greater Spotted Eagle / Bastaardarend Aquila clanga, juvenile, Biebrza marshes, Poland, 23 July 2008 (Jan
Lontkowski). Less spotted individual. Note pattern on uppertail-coverts and tips of tail- and ight-feathers and inner
primary coverts.
543 Greater Spotted Eagle / Bastaardarend Aquila clanga, juvenile, Biebrza marshes, Poland, July 1999 (Grzegorz
Maciorowski). Extremely uniform individual. Note drop-shaped small spots on rump. Characteristic pattern on up-
pertail-coverts with wide pale tip and diffuse pale edge to tail-feathers (cf plate 538).
544 Greater Spotted Eagle / Bastaardarend Aquila clanga, juvenile, Biebrza marshes, Poland, 23 July 2008 (Jan
Lontkowski). Classic rst plumage with grey ight-feathers and fading bars. Note barely discernible dark and diffuse
streaks on breast, paler on belly.
545 Greater Spotted Eagle / Bastaardarend Aquila clanga, juvenile, Biebrza marshes, Poland, 21 July 2009 (Jan
Lontkowski). Typical juvenile with darker secondaries but almost no barring. Note pattern on body with paler streaks
below darker breast and narrower but diffuse pale tips to ight- and tail-feathers.
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
times almost to the forehead. On the other hand,
in several birds the patch included just a few
feathers, which made it almost invisible in the
Breast streaking
Some birds have sharply dened, ochre to bufsh,
rather narrow streaks on the breast. The streaks
can form a patch. Such a streaked pattern does not
occur in clanga but can be present in hybrids. A
slightly streaked pattern on the breast can be
shown by clanga but, if present, it is brown, dif-
fuse and only slightly paler than the background.
Instead, in clanga, sharply dened and contrast-
ingly pale yellowish streaks can occur on the belly
and thighs, forming a very pale background. This
546 Hybrid Greater Spotted x Lesser Spotted Eagle / hybride Bastaard- x Schreeuwarend Aquila clanga x pomarina,
juvenile, Kaplonosy, Lublin province, Poland, 27 July 2008 (Leszek Niejedli). Very pomarina-like individual. Straw
nape patch and spots on upperparts and uppertail-coverts too pale and too big for pomarina with large tips typical of
clanga, but pale colour of basal part typical for pomarina. Only male pomarina parent was seen and juvenile identi-
ed by comparison with other birds.
547 Hybrid Greater Spotted x Lesser Spotted Eagle / hybride Bastaard- x Schreeuwarend Aquila clanga x pomarina,
juvenile, Biebrza marshes, Poland, 24 July 2008 (Jan Lontkowski). Dark individual. Note blackish tail with distinctly
contrasting pale tip. Uppertail-coverts with atypical pattern found in hybrid only. Brown nape patch diagnostic of
hybrid. Parents identied on nest by plumage: female clanga and male pomarina.
548 Hybrid Greater Spotted x Lesser Spotted Eagle / hybride Bastaard- x Schreeuwarend Aquila clanga x pomarina,
juvenile (same as 547), Biebrza marshes, Poland, 24 July 2008 (Jan Lontkowski). Very dark individual like clanga,
with wing and tail pattern typical of pomarina. Note darker undertail-coverts. Parents identied by plumage: female
clanga, male pomarina, probably hybrid.
549 Hybrid Greater Spotted x Lesser Spotted Eagle / hybride Bastaard- x Schreeuwarend Aquila clanga x pomarina,
juvenile, Biebrza marshes, Poland, 22 July 2009 (Jan Lontkowski). Generally clanga-like individual but breast patch
too pale, brown nape patch present and tail-tip typical of pomarina. Parents identied by plumage: female clanga,
male pomarina, probably hybrid.
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
pattern does not occur in pomarina. Hybrids can
have a mixed pattern with evenly pale streaking
on both breast and belly but can also be similar to
one of the parent species.
Greater Spotted Eagle
In juvenile plumage, clanga is the most easily
identied species among spotted eagles (includ-
ing hybrids) and Steppe Eagle. In spite of the indi-
vidually variable pale pattern on the upperparts,
the identication characters are much more con-
stant than in pomarina. In clanga, even subtle de-
viations indicate a hybrid.
The coverts are dark brown, much darker than in
pomarina, with a more extensive pale tip, includ-
ing up to one third of the distal part of the feather.
Such a pattern forms a wide whitish ‘U’ at the
base of the tail. In several cases, the pattern was
different, with an entirely dark feather exhibiting a
long pale patch of variable width along almost its
entire length. No such pattern was found in poma-
rina but it was observed in hybrids (it cannot be
excluded that the pattern is a trace of earlier hy-
The pattern on the secondaries is well known and
described in detail in the publications mentioned
earlier (Svensson 1975, Forsman 1991, 1999). It is
noteworthy that unpatterned secondaries and in-
ner primaries occurred exclusively in clanga. It is
a very constant character. Any apparently ‘strange
looking’ or ‘aberrant’ clanga is most probably ‘a
normal hybrid’. Thus, secondaries with an evenly
barred pattern over their entire length, without
fading effect or with bars reaching the end of the
feather with a narrow and sharply dened termi-
nal band, indicate a hybrid.
