Red phalarope

Phalaropus fulicarius is a bird of the family Phalaropodidae that, although classified as a shorebird, acts at sea like a surface-feeding, planktivorous seabird ^[1]; WoRMS lists it in English as red phalarope or grey phalarope and in Spanish as falaropo picogrueso ^[2]. It breeds on the coastal tundra of the Arctic and, once breeding ends, spends most of the year at sea, where it feeds on zooplankton at the surface ^[1]. Part of the North American birds winter in the Pacific, mostly off the coasts of Peru and Chile ^[1]. Its global category on the IUCN Red List is Least Concern ^[3].

In breeding plumage the female is usually showier than the male, the reverse of the usual pattern in birds; male plumage varies more, and the brightest males can approach the look of females ^[4]. Colour therefore does not settle the sex: a bird incubating four eggs, with a plain black crown and reddish body feathers, turned out to be a male according to a DNA analysis ^[4].

An earlier study at Igloolik, whose measurements Giroux and colleagues tabulate, gave a wing average of 128.4 mm in 48 males and 134.9 mm in 14 females, and a bill of 22.2 mm in males and 22.7 mm in females ^[4]. The size difference exists but is small, especially in the bill ^[4].

It breeds on the coastal tundra of the Holarctic, where it spends 1 to 2 months nesting ^[1]. Outside the breeding season it moves into the pelagic environment: some winter in the Pacific Ocean, mainly off Peru and Chile and occasionally as far north as northern California, and others in the Atlantic, from southern North Carolina to the Caribbean ^[1]. There are therefore probably 2 populations in North America, although where the divide between them lies is unknown ^[1].

In the pelagic environment the birds are often far from the coast (for example 80–160 km), according to earlier studies summarised by Saalfeld and colleagues, and are associated with places where food is concentrated, such as ocean fronts and upwellings ^[1]. In a study of seabirds of the Humboldt Current in northern Chile it appears only as a species seen outside the counting transects, with no figures of its own ^[5]. One female fitted with a satellite transmitter wintered about 44 km off the coast of Concepción, Chile, in an area of about 24,500 km² ^[1].

It is socially polyandrous with reversed sex roles: females mate one after another with several males, and the males alone sit on the nest and look after the chicks ^[1]. Incubation lasts 19 days ^[1].

When breeding ends, females leave their last breeding site between late June and mid-August, on average 17 days earlier than males ^[1]. In that study 103 birds were fitted with satellite transmitters at 7 tundra sites spread across Arctic Alaska and central Canada, and 72 sent data after nesting ^[1]. The birds left the tundra obligatorily, but once at sea they combined flying and foraging with many stops, so that routes were indirect and highly variable ^[1].

In northern Chile 166 dead birds were found between September and December 2005, and the sex of 46 of them was determined by DNA; females appeared from September to early October and males from late October, about 26.8 days later on average ^[6]. This points to females reaching the Chilean wintering areas first, although arrival date is inferred from the date of discovery ^[6].

The one female followed to the south travelled 24,253 km, reached her wintering area off Chile in early December and on 25 March set off north again ^[1].

It feeds on zooplankton that it takes at the sea surface; large copepods are one of its main foods ^[1]. At the ice edge of the Beaufort Sea, according to an earlier study summarised by Saalfeld and colleagues, birds fed mainly on gammarid amphipods, along with mysids and euphausiids ^[1].

At sea it chooses places where food is abundant: productive currents, ocean fronts and upwellings ^[1]. It also feeds near broken sea ice and near whales, whose feeding behaviour brings zooplankton to the surface ^[1]. In the Beaufort and Chukchi seas, females often stopped in the marginal ice zone, whereas males stayed on land or in open water ^[1].

In all, nearly 500 stopover areas were identified, in which the birds spent an average of 6 days and moved within a mean area of 1880 km² ^[1].

Its global category on the IUCN Red List is Least Concern ^[3].

Even so, recent data suggest that its populations are declining, probably because of threats during the non-breeding season, when it lives at sea ^[1]. Among them, the authors point to ocean warming and sea ice loss, which can change the amount and kind of zooplankton available, along with oil and gas exploration, vessel traffic and offshore wind farms ^[1].

Because it feeds at the surface and favours convergence zones and eddies, it appears especially exposed to ingesting plastics ^[1]. In that study the birds often stopped in the North Pacific Current, on the edge of the so-called Great Pacific Garbage Patch ^[1].

In Peru, the available information places it at sea and not on the coast, but it is scarce. Between 2017 and 2020, a single female fitted with a satellite transmitter stopped at sites off Ecuador and Peru and then followed the Humboldt Current to her wintering area off Chile ^[1]. That work gives no Peru-specific data; it only places Pacific wintering mainly off Peru and Chile, and mentions that in the pelagic environment the birds are often far from the coast (for example 80–160 km) ^[1].