Left: Stewart Island’s Anglem coast. Right: Auckland Islands
From Banks Peninsula to Bluff
The Trust’s work is not geographically restricted; rather we assist landowners wherever yellow-eyed penguins are found, from Banks Peninsula to Bluff.
Since 1999, the Trust’s studies on Stewart Island and the outlying islands have shown a rapid decline in numbers. Traditionally Codfish Island/Whenua Hou was considered to be a stronghold with a stable population, partly because it is predator-free. However the number of 61 nests found in 2001 had dropped to 46 in 2009, with a further decline in 2011 to 39. This consistent reduction in the number of nests means fewer eggs laid and fewer chicks hatched then fledged.
To try and isolate the possible reasons for this marked and continued decline, it is urgent to continue monitoring the population of yellow-eyed penguins on Stewart and Codfish Islands. Further foraging studies of the yellow-eyed penguins in the marine environment, of which little is known, should be included in future research proposals.
Population estimates for yellow-eyed penguins are based on the number of breeding pairs. Before 1999, the estimate for Stewart Island/Rakiura was 470 to 600 breeding pairs but, based on extrapolation from partial surveys carried out in early years, this number was viewed with ‘a great deal of skepticism’(McKinlay 2001).
To rectify this, the Yellow-eyed Penguin Trust, in collaboration with the Department of Conservation, carried out a more comprehensive census of yellow-eyed penguin numbers on Stewart Island (1999 and 2000) and some of its outliers including Codfish Island/Whenua Hou (2001). The results showed a much lower than expected number of breeding pairs on Stewart Island (79) and very few juvenile birds compared to those observed on Codfish Island/Whenua Hou. This led the Trust to believe that feral cats might be affecting breeding success on Stewart Island.
Between 2003-2008 a study of factors affecting breeding success on the north-east (Anglem) coast of Stewart Island (where cats are present) was compared with two outlying island sites (Codfish Island/Whenua Hou and the Bravo Group) where cats are absent. On the Anglem coast, no evidence of predation was found, but chicks were dying from starvation and disease, breeding success was consistently poor, and the number of breeding pairs had declined by 50%. In comparison, breeding success at the island sites fluctuated, while nest numbers remained relatively stable.
During this five-year study, various other complementary studies were carried out. Between 2004 and 2006, the foraging behavior of penguins was studied with GPS dive loggers. These devices, which determine the penguins’ geographical position after each dive and record dive depths and ambient temperatures at 1-second intervals, allow a detailed analysis of the birds’ foraging behaviour and effort. The main aim of the study was to examine whether the observed chick mortality was as a result of prey shortage within range of the breeding sites. Usually, prey shortages are compensated for by penguins travelling further and diving deeper. However, penguins from Stewart Island were foraging close to shore and revisiting distinct areas to search for prey. This indicated that their foraging ranges were greatly limited, most likely due to the degradation of the sea floor ecosystem as a result of the commercial oyster extraction. In comparison, the penguins from Codfish Island had wide foraging ranges, but this was nevertheless indicative that the prey situation closer to their nesting sites was poor. Because the number of breeding pairs in the last five years declined considerably on Codfish Island, follow up foraging studies will allow us to assess whether the food situation for the penguins has further deteriorated.
Following the five-year study, a census of Stewart Island/Rakiura repeated in the 2008/2009 season found that the decline was localized to the Anglem coast, and that there was a shift in distribution of yellow-eyed penguin breeding sites. In 2009/2010, a repeat census on Codfish Island/Whenua Hou found a decline of 24.5% in the number of breeding pairs (46 compared to the 61 found in 2001), and in 2011 a further 15% decline (39 compared to 46).
The Auckland Islands, at latitude 50 degrees south, are the largest of New Zealand’s subantarctic islands, with over 500 km of coastline, much of it steep and inaccessible to penguins and people, particularly on the exposed western side. Uninhabited now, the main island was once farmed by a hardy few, whose legacy is feral cats and pigs. Surprisingly, rats have never managed to colonise the islands.
In 2012 the Trust again supported a Department of Conservation (DOC) led expedition to survey the yellow-eyed penguins at the Auckland Islands. The trip aimed to build on the distribution survey carried out by the Trust and DOC in 2009, and repeat beach counts last carried out in 1989 by Peter Moore. Along with beach counts, a team stayed on Enderby Island to nest search, mark the breeding birds, and carry out beach counts to help interpret the data collected by the rest of the team.
The team of 12 was made up of DOC staff, Trust staff and 6 volunteers that contributed to the cost of the expedition, and were based off the yacht ‘Evohe’. With just 11 days for the survey including travel time to the island it was expected that beach counts will be carried out every morning, before repositioning the boat in the afternoon and scouting the next site for locations of each observer for the next morning’s beach count.
Visiting the islands between 6 November and 7 December 2009 were team members Leith Thomson and Sandy King (both representing the Yellow-eyed Penguin Trust), Jo Hiscock (team leader, DOC), Jo Ledington and Callum Lilley (DOC), and Kate Beer (Wildlife Management student from the University of Otago). The Trust contributed to the cost of transport and accommodation provided by Henk Haazen on his 15m yacht Tiama. Crew member Steve Parsons completed the team of eight.
Almost 200 km of coastline was surveyed, with identification of 301 landing sites. These were regarded as a minimum because some sections of coast accessible to penguins couldn’t be surveyed because of sea conditions. Most landing sites would be used by one or more pairs, though probably some would be used by non-breeders.
The pig- and cat-free islands had more landing sites per kilometre of coast surveyed than the main island, which raises questions about the impact of these animals on yellow-eyed penguin and other ground-nesting birds. Areas of the main island adjacent to these islands - the northern shore of Carnley Harbour, and Port Ross and northern harbours – also had a higher number of landing sites than the coast in the middle of the main island. This suggests that perhaps the predator-free islands act as reservoirs whose overflow sustains the population.