The Short-tailed Shearwater (Puffinus tenuirostris), also known as the Yolla or Moonbird, is one of the most remarkable seabirds native to Australia. It holds the distinction of being the most abundant seabird species in Australian waters and plays an important ecological and cultural role in the region. Notably, this species is one of the few Australian native birds whose chicks are traditionally and commercially harvested for food and oil, particularly in Tasmania. The Short-tailed Shearwater is a long-distance migratory bird, exhibiting fascinating seasonal movements that span hemispheres and vast oceanic distances. This article explores the taxonomy, geographic range, physical features, behavior, breeding, and conservation of this extraordinary seabird.
Scientific Classification
The Short-tailed Shearwater belongs to the family Procellariidae, which includes petrels, shearwaters, and other tubenose seabirds. Its scientific name is Puffinus tenuirostris. The genus Puffinus comprises many shearwater species, but recent genetic studies suggest that the larger shearwaters, including the Short-tailed Shearwater, may be better placed in the genus Ardenna, though this is still under scientific discussion. The species was first described by John Gould in 1838. It shares close evolutionary ties with the New Zealand Sooty Shearwater (Puffinus griseus) and the Great Shearwater (Puffinus gravis), all species characterized by their relatively blunt tails and black bills.
Phylogenetic analyses indicate that these shearwaters form a distinct clade within the shearwater group, though their precise relationships remain somewhat unclear. These birds are part of the order Procellariiformes, known for their tubular nostrils that aid in their exceptional olfactory abilities, crucial for navigation and foraging across vast ocean distances.
Geographic Range & Distribution
The Short-tailed Shearwater is a highly migratory seabird with a remarkable annual journey between breeding and feeding grounds. It breeds predominantly on small islands off the coast of Tasmania and within the Bass Strait, including the Furneaux Group of islands. Tasmania hosts the largest breeding colonies, with millions of pairs nesting in burrows dug into sandy soils and grassy areas on these islands.
After the breeding season, which occurs during the austral summer, the birds embark on an extraordinary migration to the Northern Hemisphere. Their migratory route takes them across the Pacific Ocean to the seas surrounding the Aleutian Islands and the coast of Kamchatka in Russia. Here, they spend the boreal summer feeding intensively in the productive northern waters. In the austral spring, the shearwaters travel southwards along the coast of California before crossing the Pacific Ocean once again to return to their breeding grounds in Australia.
This round-trip migration is one of the longest of any bird species, with individual shearwaters covering distances exceeding 30,000 kilometers annually. The species’ presence is thus cosmopolitan across the Pacific Ocean, but their breeding range remains largely confined to Tasmania and nearby islands. Outside the breeding season, they are pelagic, spending most of their time far from land, rarely seen except by researchers and birdwatchers on pelagic trips.
Physical Description
The Short-tailed Shearwater is a medium-sized seabird, measuring about 33 to 38 centimeters in length, with a wingspan ranging from 89 to 105 centimeters. It weighs between 350 and 600 grams, though adults can vary slightly depending on time of year and individual condition. The bird’s name derives from its relatively short tail compared to other shearwaters, which is noticeably blunt-tipped.
Its plumage is predominantly dark brown to black on the upperparts, including the head, wings, and back, while the underparts are a lighter, buffy white, giving it a sleek, streamlined appearance ideal for long-distance flight. The bill is slender, black, and slightly hooked at the tip, adapted for grasping slippery prey. Legs and feet are also dark, with webbing that facilitates swimming and takeoff from water surfaces.
In flight, the Short-tailed Shearwater exhibits a characteristic gliding style, often seen skimming low over the ocean surface with stiff, shallow wingbeats interspersed with long glides. This efficient flight pattern allows it to cover vast distances with minimal energy expenditure during migration and foraging.
Behavior & Diet
Short-tailed Shearwaters are highly pelagic outside the breeding season, spending much of their time over open ocean waters. They are known for their remarkable endurance and navigational skills, which enable them to perform their epic migratory journeys annually. These birds are mostly nocturnal at their breeding colonies, returning to nests under the cover of darkness, likely as a predator avoidance strategy.
