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Comparing terns

Terns are quick and pale and all look alike at first glance. Yet a few features usually separate them: the colour of the bill (and whether it has a black or yellow tip), the legs, the head, the tail and where you see them. Tap what you see below; the list then shows only the species that fit everything.

• Within one row you can pick several values (red or orange legs); across rows everything must match.
• Everything refers to adult birds. The head changes with the season, so breeding and winter plumage are listed separately. Young terns are much harder; see the species pages for them.
• Bill and leg colour vary with season and light, and at a distance a bill often looks darker. If in doubt, pick two values.

Species	Length	Legs	Bill	Head, summer	Head, winter	Tail	Mantle	Underparts	Where	What to look for
Large terns
Caspian TernHydroprogne caspia	48–60 cm	Black/dark brown	Red/orange-red	Black cap	Streaked cap	Short	Pale grey	White/pale grey	Coast and inland	The largest tern: a huge coral-red bill with a dark tip, black legs and a short, shallowly forked tail. In winter the cap stays heavily streaked.
Greater Crested TernThalasseus bergii	46–49 cm	Black/dark brown	Yellow to orange	Cap with crest	White forehead	Forked	Medium grey	White/pale grey	Coast and sea	Large tern with a heavy yellow to greenish-yellow bill, black legs and a long, shaggy crest; mantle darker than Sandwich Tern.
Elegant TernThalasseus elegans vagrant	39–43 cm	Black/dark brown	Yellow to orange	Cap with crest	White forehead	Forked	Pale grey	White/pale grey	Coast and sea	Black cap with a long, loose crest and a long, thin, slightly drooping orange-red bill; black legs. A vagrant from America.
Sooty TernOnychoprion fuscatus	36–45 cm	Black/dark brown	Black	Cap, white forehead	White forehead	Long streamers	Black	White/pale grey	Coast and sea	Black above and white below, with a white forehead patch; black bill and legs and a deeply forked tail. A species of the open sea.
Medium terns
Lesser Crested TernThalasseus bengalensis	35–43 cm	Black/dark brown	Yellow to orange	Cap with crest	White forehead	Forked	Medium grey	White/pale grey	Coast and sea	Orange bill without a black tip, black legs and a full black crest; smaller and slimmer than Greater Crested Tern, with an orange rather than yellow bill.
Sandwich TernThalasseus sandvicensis	36–41 cm	Black/dark brown	Black, yellow tip	Cap with crest	White forehead	Forked	Pale grey	White/pale grey	Coast and sea	Black bill with a yellow tip, black legs and a shaggy crest; snow-white below and pearl-grey above, with a short fork in the tail.
Gull-Billed TernGelochelidon nilotica	33–42 cm	Black/dark brown	Black	Black cap	Eye patch	Short	Pale grey	White/pale grey	Coast and inland	Thick, short, gull-like black bill, black legs and a pale, broad-winged look; often hunts insects over land and marsh rather than plunge-diving.
Roseate TernSterna dougallii	33–38 cm	Red	Black, red base	Black cap	White forehead	Long streamers	Pale grey	White/pale grey	Coast and sea	The palest tern, almost white, with very long thin tail streamers reaching well beyond the wings; black bill with a red base and red legs.
Forster's TernSterna forsteri vagrant	33–36 cm	Orange	Red/orange-red	Black cap	Eye mask	Long streamers	Pale grey	White/pale grey	Coast and inland	Orange bill with a black tip and orange legs; in winter a black eye mask on a white head (no black cap on the nape). Long, deeply forked tail.
Arctic TernSterna paradisaea	33–36 cm	Red	Red/orange-red	Black cap	White forehead	Long streamers	Medium grey	White/pale grey	Coast and sea	Blood-red bill without a black tip, very short red legs, grey underparts and long tail streamers; the primaries look translucent from below.
White-Cheeked TernSterna repressa	32–34 cm	Black/dark brown	Dark red	Black cap	White forehead	Forked	Medium grey	Grey	Coast and sea	Slender, with a black cap, white cheek and clearly grey underparts; a dark, reddish-black bill and dark legs. A coastal species of warm seas.
Common TernSterna hirundo	31–35 cm	Red	Red/orange-red	Black cap	White forehead	Forked	Pale grey	White/pale grey	Coast and inland	The everyday tern: an orange-red bill with a black tip, red legs and pale-grey underparts; the tail streamers reach about to the wing tips.
Bridled TernOnychoprion anaethetus	30–32 cm	Black/dark brown	Black	Cap, white forehead	White forehead	Long streamers	Dark grey	White/pale grey	Coast and sea	Grey-brown above and white below; the white forehead continues as a stripe behind the eye (the ‘bridle’). Black bill and legs, deeply forked tail.
Small terns
Whiskered TernChlidonias hybrida	24–28 cm	Red	Dark red	Black cap	White forehead	Short	Medium grey	Grey	Marsh, fresh water	Black cap with a broad white cheek, dark-grey body, dark-red bill and red legs; short, shallowly forked tail without long streamers.
Black TernChlidonias niger	22–26 cm	Black/dark brown	Black	Head+body black	Eye patch	Short	Dark grey	Black	Marsh, fresh water	Black head and body with dark-grey wings and a black bill; in winter white with a dark patch behind the eye and a dark patch at the breast side.
Little TernSternula albifrons	21–25 cm	Orange	Yellow to orange	Cap, white forehead	White forehead	Short	Pale grey	White/pale grey	Coast and inland	Tiny, with a yellow bill tipped black, orange-yellow legs, a white forehead and a very short tail; fast, flickering flight.
White-Winged TernChlidonias leucopterus	20–24 cm	Red	Dark red	Head+body black	Eye patch	Short	Black	Black	Marsh, fresh water	Black body with strikingly white upperwings and tail; dark-red bill and bright red legs. In winter almost white with a dark patch behind the eye, but without the dark breast-side patch of Black Tern.

The features come from the species accounts in this guide, supplemented from standard field guides. Lengths are those on the species pages and include the tail streamers; the groups are a convenience, not a fixed classification.