SPECIES

Pink-footed Shearwater Ardenna creatopus Scientific name definitions

Ryan D. Carle, Valentina Colodro, Jonathan Felis, Joshua Adams, and Peter J. Hodum
Version: 2.0 — Published April 9, 2022

Behavior

Introduction

Throughout their lives, Pink-footed Shearwater are migratory, forage over great distances at sea, take prey near the ocean surface by several means, excavate and maintain deep subterranean burrows for nesting, and engage in interspecific social interactions on breeding colonies and in flocks at sea (PJH, RDC). Behavioral aspects of the lives of this species, however, are not well studied.

Locomotion

Walking, Running, Hopping, Climbing, etc.

Although most adept at flying, Pink-footed Shearwater can also walk, though not strongly so. Because the legs are set relatively far back for swimming, walks with a wide-set gait in a hunched-over, forward-leaning posture. Birds breeding in the dense forest of Isla Mocha climb trees to gain enough elevation to take off out of the forest (34). When climbing trees, birds gain traction with their sharp toenails and flap their wings to maintain balance (RDC).

Flight

Flight styles vary according to wind speed and direction in association with an individual shearwater’s trajectory. Classified as a glide flapper (54), and depending on conditions it will vary the amount and amplitude of flapping required for movement through the ocean environment (55). In calm conditions, remains mostly on the water, but when in flight individuals fly low over the water by alternating flapping with bouts of gliding, extracting energy using the ground effect, whereby they press the air under their wings against the ocean’s surface. As wind speed increases, the amount of gliding increases. Shearwaters are less likely to fly directly into the wind during higher wind speeds (55), because doing so decreases their flight speed significantly. As wind speed increases from 3–15 m/s, and with preferred crossing winds, flight speed increases (13–15 m/s; 54) as they initiate a flight mode called dynamic soaring. While dynamic soaring, birds face their underwings to the wind and are propelled upward to an apex, where they tilt to face their dorsal surface to the wind. Then, also propelled by gravity, they accelerate back down toward the ocean’s surface (56). As wind speed increases the arc becomes higher from the sea surface, and eventually in very strong winds there is little flapping (55). Under moderate winds, birds initiate a few flapping adjustments at the bottom of the arc. In this manner, individuals fly long distances, rapidly tracing a sinusoidal path, and expend little energy.

Swimming and Diving

Shearwaters display adaptations that enable both efficient flight and diving. As a group, the Puffinus and Ardenna shearwaters show a relatively linear increase in maximum dive-depth with increasing body mass (57).

Diving behavior of Pink-footed Shearwater was studied using time-depth recorders on 6 chick-rearing adults breeding at Isla Mocha (28). Dives occurred during the day (62% of dives), night (22% of dives), and twilight (16% of dives; 28). Mean dive duration from that study was 4.7 s ± 4.8 SD (range 1–26). The overall distribution of dive duration was skewed, with the majority of dives lasting < 6 s. Maximum (10.1 m) and mean maximum depths (4.6 m ± 2.8 SD) achieved (28) were less than what would be predicted allometrically compared with several other diving shearwaters, such as Sooty Shearwater (Ardenna grisea) (46). Diving ability seems more similar to the Calonectris shearwaters than to other Ardenna shearwaters (e.g., 48, 57). The shallow diving of Pink-footed Shearwater is consistent with its frequent associations with subsurface predators (e.g., predatory fishes, cetaceans, and seabirds), on which they may rely to make prey available near the surface (58, 45, 50). The shallow-diving Pink-footed Shearwater often co-occurs with the deeper-diving Sooty Shearwater (Table 3 in 40, 45), suggesting that vertical partitioning of foraging habitats could occur.

Self-Maintenance

Preening, Head-Scratching, Stretching, Sunbathing, Bathing, Anting, etc.

Has been observed preening while in nest burrow, outside of burrow in the breeding colony at night, and on water (PJH).

Sleeping, Roosting

Has been observed sleeping while in nest burrow, outside of burrow in the breeding colony at night, and on water (PJH).

Daily Time Budget

Arrives and departs colonies at night, and nocturnally active outside of burrows in the breeding colony (29, 38). No other information.

