Jared Tan

During each migration season, the arrival of Whiskered Tern Chlidonias leucopterus and White-winged Tern C. hybrida brings about much added life to our coastal waters and freshwater bodies. Whiskered Tern are usually seen in Singapore from September to October, while White-winged Tern are usually encountered from September to January and April to May and often occur in larger numbers.

While adult Whiskered and White-winged Tern are straightforward to identify in both breeding and non-breeding plumage, immature birds are often misidentified. Here we shed some light on the various characteristics which can be used to differentiate between these two similar-looking species and some other tern species as well.

Feeding behaviour

Whiskered Tern and White-winged Tern are known as marsh terns, which typically feed by skimming and snatching food from the water surface. This is in contrast with the feeding behaviour of our resident Little Tern Sternula albifrons, which usually plunge-dives for food. While marsh terns usually engage in skimming, nevertheless it is still possible for them to sometimes engage in steeper dives to catch prey when the opportunity arises.

Immature plumage

Whiskered Tern are larger (24-28 cm), and have a heavier-built appearance than White-winged Tern (20-24 cm). Whiskered also have a longer, heavier bill compared to that of White-winged. While wing length may be difficult to discern in the field, the wings of Whiskered Tern are slightly longer and have a more uniform width throughout the wing length than that of White-winged. In addition, the tail of Whiskered Tern is generally slightly more notched than in White-winged. It should be noted that these differences may be minute at times, and may not be the most reliable of features to depend on for identification purposes.

It is often said that the presence of ‘headphones’ equates to a bird being a White-winged Tern. However, immature Whiskered Tern also gives off the impression of having ‘headphones’, thus the mere use of the word ‘headphones’ as a distinguishing feature can be rather misleading. In Whiskered Tern, the dark patch on the ear coverts does not extend as far down as in White-winged, and the white patch behind the ear coverts also does not extend as far up onto the crown and inwards towards the eye. While this may be one of the most talked about features, there are also other important distinguishing features to look at especially when the head pattern does not give a conclusive ID.

Immature birds of both species display a brown mantle and scapulars, which can be very useful in determining the identity of the bird. The scapulars of Whiskered show prominent contrasting dark crescents, in comparison to the generally more uniformly brown coloured scapulars of White-winged.

Another important feature to look at is the collar of the bird. In Whiskered, the black cap touches, or almost touches the mantle, leading to the lack of a white collar or just a narrow one. On the other hand, the black cap of White-winged does not touch the mantle, giving it a wide, obvious white collar.

The rump of the bird is also a useful indicator of the species. In Whiskered, the rump is a similar pale grey colour to the tail and upperwings, while it is white in White-winged. It is important to note that this feature only applies to immature birds, as the rump eventually becomes pale grey in adult White-winged Tern. Overexposed photos may also lead to the pale grey rump of Whiskered Tern appearing white, so care should be taken to ensure that the colours turn out accurately.

Lastly, the marginal coverts also differ. Whiskered generally show marginal coverts similar in colour to the rest of the upperwing, while White-winged usually have darker marginal coverts which are more contrasting compared to the rest of the upperwing. The upperwing of Whiskered is also slightly paler compared to that of White-winged.

Adult plumage (non-breeding)

Adult Whiskered Tern in non-breeding plumage do not have ‘headphones’, but instead display a streaked greyish cap, with the dark areas behind the eye not extending downwards onto the ear coverts like in immature birds. On the other hand, the ‘headphones’ of Adult White-winged Tern in non-breeding plumage look similar to that of immature birds. Given that the head patterns of both species look very different in adult non-breeding plumage, there should not be much confusion with regards to their identification.

Both species lack the brown mantle and scapulars found in immature birds and display a pale grey rump. Thus, unlike immature birds, the scapulars and rump can no longer be used to distinguish between adults of the two species.

Adult plumage (breeding)

White-winged Tern and Whiskered Tern in full breeding plumage are even more unmistakable and easy to distinguish – Whiskered has a black cap, white ‘cheeks’, smoky grey body, and a red bill, while White-winged has a black head, body, and underwing coverts, black bill, and a white tail. However, due to the time of the year when they are usually seen in Singapore, most adult birds seen in Singapore are either already in or moulting into non-breeding plumage. Still, birds which have not fully moulted but retain traces of breeding plumage can still be easily identified based on these features.

Distinguishing from resident tern species

It is also not uncommon to see our resident terns – the Little Tern and Black-naped Tern Sterna sumatrana also sometimes being mixed up with Whiskered and White-winged Tern. Little Tern share the exact same habitat as the marsh terns, inhabiting both inland and along the coast, while Black-naped Tern are exclusively found along our coastal waters.

Little Tern are similar in size (20-25 cm) to White-winged Tern and smaller than Whiskered Tern. On the other hand, Black-naped Tern are the largest of these (30-35 cm). Little and Black-naped Tern are more slender-built compared to the stockier Whiskered and White-winged Terns. As mentioned previously, Little Tern climb to a significant height before plunge-diving into the water to feed. On the other hand, Black-naped Tern feed by making short plunges to snatch fish from the water without fully submerging their bodies.

Little Tern in breeding plumage are unmistakable, possessing a yellow bill with a black tip, black crown, nape and eyestripe, white forehead, and tail streamers. However, birds in non-breeding plumage may be challenging to identify at times as they may look somewhat similar to immature Whiskered and immature/non-breeding White-winged Tern. Non-breeding Little Tern have a sharper, dagger-like black bill, white lores and forecrown, blackish hindcrown with whitish streaks and a black nape. Unlike Whiskered and White-winged whereby it cuts inwards, the black on the ear-coverts is straighter and curves slightly outwards in Little Tern.

Black-naped Tern have a long, thin black bill, with a narrow black eyestripe stretching from slightly in front of the eyes to the hindnape, as well as a white crown. The overall plumage is clean white, with the mantle and upperwings very pale whitish-grey. Similarly, the black on the ear coverts is straighter and curves slightly outwards instead of inwards.

Black Tern in Singapore???

While enjoying views of Whiskered and White-winged Tern as they return to our shores, do also keep a lookout for another possible vagrant – the Black Tern. While not yet recorded in Singapore, this species has been recently spotted in Malaysian waters off Kedah for the past two years (2022 and 2023).

Without going into too much specifics, Black Tern look similar to White-winged Tern in both breeding and non-breeding plumage. Black Tern have darker upperwings, a slightly longer bill, and the patch behind the ear coverts does not extend as far upwards and near to the eye and as in White-winged, giving it a “fuller” appearance. However, for birds in non-breeding and immature plumage (which we would be more likely to encounter), the diagnostic feature to look out for would be the presence of a dark mark on the side of the breast. Who knows, you may the one to spot Singapore’s first Black Tern!

Note: This article was lightly edited on 8 Sep thanks to suggestions from Dave Bakewell.