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Identification of Little
& Saunders's Terns in Asia
~by Sumit K Sen
Note: This is not an original work
but more a compilation of available information strengthened by field
observations.
Introduction
Terns are mostly sea-birds but are found in inland rivers,
marshlands, lakes and ponds as well. They are adapted to life in a water world
and seldom, if ever, use terrestrial habitats. They form a lineage with gulls and skimmers which in turn
are related to skuas and auks. Terns have a worldwide distribution.
Most terns belong to one genus –
Sterna.
However, recent phylogenetic work based on
mtDNA sequences by Bridge, Jones & Baker (2005) support the splitting of Sterna
into several smaller genera. The AOU has accepted this split and as a result
the coherent sub-group of little white terns has been recognized as a separate
genus - Sternula. For the purposes of our note, this split is useful as it
helps us to focus on the species level differences in the same genus. Our field
experience is also supportive of the split as these 'little white terns' are
behaviourally different from current congeners.
There are seven species worldwide in the genus Sternula. Of these, we are
concerned with two – Little Tern Sternula albifrons (or, Sterna
albifrons) and Saunders's Tern
Sternula saundersi (or, Sterna
saundersi). Mention, however, must be made
here of another species in the genus - the Least Tern Sternula
antillarum.
Both Saunders's and Least were formerly
considered a subspecies of Little Tern and, not surprisingly, very similar to
Little Tern in general appearance and habits.
Purpose:
Little Terns and
Saunders's Terns are almost identical to the observer in the field and
small differences help to separate them. This note deals with the
identification points that can be useful to separate Little and Saunders's in
areas where both species are known to overlap in range – Eastern Africa and Asia.
Species
Description:
Little Tern
Sternula albifrons
Breeding albifrons Little Terns, Harike,
Punjab ~ Nikhil Devasar
Description:
This
is a small whitish tern with a black cap and a long pointed yellow bill.
Size:
23 cm long with a 41-47
cm wingspan
Subspecies:
There are three subspecies:
i) albifrons occurs in Europe, Africa through West Asia to western India.
ii) guineae
occurs in Africa from Ghana to Gabon.
iii) sinensis ranges in from Southeast Asia to Australia
This note considers only the
albifrons
and sinensis
races of the Little Tern.
Habitat:
Beaches, seacoasts, rivers, lakes.
Habits:
This is a migratory flocking species and nests in small colonies on
scrapes in sand/gravel. Species often hovers with rapid wing-beats before
plunge-diving for fish. The offering of fish by the male to
the female is part of a courtship display.
Range:
This species has a large range, with an estimated global extent of occurrence
of 1,000,000–10,000,000 km².
Saunders's Tern
Sternula saundersi
Non-breeding Saunders's Tern, Salalah, Oman ~ Daniele
Occhiato
Description:
Small
whitish tern with a black cap and long pointed yellow bill.
Size:
23 cm long with a 41-47
cm wingspan
Subspecies:
None
Habitat:
A marine tern. Beaches and seacoasts.
Habits:
Poorly known but may be very similar to Little.
Range:
This species has a large range, with an estimated global extent of occurrence
of 100,000–1,000,000 km². Ranges from North-east Africa and along the coasts
of the Red Sea to the Persian Gulf from there to Pakistan and India.
North-east African birds move south as far as Tanzania in winter. Birds in
Somalia, Sudan and Socotra are resident. Other populations appear to migrate
eastwards to the west coast of India, Sri Lanka and Maldives.
Identification:
According to Chandler and Wilds (1994) many of the features supposedly
distinguishing Saunders's from Little intergrade with characters of that
species. Areas for possible confusion do exist! Many intermediates occur and
only those with a combination of all characters can be can be identified with
certainty in the field - and only in adult summer plumage.
Conclusive identification in winter and immature plumages is almost impossible
in the field.
|
Features |
Little |
Saunders's |
Size
General Appearance
Habits |
Similar |
Similar.
Saunders's a little smaller and sitting lower. |
|
Head
Breeding
|
|
|
Br. |
§ Black cap
and triangle shaped white forehead with black loral stripe.
§ The white forehead corners taper to a point indenting into the black area
and gradually narrows in a triangle towards the eye.
§ These corners extend well behind the eye giving a 'meaner' facial
impression. |
§ Black cap
and triangle shaped white forehead with black loral stripe. Lacks Little's
suggestion of a white supercilium.
§ The shorter white forehead patch has rounded corners with no tapered
points and has a straight upper border across the forehead.
§ The white on forehead does not reach top of eyes but ends in front of eye. |
|
NBr. |
§ Dull black,
grey spotted mask which is diffusely demarcated from the white-flecked
crown.
§ The black spot in front of eye stands out against white lores and face. |
§ Similar. No
clear distinguishing features. |
|
Loral Stripe |
|
§ Black loral
patch normally reaches to the eye, or only 1mm above. |
§ Much
broader than in Little, appearing as wide as the black surrounding the eye.
