The Little Shearwater weighs 142-201 g, and is 24-31 cm long with a wingspan of 55- 60 cm (29/62, these values representing body length/wingspan in cm are sourced from
Harrison, 1985 when available). The smallest species within the genus Puffinus, the Little Shearwater is similar in size to Audubon’s Shearwater (30/69, 150-230 g). Species within the Audubon’s and Little Shearwater complex are closely related (Austin et al. 2004) and are all winter breeders, with similar egg sizes, incubation and fledging periods. However, unlike the Little Shearwater, colonies of Audubon’s Shearwater (and the Christmas Island Shearwater Puffinus nativitatis 36/76) arrive at the colony during the day to feed nestlings and lay eggs throughout the year, although individual pairs do not relay (Harris 1969b).
The Little Shearwater is part of a congeneric complex of birds that are recognised by their counter-shading (being essentially white below and grey above). These include Audubon’s Shearwater, the slightly larger Fluttering Shearwater Puffinus gavia (33/76), Manx Shearwater Puffinus puffinus (34/82), Hutton’s Shearwater Puffinus huttoni (38/90) and the much larger Buller’s Shearwater Puffinus bulleri (46/97) (Slater et al. 1986, Marchant and Higgins 1990, Johnstone and Storr 1998). Among these, the Little Shearwater is the only species with blue legs. However, at sea, the Little Shearwater can be mistaken for smaller species in this complex. Other shearwaters, such as Cory’s Shearwater (49/111) and the Streaked Shearwater Calonectris leucomelas (length: 46-51 cm) are similar in colour, but are much larger and belong to a different genus.
The Little Shearwater is a polytypic species, whose taxonomy needs revision (Austin et al. 2004). Currently, accepted taxonomy recognises the existence of a Puffinus assimilis tunneyi on islands off the Western Australian shore (Marchant and Higgins 1990). Another six subspecies breed on islands at different locations around the globe, with only one found in the northern hemisphere, in theNorth Atlantic, off the
north-west African coast (Warham 1990). Several subspecies of the Little Shearwater have been studied, for instance the larger and heavier P.a. haurakiensis on islands off the north-eastern coast of the North Island in New Zealand (Booth et al. 2000, Booth et al. 2000b) and P.a. assimilis on Lord Howe Island off the East Australian coast (Bester 2003). P.a. baroli was studied in theNorth Atlantic on Selvagem Grande (Hamer 1994) at approximately 30° N and 16° W and is more closely related to Audubon’s Shearwater than the other currently recognised subspecies of the Little Shearwater (Austin et al. 2004). The Western Australian subspecies was studied on Eclipse Island, near Albany, off the south-western coast of Western Australia (Glauert 1946, Warham 1990). Other subspecies breed on small islands in the southern
Pacific, P.a. kermadecensis on the Kermadec Islands and P.a. elegans on the
Chatham and Antipodes Islands, while, P.a. myrtae breeds in the Austral Group and southern central Pacific Ocean (Glauert 1946, Warham 1990). P.a tunneyi is the smallest race of the species (Marchant and Higgins 1990).
Current phylogenetic investigation based on mitochondrial DNA cytochrome-b gene suggests that the northern hemisphere, P.a. baroli is more closely related to
Audubon’s shearwaterand differs from the southern hemisphere and subtropical- subantarctic clade containing the Australasian and Southern Ocean assimilis taxa. This is indicative of the existence of a physical barrier between the southern and northern hemisphere. Within the Australasian and Southern Ocean cladode,
speciation appears to have occurred on individual islands or island archipelagos, with P.a. myrtae the least similar of the other five P. assimilis and possibly more closely related to Newell’s Shearwater P. newelli (Austin et al. 2004). This suggests that
research conducted in the Northern Hemisphere, focused on P.a. baroli (Hamer 1994), may not be as relevant to P.a. tunneyi as research focused on P.a. haurakiensis in New Zealand (Booth et al. 2000, Booth et al. 2000b). Furthermore, the New Zealand subspecies exist in the same hemisphere, although breeding at a higher latitude.
Little Shearwaters breed at mid to high latitudes in both hemispheres, although most breeding activity occurs in the southern hemisphere. Little Shearwaters frequent subantarctic, subtropical and occasionally tropical waters (Marchant and Higgins 1990), but it may be assumed that adults forage in cool waters. During the winter months, the warm Leeuwin Current streams southwards, west of the Houtman Abrolhos Islands, while, along the coast, an opposing current of cooler water moves northwards. Initially, it was predicted that the Little Shearwater would utilise these inshore, cool waters for foraging. Observations on fishing vessels and existing information were used to examine this proposition (Chapter 8). Furthermore, a cold- water forager may be expected to thrive in years of low Leeuwin Current flow, when offshore waters remain cooler, unlike tropical, summer breeding birds that have been extensively monitored along the Western Australian coast.
Glauert (1949) published data collected by two lighthouse keepers on Eclipse Island off the south-west coast of Western Australia near Albany, which focused on P.a. tunneyi. To date, this summation of the research conducted mainly by A.V. Newman and instigated by A. Blythe provides the most detailed account of the subspecies breeding in Australian waters. Little Shearwaters arrive at the colony at night. Eggs are laid in June to July, which hatch in late August to September. Nestlings fledge in
late October to mid November (Table 1.1b). An incubation period of 52-58 days (n = 4) was recorded and adults were thought to relieve partners every two days. A nestling period of 70-75 days was observed, with the nestling fed every second night by both parents for the first fortnight and then once or twice every five nights
thereafter. A fasting period of 8-10 days was observed before fledging (Glauert 1946).