Townsend's (P. a. auricularis) and Newell's shearwaters (P. a. newelli) are currently considered subspecies of P. auricularis by the American Ornithological Union and the Howard and Moore Checklist of the Birds of the World (2003). However, Brooke (2004) recognized them as separate species and various conservation organizations have adopted that recommendation. They have non-overlapping distributions, vary somewhat ecologically, and are morphologically distinguishable. Care was taken to distinguish between information on P. a. auricularis and P. a. newelli in this account to recognize these differences.
Shearwaters were considered an omen of death by native Hawai'ian islanders because of their long absence from terrestrial breeding colonies each year.
Townsend's and Newell's shearwater use vocalizations to communicate among themselves. Adults use an "aerial" call in flight or on the ground near their nesting burrows. It is characterized as a series of 2 to 6 gruff, braying calls. The native Hawai'ian name for Newell's shearwaters is "a'o" - which mimics the aerial call. Hatchlings make a squeakier version of the aerial call, their voices deepen as they age. When mated pairs are at a burrow together, they duet with aerial calls. Vocalizations in colonies are generally at night, with birds vocalizing when they arrive and depart.
Communication Channels: visual ; acoustic
Other Communication Modes: duets
Perception Channels: visual ; tactile ; acoustic ; chemical
Puffinus auricularis is critically endangered as both P. a. auricularis and P. a. newelli. Newell's shearwaters (P. a. newelli) are threatened under the U.S. Endangered Species Act.
Townsend's shearwaters have been extirpated from two breeding islands, Clarión and San Benedicto islands. Townsend's shearwater populations on Clarión Island were ravaged by introduced sheep, pig, and rabbit populations, resulting in total extirpation by 1988. Populations on San Benedicto Island were destroyed by a volcanic eruption in 1952 and have not been recorded breeding on the island since then, although small numbers are reported on the island. The population is now limited to a single, small breeding area on Socorro Island where the vegetation has been seriously degraded by sheep (Ovis aries) grazing. Feral cats (Felis catus) are also found on this island and are reducing their numbers. Up to 92% of cat scats on Socorro Island above 500 m contain shearwater remains and it was estimated that cats take about 350 females yearly. Estimates of the population size on this island were around 1100 in 2004. These estimates suggest demographic instability and extinction within 100 years. Sea censuses suggest larger population sizes, as many as 46,000 (but with a range estimate of 18,000 to 89,000, and representing approximately 10,600 breeding birds). The eradication of introduced mammals on Socorro Island is vital to protecting the population. The Mexican navy has greatly reduced sheep populations, but rabbit eradication programs have not been successful. Pigs and sheep were eradicated from Clarión Island in 2002 and taped playback of Townsend's shearwater calls are being used to attract potential breeding birds.
Newell's shearwaters were thought to be extinct in Hawaii by 1908, but a population was rediscovered off Kaua'i in 1947. Populations on Hawaii have declined dramatically, by over 60% in just a 3 year period between 1999 and 2001 and about 72% from 1993 to 2001. Introduced mongooses (Herpestes javanicus), rats (Rattus), cats (Felis catus), and barn owls (Tyto alba) all prey on these shearwaters in Hawai'i. Introduced pigs (Sus scrofa), goats (Capra hircus), and strawberry guava (Psidium cattleianum) are resulting in habitat degradation affecting nesting colonies. Newell's shearwaters are attracted to man-made lights in Hawai'i and this attraction has resulted in high mortality, especially of fledglings. Shielding light sources so that they don't shine upwards decreases their attraction to shearwaters. These shearwaters also suffer mortality as a result of collisions with man-made structures, especially power lines. Hundreds of shearwaters die from collisions with powerlines each year, the majority are fledglings and most collisions seem to occur because power lines are located in river valleys used for traveling from colonies to the ocean or because fledglings are attracted towards the land by man-made lights. Sea censuses indicate population sizes of approximately 84,000 (but with an estimate range of 57,000 to 115,000, and representing approximately 18-19,000 breeding birds). Vocalization play back and burrow construction are being used to attract birds to breeding colony sites at Kilauea Point National Wildlife Refuge, where there are few obstacles and little artificial lighting to interfere with the movement of shearwaters. All non-essential lights are turned off or shielded in Kauai'i from mid-September to mid-December, when juveniles are leaving breeding colonies.
