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Little Tern vs Saunders's Tern

For a more in-depth introduction to the separation of these two fascinating species, see the link on the OSME website here.

 

These two taxa have been long-confused both in the UAE and well beyond, but, following the publication of a 2022 paper in the journal Dutch Birding it is now clear that they can be reliably separated in all plumages and, with care, even at distance, providing lighting conditions are good and views sufficiently prolonged to allow careful evaluation of plumage. Due to prior confusion, many older texts, including almost all popular field guides, give erroneous information about the relative status of the two species.

The UAE Annotated checklist spells out the current state of knowledge, which is very different to what it was thought to be as recently as 2020:

 

Little Tern Sternula albifrons

Common passage migrant both coasts from March to May and August to October, singles and small groups quite regularly recorded at inland sites during spring migration.

Common winter visitor both coasts and at least small numbers of non-breeders present both coasts throughout summer.

 

Saunders's Tern Sternula saundersi

Locally fairly common breeding visitor to Arabian Gulf islands mainly in Abu Dhabi Emirate; possibly also a passage migrant. Breeding population estimated as 200-800; colonies small and dispersed.

Returns to Arabian Gulf breeding sites from late February; post-breeding dispersal from early June onwards.

Migrant on the East coast, probably scarce here.

Apparently completely absent throughout UAE waters (and indeed all Arabian waters) throughout winter (early October to late February) and seemingly scarce or very scarce from August onwards. No confirmed inland records.

There are now known to be a number of plumage features that will readily allow separation of all ages. The most important are listed below:

Little Tern

1. Adult breeding:

  • Rather dark, leaden or blue-grey upperparts with rather contrasting pale rump (but see adult non-breeding below).

  • Narrow outer primary wedge that is very dark grey to blackish, so limited contrast with upperwing.

  • Narrow, well-defined pale trailing edge to the secondaries.

  • Pale forehead patch reaches in a short eyestripe over the eye, so eye is contained within black loral line.

2. Adult non-breeding:

  • Upperparts as adult breeding, but sometimes appear even darker grey. On many, rump concolorous grey too, giving an almost Whiskered Tern like impression. On some, the rather dark grey rump may be retained well into the breeding season.

  • Other primary wedge maybe broader (depending on wear and moult) but again is dark greyish-black, not jet black and so there is limited contrast with the grey upperparts.

  • Head rather dark; crown invariably dusky washed, framing narrow, sharp white notch from the whiter forehead to above the eye (mimicking the pattern in breeding adults).

 

3. Juveniles

  • Upperparts again rather dark overall, strongly grey secondaries with narrow white tips forming a narrow white trailing edge; comparatively limited contrast with leading edge and darker grey to blackish outer wing.

  • Head pattern as adult non-breeding, invariably showing a trace of white eye stripe.

 

UAE photos of Little Tern - here

 

Saunders's Tern

1. Adult breeding:

  • Markedly pale, pearl-grey upperparts with rump similar so never contrastingly pale

  • Outer primary wedge is virtually jet black, so clearly contrasts against the upperparts.

  • No hint of narrow white trailing edge to the secondaries as secondaries are almost entirely whitish, or very pale grey, forming a broad, ill-defined pale panel.

  • Pale forehead patch restricted; never reaches back over the eye, so eye is contained within the black cap.

 

2. Adult non-breeding:

  • Upperparts as adult breeding, i.e. very pale with secondaries palest part of the wing.

  • Other primary wedge again jet black and so strongly contrasting, leading edge of wing looks more contrasting too.

  • Head always obviously pale; crown unmarked so has eye mask effect, somewhat akin to Black-naped Tern; on some the mask is quite restricted. Never a hint of any ‘eye notch’.

3. Juveniles

  • Easy to identify even from a distance; appears to have a ‘Sabine’s Gull’ pattern: strikingly pied with very white head, body, upperparts and trailing edge of wing, contrasting with very black leading edge and outer primaries.

  • Head pattern as adult non-breeding, hence always look pale and never a hint of white notch over the eye. Birds just fledged may show a duskier crown but this is soon moulted out.

 

UAE photos of Saunders's Tern - see here

 

A little bit of care and common sense needs to be used when applying the above criteria, as judging contrast and paleness (or otherwise) in the field can be quite tricky and, whilst the exact secondary pattern can be very difficult to read in the field, it can be even more confusing in single photos when, depending on how the wing is flexed, both species can show a pattern momentarily that resembles that of the other. So as always, use multiple criteria and, if working from images, multiple images too.

When the original paper is duly made available online, that will be at the Dutch Birding website.

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