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Ageing, sexing and subspecific identification of Osprey, and two WP records of American Osprey


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[Dutch Birding 35: 69-87, 2013]
Ageing, sexing and subspecic
identication of Osprey, and two
WP records of American Osprey
Roine Strandberg
n autumn 2002, I conducted eldwork for my
master thesis at Lake Hammarsjön in southern-
most Sweden. My research focused on foraging
strategies during migration of Osprey Pandion
haliaetus (Strandberg 2002, 2004, Strandberg et al
2006). The studies have continued since, with sat-
ellite tracking of Swedish Ospreys by the Raptor
Research Group at Lund University (RRGL). My
interest in Ospreys encouraged me to examine, in
addition to free-ying and handheld birds, 1000s
of photographs online (mostly from www.artpor- and to reveal useful
characters for identication. In 2010, I started to
look more closely at the differences between birds
of the European and North American population,
ie, between nominate P h haliaetus (hereafter
haliaetus) and American Osprey P h carolinensis
(hereafter carolinensis). During a visit to Veracruz,
Mexico, in autumn 2010, I observed nearly 600
carolinensis in the eld, which was the key to re-
vealing subspecic differences.
Four subspecies are traditionally recognized
(Poole 1989, del Hoyo et al 1994, Ferguson-Lees
& Christie 2001): haliaetus (Palearctic), carolinen-
sis (North America), ridgwayi (Caribbean region)
and cristatus (coastal Australia and Indonesia to
New Caledonia); note that cristatus has been giv-
en species status recently (Eastern Osprey P crista-
tus; cf Christidis & Boles 2008, Gill & Donsker
2013). The population of haliaetus breeding along
the Red Sea differs distinctly from the rest of halia-
etus. In this paper, short basic descriptions of all
97 Osprey / Visarend Pandion haliaetus haliaetus, adult male, Hammarsjön, Sweden, 11 April 2009
(Patrik Olofsson)
subspecies are given, while focusing on haliaetus
and carolinensis.
With the information found in current literature
in mind, it was clear to me that there is need for a
fresh comprehensive Osprey identication paper
dealing with accurately given characters for age-
ing and sexing and for subspecic identication.
My research also resulted in the discovery of two
Western Palearctic (WP) records of carolinensis,
from the Azores and Iceland.
Current knowledge on identication
Even though species recognition and ageing of
Ospreys is rather straightforward, identifying sub-
species and sexing has received very little atten-
tion in the literature. Concerning sexing, most
handbooks and eld guides note that females are
larger than males and highlight that females have
a breast-band which is ‘darker, broader, wider,
better marked, more prominent, more pro-
nounced, more heavily patterned or browner’
FIGURE 1 Ospreys / Visarenden Pandion haliaetus haliaetus. A adult female, Skagen, Denmark, 19 April 2005 (Carsten
Gadgaard); B rst calendar-year female, Stevns, Denmark, 25 August 2007 (Frank Abrahamson). Combination of
fresh plumage, pale tips to ight-feathers and upperparts, rusty yellow wash to underwing-coverts and orange-yellow
iris are rst-autumn characters. Young females often lack the distinct dark drop-spots on the underwing-coverts that
adult females show. Note also female characters shown by both birds, including large head, broad and long wings,
long tail, large feet and robust breast/belly. Pattern on greater underwing-coverts is often hard to judge and also vari-
able (see gure 6-7 and 14). Looking closer at the adult female (A), tips of often concealed outer median underwing-
coverts are visible.
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 2 Ospreys / Visarenden Pandion haliaetus haliaetus. Comparison of iris colour between adult and juvenile.
A adult female, Grimsö, Sweden, 5 July 2007 (Raymond Klaassen); B rather typical juvenile male, Hammarsjön,
Sweden, 8 August 2010 (Patrik Olofsson). Note bluish tinged orbital ring and gape (compare with P h carolinensis in
gure 12).
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
than in males and that the breast-band character
overlaps between the sexes (Cramp & Simmons
1980, del Hoyo et al 1994, Wheeler & Clark 1995,
Forsman 1999, Ferguson-Lees & Christie 2001,
Gensbøl 2004, Liguori 2005, Olsen 2007, Dennis
2008, Svensson et al 2009, van Duivendijk 2011).
Aside from the breast-band character, the most
up-to-date information is found in Forsman (1999),
who describes the sex differences as: ‘males have
narrower wings and a slimmer body, particularly
around the belly and vent, than females’ and
‘males also show more uniformly white lesser and
median underwing-coverts than females, which
often show a more patterned forearm, with several
rows of dark spots to their lesser and median
Very little is said about the sexing of juveniles
but Forsman (1999) concludes that ‘nothing is
known about sexing juveniles by plumage’ and
Prevost (1982) notes that juveniles overlap com-
pletely in breast coloration and underwing-covert
According to Ferguson-Lees & Christie (2005),
compared with haliaetus, carolinensis is slightly
larger, the forehead, back and wings are darker
brown, the crown and chest are whiter and it has
almost no gorget streaks; cristatus is smaller and
has shorter wings, the whole head is whiter, the
eye-stripe narrower and ‘less continuous’ and the
gorget stronger.
Before starting with identication, it must be con-
sidered that, even though subspecic and sex dif-
ferences are relatively reliable, every single char-
acter overlaps. There are individuals that will be
impossible to identify with certainty in the eld.
However, most adult birds are possible to sex with
some practice. Usually, size and jizz are the most
evident sex differences but they still require expe-
rience. Using eld marks only, juvenile Ospreys
(of the two subspecies) are often ‘easier’ to assign
to subspecies than to sex. To simplify the text
when describing characters, I have tried to limit
the use of phrases like ‘most often’ or ‘the major-
ity show’, which could be added to every single
character. Hence, when reading the text, keep in
mind that a combination of characters always
gives a more reliable identication.
Ageing (all subspecies)
Because subadult birds (rst-winter to third-sum-
mer) do not occur regularly in northern latitudes
(Dennis 2008, Bai & Schmidt 2012, RRGL unpub-
lished) and young Ospreys complete a full moult
in c 18 months (Prevost 1983), this paper only
deals with Ospreys in adult and juvenile plumage.
Ageing has been thoroughly dealt with by most of
the current identication guides (eg, Wheeler &
Clark 1995, Forsman 1999, Svensson et al 2009).