Breeding bird populations on San Benedicto Island, previously an important breeding colony site for Townsend's shearwaters, have changed substantially in recent decades. Possible changes in local marine ecosystems have resulted in populations of central Pacific birds starting to breed on this island, including Laysan albatrosses (Phoebastria immutabilis), black-footed albatrosses (Phoebastra nigripes), red-tailed tropicbirds (Phaethon rubricauda), and brown boobies (Sula leucogaster).
US Migratory Bird Act: protected
US Federal List: threatened
CITES: no special status
IUCN Red List of Threatened Species: critically endangered
There are no known adverse effects of Townsend's or Newell's shearwaters on humans. They are found in remote areas and have few direct interactions with humans.
Townsend's and Newell's shearwaters are important members of pelagic ecosystems, although their current numbers suggest they have minimal impact in pelagic food webs. When they were abundant on the Hawai'ian Islands, native Hawai'ians collected shearwaters for food.
Positive Impacts: food
Townsend's and Newell's shearwaters are rare and are unlikely to have significant ecosystem impacts, although they are predators of small fish and squid. Ectoparasites recorded include biting lice (Mallophaga) and nest mites (Ornithodosis capensis). Plasmodium has been found in the blood of Newell's shearwaters, but none have shown signs of avian malaria. This is true of wedge-tailed shearwaters (Puffinus pacificus) in Hawai'i as well, suggesting that these birds are not prone to avian malaria. These shearwaters may forage in association with tunas (Thunnus) and porpoises (Phocoenidae) to take advantage of small fish scared to the ocean's surface. Jaegers (Stercorarius species) and South Polar skuas (Stercorarius maccormicki) steal fish from Townsend's and Newell's shearwaters.
Mutualist Species:
Commensal/Parasitic Species:
Townsend's and Newell's shearwaters use a pursuit-plunge foraging style. They fly above the water's surface and dive in when they see prey. They continue swimming with partly folded wings underwater and can swallow prey while swimming. They are estimated to reach depths up to 10 meters using this strategy. Prey are not well reported in the literature and only squid were recorded as part of regurgitates at nests of Newell's shearwaters. These shearwaters probably eat primarily fish and squid.
Newell's shearwaters are documented foraging at sea along ocean fronts in the Equatorial Counter Current. Like, Townsend's shearwaters, they concentrate foraging effort on highly productive areas, which often involves a high investment in travel to foraging areas, and rest often. Newell's shearwaters are known as "tuna birds," birds that form multi-species flocks and forage above tuna schools. They seem to rely on the presence of schools of predatory fish, especially tunas, to drive suitable fish prey to near the ocean's surface.
Townsend's shearwaters seem to forage along upwelling fronts of the Costa Rica Current over the continental shelf along Mexico's west coast. Shearwaters travel far to forage, but focus their foraging on highly productive areas and rest frequently. Townsend's shearwaters forage in areas where prey occurs closer to the surface and are not known to typically associate with schools of tuna. However, they do forage near groups of foraging porpoises, which may also drive prey to nearer the surface.
Animal Foods: fish; mollusks
Primary Diet: carnivore (Piscivore , Molluscivore )
Puffinus auricularis has a disjunct range, with two subspecies occurring in different parts of the Pacific Ocean and associated breeding islands. Some authorities recognize these two subspecies as separate species based on their range differences and some morphological and ecological differences.
Townsend's shearwaters (Puffinus auricularis townsendi) are found on breeding colonies in the Revillagigedo Islands, off the west coast of Mexico. They were previously known to breed on 3 islands: Clarion, San Benedicto, and Socorro, but are now only found breeding on Socorro Island. When not at breeding colonies they are found over oceanic waters over the continental shelf off the western coast of Mexico and Central America.
Newell's shearwaters (Puffinus auricularis newelli) are found in breeding colonies on the Hawaiian Islands. They once bred on islands throughout the Hawaiian archipelago, but are now found on Moloka'i, Kaua'i, and Hawai'i and possibly O'ahu, Maui, Lana'i, and Lehua Islet. When not at breeding colonies they are found over deep, tropical oceanic waters south and west of the Hawaiian Islands.
Biogeographic Regions: oceanic islands (Native ); pacific ocean (Native )
Townsend's and Newell's shearwaters are pelagic birds that breed at higher elevations on oceanic islands. These shearwaters cannot take flight from the ground so must take advantage of either elevation to take flight or must climb a tree or rock outcrop to gain sufficient height to take flight. The two subspecies of Puffinus auricularis differ in their pelagic habitats, but both avoid nearshore waters generally, except when they form large evening rafts before returning to breeding colonies.