The pattern on the uppertail is another very impor-
tant feature. It is blackish, on average less solid ly
black than in pomarina, with a narrower, less con-
trasting, diffuse pale bar at the tip. Often, espe-
cially when the tail is more clearly barred, the tip
is paler grey. Seen from below, the tail usually has
a similar pattern, ie, with a diffuse pale edge,
though rather often the pale terminal band is
sharply dened and contrasting, as in pomarina.
There is wide individual variation in the number
and size of spots on the rump. Normally, clanga
has a more distinctly pale spotted rump, com-
pared with pomarina. Only two of the examined
birds had no pattern at all (against 53% of poma-
rina). However, more than 50% had the pale patch
wider than half of the feather width, never found
in pomarina. Contrary to pomarina, the shape of
the pale patch is oval or drop-like, with rounded
lateral margins, even in birds with narrow streak-
ing, and not wedge shaped with straight sides,
which is characteristic for pomarina.
Nape patch
There is no ochre or rusty nape patch in clanga.
Rarely, in individuals with an extensive rusty/
brown or almost orange streaking on the whole
body, the head can also be of the same colour but
still there is no well-dened nape patch. Some in-
dividuals can have a dark brown patch, subtly and
only slightly paler than the rest of the dark plum-
age, but the patch is never ochre or orange.
Lesser and median upperwing-coverts
Among clanga, there are no birds with brown
arms (upperwing-coverts); the mantle is always
blackish-brown and uniform. Normally, clanga is
more strikingly patterned than pomarina but this
is not a good feature, because the overlap is con-
siderable, and hybrids can be identical. We ob-
served a single clanga with no pattern at all; c 20%
had, besides the greater coverts bar, very delicate
small streaks on the outer median coverts. Usually
though, the streaks on the median coverts are on
average larger, wider and more numerous than in
pomarina, forming another line. Also the pale tips
on the scapulars and tertials are larger and resem-
ble the uppertail-coverts with the entire distal part
As in pomarina, juvenile clanga in most cases has
the undertail-coverts pale cream-coloured. Only
two birds (3%) had a rusty undertail and three
very dark brown, almost the same colour as the
In both species, there are birds with pale and dark
thighs and ‘trousers’. Some clanga with blackish
thighs have a narrow white edge just near the toes.
This character was indicated by Corso (2009) as a
diagnostic feature for clanga. Indeed, we never
encountered any pomarina with such plumage
but it was shown by some hybrids, which makes
the character of limited value.
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
550 Lesser Spotted Eagle / Schreeuwarend Aquila pomarina, juvenile, Margole, Lublin province, Poland, 22 July
2006 (Dorota Łukasik). Typical darker rump/tail pattern. Note small ‘nger-nail’ tip to uppertail-coverts which are
paler than rump. Note also contrasting tail tip.
551 Lesser Spotted Eagle / Schreeuwarend Aquila pomarina, juvenile, Tajno, Lublin province, Poland, 24 July 2008
(Jan Lontkowski). Note rump with characteristic wedge-shaped spots with straight sides and ‘opened’ end. Note also
brown uppertail-coverts paler than rump and tail.
552 Greater Spotted Eagle / Bastaardarend Aquila clanga, juvenile, Biebrza marshes, Poland, 21 July 2009 (Jan
Lontkowski). Very characteristic individual. Note oval and wide spots on rump, blackish uppertail-coverts with whit-
ish distal part and unbarred tail-feathers with diffuse pale tip.
553 Greater Spotted Eagle / Bastaardarend Aquila clanga, juvenile, Biebrza marshes, Poland, 23 July 2008 (Jan
Lontkowski). Typical pattern with relatively narrow pale tip to tail-feathers.
The individual variation in hybrids is wide, rang-
ing from birds looking almost like a pure pomari-
na, through different mixed stages, up to almost
pure clanga-like individuals. Our identication of
hybrids was based on a set of ve characters:
1 nape patch, 2 uppertail-coverts, 3 secondaries,
4 tail-feathers and 5 rump. Deviation of even one
of these features from the typical appearance of
either species indicates a hybrid. The above char-
acters can look exactly like those of one of the
parental species or differ to a varied extent. In
general, the tail and rump pattern are only inform-
ative when they are similar to the pattern typically
shown by one parent species, while the bird si-
multaneously shows a suite of characters typical
for the other species. The patterns which differ
from those typical for either of the parental spe-
cies are described below.
The pattern can be a pale wedge, pointing to the
base of a dark brown feather. Another hybrid type
pattern is similar to pomarina with a small tip but
with a very dark, blackish basal part, much darker
than normal. Finally, it can be clanga-like with a
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
large whitish distal part but with a pale bufsh-
brown inner vane, characteristic for pomarina.
The pattern characteristic for hybrids is barring
over the entire length of the feather, like in poma-
rina, but with the last bar thinner and dashed. It
does not fade away, as in clanga, nor is it evenly
barred to the very end of the feather, as in poma-
rina. Only in two cases was the pattern similar to
that of clanga, with the barring fading away c 4
cm from the end, while other characters were
rather similar to pomarina.
Nape patch
The patch is brown, not ochre or orange, darker
than in pomarina. Any ‘typical’ clanga or pomari-
na with a brown nape patch is a hybrid.