For information concerning moult, see Prevost
(1983) and Forsman (1999). A summary of the
most useful juvenile characters that separate juve-
niles from adults (gure 1) includes: 1 pale tips to
ight-feathers and upperparts; 2 pronounced bar-
ring to greater underwing-coverts (note that these
are barred in all age classes but the majority of
adults have a broader dark outer band fading in-
wards to greyer coloration, while juveniles show
dark hourglass shapes or two equally broad black-
ish bands on white background); 3 barring on sec-
ondaries more distinct and regular; 4 rusty-yellow
wash to underwing-coverts (adults show sandy
wash on close views); 5 orange-yellow to reddish
iris (yellow in adults); and 6 fresher plumage in
Sex differences in adult haliaetus
Haliaetus is relatively easy to sex and even though
most individuals overlap in one or a few charac-
ters, most have either a typical female or male ap-
pearance. Figure 3 summarizes, in order of prefer-
ence, the most useful characters for sexing halia-
etus: 1 wing shape; 2 pattern of underwing-coverts
and axillaries; 3 breast and belly shape; 4 head
and bill shape (same female in gure 9 from a bet-
ter angle to show head jizz); 5 breast-band pat-
tern; 6 tail length; and 7 under primary coverts
pattern/carpal patch shape. More subtle differ-
ences can be found in the upperparts coloration.
Differences summarized in gure 3 are discussed
below. Furthermore, females typically show ac-
tive moult during the breeding season; males
moult continuously but suspend the moult of
ight-feathers until they reach their autumn stop-
over or wintering grounds (though beware of un-
successful breeders).
Size and jizz (wing shape, breast and belly shape,
head and bill shape and tail length)
The size difference between the sexes is a good
clue as females are distinctly larger than males,
adding to the overall differences in jizz. How-
ever, measurements overlap and when dealing
with birds showing intermediate size and jizz one
needs to consider plumage characteristics. Obvi-
ous ly, this is impossible with distant birds. With
practice, it is apparent that a typical female has
broader and longer wings, a longer tail, a more
pronounced head (often with a bushier neck)
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 3 Ospreys / Visarenden Pandion haliaetus haliaetus. A adult female, Åsnen, Sweden, 1 July 2008 (Håkan
Berg); B male, Färjansö, Sweden, 25 April 2011 (Lars Petersson/ Numbers refer to sexing characters
mentioned in text. Blue lines indicate differences in ratio of feet and tail.
with a somewhat heavier bill, larger feet and a
more pronounced breast and belly (often giving
a ‘beer-bellied’ look). A typical male is more
‘athletic-looking’, with narrower wings, muscular
breast and atter belly. In females, the remiges
are longer, giving a more disproportionate
appearance with a large wing area. This can be
especially hard to judge from photographs as an
instant frozen angle often gives a skewed appear-
ance. The longer tail of females is best judged in
prole, with the feet ending well short of half the
tail length. The feet of males extend to about half
or slightly less than half of the tail length.
However, this is rather hard to judge from images
as it depends on the angle and most probably is
subject to individual variation. Many Ospreys
pictured at close range are ying away from the
photographer, at which point the tail is often
spread and the feet pushed backwards. Remember
that the size of the feet (larger in females) is dif-
cult to judge in ight as they are often concealed
by feathers. Females show a bigger head (or, may-
be more correctly, are longer necked) although
this can be very hard to judge because females
are larger overall. Hence, this feature is best ob-
served in perching birds or in a prole view (and
with experience).
The character that most eld guides focus on, the
breast-band, is quite a good start when examining
the plumage. The majority of haliaetus females
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 4 Ospreys / Visarenden Pandion haliaetus haliaetus, Ivösjön, Sweden, 1 April to 5 June 2010 (Raptor Research
Group at Lund University). Variation in breast-band in nominate haliaetus illustrated by three adult males (A-C),
compared with rather typical adult female (D). Note also larger size, feet and head, longer tail, paler shoulders (wing-
coverts) and bushier neck of female.
FIGURE 5 Ospreys / Visarenden Pandion haliaetus haliaetus. A adult female, Ivösjön, Sweden, 6 July 2008 (Linda
Niklasson); B adult male, Armsjön, Sweden, 25 April 2012 (Leif Strandberg). Comparison of underwing patterns in
well-pigmented individuals.
have a broader, darker and more visible breast-
band than males, even though there is overlap
between the sexes. The bird in gure 7A shows a
rather typical breast-band for male haliaetus.
However, of 480 sexed adult Ospreys in a gallery
of images from (c 70% of
which were males, which are overrepresented in
photo galleries due to the species’ behaviour dur-
ing the breeding period males forage while fe-
males care for the young), 12% of the males
showed a pale, sparsely streaked to sometimes
nearly invisible breast-band (with a faint pale
brown wash). Hence, a minority of haliaetus males
shows incomplete markings or faint coloration on
the breast but I have not found one single male,
either in the eld or in photo galleries, that lacks
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 6 Ospreys / Visarenden Pandion haliaetus haliaetus, adult females. A Havgårdssjön, Sweden, 20 August 2008
(Christian Ljunggren); B Jordan, 25 April 2011 (Mats Wallin); C Havgård, Sweden, 26 August 2011 (Christian
Ljunggren). Typically, females appear heavier with larger head (longer neck), bigger feet, broader wings and longer
tail than males. Underparts are overall more spotted and barred than in males. Note variation in underwing patterns
and extent of breast-band.
FIGURE 7 Ospreys / Visarenden Pandion haliaetus haliaetus, adult males. A Foteviken, Sweden, 29 April 2010 (Tommy
Holmgren); B Vänern, Sweden, 16 July 2012 (Patrik Olofsson); C Ivösjön, Sweden, 2 May 2010 (Linda Niklasson).
Typically, males appear slimmer with smaller head, smaller feet, narrower wings and shorter tail than females.
Underparts are overall less spotted and barred than in females. Note variation in underwing patterns and extent of
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
any colour tone on the breast. At the other end of
the spectrum, c 10% of the males had a well-
marked breast-band as in typical females, some-
times at the extreme end even for a female (gure
4). As most photographed presumed males with
exceptionally pronounced breast-bands exhibit a
set of female-like plumage characters due to a
general high amount of feather pigmentation, they
are best left unsexed by the inexperienced observ-
er. In females, more than 80% have a broad and
heavily marked breast-band, most often continu-
ing as an intact band on the neck sides, while
c 5% show a reduced breast-band, even less de-
veloped than in a typically marked male. Hence,
one out of 10 males shows a female-like breast-
band while females rarely show reduced breast-
bands, making this a rather good start when sex-
ing haliaetus.
Underwing-coverts and axillaries
The spot markings on the underwing-coverts (g-
ure 5-7) are a very good sexing character, apart
from jizz. In both sexes, most birds have a black-
ish to greyish centre to the outer median under-
wing-coverts. However, in most birds this pattern
is completely or partly concealed by the next row
of coverts (see adult female in gure 1). A typical
female shows one or two additional rows of rela-
tively large and drop-like spots on the median
underwing-coverts (‘drop-spot band’), the spots
often continuing up on to the anks and some-
times even onto the belly (gure 9). Females can
also show spotting on the lesser underwing-cov-
erts. Well-pigmented males show one row of me-
dium-sized spots (often consisting of elongated,
pale brown drop-like spots) and one row of small
spots on the median underwing-coverts, often
combined with spotless axillaries.
