Humboldt penguin

Spheniscus humboldti is a penguin of the family Spheniscidae, described by Meyen in 1834 ^[1]. It is known in Peru as «pingüino de Humboldt» ^[2]. Its breeding colonies are spread along the Pacific coast of South America, from La Foca Island in northern Peru to Metalqui Island in southern Chile ^[3]. The IUCN Red List classifies it as Vulnerable in its 2020 assessment ^[4], and Peru's official list of threatened wildlife, approved in 2014, places it in the Endangered category ^[5].

A census carried out in Peru in 1999 and 2000, after the 1997-1998 El Niño, found penguins from La Foca Island (5° 12′ S) to Punta Coles (17° 42′ S); on the central and southern coast, which holds 97 % of the country's population, the mean count was 4425 birds ^[6]. Nearly four in five birds, 78 %, were at just five localities: Punta San Juan, San Juanito Islet, Hornillos Island, Pachacamac Island and Tres Puertas ^[6].

Most of these sites lie in marginal, hard-to-reach places that are occasionally flooded by heavy swells ^[6]. Across the whole range, a review of the literature combined with fieldwork recognised 73 breeding colonies and concluded that the bulk of the population has shifted southward in recent decades ^[3].

The penguin also settles on structures built by people. On the breakwater of the Melchorita marine terminal in southern Peru it established a permanent breeding colony about 3.5 years after human activity at the site ended ^[7]. In El Ferrol Bay it was recorded again in 2024, after more than 70 years with no known presence, with 148 birds counted and a nest holding one egg and one chick ^[8].

At Punta San Juan, between 1993 and 1997, egg-laying ran from the middle of March into early December, with one peak in April and another in August and September ^[9]. The season was so long because about half of the females laid twice a year, and in 73 % of those cases the second clutch was a new brood rather than the replacement of a lost clutch ^[9].

Each cycle, from laying to the chick leaving, takes about 4 months, so females that start laying in early April have more time to raise two broods in the year and achieve greater success ^[9]. Over 3 consecutive years, each female produced on average 4.54 chicks that reached independence ^[9].

A genetic study of 11 main colonies, covering the species' entire range, used nuclear markers to separate three groups that follow geography: Peru, northern Chile and central-southern Chile ^[10]. Of the individuals, 86 % were assigned to the colony where they had been sampled, a sign that birds tend to return to breed where they came from ^[10].

While raising chicks, adults feed by day with brief dives that rarely go deeper than 30 m ^[11]. They combine trips that include a night away, lasting about 25.8 hours, with daytime trips of about 10.4 hours; the former made up 68.2 % of all trips, and males reached greater maximum depths than females ^[11].

In Chile, a comparison of two colonies with different prey availability showed that where food was scarce, adults did not dive harder but stretched their trips (36.5 hours versus 19.0 hours), and their chicks grew less and survived less ^[12].

Its global category is Vulnerable ^[4]. In Peru it is classified as Endangered, and the regulation that lists it prohibits the hunting, capture, possession, trade, transport and export for commercial purposes of the species included ^[5].

Punta San Juan, the country's largest colony, lost 51 % of its birds between 1980 and 2008, with marked drops in El Niño years ^[3]. After the 1997-1998 El Niño, one-year-old birds made up only 0.2 % of those counted in 1999, against 7 % in 2000 ^[6].

In the 15 years before that census, penguins left Punta Corio, Sombrerillo and Morro Sama, and their numbers fell at Punta San Fernando and Punta La Chira, two sites where local fishing had brought more human disturbance; by contrast, they increased at sites with some protection ^[6]. Half of the birds were in guano reserves, which shelter them from land predators, although periodic guano harvesting lowers their breeding success ^[6].

Incidental capture in fishing nets is one of its most serious threats ^[13]. At the port of San Juan, 922 penguins were documented being landed between November 1991 and June 1998, mostly in the years when surface drift gillnets were in use, and a population model indicated that the mortality of the early part of that decade was not sustainable ^[14]. Surveys of 779 fishers at 39 landing sites in Peru and Chile estimated 4067 penguins caught in 2023, most of them in gillnets, with Tambo de Mora and San José among the Peruvian ports with the most interactions ^[13].

To reduce these catches, it has been proposed that, in areas where penguins feed, no surface nets go in the water at night and, by day, no nets be placed in the top 0 to 30 m ^[11]. In 29 birds from Punta San Juan, mercury and the other toxic elements measured in blood and feathers did not reach levels usually regarded as harmful, although the authors advise continued monitoring ^[15].

The largest colonies are on headlands, islands and islets of the central and southern coast, mostly marginal, hard-to-reach places; in the 1999-2000 census, Punta San Juan held 36 % of Peru's penguins, followed by Pachacamac Island (12 %), San Juanito Islet (11 %), Hornillos Island (10 %) and Tres Puertas (9 %) ^[6]. On the Melchorita breakwater the number of birds grew to 2091, peaking during the January moult ^[7].