Agonistic Behavior

Physical Interactions

Individuals sometimes engage in physical confrontations with conspecifics while outside of burrows in the breeding colony (PJH). Agonistic physical interactions with European rabbit (Oryctolagus cuniculus) in burrows have also been observed (PJH).

Communicative Interactions

Vocalizes while flying into breeding colony, and outside of burrow in the breeding colony; reasons unknown (PJH).

Territorial Behavior

Birds in burrows will vocalize at birds outside burrows, presumably as a form of burrow defense (PJH).

Sexual Behavior

Mating System and Operational Sex Ratio

Presumed to be monogamous. Operational sex-ratio unknown.

Courtship, Copulation, and Pair Bond

Little information. Based on a single trail-camera observation ( ), will copulate outside burrow on the breeding colony. In that video, the male mounted the female for approximately 15 seconds; during copulation, the male billed the female's head and bill repeatedly, and one or both birds made short, repetitive vocalizations.

Extra-Pair Mating Behavior/Paternity

Incidence of extra-pair copulations has not been investigated.

Brood Parasitism of Conspecifics

No information.

Brood Parasitism of Other Species

Not reported.

Social and Interspecific Behavior

Degree of Sociality

Nests colonially or semi-colonially on all breeding islands (33, 4, 37), with some colonies exceeding 3,000 burrows on the Juan Fernández Islands. On Isla Mocha, colonies are less well-defined and nests occur at varying densities in suitable habitat (34, 35, 38).

Nonpredatory Interspecific Interactions

At sea, may form large aggregations, and often associates with flocks of Sooty Shearwater (Ardenna grisea) (40, 45), with which it is also observed to compete for prey (K. Morgan, personal communication). Also forages in association with large fishes, pinnipeds, and Stenella dolphins (50, 45, 2). Has been observed associating and competing for prey with Kelp Gull (Larus dominicanus) attending fishing boats near Isla Mocha, Chile (T. Varela, personal communication).

Predation

Kinds of Predators

The species has few native predators on its breeding islands. In the Juan Fernández Islands, the Short-eared Owl (Asio flammeus suinda) preyed on smaller Pterodroma petrels (59) and could conceivably depredate Pink-footed Shearwater, although there was no evidence that this occurred during nearly 20 years of colony monitoring (Oikonos, unpublished data). There are five species of native rodents on Isla Mocha (60, 61), as well as native raptors (62); whether either preys on Pink-footed Shearwater is not known. There is no information on predation at sea.

No introduced mammals are present on Isla Santa Clara, but introduced mammalian predators are a major threat on Isla Robinson Crusoe and Isla Mocha. Feral cat (Felis catus), feral dog (Canis lupus familiaris), Norway rat (Rattus norvegicus), and black rat (Rattus rattus) were present in shearwater breeding colonies on both Islas Robinson Crusoe and Mocha (63, 64, 62, 38). South American coati (Nasua nasua) and house mouse (Mus musculus) were present only on Isla Robinson Crusoe (63, 64, 38). Of these predators, feral cats and rats (Rattus spp.) were the most commonly observed by trail cameras within shearwater breeding colonies on both islands (38). See Conservation and Management: Effects of Invasive Species for details.

Manner of Depredation

South American coati have killed Pink-footed Shearwater by digging up shearwater burrow and extracting birds (38). Predation by feral cat has not been directly observed, but many carcasses have been found with external wounds suggestive of cat predation, and trail cameras have captured images of feral cat entering nest burrow and appearing to pursue shearwater outside of burrow (38). Feral dog have likewise been documented on trail cameras digging into shearwater burrow (38).

Response to Predators

The species is clumsy on the ground and behaviorally is not well-adapted to avoid ground-dwelling predators on breeding colonies. Like many procellariiform seabirds, the species presumably evolved in the absence of terrestrial predators. Based on captures of adults outside of burrows by researchers (RDC), and on trail camera images (38), allows relatively close approach by predator before fleeing. May flee on foot or by jumping down steep slopes (RDC, PJH).

Recommended Citation

Carle, R. D., V. Colodro, J. Felis, J. Adams, and P. J. Hodum (2022). Pink-footed Shearwater (Ardenna creatopus), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.pifshe.02