Shorebirds and gulls, in the diverse order Charadriiformes
Costa Rica has about 70 species of shorebirds and gulls, in the diverse order Charadriiformes. Almost all are known to North American visitors. Some, such as the familiar herring gull (gaviota argéntea; Larus argentatus) are Holarctic (found in all northern continents). Many are winter migrants to Costa Rica and few are seen in summer.
The most common gull is the laughing gull (gaviota reidora; Larus a tricilla) , which is a widespread and abundant migrant (September to November and April to mid-May) but is also present in large numbers year-round, especially on the Pacific coast.
The most widespread shorebird is the spotted sandpiper (andarríos maculado; Actitis macularia), found along inland lakes and rivers up to 1850m as well as on both coasts. It is often seen from August to May but rarely in the summer. It is small, brown above and white below, with a faint white eye stripe and yellowish legs. Its most distinctive feature is its teetering back and forth while walking and foraging.
It is usually seen singly. The most abundant shorebird is the western sandpiper (correlimos occidental; Calidris mauri), which is grayish-brown above with fine streaks and white below. This bird is seen in flocks of hundreds along both coasts, but especially the Pacific, from August to April. Also common is the sanderling (playero arenero; Calidris alba), especially from mid-August to October and mid-March to early May. Fewer birds are seen in winter and almost none in summer. This shorebird is found in small flocks on both coasts and is paler than other similar shorebirds. It runs up and down the surf line with a distinctive gait like a clockwork toy.
A favorite of many visitors is the northern jacana (jacana centroamericana; Jacana spinosa), which has extremely long, thin toes that enable it to walk on top of aquatic plants, earning it the nickname 'Iily-trotter.' They are common on many lowland lakes and water ways. At first glance, their brown bodies, black necks and heads, and yellow bill and frontal shield seem rather nondescript, but when disturbed the birds stretch their wings to reveal startling yellow flight feathers. This may serve to momentarily confuse would-be predators and makes them easy for us to identify. The female is polyandrous, mating with up to four males within her territory. The males do most of the nest building and incubation whether the female manages to lay the right eggs in each father's nest remains in doubt.