Gull-billed Tern (“Mr Bill”)

The Gull-billed Tern is much smaller than the Sandwich, but slightly larger than Forster’s and Common. It’s named for its bill which is thick and black. The Gull-billed is uncommon, but regular on the Texas Coast where it frequents sand flats and grassy marshes year-round, swooping low to snatch prey from the water or ground surface.

In alternate plumage the Gull-billed shows a black head, with very little crest. It is whiter and has proportionately longer legs than other terns.

In basic plumage the head of the Gull-billed is white with a smudgy patch behind the eye.

In flight the Gull-billed is pale backed, short-necked and shows a black stubby bill.

In basic plumage the Gull-billed is a pale, almost white bird.

Forster’s Tern (“the Pirate”)

The Forster’s Tern is a year round denizen of the Texas Coast and is common in winter at inland lakes as well. I’ve dubbed it “the pirate” for the “eye-patch” it wears in basic plumage.

With its bright orange & black bill, orange legs, black cap and long streamer tail the Forster’s in alternate plumage is spectacular when seen well!! Note that the streamer tail usually extends past the primaries.

Common Tern (“common carpel”)

The Common Tern is a fall and spring migrant on the Texas Coast, and a few over-winter as well. At some locations during migration it can be the most numerous medium tern. I’m calling it the “Common Carpel” because in basic plumage it usually shows a dark carpel bar where the upper-wing bends into the body.

In alternate plumage the Common has a black cap, red & black-tipped bill (sometimes appears black & black-tipped) and a grayish body.

With good looks, the Common may be identified in flight based on its black cap, gray body, black-appearing bill, shorter tail and, depending on season, black carpel bars.

Forster’s Vs Common

The Forster’s and Common are the 2 most difficult terns to distinguish. It’s important to consider the time of year and which plumage the bird is in when deciding between these 2 .

In basic plumage the 2 are readily separated by the black on the head and nape. In basic plumage the Forster’s sports an “eye-patch” — dark feathers which surround the eye, but do not continue on the hind-crown and nape. While on the Common in basic plumage the black includes the hind-crown and nape.

Forster’s in basic: the black on the head does not continue on the hind-crown nape. Note that in basic, the bill is pretty much black on both Forster’s and Common.
Common in basic: showing the black of the head extending around the hind-crown & nape. Note that in basic, the bill is pretty much black on both Forster’s and Common.
In basic the Common (left) shows a grayer back, black carpel bar, black hind-crown & nape. Though not always apparent it is also slightly shorter-legged and smaller-billed than the Forster’s (right).

The 2 are can be more difficult to identify in alternate plumage.

The Common (left) is a grayer bird, shows a burnt-red & black-tipped bill and has slightly shorter, less-bright legs and a smaller bill. The Forster’s (right) shows a whiter body, orange black-tipped bill and is slightly longer-legged and larger.

The bill color on alternate terns can be ambiguous, but in general the Forster’s is orange (analogous to the Baltimore Oriole), while I call the bill color of the Common “burnt-red” (analogous to the Orchard Oriole). When transitioning from basic to alternate the Forster’s bill can also appear burnt-red, so care must be taken with this field mark.

The bill of the Forster’s in alternate is orange (analogous to the Baltimore Oriole).
I call the bill color of the Common in alternate “burnt-red” (analogous to the Orchard Oriole). The Common’s bill color can also be a brighter red.
The more orangey billed & longer legged Forster’s is in the back. 2 more burnt-red billed Common are in the center.
The more orangey-billed and paler bodied Forster’s is in front. Grayer Common is in back.
The more orangey-billed and paler bodied Forster’s is on the left. The grayer Common is on the right.
Here we have a Common on the right based on redder bill & legs and tail shorter than primaries. On the left is a Forster’s based on the “eye patches” and hind-crown and nape transitioning to black. The streamer primaries of the Forster’s can just be seen and appear to be at least equal to the primaries. The Forster’s shows a larger head and bill. However, the Forster’s also, shows a couple of ambiguous features: the bill appears more burnt-red and there appears to be a bit of dark carpel bar. However I believe these features are due to the fact that this bird is transitioning from basic to alternate which occurs later than Common. This photo was taken on May 1st.

Forster’s vs Common — In-Flight

At inland lakes in winter the Forster’s is the default tern of any size. In basic the “pirate eye-patch” is often visible. The 2-toned appearance of the upper wings, with grayer secondaries and tertials and paler primaries is often cited as an in-flight fieldmark, however, I find this to often be absent or to be difficult to see on a distant, flying bird.

In this edge-on photo of a Forster’s the primaries appear darker than the secondaries and mantle. This seems to be an illusion caused by the angle of view, but it demonstrates the ambiguity of this field mark. Note that the white rump and “pirate eye-patch” are visible.

A medium tern in basic with a black hind-crown & nape can be safely identified as a Common. (No photos as yet).

In alternate plumage the Common usually shows more black in the primaries.

(See page 1 of terns)

(See page 3 of terns)