EN
Hutton's Shearwater Puffinus huttoni



Justification

Justification of Red List Category
Although this species is believed to have a stable population, it suffered a historical decline in range and population size. It qualifies as Endangered because breeding is now restricted to just two colonies, which remain vulnerable to feral pigs that occur in adjoining areas of the Kaikoura Mountains. 

Population justification
Cuthbert and Davis (2002) estimated 106,000 breeding pairs. Brooke (2004) estimated a total population of 300,000-350,000 individuals.

Trend justification
For many years, this species has been considered to be in a long-term decline (Sherley 1992, Heather and Robertson 1997), but a major study has indicated that the population was stable from at least 1990 to 2000 (Taylor 2000). Recent evidence even points to an increase in the population for the Kowhai Valley at an annual rate of 1.7% over the last 20 years, based on burrow density (Sommer et al. 2009).

Distribution and population

Puffinus huttoni breeds in the Seaward Kaikoura Range, north-east South Island, New Zealand. The population comprises two main colonies (Kowhai Valley and Shearwater Stream), sited 10-18 km inland. These were estimated to consist of 106,000 pairs at Kowhai and 8,000 pairs at Shearwater Stream (Sommer et al. 2009). The total population is estimated to number 300,000-350,000 individuals (Brooke 2004). Numbers and distribution within the Kaikoura Ranges have decreased, with 8 of 10 known colonies having been extirpated this century (Cuthbert 1999). Six out of eight colonies discovered in the high Kaikoura Mountains were likely extirpated by feral pigs, which remain a potential threat to the remaining two colonies (Harrow 2009). Since the rapid extirpation of colonies was detected, a third population on the Kaikoura peninsula has been established through translocation of chicks (Anon 2007, Ombler 2010).
In the non-breeding season, birds migrate to waters off southern, western and north-western Australia (Heather and Robertson 1997). 

Ecology

The species digs its burrows on gentle to steep mountain slopes at 1,200-1,800 m, under tussock grass or low alpine scrubland (Marchant and Higgins 1990). First breeding is thought to occur at 4-6 years of age. The species feeds mostly on small fish and krill (Heather and Robertson 1997). Birds gather food for chicks as far south as the Otago Peninsula and often fish around Banks Peninsula bays (Harrow 2009). Kapiti Island and Cook Strait are common feeding areas in the north, with foraging individuals also recorded near the Chatham Islands (Harrow 2009). Frequently diving to feed at c. 25 m, they have been recorded as deep as 36.6 m (Harrow 2009). Levels of burrow occupancy in both original colonies in 2006/2007 was found to be similar to the 1990s. In contrast, breeding success in both main colonies was thought to be due to poor at-sea feeding conditions, rather than increases in stoat predation, as no evidence pointed to the latter (Sommer et al. 2009). Annual adult survival, breeding success and burrow occupancy averaged 93%, 47% and 71%, respectively (Sommer et al. 2009). Low levels of breeding success, particularly at Shearwater Stream colony, point to the possibility of the colony levels being maintained by immigration from the more successful Kowhai Valley colony (Sommer et al. 2009).

Threats

Introduced stoats Mustela erminea are known to prey on burrowing seabirds (Moors and Atkinson 1984, Lyver 2002), and their continued presence in both remaining colonies is of major concern for the future survival of the species (Sherley 1992). Initially, stoats were thought to be the primary cause of the species’s decline (Sherley 1992, Heather and Robertson 1997); however, longer-term research has shown that only a small proportion of adults are taken, and the impact on breeding success could be insignificant (Cuthbert 1999, Cuthbert and Davis 2002). Predation and disturbance by feral pigs and cats are considered a major potential threat, but are normally absent from the breeding range (Cuthbert 1999, Taylor 2000, Cuthbert 2002). Habitat destruction and predation by feral pigs Sus domesticus, along with heavy browsing by a range of introduced herbivores may have been the cause of the complete destruction of some sub-colonies, contributing considerably to habitat loss and range contraction (Sommer et al. 2009). At least one feral cat Felis catus was present in the Kowhai valley colony in the 1998/99 season (Cuthbert 2003), but cats were otherwise absent from the colony, hence only occasionally do cats appear to contribute to species mortality.

Incidental capture in set-nets and inshore long-liners is also reported, with up to 80 individuals being caught in a single net (West and Imber 1985, Darby and Dawson 2000, Harrow 2009). In addition, long-term over-harvesting of some inshore fish species could compromise prey availability to Hutton’s Shearwaters with potentially severe impacts (Taylor 2000). Modelling has demonstrated that colonies are most vulnerable to the loss of breeding adults; therefore, maintaining high survivorship is paramount (Cuthbert et al. 2001).

Climate change poses a potential threat to the species, due to its geographically bounded distribution; its altitudinal distribution falls entirely within 2,000 m of the highest mountain top within its range (2,885 m) (BirdLife International unpubl. data). Breeding at high altitude also makes the species susceptible to detrimental effects of abnormal amounts or timing of snowfall; heavy snowfall can crush burrows, and late snow cover can delay or prevent breeding (Taylor 2000).

Conservation actions

Conservation Actions Underway
Ongoing control of browsing animals has resulted in a substantial improvement in vegetation cover (Heather and Robertson 1997), and a decrease in the number of burrows destroyed by trampling. Long-term projects to monitor threats and to study population dynamics are ongoing (Taylor 2000). Pigs are controlled on the colony boundaries (Cuthbert 1999). A third population is being established on the Kaikoura Peninsula: 10 fledglings were transferred there in 2005, 80 in 2006, c.100 in 2007 and 100 in 2008 (Anon 2007, Ombler 2010), and a further 200 in 2012 and 2013. 30 birds from the early translocations are producing 6 to 8 fledglings per year and the first of these are now returning to the colony. Over 60 birds were present in 2015/2016, including 3 returned chicks and 28 of the fledglings translocated in 2012 and 2013, which will potentially be part of the breeding population in 2017 and after (Rowe unpubl. data, Rowe 2016). Predator-proof fencing around the newly established breeding site was introduced in 2010. Researchers are investigating the species's food sources and potential effects of climate change.    

Conservation Actions Proposed
Census the population every five years using burrow plots and photopoints. Monitor focal burrows annually and correlate results with climatic and marine fluctuations. Commence nest protection if new research indicates that predation is having a significant effect. Assess the impact of local fisheries on food availability (Taylor 2000). Re-establish colonies at accessible sites along the flight path (Cuthbert 1999).

Identification

38 cm. Medium-sized shearwater, generally black above and white below. Uniform blackish-brown upperparts, merging at side of head below eye to whitish chin, throat. Mostly dull white underparts with brownish sides to breast, thigh patches. Greyish underwing, darker brown at trailing edge. Similar spp. Difficult to distinguish from Fluttering Shearwater P. gavia. Typically, P. huttoni has longer bill, greyer chin, throat, lateral undertail-coverts, blacker upperparts. P. gavia has sharper demarcation of dark side of head and white throat. Voice Generally quiet at sea. Noisy in flight and on ground at colony.

Acknowledgements

Text account compilers
Calvert, R., Moreno, R., Stattersfield, A., Stuart, A., Taylor, J., Wheatley, H., Benstead, P., Fjagesund, T., Anderson, O., Hermes, C., Mahood, S., Martin, R., McClellan, R.

Contributors
Cuthbert, R., Rowe, L.


Recommended citation
BirdLife International (2019) Species factsheet: Puffinus huttoni. Downloaded from http://www.birdlife.org on 22/09/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/09/2019.