Ardenna creatopus

Ardenna creatopus is a shearwater of the family Procellariidae, described by Coues in 1864 under the name Puffinus creatopus ^[1]. In Peru it is called «pardela de pata rosada», and the official 2014 list of threatened wildlife classifies it as Vulnerable ^[2]. It breeds on only 3 islands of central Chile, but part of the birds spend the whole non-breeding season at sea off Peru, and another part crosses Peruvian waters on the way to North America ^[3],[4].

The current name joins the genus Ardenna, proposed by Reichenbach in 1853, with the species name that Coues gave in 1864 ^[1]. The species was described within Puffinus; that original name is now listed as an unaccepted synonym, which is why the author appears in parentheses ^[1].

It breeds only on 3 islands of central Chile. At least 70% of the population is estimated to nest on Isla Mocha, up to 20% on Isla Robinson Crusoe and up to 10% on Isla Santa Clara, these last two in the Juan Fernández archipelago; the world population is estimated at about 60000 birds ^[4].

It nests in burrows. On Mocha, the monitored colonies lay in mature forest with a fairly closed canopy, between 200 and 350 m above sea level; at Piedra Agujereada, on Robinson Crusoe, the colony covers about 12.3 ha of a deforested 30° to 40° slope, and at the camera points the vegetation was mostly grasses and herbs up to 30 cm tall ^[4].

Outside the breeding season, 42 birds tracked by satellite between 2006 and 2015 showed two strategies: 28% moved 1600 to 2500 km north and stayed off Peru for the whole season, while 72% covered 8000 to 11000 km to waters running from Baja California, in Mexico, to southern Canada ^[3].

Birds continuing to North America made landfall in Peruvian waters on both the outward and the return journey, and the authors call that zone a migratory bottleneck; one of the species' use cores is the continental shelf and slope between Trujillo and Lima ^[3]. In Canadian waters, its presence is linked mainly to latitude and to distance from the edge of the continental shelf ^[5].

Cameras in colonies on Mocha and Robinson Crusoe showed that the birds arrive at the colonies around late September or October: on Robinson Crusoe they appeared regularly from the last week of September and were detected almost every night from 8 October 2019; on Mocha the first detection of the season was on 16 October 2016, the same date as the first camera deployment, so arrival may have been earlier. The last detections were in early June on Mocha and on 23 May on Robinson Crusoe ^[4].

On both islands activity on the colony surface was strictly nocturnal, with one peak early in the night (21:00 to 23:00) and a larger one before dawn (03:00 to 06:00); on Robinson Crusoe the pre-dawn peak was between 05:00 and 06:00, and on Mocha between 03:00 and 04:00 ^[4].

Detections were high from November to February, during courtship, egg laying, incubation and early chick rearing; on Robinson Crusoe the monthly peak was in November. On Mocha they fell in late February and rose again in May, when chicks begin to fly ^[4]. On Mocha, burrow density in a separate study averaged 0.04 per m², with a maximum of 0.11, and at Piedra Agujereada the cameras covered areas of 0.10 to 0.15 burrows per m² ^[4].

In the colonies, cameras recorded many introduced animals. In 5 colonies on Mocha, monitored between 2015 and 2020, rats were the most seen animal after the shearwaters and cats were present in all of them and in every month monitored; dogs and European hares appeared only in 2 colonies near trails ^[4].

At Piedra Agujereada, between February 2019 and February 2020, European rabbits were the most recorded animal, with a detection rate more than 7 times that of shearwaters, and cats were present all year; cattle entered the breeding area despite a 2011 fence, trampled burrows and changed the vegetation ^[4].

Rats may prey on eggs and chicks, although direct evidence is scarce and limited to descriptions, and coatis were seen pulling shearwaters from burrows and killing them at the Vaquería colony on Robinson Crusoe. Rabbits probably compete for burrows: occupancy rose after they were eradicated from Santa Clara, the only known colony free of introduced vertebrates ^[4].

In Peru it is categorised as Vulnerable in the official list of threatened wildlife ^[2].

The authors of a study of the colonies list, among the species' threats, introduced mammals in the colonies and mortality from fisheries bycatch; they conclude that the regular presence of cats, rats, rabbits and cattle inside the colonies is a serious threat, and that neither Mocha nor Robinson Crusoe has a biosecurity system ^[4].

Satellite tracking found evidence of bycatch in 6 of the 12 exclusive economic zones the birds visited north of their breeding range, and the authors highlight the importance of international cooperation for their conservation ^[3].

On Mocha about 650 people live in scattered homesteads on the coastal plain, and the monitored colonies were 1 km or less from human settlement; one was crossed by a heavily used tourist trail and another lay beside a trail used mainly by local people ^[4]. About 1000 people live on Robinson Crusoe in San Juan Bautista, the only town on the island, and the Piedra Agujereada colony is 2.2 km in a straight line from the town ^[4]. On Mocha, the dogs seen in the colonies were often recognisable as residents' pets, and dogs are known to follow tourists along the trails into the colonies ^[4].

It does not breed in Peru: its colonies are on 3 islands of Chile ^[4]. It is an open-sea bird, and satellite tracking from 2006 to 2015 placed one of its use cores on the continental shelf and slope between Trujillo and Lima, so part of the birds spend the non-breeding season off that coast ^[3].