Rarely, females lack a second drop-spot band to
the median underwing-coverts but instead show a
few randomly distributed spots, especially in the
centre of the coverts area and onto the axillaries.
A few females even lack typical drop-spot bands
but have big scattered drops on the median under-
wing-coverts and randomly distributed spots else-
where on the coverts and axillaries. In most cases,
they show other reliable female characters as well.
Males in general have, with the exception of the
outer (often concealed) median coverts band, an
almost completely white coverts area with one or
a few spots in the centre. Less than 10% lack these
central spots, while the same amount of birds
shows two rather obvious but pale brownish bands
of small spots, and 1-2% show two prominent
bands with female-type spots that are, however,
slightly smaller than in typical females (gure 5).
The band formed by the blackish tip of the greater
underwing-coverts is solid and narrow in males,
while females have slightly longer feathers (giving
a banded appearance) with irregular gaps (due to
moult during northern summer). However, indi-
vidual variation is large in this aspect.
Under primary coverts and carpal patch
Males show an open white eld to the inner hand
and greater under primary coverts, often divided
by a dark border line to the outer greater under
primary coverts. Females give a more barred ap-
pearance with one thinner proximal and one
broader distal band or two broad dark bands
across the greater under primary coverts. When
males show a female-type central band across the
greater under primary coverts, the band is typi-
cally paler and narrower. The black solid part of
the carpal patch is generally more restricted in
males, while females can have a more solid black-
ish coloration to the median under primary cov-
erts, even similar to carolinensis.
The brown upperwing and back are slightly paler
brown in females, often looking mottled, whereas
males are plainer blackish. This may be most pro-
nounced in autumn when females are in active
moult, with sun-bleached feathers (from sunny in-
cubating days) admixed with fresh feathers, while
males show fewer extremely sun-bleached feath-
ers and have fewer fresh feathers due to a lower
rate of summer moult.
Sex differences in adult carolinensis
In gure 8, typical carolinensis adults are shown,
with the differences between sexes described in
the captions.
Size and jizz
The differences between the sexes seem to be
slightly less pronounced in carolinensis than in
haliaetus. Females are rarely as massive looking as
in haliaetus, maybe due to a slightly narrower
wing and slimmer body. However, the general jizz
differences given above for sexing haliaetus also
apply for carolinensis.
In typical birds, the breast-band is almost absent
on males, reduced to a few central spots/streaks
but rather well dened by several rows of spots on
females. There is overlap, probably larger than in
haliaetus. Poole (1989) noted that he was able to
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 8 American Ospreys / Amerikaanse Visarenden Pandion haliaetus carolinensis. A adult female, Bahamas,
14 March 2010 (Craig Nash); B adult male, Wyoming, USA, 10 July 2007 (Mats Wallin). General sex appearance is
same in carolinensis as in haliaetus but difference is slightly less obvious as the size difference seems to be less.
Nevertheless, wings, tail and neck are typically longer in females while the belly is less pronounced in carolinensis
females, making body shape more even between sexes. Furthermore, females show stronger markings with spotted
underwing-coverts area and heavily spotted breast-band. Note also big solid carpal patch in both sexes and slightly
broader bands across greater under primary coverts in female.
sex only 50-70% of the pairs studied in North
America when relying on breast-band alone.
Underwing-coverts and axillaries
Females show distinct spotting to the underwing-
coverts with, in most birds, a central cluster of
spots fading outwards and an irregular band of
spots along the outer median underwing-coverts.
Some females have two or more drop-spot bands
as in haliaetus. Males often show an identical
drop-spot band as females to the outer median
underwing-coverts but are often plain white on
the remainder of the underwing-coverts.
Under primary coverts and carpal patch
Both sexes often show barred greater under pri-
mary coverts. However, females have a broader
terminal bar while males are paler barred, some-
times lacking obvious bars. The carpal patch,
which includes the median under primary coverts,
is typically solid black in both sexes but some in-
dividuals especially males have sparsely white-
spotted median under primary coverts.
The upperparts are blackish to blackish-brown
with females generally slightly paler than males.
Subspecies identication: adult haliaetus and
Distinguishing adult carolinensis from haliaetus is
difcult but not impossible, and as adults are very
unlikely to be recorded on the opposite continent
it will usually not be a signicant problem (see
below for WP records). The key is to age and sex
the bird correctly and combine the critical charac-
ters accordingly. The important characters for sep-
arating adults of both subspecies are listed below
(see also gure 9).
General coloration
Haliaetus: brownish, females paler and often
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 9 Ospreys / Visarenden Pandion haliaetus. A P h carolinensis, adult female, Cape May, New Jersey, USA,
20 September 2010 (Mats Wallin); B P h haliaetus, adult female, Åsnen, Sweden, 1 July 2008 (Håkan Berg);
note extremely dark median under primary coverts for a haliaetus; C P h carolinensis, adult male, Wyoming, USA,
10 July 2007 (Mats Wallin); same bird as in gure 8B; D P h haliaetus, adult male, Dakar, Senegal, 22 November
2006 (Patrik Olofsson)
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 10 Ospreys / Visarenden Pandion haliaetus, rst-year females. A P h haliaetus, Djoudj, Senegal, 21 November
2006 (Patrik Olofsson); B P h haliaetus, Falsterbonäset, Sweden, 31 August 2011 (Christian Ljunggren); C-D P h caro-
linensis, Cape May, New Jersey, USA, 28 September 2010 (Stefan Magnusson). Most useful characters to distinguish
between young birds is illustrated in these females. Note prominent breast-band in haliaetus, continuing all the way
up onto neck sides, while carolinensis has a spotted band reduced to a breast-patch. No direct subspecies differ-
ences are recognized concerning carpal patches. Iris color differs with more orange-yellow to reddish eyes in caro-
linensis. Also compare belly shape.
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 11 Ospreys / Visarenden Pandion haliaetus. A P h haliaetus, juvenile, Hammarsjön, Sweden, 2 July 2011
(Roine Strandberg); B P h carolinensis, juvenile, West River, Shady Side, Maryland, USA, 30 July 2011 (Eliot
Malumuth). Note differences in upperwing coloration, with haliaetus showing less contrast, narrower and rustier pale
tips to wing-coverts and also typically a paler patch in centre of wing-coverts.