It is 3-6mm broad in front of the eye. |
|
Bill |
Br. |
§ Brighter
yellow than Saunders's |
§ Duller
yellow compared to Little |
|
NBr. |
§ Black |
|
|
Upperparts |
|
|
§ Species
paler than Little Tern in alternate plumage but darker than Little in
basic plumage. |
|
Br. |
§ Pale
blue-grey with outermost 1-3 primaries forming a distinct black leading edge
to the wing. |
§ Paler grey
upperparts contrasting with solid, 'matt' black outer primaries, of which
there are normally three, not two as in Little.
§ These 3 primaries are deeper black than on Little, with black shafts. |
|
NBr. |
§ Lesser
coverts become darker. |
|
|
Wings |
Br. |
§ 2-3 outer
primaries are blackish-grey or slate black contrasting with grey of rest of
upperwing.
§ Shafts of 1st 3 primaries blackish brown to brownish-white. White to horn
in sinensis and black in nominate.
§ There are also birds with one, three or four black primaries, and the
number need not be the same in both wings. |
§ 3 or 4
outer primaries black.
§ Shafts of first 3 (or 4) primaries black and forming a broader, and pure
black leading edge to the outer wing contrasting with rest of upperwing. |
|
NBr. |
§ Shows more
diffuse dark greyish outermost primaries with with white shaft and less
contrast.
§ In juveniles all primaries are darker and the four or five outermost are
deep black. |
§ Saunders´s
moults later and normally retains the outer primaries which are deeper black
compared to Little.
§ Number of black outer primaries is variable. |
|
Rump and tail
 |
|
|
Br. |
§ Rump is
paler (whitish) and the tail is pure white.
§ Back color is usually contrasting with the rump and tail
color.
§ Race sinensis has grey rump & shows
whitish primary shafts. |
§ Rump is
dark ish grey and the tail darkish grey.
§ Grey of the rump is concolourous with the mantle and extends to the
central tail feathers.
§ Contrast between the back and rump/tail is generally lacking.
§ Tail streamers never as long as in Little. |
|
NBr. |
§ White rump
contrasts with grey back and any grey tail feathers. Jul-Aug: Rump is
normally paler and stands out more clearly against darker grey upperparts.
§ Many Little Terns within Saunders's range have an equally grey rump and
tail
|
§ Rump is
pale grey and the tail pale grey.
§ In fresh plumage the rump and uppertail-coverts have white edges and appear whiter. |
|
Legs and feet |
|
|
§ Shorter |
|
Br |
§ Bright
orange-yellow to yellow |
§ Dull olive
or reddish brown to mid-brown.
§ Any yellow present restricted to the feet or rear tarsus |
|
NBr |
§ Grey or
brown, sometimes tinged yellow |
§ Dusky
yellow-olive |
|
Call |
§ Harsh 'ket-ket' |
§ Softer 'kit-kit' |
|
Distribution |
|
Images:
Little Terns
External Images:
1.
Breeding Saunders's;
Oman by H. & J. Eriksen
2.
Non-breeding Saunders's; Oman by Daniele
Occhiato
3.
Breeding Saunders's;
Gujarat, India by A Deomurari
4.
Non-breeding sinensis Little Tern,
Malaysia by D Bakewell
5.
Nesting Little Tern, Karnataka, India by N
Sant
6.
Some confusing sternula terns
References,
sources and further reading:
1. Bulletin of the African Bird Club, vol 2.2, September 1995:
Field identification of Little and Saunders's Tern by Olsen K.M., Larssen H.
2. Collinson, M. (2006). Splitting headaches? Recent taxonomic changes
affecting the British and Western Palaearctic lists. British Birds 99(6):
306-323.
3. Bridge, E. S.; Jones, A. W. & Baker, A. J. (2005): A phylogenetic framework
for the terns (Sternini) inferred from mtDNA sequences: implications for
taxonomy and plumage evolution. Molecular Phylogenetics and Evolution
35.
4. Chandler, Dr. R.J. and Wilds, C. 1994. Little, Least and Saunder's Terns.
British Birds Volume 87. No.2
5.
Notes on biometry, sex determination and moult in Little
Tern Sterna albifrons by Henning Behmann and Christer Persson.
6.
SMSO.net
7.
Louisiana Museum of Natural History
8.
IUCN Red List
9. Image collection at
Oriental Bird Images
Acknowledgements:
1. Daniele
Occhiato and Nikhil Devasar for allowing use of their images
2. Gopi Sundar for corrections and helpful comments on the draft.
3. Clive Mann and Eckhard Möller for help with research papers.
© Sumit K Sen 2008
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© Sumit K Sen 2001 - 2008
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Last updated
12 Oct 2008
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