The great Yellow-eyed Penguin count

Forest and Bird, Volume 16, Issue 2, 1 May 1985, Page 17

The great Yellow-eyed Penguin count

From of the Otago mid-70s has onwards, _ frequent the concern Otago has _ been expressed that probably the rarest penguin in the world — the yellow-eyed penguin — has been gradually disappearing from tts traditional nesting grounds on the Otago Peninsula. In order to gauge the accuracy of this feeling, a dedicated group of Otago people has been doing uts arithmetic. John Darby, vertebrate zoologist of the Otago Museum, reports on the findings of this penguin census.

S ince October 1981, dozens of Otago and Southland people from all walks of life have spent a total of 846 hours sitting motionless gazing out to sea. From windswept, often wet, and mostly cold vantage points on the Otago and Southland coasts they have patiently counted yellow-eyed penguins as they come ashore. During this time 5,014 birds have been recorded leaving the sea, of which 473 were juveniles. Three hundred and sixty nine birds were recorded entering the sea, mostly from midday onwards. In fact penguins have been counted every hour of the day and two nights were spent counting them with the aid of a zeniscope. So why this counting exercise on the grand scale? The fact is that for some time now people have believed the penguin is disappearing, particularly on the Otago Peninsula. Geoff Harrow, writing in Notornis in 1971, suggested that one of the reasons why the yelloweyed penguin had established on Banks Peninsula was because humans were disturbing them on the Otago Peninsula. In 1981 the Otago Peninsula Trust sponsored a penguin seminar which brought together interested groups to discuss the problem. It was this seminar that acted as the catalyst for the present programme. Counting was not thought at the time to be an activity that would become a major part of the programme, but it was soon to become almost a pastime in local circles. Anti-social penguins The yellow-eyed penguin is a secretive nester. It does not fit into the traditional penguin image of hundreds of squawking birds crowding together with two or three nests per metre. In fact, their nesting strategy appears to be that the further they can get away from their next door neighbours during the breeding season, the better. We have now followed nearly 500 nests over the last four years and only on three occasions have we found birds nesting within sight of their next door neighbour. Of those six nests only one has succeeded and only one bird has returned to its original nest site. A little more than half of the birds use the same nest site from year to year. Frequently they alternate between two and some may even select a different nest site each year. Perhaps it was because many people considered that penguins use the same nest site from year to year that they thought birds were disappearing from the Peninsula. While many nests are fairly easy to find, most of them are not. In our first year it took us an average of 1.4 hours, often clambering through very difficult terrain, to find each nest.

Birds use almost every type of cover available: from traditional coastal forest habitat to flax; nettle; hebe; scrub; tussock; under logs and rocks. All nests have two things in common. Firstly all have a back to them — the base of flax plant is highly favoured — and secondly, the nesting pair must not be able to see the adjacent pair of birds. We have found nests nearly 600 metres inland and only time will tell us how far penguins will go into forests to nest; from the signs we have found, probably at least one kilometre. All of this suggests that nests are not easy to find, especially if you are trying to find every single one. An early suggestion for carrying out the penguin census was simply to count

their footprints in the sandy shores that they are supposed to favour. Two disadvantages soon showed: counting footprints makes no distinction between adult and juvenile birds and secondly, there is no evidence whatsoever (despite popular belief) that the yellow-eyed penguins prefer sandy shores. In fact we have found more penguin colonies near rocky shores than we have sandy ones The remaining option left was to sit down and count penguins at different stages of their annual cycle. It is reasonable to assume that the number of birds nesting in an area bears some relationship to the number of birds that cross the beach into the breeding area. Counting penguins this way allowed us to make the impor-

tant distinction between adults (potential breeders) and juveniles (definitely not breeders). And that is why we have counted so many penguins for such a long time. More males than females The late Dr Lance Richdale elucidated much of our knowledge of the breeding and behaviour of the yellow-eyed penguin. About half the females may breed at two years of age, almost all by the age of three. A few males only will breed as two-year-olds and not until the males are five to six-year-old do they become established breeders. There is, according to Richdale, an imbalance of sexes with more males than females, hence the difference in the breeding age for the two sexes. Eggs, nearly always two, are almost equally sized and are laid any time from mid-September to early October. Incubation lasts for six weeks and this is shared equally by the sexes although not always. Most eggs are hatched by the first two weeks of November and from hatching

one parent will always be in attendance at the nest for the first six weeks. This is called the guard stage. From mid-December onwards both adults daily return to the sea to catch sufficient food for the needs of two chicks. I have found that in years in which a plentiful supply of food is available, the guard stage may be extended by up to a month and in pairs that have a single chick the guard stage may continue until the chick fledges at the end of February. In the rare occasions that one of the pair of adults dies after the beginning of the post-guard stage, a single parent is capable of fledging a chick. From the 90 gram chick hatched in November, most will leave for the sea weighing between 5 to 6 kilograms. Juvenile birds do not have the yellow crown completely around their head until they undergo their second*moult in February of the following year. Juveniles appear to go north for their first three months, possibly spending all their time at sea. The few records we have from northern areas are nearly always of dead birds.