Other features
Some features overlap considerably between
clanga and pomarina and their value for eld
identication is limited. They can support other
characters when they occur in their most extreme
form. These features are: 1 barring on inner prima-
ries. It varies in intensity but is always present. The
barring can be very similar in both species but a
total lack of the pattern was observed only in clan-
ga; 2 lesser and median upperwing-coverts. These
are mostly brownish, contrasting with the blackish
greater coverts and ight feathers. Such a colora-
tion is different from that of any clanga (although
in the rare pale morph fulvescens this contrast is
of course much pronounced). However, in c 20%,
all the upperwing coverts are very dark, blackish-
brown and of the same colour as the ight feath-
ers, as in clanga. In such individuals other charac-
ters described above become very important, par-
ticularly in those individuals that have a very small
nape patch that is hardly discernible in the eld;
3 undertail-coverts. Most birds have pale cream
undertail-coverts; c 6% have the coverts rusty, and
in 13% they are dark brown, in some individuals
with a paler centre of variable width. This should
be kept in mind when ageing, since dark under-
tail-coverts are regarded as characteristic for older
birds; and 4 pale-spotted tips on upperwing-
coverts. Generally, pomarina has fewer and small-
er pale tips. Mostly (52%), there is one row formed
by pale tips on the greater coverts. In three cases,
there was no pale pattern at all. The parents of all
the no-pattern birds were seen well and identied
as pomarina, contrary to Dombrovsky (2009),
who stated that nestlings without pattern on the
upperwing were hybrids. 33% had a clear second
pale bar formed by the tips of the median coverts,
and in 13 birds (9%) clear pale streaks were
present also on the lesser coverts. A similar pat-
tern is typical for many clanga, although the
streaks are often much more distinct than in most
patterned pomarina. The hybrid pattern can be
identical to that of either species. The pale tips of
the inner primary coverts are usually sharply de-
ned in pomarina, which corresponds with the
pattern on the tail-feathers.
554 555
554 Hybrid Greater Spotted x Lesser Spotted Eagle / hybride Bastaard- x Schreeuwarend Aquila clanga x pomarina,
juvenile, Biebrza marshes, Poland, 24 July 2008 (Jan Lontkowski). Note too extensive spotting on rump for any
pomarina but ‘proper’ wedge-shape for it, unlike clanga. Uppertail-coverts with clanga-type pattern and tail of poma-
rina-type but with narrow pale tip.
555 Hybrid Greater Spotted x Lesser Spotted Eagle / hybride Bastaard- x Schreeuwarend Aquila clanga x pomarina,
juvenile, Biebrza marshes, Poland, July 2006 (Grzegorz Maciorowski). Typical mixture of characters with clanga-type
tail pattern and pomarina-type uppertail-coverts with small ‘nger-nail’ tips.
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
Identication of hybrids
In spite of the strong individual variation, the char-
acters of the two European spotted eagles in juve-
nile plumage in fact do not overlap. Thus, identi-
cation is rather easy, if thorough scrutiny is pos-
sible. Any discrepancy or mixture of characters
strongly indicates a hybrid. Typical cases are birds
with the following characters:
Pomarina-like hybrids are identied by any
(combination) of the following features: 1 brown
nape patch; 2 barring on secondaries with the last
bar thinner than others and dashed; 3 tail with
narrow and diffuse tip; 4 uppertail-coverts with
wide pale tips; 5 uppertail-coverts with very dark,
blackish basal part; 6 streaks on rump oval or
rounded; and 7 streaks on breast wide, diffuse and
barely paler than dark ground colour, and clearly
pale and sharp on belly.
Clanga-like hybrids are characterized by: 1 the
presence of a nape patch; 2 barring on secondar-
ies even along entire feather length; 3 whitish,
sharply dened terminal tail band; 4 pale upper-
tail-coverts with a small tip; 5 streaks on rump
wedge-shaped with straight sides; 6 clear, narrow
and yellowish streaks on breast; and 7 brown arms
(lesser and median upperwing coverts). An exam-
ple of such a bird can be found in Forsman (1999):
plate 411 in fact shows a hybrid. The barring on
the secondaries is even over the entire length of
the feathers, the breast has clear, sharp yellowish
streaks and the white terminal tail-band is very
It should be stressed that identication of spot-
ted eagles in juvenile plumage, the easiest plum-
age of the species, calls for special attention. We
should keep in mind that a bird seen from above,
identied as clanga, can still prove to be a ‘classic
hybrid’ after the underwing has been examined. It
is important to consider the possibility of a hybrid
when a ‘strange’ clanga is observed far south of
the regular wintering grounds, or when an appar-
ent pomarina is still present on the breeding sites
in November or later.
This work was supported by the Financial Instru-
ment for the Environment (LIFE+), project LIFE08
NAT/PL/000510 AQC Plan ‘Securing the popula-
tion of Aquila clanga in Poland: preparation of the
National Action Plan and primary site conserva-
tion’. Our sincere thanks go to Michał Skakuj for
the excellent plates. We are grateful to the forestry
staff from Rajgród, conservation staff of the
Protection Districts and ornithologists from the
Biebrza National Park engaged in spotted eagle
protection for their co-operation, and to our col-
leagues Sylwester Aftyka, Paweł Baranowski,
Andrzej Batycki, Kordian Bartoszuk, Michał
Białek, Michał Jankowski, Antoni Kasprzak, Jan
Kowalski, Paweł Mirski and Tadeusz Mizera for
their help in the eld. Invaluable help from Janusz
Wójciak during data collecting in the Lublin re-
gion and from Adam Czubat and Kuba Sebastian
in the Opole region is gratefully acknowledged.