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 12 Ospreys / Visarenden Pandion haliaetus. A P h carolinensis, juvenile, Tashmoo, New England, USA,
2 August 2008 (Rob Bierregaard); B P h haliaetus, Grimsö area, Sweden, 19 July 2007 (Raymond Klaassen). Note in
carolinensis reddish iris, blackish plumage, darker upper gape, black eyeliner, and lack of gorget streaks, and in
haliaetus yellow-orange iris, brownish plumage, equally bluish upper and lower gape, blue-grey eyeliner and black
gorget streaks.
mottled brown and pale brown on upperwing-
coverts. Carolinensis: blackish-brown, males often
blacker on upperwing-coverts.
Haliaetus: intact broad and blurry breast-band.
Males can show very pale wash but still often over
a relatively broad area while females are richer
brown in a broader band all the way up onto the
neck sides. Carolinensis: distinctly spotted breast-
band. The band is often absent in males, while
females show distinct and large spots producing a
relatively narrow ‘mosaic’ band across the breast.
Haliaetus: blackish or barred greater underwing-
coverts. Males commonly show a black central
spot in a white coverts area (median and lesser
underwing-coverts), while females have two dis-
tinct bands on the underwing-coverts. Carolinensis:
distinctly black greater underwing-coverts. Males
commonly show completely white coverts area,
while females have a distinct central cluster of
spots on the underwing-coverts. Both sexes gener-
ally have dark spots irregularly distributed on
outer median underwing-coverts (only visible if
not concealed).
Under primary coverts and carpal patch
Haliaetus: incompletely barred greater under pri-
mary coverts; males can lack barring, females
have one or two broader bands. Carpal patch ex-
cludes median under primary coverts; median un-
der primary coverts of females heavily spotted, in
males with smaller sparsely distributed spots.
Carolinensis: completely barred greater under pri-
mary coverts, in males paler barred than in fe-
males. Carpal patch includes median under pri-
mary coverts, uncommonly showing white-spot-
ted median under primary coverts.
Subspecies identication: juvenile haliaetus and
Juveniles of carolinensis are separated from adults
by the same criteria as in haliaetus. However, ju-
venile carolinensis differs signicantly from juve-
nile haliaetus and can be distinguished using a
combination of important characters (gure 10-
General coloration
Juvenile carolinensis looks very pied when
perched. In addition, carolinensis often lacks the
whitish patch on the upperwing-coverts that halia-
etus usually shows (gure 11) and has distinct
white scaling to the feathers. Haliaetus looks a bit
sordid in comparison.
The character somewhat overlaps but most halia-
etus show a rather prominent breast-band all the
way up onto the neck sides, while carolinensis has
a large patch of spots conned to the breast (fe-
male type) or just a row of ne spots in the centre
of the breast (male type).
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 13 Ospreys / Visarenden Pandion haliaetus. A P h cristatus, adult female, Flores, Indonesia, 10 August 2010
(Lars Petersson/; B P h ridgwayi, adult male, north Yucatan, Mexico, 6 February 2012 (Greger
Flyckt); C nominate haliaetus of Red Sea form, juvenile male, Hurghada, Egypt, 8 August 2010 (Stefan Magnusson).
In cristatus, note large feet and head in combination with shorter tail and large wing area, well-marked breast-band
combined with few droplets conned to outer median underwing-coverts. In ridgwayi, note black-and-white plum-
age, distinct carpal patches, pure white median and lesser underwing-coverts and lack of breast-band. In Red Sea
haliaetus, note sandy wash to overall very pale underparts and lack of breast-band and spotting.
Juveniles show the same differences as in adults
but the majority of individuals seem to have an
unspotted underwing-coverts area.
Under primary coverts and carpal patch
As in adults but juveniles of both subspecies have
white and rusty scaling on the under primary cov-
erts. No direct subspecies differences are recog-
nized but haliaetus, especially males, can show a
more restricted carpal patch.
Iris color
Haliaetus: yellow to orange-yellow (orange un-
common); carolinensis: orange-yellow to red-or-
ange (yellow uncommon) (gure 12). Note that
the iris of haliaetus seems to get paler and more
yellowish at a younger age than in carolinensis.
Eye region
Haliaetus is paler around the eye with most often
a bluish-grey orbital ring, while carolinensis is dis-
tinctly blackish around the eye (as if using mas-
cara), with a reduced or absent bluish-grey orbital
ring (gure 12).
Facial pattern
Haliaetus has a bluish to grey upper gape in the
same colour tone as the lower gape, while caroli-
nensis typically shows a blackish to dark grey up-
per gape. Furthermore, haliaetus most often shows
noticeable black gorget streaks (more common in
females), while carolinensis lacks gorget streaks or
shows very ne striping that is difcult to detect.
Other subspecies: cristatus, ridgwayi and south-
ern form of haliaetus
Ospreys breeding in southern (sunnier) regions
(cristatus, ridgwayi and southern form of haliaetus)
are generally plainer than northern birds, showing
a paler back and whiter underparts (gure 13).
Typical for all three is that the underwing is very
clean, with unmarked median and lesser under-
wing-coverts and a large white area across the
base of the primaries and greater under primary
coverts, with no prominent banding.
Cristatus (Australasia) is the smallest taxon, with
a pronounced white crown. Males also have re-
duced black on the neck sides, creating a typical
‘bandit mask’. The upperparts are generally paler
brown than in other subspecies. Compared with
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
FIGURE 14 Ospreys / Visarenden Pandion haliaetus haliaetus, showing variation in underwing pattern. Left row: fe-
males; right row: males. A-F north-eastern Germany, 27 June to 13 July 2005 (Daniel Schmidt); G Grimsö area,
Sweden, 9 July 2007 (Patrik Olofsson); H Ivön, Sweden, 15 August 2009 (Linda Niklasson). Note larger size of fe-
males with broad and long wing, long tail, large head and feet, as well as robust body. Females also show double-
barred under primary coverts, big carpal patch, large drop-spots to median underwing-coverts and well dened
breast-band. Palest males show only ne rusty yellow streaking to breast. Upper female (A) shows very male-like
drop-spots (elongated and diffuse) in combination with very pale plumage and is best sexed by jizz (however, note
that photograph is slightly overexposed).
the other subspecies, cristatus has large feet and a
large head (most likely due to smaller body size)
in combination with a shorter tail and large wing
area. In adults, the sex characters seem to be as in
other subspecies: the breast-band is very well
marked in females but often absent in males. The
droplets are mainly conned to the outer median
underwing-coverts, with differences between the
sexes hard to judge.
Ridgwayi (Caribbean) is rather close to caroli-
nensis, showing black-and-white plumage with
large blackish carpal patches. However, from be-
low, the body and median and lesser underwing-
coverts are pure white with no breast-band or
spotting. Females have a slightly darker wash on
the breast and only a few diffuse spots on the out-
er median underwing-coverts.
