Notes on Field Identification1:

Little & Saunders's Terns

~ presented by Birds of India

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

? Nikhil Devasar
     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

? Daniele Occhiato
 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

? Sumit Sen
                  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

 ? Sumit Sen

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

? Sumit Sen

Images:

Little Terns

? Sumit Sen


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 Moller for help with research papers.


© Sumit K Sen 2008

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