De t e r m i n a t i e v a n j u v e n i e l e Ba s t a a r Da r e n D ,
sc h r e e u w a r e n D e n h y B r i D e n Veldherkenning van
Bastaard arend Aquila clanga en Schreeuwarend
A pomarina vormt een lastig probleem dat
uitgebreid is behandeld in de literatuur. Een tot nu
toe onderbelicht aspect betreft de herkenning van
hybriden A clanga x pomarina. Zulke hybriden
komen geregeld voor in het gebied waar beide
soorten naast elkaar voorkomen, grofweg van
Oost-Polen tot West-Rusland en zuidelijk tot de
Zwarte Zee. In dit artikel wordt de veldherkenning
beschreven van juve niele hybriden gebaseerd op
65 juveniele clanga, 160 juveniele pomarina en
35 hybriden. In alle gevallen is de identiteit van de
juveniele vastgesteld aan de hand van de identiteit
van de oudervogels.
Belangrijk bij de herkenning van juveniele van
beide soorten en hun hybriden zijn de boven-
staartdekveren, de armpennen, het staartpatroon,
de stuit en de aanwezigheid van een achter-
hoofdsvlek. Het is van belang al deze kenmerken
vast te stellen: beide soorten verschillen op deze
punten en hybriden zijn variabel en kunnen com-
binaties van patronen tonen die vergelijkbaar zijn
met die van beide oudersoorten. De typische te-
kening en variatie van de belangrijkste kenmerken
wordt voor alle drie de ‘vormen’ gedetailleerd be-
Juveniele pomarina is eenvoudig op naam te
brengen door de donkergele achterhoofdsvlek, de
bruine bovenvleugeldekveren die lichter zijn dan
de hand- en armpennen en de gelijkmatig geban-
deerde armpennen. In de belangrijke kenmerken
is pomarina meer variabel dan clanga. Donkere
vogels kunnen qua uiterlijk clanga benaderen;
hybriden tonen normaliter ten minste enkele van
de genoemde kenmerken.
Van de drie vormen is clanga het meest con-
stant in de belangrijke kenmerken en daardoor
het eenvoudigst op naam te brengen.
Hybriden zijn zeer variabel en kunnen sterk lij-
ken op zowel clanga als pomarina. In een aantal
aspecten kunnen hybriden afwijken van beide ou-
dersoorten. Belangrijk zijn de bovenstaart dekveren
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
Identication of juvenile Greater Spotted Eagle, Lesser Spotted Eagle and hybrids
en het patroon van de bandering op de onderzijde
van de armpennen. Een bruine achterhoofdsvlek
is diagnostisch voor hybriden.
Een aantal andere kenmerken kan de determi-
natie ondersteunen: 1 afwezigheid van bandering
op de onderzijde van de binnenste handpennen is
diagnostisch voor clanga; 2 bij 20% van de hybri-
den zijn de bovenvleugeldekveren zo donker dat
ze niet te onderscheiden zijn van clanga; 3 som-
mige vogels hebben donkere onder staartdekveren,
wat verwarrend kan zijn bij de leeftijdsbepaling;
en 4 afwezigheid van witte toppen aan de boven-
vleugeldekveren komt voor bij pomarina en is
geen indicatie voor een hybride.
Ondanks de variatie is er geen overlap in de
kenmerken van clanga en pomarina, waardoor ze
relatief eenvoudig zijn te onderscheiden. Elke af-
wijking en elke combinatie van kenmerken ty-
pisch voor verschillende soorten is daarom een
sterke aanwijzing voor een hybride.
Typische pomarina-type hybriden zijn vogels
met de volgende kenmerken: 1 bruine achter-
hoofdsvlek; 2 bandering op armpennen waarbij
laatste band smaller is dan overige; 3 staart met
smalle diffuse eindband; 4 lichte bovenstaart-
dekveren met kleine donkere punt; 5 bovenstaart-
dekveren met erg donker basaal deel; 6 vlekken
op stuit ovaal of afgerond; en 7 diffuse, weinig
contrasterende brede streping op borst en scherpe
en lichte streping op onderdelen.
Typische clanga-type hybriden zijn te herken-
nen aan: 1 aanwezigheid van achterhoofdsvlek;
2 bandering over hele armpennen; 3 witachtige,
scherp afgetekende staartband; 4 lichte boven-
staartdekveren met kleine donkere punt; 5 vlek-
ken op stuit wigvormig met rechte zijden; 6 dui-
delijke, smalle gelige strepen op borst; en 7 bruine
middelste en kleine dekveren op bovenvleugel.
Corso, A 2009. Identication of some autumn raptors in
Egypt. Birding World 22: 300-308.
Dombrovski, V 2009. About species identication of
Lesser and Greater Spotted Eagles and their hybrids in
the eld. Raptors Conserv 15: 97-110. [In Russian,
with English summary.]
Forsman, D 1991. Die Bestimmung von Schell- Aquila
clanga, Schrei- A. pomarina und Steppenadler A. ni-
palensis. Limicola 5: 145-185.
Forsman, D 1999. The raptors of Europe and the Middle
East: a handbook of eld identication. London.
Helbig, J A, Seibold, I, Kocum, A, Liebers, D, Irwin, J,
Bergmanis, U, Meyburg, B-U, Scheller, W, Stubbe, M
& Bensch, S 2005. Genetic differentiation and hybrid-
ization between Greater and Lesser Spotted Eagles
(Accipitriformes: Aquila clanga, A. pomarina). J Orni-
thol 146: 226-234.