Haliaetus breeding along the Red Sea differ
from the rest of the population signicantly. They
are rather pale brown on the upperparts and juve-
niles have a sandy (not rusty as in haliaetus) wash
to the underparts. As in cristatus and ridgwayi,
Red Sea birds lack prominent breast-bands and
spotting on the underwing-coverts. I think there is
a need for further investigation to judge if this
population warrants treatment as a distinct sub-
species or not. At least, the breeding population is
geographically separated from the other subspe-
cies and birds are relatively easy to identify in the
Western Palearctic records of carolinensis
During my research, I came across two well-doc-
umented records in the WP of birds that I identi-
ed as carolinensis. If accepted by the relevant
rarities committees, these records constitute the
rst for the Azores and Iceland, respectively, and
the rst and second for the WP.
Iceland, September 2008
On 22 September 2008, a young male Osprey
showing characters of a male carolinensis was
photographed at close range at Hafnarfjörður,
Iceland (plate 98-100). I found the photographs at
the website
html and contacted the photographer, who kindly
sent me the images. No additional information
was given to the observation other than that it was
the 22nd Osprey record for Iceland. Typical char-
acters shown in the photographs are the generally
blackish-brown coloration with clear-cut white
scaling, narrow small-spotted breast band, black
lining to the gape, lack of gorget streaks (although
prominent gorget streaks is rst and foremost a
female character), orange iris with blackish eye-
liner, large carpal patch and distinctly black hour-
glass patterned greater underwing-coverts.
Azores, October-November 2011
From 13 October to 4 November 2011, a young
Osprey was present on Flores, Azores (plate 101-
102). As Osprey is a very rare visitor to the islands,
which are a magnet to American vagrants, I re-
ceived a letter with photographs of the bird from
Olof Jönsson, who asked my opinion about it. The
photographers, Mika Bruun and Jan Kåre Ness,
had realised that the black-and-white appearance
was odd for a northern European Osprey. Going
through the characters one by one, none cor-
responded with haliaetus! As the bird was easily
recognized as a female, the characters pointed
to a rst-year carolinensis: generally black-and-
white appearance, yellow-orange iris (in October),
black ish gape, distinctly black around the eye,
lack of obvious gorget streaks and unspotted axil-
laries in combination with a typical cluster of
spots (as in adult females) in the centre of the un-
derwing-coverts. Furthermore, the breast-band
was rather restricted, which is rarely the case in
young haliaetus females that show well-spotted
underwing-coverts as this bird. For more images
of this bird, see
With an increased knowledge and awareness, it
seems likely that carolinensis will show up in the
Old World more often in the near future (and
probably haliaetus in North America), either being
wind drifted or ship assisted over the Atlantic
Ocean. Another interesting record concerns an
adult male Osprey photographed on board a ship
at sea south-west of the Azores in October 2007
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
98-99 American Osprey / Amerikaanse Visarend Pandion haliaetus carolinensis, rst-year male, Hafnarfjörður,
Iceland, 22 September 2008 (Dagur Brynjolfsson)
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
100 American Osprey / Amerikaanse Visarend Pandion haliaetus carolinensis, rst-year male, Hafnarfjörður, Iceland,
22 September 2008 (Dagur Brynjolfsson) 101 American Osprey / Amerikaanse Visarend Pandion haliaetus caroli-
nensis, rst-year female, Flores, Azores, 20 October 2011 (Jan Kåre Ness) 102 American Osprey / Amerikaanse
Visarend Pandion haliaetus carolinensis, rst-year female, Flores, Azores, 22 October 2011 (Mika Bruun)
(, showing no obvious
breast markings (and a black eye region, no gorget
streaks and pied appearance), and as the record
location was closer to the American continent
than to the European, this suggests that the bird
was a carolinensis. However, as there is only one
photograph of this bird perched, it will remain
unidentied to subspecies. No other decent
Osprey photograph in the www.birdingazores.
com photo gallery ts carolinensis and most pho-
tographs appear to show haliaetus.
Further research
I hope this paper will encourage birders to pay more
attention to Osprey identication. Hopefully, the
features mentioned in this paper will be tested fur-
ther and other features will be added in the future.
First and foremost, I like to thank Mikael Hake for
sharing his expertise during long and encouraging
Osprey discussions, not the least during our eld-
work. I also thank the rest of the Raptor Research
Group at Lund University, especially Thomas
Alerstam, Nils Kjellén, Raymond Klaassen (the
Netherlands), Patrik Olofsson and Mirja Ström-
Eriksson. Thanks also go to Rob Bierregaard
(Pennsylvania, USA), Alan Poole (Massachusetts,
USA) and Daniel Schmidt (Germany) for corre-
spondence. My gratitude goes to Eduardo Martínez
Leyva (Mexico) and the crew at ProNatura Vera-
cruz for hosting Mirja and me as volunteers dur-
ing a fantastic migration season in 2010. Thanks
go to Jörgen Bernsmo, Olof Jönsson, Hans Larsson
and Oskar Nilsson for providing some important
references and discussion. Thanks also to Greg
McIvor for correcting and improving my English
and Mirja Ström-Eriksson for advices on the manu-
script. I also wish to thank Frank Abrahamson
(Denmark), Håkan Berg, Rob Bierregaard, Mika
Bruun (Finland), Dagur Brynjolfsson (Iceland), Per
Schans Christensen (Denmark), David Erterius,
Greger Flyckt, Carsten Gadgaard (Denmark), Tom-
my Holm gren, Raymond Klaassen, Christian
Ljung gren, Stefan Magnusson, Eliot Malumuth
(Mary land, USA), Craig Nash (Northern Ireland),
Jan Kåre Ness (Norway), Linda Niklasson, Patrik
Olofsson, Lars Petersson, Daniel Schmidt, Leif
Strandberg, Mattias Ullman and Mats Wallin for
kindly allowing me to use their photographs.
Be p a l i n g v a n l e e f t i j d , g e s l a c h t e n o n d e r s o o r t v a n
vi s a r e n d e n t w e e wp-g e v a l l e n v a n am e r i k a a n s e v i s a r e n d
In dit artikel worden kenmerken besproken waarmee
leeftijd, geslacht en ondersoort van Visarend Pandion
haliaetus kunnen worden bepaald. Hierbij ligt de na-
druk op de Europese ondersoort P h haliaetus (hierna
haliaetus) en Amerikaanse Visarend P h carolinensis
(hierna carolinensis). Afzonderlijke kenmerken vertonen
overlap en een combinatie van kenmerken levert de
meest betrouwbare determinatie. Grootte en ‘jizz’ zijn
de beste geslachtsverschillen maar zonder ervaring las-
tig te gebruiken; juveniele zijn vaak gemakkelijker op
ondersoort dan op geslacht te determineren. Juveniele
verschillen van adulte door: 1 lichte toppen aan slag-
pennen en veren van bovendelen; 2 duidelijkere en re-
gelmatigere bandering op armpennen; 3 roestgele waas
op ondervleugeldekveren; 4 oranjegele tot roodachtige
iris (geel bij adulte); en 5 verser verenkleed.
