Caspian tern
Sterna caspia
Identification Tips:
- Length: 20 inches Wingspan: 53 inches
- Sexes similar
- Dives into water for prey
- Large, barrel-chested tern with long, thick, reddish bill
- Short, notched tail
- Hints of a crest at the rear of the head
- Pale underwings with dark patch in primaries
Adult alternate:
- Deep red bill, often with indistinct black ring at tip
- Black legs
- Black cap with very slight crested appearance
- White face, neck, breast, and belly
- Pale gray back and upperwings
- Pale underwings with dusky gray on outer 5-6 primaries
- White tail
- Takes three years to reach full adult plumage
Adult basic:
- Similar to adult alternate, but has a black cap streaked with white
and darker, more worn, primaries
Juvenile:
- Pale legs
- Deep orange bill
- Brownish cap streaked with white
- Upperwing coverts and scapulars marked by crisp, black scalloping
- White face, neck, breast, and belly
- Pale upperwing has darker outer primaries and secondaries
- Grayish tail
Immature:
- First-year birds are like basic-plumaged adults but have darker
uppersurfaces to the outer primaries, dark secondaries, a grayish tail, and a
pale forehead
- Second-year birds are almost identical to alternate-plumaged adults, but
have often white spots in the cap, darker outer primaries and some gray in the
tail
Similar species:
When trying to identify terns, it is safest to use a combination of
field marks instead of relying on a single field mark. The Royal and Elegant
terns are the only other large, orange-billed terns and are quite similar.
Elegant Terns are very small compared to Caspians, are very slim-winged, have
slimmer orange bills, have much more forked tails and less black on the
undersurface of the primaries. The Caspian can be separated from the Royal by
its thicker, reddish bill, dark wedge on the outer portion of the underwing,
more shallowly-forked tail, broader wings and its tendency to have an almost
complete cap in basic and immature plumages. The smaller Sterna terns have
slimmer, black or black-tipped bills, slimmer bodies and wings and a much more
deeply-forked tail.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.