Pomarine Jaeger

How to find it

Go out on a boat, because scanning from shore is unlikely to work. Costa Rica has no regularly scheduled pelagic trips, so birders arrange a deal with a fishing boat or ride the Puntarenas to Paquera ferry, where a jaeger is possible among other seabirds. Pelagic trips out of Malpais have been arranged through Cabuya Bird Watching. The captains there are professional fishermen who stay in touch with other boats and know where the fish are, and so where the birds will be. Sightings can be brief: a dark juvenile seen from the ferry back to Puntarenas flew off as soon as the birders noticed it, so be ready to look fast.

How to recognise it

This is the biggest and heaviest of the three jaegers, about the size of a Ring-billed Gull. Look for a barrel chest, broad wings, a large head and bill, and slower wingbeats than other jaegers.

Light-morph adults have a brown back, mostly white underparts, a black cap and a yellowish-white neck. All morphs show a white flash on the dark wing tips, which appears as a double flash on the underwing. Breeding light-morph birds have a pinkish bill with a dark tip, more barring on the flanks and breast than Parasitic Jaeger, and no white spot above the bill base.

Breeding adults carry two long central tail feathers that are broad, blunt and twisted, called spoons, which show clearly in side view. Most birds in Costa Rican waters will lack them. Most adults drop their streamers soon after leaving the Arctic in mid or late summer, and winter adults are barred above and below, with central tail feathers that barely stick out.

Behaviour and diet

The Pomarine Jaeger is a pirate. It chases gulls, terns and even gannets to steal their catches, and it keeps this up all year with great agility. It also eats fish, carrion and scraps.

That habit helps explain why one followed a fishing boat in Costa Rica. Pomarine Jaegers usually stay farther from land than Parasitic Jaegers and gather over upwellings and current boundaries, so those are the places to scan from a boat.

Where it lives

Range wide, this is a bird of tropical oceans in the non-breeding season and of Arctic tundra when breeding. In Costa Rica it is a seabird of open water, recorded on a Pacific pelagic trip and also at Tortuguero on the Caribbean coast.

From Malpais, on the Nicoya Peninsula, the boat reaches the continental shelf in about an hour. One exhausted adult male was even found inland in a cattle pasture at 2600 m at San Gerardo, probably pushed there by bad weather from the Caribbean.

When to see it

A tour company bird list calls it a sporadic visitor off both coasts, from August to April. It is most common from December to February off the Pacific, where it can be found among Wedge-tailed Shearwaters. One Pacific day trip on 14 November found several adults and juveniles.

Similar birds

Parasitic Jaeger is the main lookalike. Pomarine is bulkier, broader-winged and less falcon-like, though juveniles and non-breeding adults are often hard to separate in the field. A Costa Rican pelagic report also found a juvenile Long-tailed Jaeger and a Parasitic Jaeger on the same waters, and two large juvenile Pomarines following a fishing boat looked like skuas.

Names and lore in Costa Rica

Costa Rican bird lists and seabird writing use the Spanish name Págalo Pomarino.

Status and conservation

The Costa Rican bird list classes it as a migrant (M), and the IUCN lists the species as Least Concern.

Photography tips

Look over upwellings and current boundaries, where Pomarine Jaegers gather, and expect them to keep farther from land than Parasitic Jaegers. A fishing boat can draw them close, and one passed only inches from a birder who was chumming the water. Sightings can be brief, so keep the camera ready.