Ferrets the felons In our first year of study, we located a total of 90 nests on the Otago Peninsula, and given the effort taken to locate them it seemed reasonable to follow them through. Once chicks started to hatch, a disconcerting pattern appeared in which penguins in some areas managed to fledge almost all the chicks that had been hatched, while those in other areas suffered a high loss of chicks. Not until the second year of our study were we to find sufficient evidence to identify the culprit. Ferrets were creating mayhem in some breeding colonies and in one all 14 chicks were lost. In another, 12 out of 13 were lost before we trapped the felon. Chicks appear to be taken by both ferrets and cats from a few days of age up to five to six weeks of age. Most breeding colonies on the Otago Peninsula appear to have resident ferrets and feral cats, and the conservative estimate for chicks lost in this area to predation is 22%. Our final conclusion on the welfare of this penguin on the Peninsula is that it appears to be more than holding its own and that while numbers are down in some areas they have increased in others. Population numbers appear to be limited by the availability of suitable habitat rather than other factors, although clearly predation of chicks, if it were to get out of hand, could be serious. How serious could only be determined by firstly testing the level of predation in areas to the north and south of Otago, and secondly by making a_ population estimate for the species throughout its range. The yellow-eyed penguin has an unusual distribution. The northernmost significant breeding area is the Otago Peninsula, although there are a few minor breeding areas to the north of the

Peninsula up to Banks Peninsula. The next most significant aggregation of these birds is centred on the Tautuku Peninsula with their northern limit at the Nuggets and their southern limit on the mainland at Slope Point in Southland. They are found on Stewart Island and its small offshore islands, on Campbell Island and the Auckland Islands but are absent from the Snares, Antipodes and Bounty Islands. We shall never know what the population of the yellow-eyed penguin once was. Richdale considered that they bred in their thousands on the Otago Peninsula. It is sobering to realise that nowhere on the east coast of the South Island is there more than a few metres of unmodified coastal forest which is inhabited by penguins. Of even more concern is the fact that there is barely half a kilometre of coastal forest, modified or not, that still retains a colony of breeding penguins. Greatest single threat A comparison of some colony sizes in the Catlins area with Richdale’s early figures

suggests losses of up to 60% in some areas. It is not that the penguins have deserted or moved away, it is their habitat that has been moved. And it is this loss of habitat to farming and recreation that must remain the greatest single threat to them. Stewart Island is probably the main stronghold of this species. But here too, as on the main Auckland Island, Campbell Island and the South Island, it shares its nesting grounds with feral cats. What lies in the future of this bird? Its population is estimated at 1200 to 1800 pairs throughout its range. About 550 pairs are to be found on the mainland, about half of those are on the Otago Peninsula. Despite Dr Richdale’s ex-

traordinary work on this species, he provided no formula for conservation other than his dedication and enthusiasm for this penguin. Many aspects of the bird’s biology need urgent attention. Habitat type determines the density of birds, but where the density is high, populations tend to be subject to high levels of predation. There are 38 known breeding areas on the South Island. On average there are 1.6 pairs per hectare on the mainland. Of the 323 hectares with breeding penguins, only 137 hectares are theoretically afforded any sort of protection on the South Island, but if we exclude the one offshore island population adjacent to the mainland (Green Island off the Otago Peninsula) only 14 hectares providing protection for 32 pairs of birds are adequately protected. By adequate protection I mean here the TOTAL exclusion of farm stock. Rarest of world’s penguins There are a number of compelling reasons why stock should be excluded from penguin breeding areas. The chief

one is the continued loss or reduction in the integrity of the habitat. The second and no less important reason is that wherever stock are found so are the ubiquitous rabbit and hare. I believe that these animals provide the dietary mainstay for ferrets and cats for most of the year; penguin chicks in season are a bonus. If we can reduce the rabbits and hares in areas adjacent to penguin breeding areas then we can probably go some considerable distance towards removing a significant threat to the survival of penguin chicks. But the main problem lies in the protection of what little remains of this penguin’s habitat. While this appears to be secure on the islands of the sub-

Antarctic and Stewart Island, this is not the case on the east coast of the South Island where even now, small remaining pockets of forest are rapidly being brought under the plough. While it is heartening that a few land owners have already taken the initiative to protect small colonies of penguins on their land, the total number of areas adequately protected on the South Island is still less than Six. In New Zealand we take the presence of this bird for granted. It is easy to forget that there is no other penguin quite like it anywhere else in the world, it is only found in New Zealand; it is the only member of its genus and is also the rarest of the world’s penguins. It surely deserves more consideration for the protection of its nesting grounds than it presently receives. oe