Townsend's shearwaters breed in rocky burrows in shrubby or grassy areas, typically at elevations above 500 m on Socorro Island. They bred at elevations above 244 m in Clarion Island and above 161 m on San Benedicto Island. These islands are arid and the vegetation tends to be shrubby. Townsend's shearwaters are found over cold, continental slope waters (depths of 200 to 2000 m) when not at breeding colonies.
Newell's shearwaters also breed in burrows, typically in areas where the roots of Metrosideros polymorpha trees form the burrows and there is a covering of uluhe fern (Dicranopteris linearis), although burrows in tussock-grass habitats also occur. They breed at elevations from 160 to 1200 meters, although breeding elevation may be influenced by the presence of wedge-tailed shearwaters (Puffinus pacificus), which are found at lower altitudes. Currently, most breeding burrows occur on steep slopes where non-native terrestrial predators are less likely to be found. Breeding islands in Hawaii are marked by their extreme mesic vegetation, with some of the highest annual rainfall amounts worldwide. Newell's shearwaters are found over deep (depths over 2000 m), tropical and subtropical oceanic waters when not at breeding colonies.
Range elevation: 161 to 1200 m.
Habitat Regions: tropical ; terrestrial ; saltwater or marine
Terrestrial Biomes: savanna or grassland ; rainforest ; scrub forest
Aquatic Biomes: pelagic
Longevity of Townsend's and Newell's shearwaters is not reported. Estimates suggest that annual adult survivorship is 90%.
Townsend's and Newell's shearwaters are medium-sized shearwaters, with body lengths of about 33 cm. They have black or sooty brown plumage on their dorsal surfaces and white on ventral surfaces. There is a sharp line from the bill along the cheek to right behind the head that demarcates dorsal and ventral surfaces. They have a white side patch that extends on to their rump dorsally on each side. Ventrally, the wings are marked by a sharp black line on the leading and trailing edges, with the feathers being white otherwise. The bill is dark gray and sharply hooked at the tip and the legs are pale pink with a black stripe that runs along the back edge of the leg and a black line along the outer surface of the toes. The eyes are brown. The undertail coverts are white at the base and black at their tips in Newell's shearwaters. Townsend's shearwaters have completely dark undertail coverts. The two subspecies can be distinguished primarily by their largely non-overlapping distribution, but also differ in tail length. Townsend's shearwaters have shorter tails, from 71 to 83 mm (76.3 mm average), Newell's shearwaters have longer tails, from 77 to 89 mm (83.9 mm average). These shearwaters have relatively high wing-loading, with short and broad wings typical of diving shearwaters and consistent with their flight style and non-migratory behavior.
Hatchlings are covered with grey down, with bare lores, foreheads, and chins. The bill is grey, the eyes are black, and the legs are pink on the inner surface and grey on the outer surface. The timing of molts is not known, although it seems to occur once yearly in adults.
There is no reported sexual dimorphism in size or color. Townsend's shearwaters are from 315 to 358 grams. Newell's shearwaters are from 342.5 to 425 grams, although these numbers are based on relatively few individuals. Wing lengths are from 220 to 238 mm in Townsend's shearwaters and 223 to 249 mm in Newell's shearwaters.
Townsend's and Newell's shearwaters can be confused with other species of shearwaters. They are larger than Audubon's shearwaters (Puffinus lhermineri) and little shearwaters (Puffinus assimilis). They are similar in size to Manx (Puffinus puffinus), black-vented (Puffinus opisthomelas), and wedge-tailed shearwaters (Puffinus pacificus). They are smaller than pink-footed shearwaters (Puffinus creatopus).
Average length: 33 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
There are no reports of native predators of Townsend's and Newell's shearwaters. Rarely a shearwater diving above a school of foraging tuna may be taken by a tuna and their nocturnal arrival and departure from breeding colonies is thought to be an adaptation to avoid avian predators. Volcanic eruptions and hurricanes have been cited as the largest source of non-human influenced mortality. With the invasion of their breeding islands by non-native mammalian predators, including rats, pigs, mongooses, barn owls, and domestic cats, mortality rates of adults, eggs, and hatchlings has soared, leading to severe population declines and the loss of entire breeding populations.
Known Predators:
Townsend's and Newell's shearwater form pairs in the year before their first breeding attempt, which is estimated to occur at approximately 6 years old. The sex ratio is 1:1 in these shearwaters and they seem to beed monogamously for life.