Vrouwtjes haliaetus zijn duidelijk groter dan manne-
tjes en hebben bredere en langere vleugels, een langere
staart, langere hals, grotere poten en een opvallende
borst- en buikpartij (‘bierbuik’); mannetjes zien er ‘atle-
tischer’ uit, met smallere vleugels, ‘gespierde’ borst en
vlakkere buik. De langere staart van het vrouwtje valt
het beste op van onder, met poten die duidelijk tot min-
der dan de helft van de staart reiken. De meeste vrouw-
tjes haliaetus hebben een bredere, donkerdere en opval-
lendere borstband dan mannetjes, hoewel hier overlap
is; c 10% van de mannetjes vertoont een vrouwtjesach-
tige borstband en vrouwtjes vertonen in zeldzame ge-
vallen een gereduceerde borstband. De vlekken op de
ondervleugeldekveren vormen een zeer goed geslachts-
kenmerk: vrouwtjes vertonen een rij van vrij grote drup-
pelvlekken op de middelste ondervleugeldekveren (vrij-
wel ongetekend wit bij mannetjes); minder dan 10%
van de mannetjes vertoont twee rijen van bruinachtige
en iets kleinere vlekken dan bij vrouwtjes. Mannetjes
hebben vaak een open wit veld op de binnenhandvleu-
gel en grote onderhanddekveren, terwijl vrouwtjes twee
donkere bandjes over de grote onderhanddekveren ver-
tonen. Het massief zwarte deel van de polsvlek is door-
gaans bij mannetjes kleiner dan bij vrouwtjes. De bo-
venzijde is bij vrouwtjes iets lichter bruin dan bij man-
Bij typische carolinensis is de borstband vrijwel afwe-
zig bij mannetjes maar te zien als verschillende vlek-
kenrijen bij vrouwtjes. Vrouwtjes vertonen meestal een
cluster van vlekken in het centrum van de ondervleugel-
dekveren (bij mannetjes vaak egaal wit). Beide geslach-
ten hebben gebandeerde grote onderhanddekveren; de
polsvlek, die ook de middelste onderhanddekveren om-
vat, is typisch massief zwart. De bovendelen zijn zwart-
achtig tot zwartbruin (bij vrouwtjes iets lichter dan bij
Het onderscheiden van adulte carolinensis en haliae-
tus is lastig maar de donkere veerpartijen zijn zwartbruin
bij carolinensis en bruinachtig bij haliaetus. De borst-
band van mannetjes haliaetus kan tot een waas zijn ge-
reduceerd (maar meestal over een vrij breed gebied),
terwijl vrouwtjes een duidelijke, smalle mozaïekband
van vlekken vertonen. Mannetjes haliaetus hebben vaak
een centrale donkere vlek op de witte ondervleugeldek-
veren, terwijl vrouwtjes haliaetus daar twee duidelijke
vlekkenrijen hebben. Mannetjes carolinensis hebben
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
doorgaans geheel witte ondervleugeldekveren; vrouw-
tjes hebben een opvallende cluster van vlekken in het
centrum van de ondervleugeldekveren. Bij haliaetus
omvat de polsvlek niet de middelste onderhanddekve-
ren, maar is bij vrouwtjes wel vaak zwaar gevlekt; bij
carolinensis omvat de polsvlek ook de middelste onder-
Juveniele carolinensis verschilt duidelijk van juvenie-
le haliaetus door een combinatie van kenmerken.
Juveniele carolinensis in zit maakt een zeer bonte indruk
met duidelijke geschubde veren, en de witachtige vlek
op de bovenvleugeldekveren van juveniele haliaetus
ontbreekt. De meeste juveniele haliaetus hebben een
vrij opvallende borstband, doorlopend tot op zijhals; ju-
veniele carolinensis hebben een grote vlekkenconcen-
tratie beperkt tot de borst (vrouwtjes-type) of slechts een
rij van kleine vlekjes in het midden van de borst (man-
Vooral mannetjes haliaetus kunnen een kleinere pols-
vlek hebben dan carolinensis. Juveniele haliaetus heeft
een gele tot oranjegele iris (oranjegeel tot roodoranje bij
carolinensis). Haliaetus heeft een blauwgrijze oogrand
en bovensnavelbasis; carolinensis is opvallend zwart
rond het oog en aan de bovensnavelbasis. Haliaetus
heeft meestal zwarte keelstreping (vooral bij vrouwtjes);
deze keelstreping ontbreekt of is zeer jn bij carolinen-
Studie van foto’s op internet leverde twee WP-gevallen
op van carolinensis: in IJsland op 22 september 2008 en
op Flores, Azoren, van 13 oktober tot 4 november 2011.
Indien aanvaard betreft het hier de eerste gevallen voor
de WP.
Bai, M-L & Schmidt, D 2012. Differential migration by
age and sex in central European Ospreys Pandion
haliaetus. J Ornithol 153: 75-84.
Christidis, L & Boles, W E 2008. Systematics and taxon-
omy of Australian birds. Melbourne.
Cramp, S & Simmons, K E L (editors) 1980. The birds of
the Western Palearctic 2. Oxford.
Dennis, R 2008. A life of Ospreys. Dunbeath.
van Duivendijk, N 2011. Advanced bird ID handbook
– the Western Palearctic. London.
Ferguson-Lees, J & Christie, D A 2001. Raptors of the
world. London.
Forsman, D 1999. The raptors of Europe and the Middle
East: a handbook of eld identication. London.
Gensbøl, B 2004. Rovfuglene i Europa, Nordafrika og
Mellemøsten. København.
Gill, F & Donsker, D (editors) 2013. IOC world bird
names (version 3.3). Website: www.worldbirdnames.
del Hoyo, J, Elliott, A & Sargatal, J (editors) 1994. Hand-
book of the birds of the world 2. Barcelona.
Liguori, J 2005. Hawks from every angle: how to identify
raptors in ight. Princeton.
Olsen, K M 2007. Rovfugle i felten. København.
Poole, A F 1989. Ospreys: a natural and unnatural his-
tory. Cambridge.
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Senegambia. PhD thesis. Edinburgh.
Prevost, Y A 1983. The moult of the Osprey Pandion
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the Osprey Pandion haliaetus. Master thesis. Lund.