Lõhmus, A & Väli, U 2001. Interbreeding of the Greater
Aquila clanga and Lesser Spotted Eagle A. pomarina.
Acta Ornithoecol 4: 377-384.
Svensson, L 1975. Större skrikörn Aquila clanga och
mindre skrikörn A. pomarina – problemet att artbestä-
ma dem. Vår Fågelvärld 34: 1-26.
Svensson, L 1987. Underwing pattern of Steppe, Spotted
and Lesser Spotted Eagles. In: Grant, P J, Sharrock, J T
R, Taggar, S & Shirihai, H (editors), International Bird
Identication, Proceedings of the 4th International
Identication Meeting Eilat 1st-8th November 1986,
Eilat, pp 12-14.
Väli, U & Lõhmus, A 2004. Nestling characteristics and
identication of the Lesser Spotted Eagle Aquila
pomarina, Greater Spotted Eagle A. clanga and their
hybrids. J Ornithol 145: 256-263.
Väli, U, Dombrovski, V, Treinys, R, Bergmanis, U,
Daróczi, S J, Dravecky, M, Ivanovski, V, Lontkowski, J,
Maciorowski, G, Meyburg, B-U, Mizera, T, Zeitz, R &
Ellegren, H 2010. Widespread hybridization between
the Greater Spotted Eagle Aquila clanga and the
Lesser Spotted Eagle Aquila pomarina (Aves: Accipi-
triformes) in Europe. Biol J Linnean Soc 100: 725-
Jan Lontkowski, Museum of Natural History, University of Wrocław, Sienkiewicza 21,
50-335 Wroclaw, Poland (
Grzegorz Maciorowski, Poznan University of Life Sciences, Department of Zoology,
Wojska Polskiego 71c, 60-625 Poznan, Poland
... The field identification of spotted eagles poses several problems. First, although spotted eagles are rather easy to identify in their juvenile state , Lontkowski & Maciorowski 2010, adult birds are hard to tell apart in the field (Génsbøl 1984, Forsman 1999, Svensson et al. 2010. Moreover, several plumage characteristics vary extensively and show overlap between species (Génsbøl 1984, Forsman 1999. ...
... The lack of barring on the tail feathers of the Greater Spotted Eagle supported the results of Cieśląk & Dul (2006), who examined only a small number of feathers. Flight feathers of juvenile and immature spotted eagles of both species are conspicuously barred (Forsman 1999, Lontkowski & Maciorowski 2010, and this characteristic has been used to distinguish these individuals from adult birds in the field. We also noticed that flight feathers of various hybrids were barred, similar to those of the Lesser Spotted Eagle, and tail feathers were even more barred. ...
... The species identity of the studied individuals was determined by morphological [36,37] and genetic analysis using a combination of neutral microsatellite and single-nucleotide polymorphism markers [34,38]. The genetic method, applied here to approximately 1500 referenced individuals sampled across Europe, separates hybrids efficiently from parental species, and, with a somewhat higher error rate, separates F 1 hybrids from backcrosses to the parental species [38]. ...
Full-text available
The relative contributions of genetic and social factors in shaping the living world are a crucial question in ecology. The annual migration of birds to their wintering grounds and back provides significant knowledge in this field of research. Migratory movements are predominantly genetically determined in passerine birds, while in large soaring birds, it is presumed that social (cultural) factors play the largest role. In this study, we show that genetic factors in soaring birds are more important than previously assumed. We used global positioning system (GPS)-telemetry to compare the autumn journeys and wintering ranges of two closely related large raptorial bird species, the greater spotted eagle Clanga clanga and the lesser spotted eagle Clanga pomarina, and hybrids between them. The timing of migration in hybrids was similar to that of one parental species, but the wintering distributions and home range sizes were similar to those of the other. Tracking data were supported by habitat suitability modelling, based on GPS fixes and ring recoveries. These results suggest a strong genetic influence on migration strategy via a trait-dependent dominance effect, although we cannot rule out the contribution of social interactions.
... Coloura�on of diagnos�c features of young hybrids of spo�ed eagles (a�erLontkowski and Maciorowski 2010) in Kampinos Na�onal Park ...
Full-text available
In 2013–2016, a mixed breeding pair of the Greater Spotted Eagle Clanga clanga (female) and the Lesser Spotted Eagle Clanga pomarina (male) was found in the Kampinos National Park. The female looked genetically pure. Each year in the study period of 2013–2016, the birds raised one young, which had more features of C. clanga. The nest was located on the same black alder throughout the study period.
... Species identification of each bird was based on 1) visual identification and 2) genotyping of adults and their chicks. Chicks were visually evaluated at the nest, when almost fully grown-up (7-8-week-old), according to personal experience and plumage identification keys (Väli & Lõhmus 2004, Dombrovski 2009, Lontkowski & Maciorowski 2010 and biometry (Väli & Lõhmus 2004). Species identification of adults was based on the widely acknowledged morphological differences between GSE and LSE (Forsman 1991, 1996, Dombrovski 2009). ...
