Swallow-tailed gull, Izabela Island, Galapagos.

Gulls of Galapagos Islands

The two resident gull species of the Galapagos are beautiful examples of island evolution. It's a pity that their biology was largely unknown at the time of Darwin's visit to the archipelago - he would certainly enjoy studying this living illustration to his theory. I was more lucky than him, because during my trip to the Galapagos in 1995, I could pay these birds all the attention they deserved. Here are some photos from that trip.

Swallow-tailed gull (Larus furcatus, commonly called Creagrus furcatus) is an unusual bird. It breeds on the Galapagos and few other small islands off Pacific coast of tropical South America. It has evolved from a smaller species, Sabine's gull (L. sabini), which nests in wet tundra along Arctic coasts, particularly in Yakutia, but winters around the Galapagos. gull
Sabine's gull, Pevek, Chukotka.
Sabine's gull, Russkaya Koshka Spit, Chukotka.
Both species can also be seen in winter throughout tropical Eastern Pacific (Sabine's gull - also in Southeastern Atlantic Ocean). As swallow-tailed gull can nest at any time of the year, "winter" is not well defined for it, but most birds disperse during October-February.
Some northern gulls, including Sabine's, become partly nocturnal when they come to the tropics in winter. This allows them to avoid overheating, as well as being robbed by frigatebirds (Fregata). Their food - small fish, squid and large plankton - is also more available at night, when it comes close to surface. When the ancestors of swallow-tailed gulls started nesting on the Galapagos instead of returning to the North, they probably suffered heavily from frigatebirds, so they became the most nocturnal of all gulls. frigatebirds
Magnificent frigatebirds (Fregata magnifica),
San Cristobal I, Galapagos.
Close-up of a swallow-tailed gull,
Baltra Island, Galapagos.
They developed some interesting adaptations to nocturnal lifestyle: in addition to large, very light-sensitive eyes, they have red eyering, which supposedly improves their ability to see bioluminescence. As soon as frigatebirds appear at dawn, gulls are usually forced to stop hunting, because their prey would be forcefully taken from them anyway. Breeding birds return to their nests before dawn, to avoid been robbed near the nesting site, and stay there all day. Probably because of their nocturnal habits, they are only slightly darker than Sabine's gulls, while most other tropical gulls have dark "sunscreen" plumage.
They are not, however, blinded by bright artificial light sources, and often follow ships at night, when ship's lights attract squid, their favorite prey. So, you can use a flash to take their pictures at night, without risk of damaging their eyesight. Unlike the eyes of many other nocturnal birds, their eyes do not reflect light. The habit of following ships is a possible reason for some recent records of these gulls outside their normal range: off Central Chile, Panama, and even near Monterey in Northern California. gull
Swallow-tailed gull at sea,
off Isla de La Plata, Ecuador.
Swallow-tailed gull and tropicbird
in a nesting cave, Islas Plazas.
Swallow-tailed gulls nest on small offshore islets, on lava cliffs or under bushes; the majority of nests is probably hidden in deep niches and small caves, where they are often joined by red-billed tropicbirds (Phaethon aethereus). Males have an unusual habit of swallowing small pebbles and then regurgitating them at nest site during nest construction. They only lay one egg; it is believed that the white bill tip helps the chick find the source of food when its parents return from the sea at night. Males prefer to return to the same nesting sites every year, but females and young birds usually change nest sites after each breeding season.
Like most other birds of the Galapagos, these gulls are very tame. They can easily be seen at nesting colonies at Islas Plazas and in other parts of the archipelago. (To look inside nesting caves, you'll need somebody to hold your legs, while you hang over the cliff edge.) It is believed that there are about 7000 pairs of swallow-tailed gulls on the Galapagos, and less than 100 on other islands; the total World's population is estimated at 30 000 birds. gull
Nesting cave of gulls and tropicbirds,
surrounded by marine iguanas, Islas Plazas.
Lava gull, Santa Cruz Island.
The other Galapagos species, lava gull (L. fuliginosus), is much more rare: there are less than 400 breeding pairs. This is a typical "dark" tropical gull. Unlike all other gulls, lava gull is highly sedentary, and have never been recorded outside the Galapagos. It is a scavenger, and commonly feeds along the coast, looking for eggs, small lizards, small fish and scraps; it can also steal fish from pelicans, and crabs from herons.
Lava gull often hangs around sea lions or people, and, despite its rarity, it is easy to see in any port of the Galapagos. It nests in small lava caves, rocky outcrops, or on remote beaches. Nesting birds are extremely vary of people, unlike most other Galapagos inhabitants. gull
Lava gull and sea lions (Zalophus californianus),
Santa Cruz Island, Galapagos.
Laughing gull, Miami, Florida.
Lava gull has probably evolved from laughing gull (L. atricilla), a common bird of the tropical coasts of the Americas, which accidentally visits the Galapagos.

Close-up of lava gull, Santa Cruz Island, Galapagos.