Their diet primarily consists of small fish, squid, and krill, which they catch by surface seizing or shallow diving. Their feeding strategy often involves following schools of predatory fish or marine mammals to capitalize on disturbed prey. During the breeding season, adults undertake long foraging trips that can reach up to 15,000 kilometers, sometimes lasting up to three weeks, to find sufficient food for their chicks. These journeys are vital for chick survival, as the adults alternate between feeding themselves and provisioning their offspring.
Short-tailed Shearwaters are colonial nesters, excavating burrows where they lay a single egg each breeding season. Outside the breeding period, they are rarely seen near land and are considered one of the most pelagic of Australian seabirds.
Breeding & Reproduction
Breeding for the Short-tailed Shearwater occurs mainly from September to April on islands in Bass Strait and Tasmania. The birds return to their natal breeding sites year after year, often reusing the same burrows. These burrows are dug into soft soil or sand, sometimes extending up to a meter in length, providing shelter and protection for the single egg laid by the female. According to RSPB, this species is well documented.
Both parents share incubation duties, which last about 50 to 55 days. The egg is incubated in shifts of several days, with one adult remaining on the nest while the other forages at sea. After hatching, the chick is fed with regurgitated food by both parents. Feeding intervals can be lengthy; parents may be absent for up to three weeks during foraging trips, leaving the chick unattended for extended periods. Remarkably, the chick grows rapidly, reaching a fledging weight of around 900 grams, which can be heavier than the adult birds themselves. According to eBird, this species is well documented.
The fledging period lasts approximately 90 days, after which the young bird leaves the burrow and takes its first flight over the ocean. This fledging coincides with the traditional muttonbird harvesting season in Tasmania, where indigenous communities and commercial operators collect chicks for food and oil. The harvesting is regulated to ensure it remains sustainable, respecting both ecological and cultural values.
Conservation Status
The International Union for Conservation of Nature (IUCN) currently lists the Short-tailed Shearwater as a species of Least Concern, reflecting its large global population estimated to exceed 23 million individuals. Their extensive breeding colonies and wide-ranging distribution contribute to this favorable status. However, the species faces several threats that warrant monitoring.
Predation by introduced mammals such as rats, cats, and foxes on breeding islands poses a significant risk to eggs and chicks. Habitat disturbance from human activities, including tourism and muttonbird harvesting, requires careful management. Climate change also presents a growing threat, potentially impacting oceanic food webs and altering prey availability. Marine pollution, including oil spills and plastic debris, can affect adult birds at sea.
Conservation efforts focus on protecting breeding habitats through island reserves, controlling invasive species, and regulating sustainable harvesting practices. Ongoing research and monitoring help assess population trends and inform adaptive management strategies to ensure the species remains abundant for future generations.
Interesting Facts
The Short-tailed Shearwater is colloquially known as the “Moonbird” because of its remarkable navigational ability, which allows it to return to the same nesting burrow year after year, often under the faint light of the moon or stars. This remarkable homing instinct is supported by a keen sense of smell, a trait shared by many members of the Procellariiformes order.
These birds undertake one of the longest migrations of any bird species, traveling from the Southern Hemisphere to the North Pacific and back annually, covering distances of over 30,000 kilometers. Their migration spans across the equator twice a year, exposing them to vastly different oceanic conditions and ecosystems.
In Tasmania, the Short-tailed Shearwater holds cultural significance for the Palawa people, the Indigenous Tasmanians, who have sustainably harvested the chicks for thousands of years. The harvesting tradition continues today and is an integral part of local heritage and economy.
Despite their pelagic lifestyle, Short-tailed Shearwaters are faithful parents, investing significant time and energy in raising a single chick each breeding season. This investment ensures the survival of offspring in the challenging marine environment.
In flight, these shearwaters exhibit graceful, gliding movements with minimal wing flapping, often flying low over wave crests. They sometimes follow fishing boats, taking advantage of discarded fish and offal to supplement their diet.
Conclusion
The Short-tailed Shearwater (Puffinus tenuirostris) is a testament to the resilience and adaptability of seabirds. Its incredible migratory feats, ecological role in marine environments, and cultural importance in Australia make it a species worthy of admiration and study. By understanding its life cycle, behavior, and the challenges it faces, nature enthusiasts, students, and birdwatchers can appreciate the complexity and beauty of this remarkable seabird. Continued conservation efforts and sustainable practices will ensure that the Moonbird continues to grace our oceans and islands for generations to come.
