Caspian Tern
Hydroprogne caspia
It is the world's largest tern with a length of 48–60 cm (19–24 in), a wingspan of 127–145 cm (50–57 in) and a weight of 530–782 g (18.7–27.6 oz). Adult birds have black legs, and a long thick red-orange bill with a small black tip. They have a white head with a black cap and white neck, belly, and tail. The upper wings and back are pale grey; the underwings are pale with dark primary feathers. In-flight, the tail is less forked than other terns, and wingtips are black on the underside.
ID text from Wikipedia, CC BY-SA 4.0
Common Tern
Sterna hirundo
The nominate subspecies of the common tern is 31–35 cm (12–14 in) long, including a 6–9 cm (2.4–3.5 in) fork in the tail, with a 77–98 cm (30–39 in) wingspan. It weighs 110–141 g (3.9–5.0 oz). Breeding adults have pale grey upperparts, very pale grey underparts, a black cap, orange-red legs, and a narrow pointed bill that can be mostly red with a black tip, or all black, depending on the subspecies. The common tern's upper wings are pale grey, but as the summer wears on, the dark feather shafts of the outer flight feathers become exposed, and a grey wedge appears on the wings. Voice: Common terns have a wide repertoire of calls, which have a lower pitch than the equivalent calls of Arctic terns. The most distinctive sound is the alarm KEE-yah, stressed on the first syllable, in contrast to the second-syllable stress of the Arctic tern.
ID text from Wikipedia, CC BY-SA 4.0
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