Full-text available
We studied a sympatric and crossbreeding population of the Lesser and the Greater Spotted Eagle in the Biebrza Valley, NE Poland. In order to follow the dynamics of hybridisation and its possible causes we monitored these two species between 1996 and 2012, using visual and genetic species identification. Individuals in up to 51 territories annually were determined as one of the two species or as a hybrid according to plumage characteristics. Feathers from adults and chicks from 114 broods were collected and genotyped using 30 nuclear markers. Hybridisation was observed with both methods already at the beginning of the study, and showed a significantly increasing trend. The proportion of broods producing hybrids of the Greater and the Lesser Spotted Eagle increased during the study by over 30%. The percentage of territories occupied by pure Greater Spotted Eagle pairs declined to 50% at the end of the study. The increasing number of mixed pairs highly significantly correlated with the decreasing number of pairs of the rare Greater Spotted Eagle, but weakly with the numbers of the more common Lesser Spotted Eagle. Mate replacement was frequently recorded and favoured the Lesser Spotted Eagle or hybrids. Adult males were the most often replaced sex (71%), possibly due to their higher mortality. Sex ratio at the nestling stage did not diverge from 1:1. Overall, 13 cases of within-pair species composition change were recorded, leading mostly to hybridisation (61%), but sometimes also to re-establishment of pure A. clanga pairs (23%). Alteration of habitat towards that preferred by the Lesser Spotted Eagle and differential sex-mortality are discussed as the most possible causes of the increasing crossbreeding rate.
Full-text available
There were 13 records of Greater Spotted Eagle Aquila clanga in Pomerania in 1985, 1986 and 2007–2012 – nine from spring, three from autumn and one from winter. Greater Spotted Eagles were recorded 8 times in Gdańsk Pomerania but just once in Central Pomerania. In Western Pomerania this species was not seen, but a bird with a satellite transmitter from Estonia, which was flying through this part of Pomerania, was recorded three times – twice in spring and once in autumn. Moreover, in spring 2012 one bird with a transmitter was recorded in eastern Pomerania, which had been ringed in the Biebrza Marshes in 2011. In total 12 individuals were recorded in Pomerania, including 11 juveniles and immatures, and one of indeterminate age. Of the 10 visual records, 9 relate to short-term observations of birds in flight, while one individual was seen for two days. The records of birds with satellite transmitters suggest that Greater Spotted Eagle occurs in Pomerania more frequently than is apparent from visual observations.
Full-text available
Report on rare birds in Spain, 2014. This report publishes 743 new records of 134 taxa of rare birds in Spain, with an acceptance rate of 91.84%. Details on 10 new taxa for Spain are included: Zino's Petrel (Pterodroma madeira), Pygmy Cormorant (Phalacrocorax pygmaeus), Great Black-headed Gull (Larus ichthtyaetus), Abyssinian Roller (Coracias abyssinicus), Egyptian Nightjar (Caprimulgus aegyptius), ‘Caspian Stonechat’ (Saxicola maurus hemprichii), Eastern Olivaceous Warbler (Iduna pallida), ‘Siberian Lesser Whitethroat’ (Sylvia curruca blythii/halimodendri), Brown Shrike (Lanius cristatus), Common Yellowthroat (Geothlypis trichas), Song Sparrow (Melospiza melodia) and Northern Waterthrush (Parkesia noveboracensis), the latter replacing Louisiana Waterthrush (Parkesia motacilla), which is removed from the Spanish list after the review of an old record. Records of six taxa have been accepted from Peninsular Spain for the first time: White-faced Storm-petrel (Pelagodroma marina) —four records; Red-billed Tropicbird (Phaeton aethereus) —two records; Kelp Gull (Larus dominicanus) —one record, the 2nd for Spain; and Yellow-legged Gull showing features of the Azorean form (Larus michahellis atlantis). This report also details the second records for Spain of Eastern Imperial Eagle (Aquila heliaca), Lesser Moorhen (Gallinula angulata), American Robin (Turdus migratorius) and Nutcracker (Nucifraga caryocatactes). The following first records for the Canary Islands are also included: ‘Eastern Subalpine Warbler’ (Sylvia cantillans cantillans/albistriata), ‘Siberian Chiffchaff’ (Phylloscopus collybita tristis) and Lapland Bunting (Calcarius lapponicus). Also of note in this report is the number of Fea's/Zino's Petrel (Pterodroma feae/madeira) records included. Finally, a new numeric rarity definition is presented for each species in order to reflect both how rare and irregular it is.
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Facts mentioned in paper give evidence of the possibility of forming the mixed pairs between Steppe and Imperial Eagles, breeding success and fertility of hybrids. All the observed mixed pairs were found in the contact zone of the two species on the periphery of the Steppe Eagle breeding range under conditions of either decrease in numbers of one species (Steppe Eagle) and the growth of another (in Western Kazakhstan), or decline in numbers of both species and the lack of birds of their own species (in Dauria). Considering the fact that the number of Steppe Eagles continues to decline, the hybridization process may amplify and this phenomenon requires a more thorough examination.