Mating System: monogamous
Newell's shearwaters return to breeding colonies in April, when mated pairs scout for nest burrows. Nest burrows are about 87.7 cm long and are re-used yearly by shearwaters. After nesting sites are established, males and females leave the breeding colony to forage and replenish nutrient reserves for egg-laying and incubation. Males and females return to the breeding colony and begin egg-laying and incubation in early June. Egg-laying is synchronized in colonies and incubation lasts 53-54 days. Hatchlings fledge after 81 to 94 days (average 92.4). Hatchlings weight about 364.6 g just before fledging.
The timing of breeding and egg-laying in Townsend's shearwaters varies slightly from Newell's shearwaters, but has not been studied as well. Estimates suggest that egg-laying occurs in January on Socorro Island. The timing of egg-laying in these shearwaters may vary across breeding colonies as well. Historical data also suggest that breeding may not be as synchronous as in Newell's shearwaters. Townsend's shearwaters fledge in less time than do Newell's shearwaters, although those measurements are not reported in the literature.
Townsend's and Newell's shearwaters begin to form pair bonds at 4 to 5 years old, presumably the age of sexual maturity.
Breeding interval: Breeding intervals in Townsend's and Newell's shearwaters are not well-understood. Shearwaters may skip breeding in alternate years , intervals may be influenced by prey availability in any given year. Non-breeding pair incidence is high: only 46% of pairs inhabiting burrows breed and only 66% of those that breed fledge young.
Breeding season: The breeding season lasts from April through November in Newell's shearwaters. The timing of breeding in Townsend's shearwaters is less well-understood, possibly varying substantially across breeding sites.
Range eggs per season: 1 to 1.
Range time to hatching: 53 to 54 days.
Range fledging age: 81 to 94 days.
Range time to independence: 81 to 94 days.
Range age at sexual or reproductive maturity (female): 4 to 5 years.
Range age at sexual or reproductive maturity (male): 4 to 5 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Male and female parents care for their young in nest burrows. Both develop incubation patches shortly after egg-laying. Observations suggest that mates share incubation responsibilities equally. Males incubate first, when females forage after egg-laying to replenish their reserves. Time spent incubating is not known and there is a possibility that eggs are neglected sometimes as parents undertake long commutes to foraging areas. Young are born in an altricial state and are unable to thermoregulate. Hatchlings are tended for 5 to 10 days after hatching and are fed at varying intervals. Estimates based on foraging commute distances and fledging period length suggest that Townsend's shearwater hatchlings are fed once every 1.2 to 1.3 days and Newell's shearwaters are less often (fledging periods are 23% longer). As soon as the young fledge, they become independent.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female)
Townsend's shearwater (Puffinus auricularis) is a rare seabird of the tropics from the family Procellariidae.
Its relationships are unresolved. Its closest relatives are probably, but not certainly, the Hawaiian shearwater (Puffinus newelli) and possibly the Manx shearwater (Puffinus puffinus) (Austin, 1996; Austin et al., 2004). It formerly contained the former as a subspecies and was long considered a subspecies of the latter. The relationship of the Rapa shearwater, P. myrtae in regard to these species are also in need of research; this taxon was until recently placed in P. assimilis (Austin et al., 2004), but now raised to full species status by the IOC and the NACC of the AOU.
This species breeds around Cerro Evermann on Isla Socorro in the Revillagigedo Islands, Mexico, though formerly present on Clarion Island and San Benedicto. The main threat to this species comes from feral cats introduced to Socorro in the early 1970s. These cats usually prey on shearwaters immediately after landing, where a lack of understory renders them exposed. Sheep and goats are also destroying breeding habitat. The Isla Clarión was eradicated in 1988, when habitat and nesting sites were destroyed by introduced pigs, sheep and rabbits, the final of which competed against the shearwaters for nesting burrows. Despite this, some breeding habitat remains to the north and north-west of Socorro's summit, where introduced animals have yet to ravage. The current mature population is estimated between 249 and 999 birds. Due to the presence of these threats, it has been classified as critically endangered. Further threat is posed by light pollution from a recently constructed airstrip and possible volcanic eruptions, the latter eradicated the San Benedicto population. Sheep and pigs have since been eradicated from Clarion, though rabbits have yet to follow. On Socorro, sheep eradication is currently in progress. [1]
The species is named for Charles Haskins Townsend (1859-1944), eminent American ornithologist and ichthyologist.
Townsend's shearwater (Puffinus auricularis) is a rare seabird of the tropics from the family Procellariidae.
