Black-tailed gull

Larus crassirostris

Photo by Tom Edelsten (Birds Korea)

Common name:
black-tailed gull (en); gaivota-do-Japão (pt); goéland à queue noire (fr); gaviota japonesa (es); Japanmöwe (de)

Taxonomy:
Order Charadriiformes
Family Laridae

Range:
This species breeds in northern Japan, extreme south-eastern Russia, Korea and north-eastern China. Some population migrate south to winter along the coasts of Japan and the East China Sea down to Hong Kong.

Size:
These birds are 46-48 cm long and have a wingspan of 118-124 cm. They weigh 440-640 g.

Habitat:
The black-tailed gull is found breeding in rocky offshore islands, sea cliffs and rocky shorelines, foraging on a variety of coastal habitats including rocky and sandy intertidal areas, tidal pools, kelp beds, seagrass beds, reefs, estuaries and also on the open sea.

Diet:
They feed on fishes, especially sand lance and Japanese anchovy, molluscs, polychaetes, crustaceans, insects and also carrion and human waste. They often follow fishing vessels in search of food and also steal food from other seabirds.

Breeding:
Black-tailed gulls breed in May-July. They form large breeding colonies and nest on sandy areas, or among rocks, in a shallow scrape that is usually lined with dry grasses. There the female lays 2-3 eggs, which are incubated for 24-27 days. The chicks fledge 35-40 days after hatching.

Conservation:
IUCN status - LC (Least Concern)
This species has a relatively large breeding range and the global population is estimated at 1,1 million individuals. The current population trend is unknown, but is suspected to be stable in the absence of evidence for any declines or substantial threats.

Franklin's gull

Larus pipixcan

Photo by Alan Vernon (Wikipedia)

Common name:
Franklin's gull (en); gaivota-de-Franklin (pt); mouette de Franklin (fr); gaviota de Franklin (es); präriemöwe (de)


Taxonomy:
Order Charadriiformes
Family Laridae


Range:
This species breeds in central North America, mostly in Alberta, Saskatchewan and Manitoba, Canada; and in Montana, North Dakota and South Dakota, United States. They migrate south to winter along the Pacific coast of South America, from Ecuador to Chile and further inland in northern Argentina.


Size:
These birds are 32-38 cm long and have a wingspan of 85-95 cm. They weigh 220-335 g.


Habitat:
The Franklin's gull breeds in marshes and inland lakes with emergent vegetation. Outside the breeding season they are found in coastal areas, lakes, marshes, cultivated fields and rubbish dumps.


Diet:
During the breeding season they mostly eat earthworms, chironomids and other aquatic insects, grasshoppers and sometimes also rodents and seeds. Outside the breeding season their diet includes a larger portion of fish, but also insects and other invertebrates, seeds and often also offal and refuse.


Breeding:
Franklin's gulls breed in May-August. They are highly gregarious, forming colonies of hundreads to over 10.000 pairs. The nest is a floating platform of vegetation, placed in thick reeds above water. The female lays 2-4 creamy-white, yellowish or greenish eggs with dark brown spots. The eggs are incubated by both parents for 23-26 days. The chicks are semi-precocial, but remain in the nest for around 3 weeks and receive food from both parents until fledging, 31-35 days after hatching.


Conservation:
IUCN status - LC (Least Concern)
This species has a very large breeding range and the global population is estimated at 470.000-1.500.000 individuals. The population has undergone a small increase over the last 4 decades.