Full-text available
Summary.—Report on rare birds in Spain, 2012-2013. This report publishes 636 new records on the presence of 151 taxa of rare birds in the whole of Spain, with an acceptance rate of 86.64%. Details on 8 new taxa for Spain are included for the first time in any rarities report: macaronesian shearwater Puffinus baroli boydi, double-crested cormorant Phalacrocorax auritus, bateleur Terathopius ecaudatus, common buzzard Buteo buteo vulpinus, red-necked stint Calidris ruficollis, Wilson’s snipe Gallinago delicata, short-billed dowitcher Limnodromus griseus and Asian desert warbler Sylvia nana. moreover it has been accepted the first records for two taxa for the Spanish peninsula: Fea’s petrel Pterodroma feae and south polar skua Stercorarius maccormicki, and the first records for a total of 6 new taxa for Spain or the Peninsula which are considered to be maintained in D category: tropical mockingbird (Mimus gilvus; first record for Spain), common bulbul Pycnonotus barbatus, African blue tit Cyanistes teneriffae, brown-necked raven Corvusruficollis, pied crow (Corvus albus; first record for Spain) and Italian sparrow (Passer italiae; first record for Spain). Also, the second records for Spain for black-bellied storm petrel Fregetta tropica and Hume’s warbler Phylloscopus humei. We also include the first records for Canary Islands of water rail Rallus aquaticus, semipalmated plover (Charadrius semipalmatus; 4th record for Spain), little auk Alle alle, great reed warbler Acrocephalus arundinaceus and little bunting Emberiza pusilla. Finally is also commented the big influxes of yellow-browed warblers Phylloscopus inornatus and new records of sandhill crane Grus canadensis.
Full-text available
During October 2008, I led a group of Italian birders around southern Sinai, Egypt. Amongst the many birds that we saw, we counted about 10,000 migrating raptors. Many of these appeared to be exhausted, having migrated through the desert area to the north, and they passed very close to us, affording excellent opportunities for study and photography. This photo gallery shows a selection of the species that we saw and offers some identification tips. Lesser Spotted Eagle This was the most abundant raptor species: we counted 2,433 during 5th-11th October. Most of the birds we saw were juveniles; there were just a few second-year and third-year birds and only a handful of adults. The plumage of juvenile Lesser Spotted Eagle is highly variable – far more so then illustrated in any field guide. Most are of an overall medium brown tone, but they vary from very pale to very dark, with the palest plumaged birds almost approaching the tone of fulvescens Spotted Eagle, while the dark ones are almost identical to typical dark juvenile Spotted Eagles. The palest plumages are very rare, however, while the very darkest extremes are commoner, but still scarce. The dark ones often look somewhat intermediate with Spotted Eagle, so they can be tricky to identify, or at least to be sure that they are not hybrids. These two species hybridise quite frequently in Eastern Europe (Bergmanis et al. 2001, Lohmus & Vali 2001, Dombrovski 2002, Vali & Lohmus 2004, Helbig et al. 2005) and many of the birds that pass through Sinai surely come from this hybridisation areas. The U-shaped pale band of feathering across the breast is typical of juvenile Lesser Spotted Eagle and lacking in juvenile Spotted Eagle. This pale band can be reduced in some Lesser Spotteds, however, and in others it can be missing altogether – and it is always so in the darkest birds. Both the upperparts and the underparts are normally quite mottled, but they can also be quite uniform in tone, particularly in the darker birds. The upperwing is normally boldly spotted with white or off white, mostly on the greater coverts, but also sometimes with smaller spots on the median and (to a very limited extent) lesser coverts, with this being more like Spotted Eagle. A pale nape patch is another character typical of juvenile Lesser Spotted Eagle rather than Spotted Eagle, but again it varies, from very obvious to almost invisible. The underwing pattern also varies considerably. Most birds show a double pale comma at the wrist, but some individuals (mostly dark birds) lack the second comma and show only the larger one at the base of the primaries, exactly like Spotted Eagle. Very occasionally, Spotted Eagle can also appear to show two pale commas at the wrist, perhaps as an effect produced, or emphasised, by missing feathers. Pale trailing edges to both the wings and tail are normally present, but typically narrow and dull, and this a very good character for distinguishing the species from juvenile Steppe Eagle at a distance, especially from individuals lacking the pale band across the underwing. However, some juvenile Lesser Spotted Eagles show a quite broad and white trailing edge to both the wings and tail, almost identical to Steppe Eagle, so this should be used with care and always combined with other characters (such as overall structure, remiges barring, nostril shape etc).
Full-text available
On the ground of description of 640 individuals of Lesser (Aquila pomarina) and Greater Spotted Eagle (A. clanga) and their hybrids, obtained during the work with Collections of Zoological museums and field studies in Belarus and European part of Russia, as well as on the basis of personal observation of adult Spotted Eagles in nature, the problems of field identification of Lesser and Greater Spotted Eagles and their hybrids were analyzed. For identification of young birds it is reasonable to use the following characters: coloration of upper and lower coverts of the wing, size of spots on the waist, coloration of head and the pattern of barring of secondaries below, as well as ten quantitative characters (bill size is the most suitable). All variants of coloration were found in young hybrid individuals, apart from poor barring of secondaries from below. Rust-coloured head was found in hybrids only, as well as lack of spots on upper coverts of the wings. The conditions of observation, particularly characteristics of the illumination, as well as the presence of sexual dimorphism strongly bias the determination of adult birds in flight. The list of contemporary diagnostic features for Spotted Eagles, which badly “work” in Belarus conditions is adduced.
Full-text available
In east-central Estonia three probably interbreeding pairs of A. clanga and pomarina were found in 1988-97; in central Estonia one possibly ,,mixed" pair in 1997. Twice the female showed characteristics of A. clanga and the male of A. pomarina, once vice versa. The hybrid nestlings had controversial characteristics. The nests were situated closer to wetlands than those of A. pomarina. Interbreeding has been also reported elsewhere in the species' overlap area. Probably the interbreeding pairs are formed in the territories of single site-tenacious A. clanga. In 1988-1997 altogether nine pairs which included at least one adult A. clanga have been studied in Estonia. Of these four had mated with A. pomarina. We suspect that taxonomically A. clanga and A. pomarina should be treated as semispecies. Some identification problems are briefly discussed.