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pysslar de med egentligen? Anser 43: 129-138.
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dependent foraging ight in the Osprey Pandion
haliaetus. Ornis Svecica 16: 150-163.
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2009. Collins bird guide. Second edition. London.
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to North American raptors. San Diego.
Roine Strandberg, Department of Biology, Ecology Building, Lund University, Sweden
Ageing, sexing and subspecic identication of Osprey, and two WP records of American Osprey
... cristatus (Vieillot, 1816) in the Indo-Pacific and Oceania (Fig. 1). The four subspecies were traditionally split on the basis of morphometry and plumage characteristics, but the differences are not straightforward [4,13]. Therefore, referring only to morphology for describing diversity and interrelationships between subspecies has led to controversies in taxonomy. ...
... The four genetic groups that we found do not entirely correspond to the four subspecies described, based on morphological characters [4,13]. The IND-AUS lineage fully matched geographically with the subspecies cristatus [48]. ...
Full-text available
Background: The Osprey (Pandion haliaetus) is one of only six bird species with an almost world-wide distribution. We aimed at clarifying its phylogeographic structure and elucidating its taxonomic status (as it is currently separated into four subspecies). We tested six biogeographical scenarios to explain how the species' distribution and differentiation took place in the past and how such a specialized raptor was able to colonize most of the globe. Results: Using two mitochondrial genes (cyt b and ND2), the Osprey appeared structured into four genetic groups representing quasi non-overlapping geographical regions. The group Indo-Australasia corresponds to the cristatus ssp, as well as the group Europe-Africa to the haliaetus ssp. In the Americas, we found a single lineage for both carolinensis and ridgwayi ssp, whereas in north-east Asia (Siberia and Japan), we discovered a fourth new lineage. The four lineages are well differentiated, contrasting with the low genetic variability observed within each clade. Historical demographic reconstructions suggested that three of the four lineages experienced stable trends or slight demographic increases. Molecular dating estimates the initial split between lineages at about 1.16 Ma ago, in the Early Pleistocene. Conclusions: Our biogeographical inference suggests a pattern of colonization from the American continent towards the Old World. Populations of the Palearctic would represent the last outcomes of this colonization. At a global scale the Osprey complex may be composed of four different Evolutionary Significant Units, which should be treated as specific management units. Our study brought essential genetic clarifications, which have implications for conservation strategies in identifying distinct lineages across which birds should not be artificially moved through exchange/reintroduction schemes.
... cristatus (Vieillot, 1816) in the Indo-Pacific and Oceania (Fig. 1). The four subspecies were traditionally split on the basis of morphometry and plumage characteristics, but the differences are not straightforward (Poole, 1989;Strandberg, 2013). Therefore, referring only to morphology for describing diversity and interrelationships between subspecies has lead to controversies in taxonomy. ...
... Our four genetic groups do not enterely correspond to the four subspecies based on morphological characters (Poole, 1989;Strandberg, 2013). The IND-AUS lineage matched geographically with the subspecies cristatus (Christidis & Boles, 2008). ...
Full-text available
Being a cosmopolitan and migratory species, the osprey Pandion haliaetus provides a good opportunity to explore how behavioural adaptations in different populations, that evolved under different ecological conditions and are widely spaced, can be the proximate causes of geographical distribution, genetic divergence, population connectivity, migratory strategies and foraging ecology. According to this, a multi-scale integrated approach has been adopted for the osprey: through an interdisciplinary framework made by molecular ecology, trophic ecology as assessed via stable isotopic analyses, spatial ecology through the use of novel biotelemetry tools, as well as population dynamics, fish censuses and assessments of levels of human disturbance, we: a) evidenced the existence of four different lineages at global scale that should be treated as Evolutionary Significant Units (ESUs) and deserve specific management; b) revealed population connectivity in the Western Palearctic; c) disentangled the migratory behaviour and winter ecology of Mediterranean ospreys and compared it with northern European populations, in an evolutionary context; d) stressed the need of adequate management measures to be adopted for three local populations of the Mediterranean basin (Corsica, Morocco and Italy). Overall, this work has led to some important advances with respect to the conservation biogeography of ospreys at different scales. Those insights are particularly valuable with respect to the effective management of this emblematic species.
... By looking at its genotype it has just one locus showing allele from America, the rest of the genotype is clearly from the Palearctic group. This old specimen was definitely collected in Portugal, but the exact origin was not clear: it could have come from Portuguese islands such as the Azores, in the middle of the Atlantic, where at least one young osprey originating from north America have been recently observed (Strandberg 2013). However, all the other six Portuguese samples (belonging to the same collection) are within the Mediterranean group. ...
Full-text available
Genetic variability and population structure in osprey were studied using DNA microsatellite markers. Special emphasis was placed on the subspecies living in the Afro-Palearctic (Pandion haliaetus haliaetus). For comparative purposes, American osprey subspecies (P. h. carolinensis, P. h. ridgway) and Indo/Australian subspecies (P. h. cristatus) were included in this analysis. 20 DNA microsatellite loci were analysed across a total of 200 individuals. Cluster analysis of genetic distances generally grouped populations of osprey in accordance with their subspecific designation and with previous results from mtDNA analysis. Ospreys from America and Australia were clearly separated from P. h. haliaetus suggesting a more ancient isolation which prevented recent gene flow across these groups. Within P. h. haliaetus, significant genetic differentiation was found between populations in northern and southern Europe, suggesting that the Afro-Palearctic group is structured into two interconnected entities (Mediterranean and continental Europe). Population structuring was supported by an assignment test and by analysis of allele-sharing among individuals. At the Mediterranean scale, no significant differences of allelic information were found between populations. Behaviours such as dispersal, migration and philopatry seem to have played simultaneously and in contrary directions in shaping the genetic structure and diversity of populations. Our results provide essential information for reconstructing gene flow and genetic variability among osprey populations at different scales, which call for caution in the proactive management and conservation of the species, namely in the Mediterranean area.
Full-text available
In 2020, a pair of ospreys nested in the north western coast of Sardinia and the successful fledging of two chicks is the first record in the island since 1968. The last reported breeding occurred in the eastern coast of the island and after that the species was considered extinct. Ospreys regularly migrate, estivate and winter in Sardinia, with a wintering population of about 40 individuals in 2018. This new breeding episode is not resulting from reintroduction projects and may be related to the dynamics of the close population of Corsica and to the exceptional absence of human disturbance along the coast due to COVID 19 lock-down.