Full-text available
Hybridization is a significant threat for endangered species and could potentially even lead to their extinction. This concern applies to the globally vulnerable Greater Spotted Eagle Aquila clanga, a species that co-occurs, and potentially interbreeds, with the more common Lesser Spotted Eagle Aquila pomarina in a vast area of Eastern Europe. We applied single nucleotide polymorphism (SNP) and microsatellite markers in order to study hybridization and introgression in 14 European spotted eagle populations. We detected hybridization and/or introgression in all studied sympatric populations. In most regions, hybridization took place prevalently between A. pomarina males and A. clanga females, with introgression to the more common A. pomarina. However, such a pattern was not as obvious in regions where A. clanga is still numerous. In the course of 16 years of genetic monitoring of a mixed population in Estonia, we observed the abandonment of A. clanga breeding territories and the replacement of A. clanga pairs by A. pomarina, whereby on several occasions hybridization was an intermediate step before the disappearance of A. clanga. Although the total number of Estonian A. clanga × A. pomarina pairs was twice as high as that of A. clanga pairs, the number of pairs recorded yearly were approximately equal, which suggests a higher turnover rate in interbreeding pairs. This study shows that interspecific introgressive hybridization occurs rather frequently in a hybrid zone at least 1700-km wide: it poses an additional threat for the vulnerable A. clanga, and may contribute to the extinction of its populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 725–736.
Full-text available
The lesser spotted eagle Aquila pomarina and the greater spotted eagle A. clanga are closely related endangered raptors whose taxonomic status, field identification, and ultimately conservation, have been complicated due to morphological similarity. However, the partial overlap in morphological features may also involve hybrids, which are known to exist, but which have so far been poorly described. This study investigated spotted eagle nestlings in Estonia, pre-identifying them according to mitochondrial DNA, nape patch and the appearance of their parents. Relative size of bill and toes (corrected for nestling growth) enabled us to separate the smaller A. pomarina, but hybrids were as large as A. clanga. All three groups had distinct plumages with hybrids being intermediate; the separation was clearest using both size and plumage indices. In all, 164 of 168 birds were correctly identified using a three-step procedure, separating: (1) A. clanga, having no nape patch; (2) 9 of 13 hybrids according to plumage index; and (3) the remaining hybrids by their large size (at least two features over the mean+2SD values of A. pomarina). Knowing the sex helped to interpret size, but not plumage, characteristics, and its overall value for assisting identification was not high. The results support the view that spotted eagles with intermediate characters are usually hybrids which can be recognised by their appearance.
Full-text available
Greater and lesser spotted eagles (Aquila clanga, A. pomarina) are two closely related forest eagles overlapping in breeding range in east-central Europe. In recent years a number of mixed pairs have been observed, some of which fledged hybrid young. Here we use mitochondrial (control region) DNA sequences and AFLP markers to estimate genetic differentiation and possible gene flow between these species. In a sample of 83 individuals (61 pomarina, 20 clanga, 2 F1-hybrids) we found 30 mitochondrial haplotypes which, in a phylogenetic network, formed two distinct clusters differing on average by 3.0% sequence divergence. The two species were significantly differentiated both at the mitochondrial and nuclear (AFLP) genetic level. However, five individuals with pomarina phenotype possessed clanga-type mtDNA, suggesting occasional gene flow. Surprisingly, AFLP markers indicated that these mismatched birds (originating from Germany, E Poland and Latvia) were genetically intermediate between the samples of individuals in which mtDNA haplotype and phenotype agreed. This indicates that mismatched birds were either F1 or recent back-cross hybrids. Mitochondrial introgression was asymmetrical (no pomarina haplotype found in clanga so far), which may be due to assortative mating by size. Gene flow of nuclear markers was estimated to be about ten times stronger than for mtDNA, indicating a sex-bias in hybrid fertility in accordance with Haldanes rule. Hybridization between the two species may be more frequent and may occur much further west than hitherto assumed. This is supported by the recent discovery of a mixed pair producing at least one fledgling in NE Germany.
The raptors of Europe and the Middle East: a handbook of field identification
  • D Forsman
Forsman, D 1999. The raptors of Europe and the Middle East: a handbook of field identification. London.
underwing pattern of Steppe, Spotted and Lesser Spotted Eagles
  • L Svensson
Svensson, L 1987. underwing pattern of Steppe, Spotted and Lesser Spotted Eagles. In: Grant, P J, Sharrock, J T R, Taggar, S & Shirihai, H (editors), International Bird Identification, Proceedings of the 4th International Identification Meeting Eilat 1st-8th November 1986, Eilat, pp 1214.
Större skrikörn Aquila clanga och mindre skrikörn A. pomarina -problemet att artbestä ma dem
  • L Svensson
Svensson, L 1975. Större skrikörn Aquila clanga och mindre skrikörn A. pomarina -problemet att artbestä ma dem. Vår Fågelvärld 34: 1-26.
Die Bestimmung von Schell Aquila clanga, Schrei A. pomarina und Steppenadler A. nipalensis
  • D Forsman
Forsman, D 1991. Die Bestimmung von Schell Aquila clanga, Schrei A. pomarina und Steppenadler A. nipalensis. Limicola 5: 145185.