Full-text available
In the 60s Osprey was extinct as breeder in Italian peninsula and Sardinia represented a key area for the breeding population with about 10 pairs. Extinction was caused by the massive use of DDT and by direct persecution. Consequently the Mediterranean meta-population was very close to extinction, in fact in Corsica, since the early 70s, there were only three pairs. Sardinia’s wetlands, especially Mistras Lagoon (a Ramsar Site near Oristano), are the most important areas for wintering of this species in the Mediterranean area, with a population of more than 40 indi-viduals. During January 2017 we made the first photo-census in Oristano wetlands and we observed a total of 22 Ospreys, with 15 individuals in Mistras lagoon only. We also collected data on ringed individuals and, when possible, we determined age and sex accord-ing to photos. Sardinia also plays an important role in the migration of the north-ern European population, in particular the Fennoscandia region (Spina, F. & Volponi, S. 2008). Over the past 10 years, wildlife man-agement projects have been carried out to promote the re-colonization of Sardinia. The construction of artificial nests and placement of decoys have had negative results. Along the coasts of Sardinia optimal conditions are still present for the reproduction of this species. Thus, it is a priority to undertake projects in Sardinia similar to those carried out in Tuscany, Spain and Portugal to restore and reinforce the Mediterranean breeding population.
Technical Report
Full-text available
This article details rare bird sightings on Corvo (Azores) since 2005, with emphasis on North American vagrants recorded on the island each autumn over the period 2010-2014.
Full-text available
Efter avklarad examen har jag fortsatt studi-erna under våren och hösten 2003, samt vå-ren 2004, den senare säsongen som dokto-rand. Det hela har resulterat i en massa in-tressant information om gjusarnas ekologi på en sydsvensk rastplats. I denna artikel hade jag dock tänkt berätta lite om gjusarnas beteende i och runt boet och inte gå in så mycket på själva flyttningen, det sparar vi till ett senare tillfälle.
Various aspects of Osprey biology, Pandion h. haliaetus, were studied from museum specimens and in the field. Size, breast markings and crown markings were found insufficient to discriminate populations, but underwing coverts were sufficient. Four subspecies were recognized, corresponding to the Palearctic, North America, the Bahamas and Australasia. However Ospreys can be divided into two groups, a Holarctic group, consisting of Palearctic, North American and Bahaman Ospreys, and the Australasian Ospreys. Ecology was studied in Senegambia during two visits in 1977-80. Over 800 Ospreys were estimated to winter there, mostly at river mouths and in mangrove. Marked Ospreys returned to the same area in consecutive years, and stayed within that area during winter. Dispersion along the coast was random except at a few localities where the birds concentrated. In mangrove, birds were regularly spaced at high tide but went to the coast or more open mangrove at low tide. Along the coast, Fish Eagles, Haliaeetus yocifer, and Ospreys seemed independently distributed, but in mangrove Ospreys avoided hunting in sight of a Fish Eagle, while along rivers and lakes eagles might have excluded Ospreys. The diet consisted mostly of Mugilidae, various Clupeidae, and, during part of winter, of Exocoetidae. Average fish size was generally 200-300 g, but fish were smaller in areas well protected from the open sea. Dive success and search time per capture varied between sites, partly because they were significantly correlated with fish size. Immatures 6 months old were less successful at catching fish than older birds. Foraging efficiency varied from 2.9 to 10 kcal/minute of foraging. Most Ospreys were found in mangrove even though foraging efficiency was lower there. This was most likely because hunting from a perch in mangrove was less demanding than hunting from flight elsewhere. Moult was studied from captured Ospreys and museum skins. A few Ospreys were caught more than once so that the development of the moult pattern of the primaries could be traced. Limits to the growth rate of feathers are emphasized as a major reason for the evolution of the Staffelmauser pattern of moult in large birds. Ospreys do not breed in the tropics, except in Australasia, even though the habitat seemed ecologically suited. In particular, foraging efficiency was as high in Senegambia as on the north-temperate breeding grounds. It is suggested that migrants Ospreys are physiologically inhibited from breeding in the tropics because daylength is too short, while south of the tropic of Capricorn, where migrants might be stimulated to breed, but six months out of phase, they are too scarce to start a permanent breeding population. It is suggested that non-migratory Ospreys have not spread their range south because of the presence of large numbers of migrants in the tropics.
Systematics and Taxonomy of Australian Birds presents an up-to-date classification of Australian birds. Building on the authors’ 1994 book, The Taxonomy and Species of Birds of Australia and its Territories, it incorporates the extensive volume of relevant systematic work since then. The findings of these studies are summarised and evaluated in the explanations for the taxonomic treatments adopted, and with the extensive citations, the book serves as a comprehensive introduction to the recent systematic literature of Australian birds. All species of birds that have been recorded from the Australian mainland, Tasmania, island territories and surrounding waters are treated and listed. Along with extant native species, all accepted vagrants, recently extinct (since 1800) native species and established introduced species are included.
We studied the foraging technique of Ospreys Pandion haliaetus during different wind speed conditions at Lake Hammarsjön, Sweden in autumn 2003. Different fishing techniques were used with a shift in relation to wind speed: (1) without hovering, (2) hovering with pure flapping flight, (3) hovering with flapping flight and gliding into the wind, and (4) hovering with pure gliding. The results supported our predictions that hovering is constrained at low wind speeds and gliding restricted to wind speeds exceeding 7 m/s. Mixing flapping and gliding flight when hovering may be done as a trade-off between increased fishing efficiency associated with flapping flight and energy-saving combined with gain in total hovering time associated with gliding intervals. The relationship between hovering time and wind speed differed significantly between males and females. At wind speeds up to about 3.0 m/s, the hovering time increased more steeply with increasing wind speed for males than for females. In contrast, hovering time was shorter for males than for females at high wind speeds. The juveniles showed a lower mean, smaller scatter, and less increase in hovering time along the wind speed gradient.
Differential migration reflects various constraints and selective forces on different individuals in a population, and has been explained by several hypotheses. Most previous studies about differential migration focused on only one aspect (e.g. spring timing, autumn timing or wintering area), which could not give a full picture of differential migration of the study population and carry out an overall investigation into the hypotheses. In this study, we analyse the migration patterns of European Ospreys Pandion haliaetus ringed in Germany based on the ring recovery database between 1980 and 2008. The migration routes of the study population form a broad front between south and southwest of the ringing area, and the wintering sites are in West Africa south of the Sahara and around the western Mediterranean. We demonstrate differential migration of the population in both spring and autumn timings as well as in the use of wintering grounds. Adult (third year and older) males return earliest to the breeding area in spring, followed by adult females and then two-year-old birds. In autumn, the adult females leave the breeding area earlier than adult males, while the migration of first-year Ospreys takes place over a wide time-span. Adult males were discovered mainly around the western Mediterranean in winter, closer to the ringing area than adult females and younger birds. We suggest that the selection for prior access to breeding resources on males shapes the patterns of differential migration in Ospreys.