Feature

Which Penguin is Rarest?

Public attention on the plight of the hoiho has meant a lack of awareness of the plight of the tawaki penguin.

Dr Ian McLean

Kiwis have been conditioned by some artful public relations and media hype to believe that our own hoiho, the yellow-eyed penguin, is the world's rarest penguin. In reality, it is not yet known which species should be awarded this dubious distinction. Of the 16 to 18 penguin species, three are up for the award.

First, the hoiho is certainly an endangered species on mainland New Zealand. But hoiho occur in good numbers on several subantarctic islands and are therefore protected from the worst ravages of human impact.

Second is the little-studied Galapagos penguin, which is the most northern of the penguins and is threatened by a variety of natural and unnatural problems. As with hoiho, Galapagos penguins are a naturally rare, island-endemic species with a limited distribution. The tropical climate of the Galapagos is marginal for penguins, and fluctuations in water temperature and food availability caused by El Nino oscillations can severely affect penguin populations. On land, Galapagos penguins endure some of the same problems as hoiho -- introduced mammals and habitat loss.

Third on the list is the tawaki, the Fiordland crested penguin. Again, this is an island-endemic species with a limited distribution. It is not as well protected from human impact as the hoiho because its range is limited to mainland New Zealand and adjacent islands. Most of the places where tawaki are found are accessible to stoats or weka, are regularly visited by humans (who could inadvertently bring rats), or are mainland sites with the standard host of problems.

Since the early 1970s, researchers at the University of Canterbury have been studying several species of crested penguin, including tawaki. Early research was not designed to find out how many penguins there were. Rather, John Warham concentrated on breeding biology, and he determined that crested penguins had one of the most curious breeding systems known in birds.

It goes like this. All the crested penguins lay two eggs, but raise only one chick. Some species, such as tawaki, hatch both eggs. Some other species, such as the erect-crested penguin, lose the first-laid egg, sometimes before the second egg is even laid. The first-laid egg is always smaller than the second-laid egg. In species that lose the first egg there can be as much as a 70% difference in weight. In species that hatch both eggs, the weight difference is around 20%.

In the late 1980s, Canterbury researchers embarked on a second round of research designed to address some of the questions identified by Warham. We now know that eggs and chicks can be moved back and forth between nests without the parents rejecting them (this result could have important management implications). There are no differences in the incubation temperatures of first and second eggs, or in the positioning of eggs within the nest. Small chicks from first-laid eggs are viable, and do just fine if they do not have a larger sibling in the nest.

There seems to be a crunch point at about 10 days after hatching when the demands of two growing chicks can no longer be met by the female (who brings all food for the first three weeks), although in some nests females refuse to feed the smaller chick from the beginning. Nests that hatch two eggs are more likely to fledge a chick than nests that hatch one egg. Warham seems to have been right in his conclusion that the first-laid egg is insurance against the accidental loss of one egg, or early death of the larger chick.

But there are still unanswered questions. Why do some species lay the first egg, then reject it within a day of the second egg being laid? In species where two eggs are incubated to hatching, the second-laid egg always hatches first (by about half a day). What mechanism ensures this unexpected hatch sequence?

I hear the reader wondering why I have strayed so far from the question in my title. Well, one consequence of the research on tawaki in the late 80s seemed to be a decline in nests at the study site. We started working with about 70 nests, and after four years only about 25 remained active. Was this evidence of researcher impact? Or was there a more insidious decline going on?

Very little information was available either on how many tawaki there were in places other than the research island, or even where tawaki might be found. Incredibly, the only comments we have found in the literature on numbers of tawaki are "thousands in the bush" by Henry (writing in 1903), and "plentiful" by Falla (1948) on Solander Island. On the research island, our counts of nests that were not being studied intensively suggested a decline, but the counts were not done accurately enough to determine the magnitude of the problem.

It was time to find out just how many tawaki there really were. In 1990, we joined with an ecotourism operation, Southern Heritage Tours, and initiated a survey of tawaki that has taken six years to complete, with the last counts this August. The Department of Conservation has been helping for the last three years by surveying areas of mainland around Haast.

Tawaki occur from beaches near Fox Glacier in the north to the southern tip of Stewart Island. It seems that they are very patchy. In southern Fiordland and Stewart Island they occur almost entirely on offshore islands; from Milford Sound south we have counted 644 nests, with only three locations having more than 100 nests: Breaksea Island (215), Solander Island (115) and Codfish Island. (144).

These results suggested many fewer tawaki than we had expected to find, and were of serious concern. Fortunately, DoC found some hundreds of tawaki nests south of Haast. It looks as though the final count for the species will be 2,000-2,500 nests. Small numbers by penguin standards, but reasonably healthy all the same.

Was there a decline? We will never know. We are confident that the research techniques we now use have minimised researcher impact. It also appears that tawaki have stabilised at current population numbers. Now that we have a full species count as a baseline, we will be better able to identify future changes in population number.

What of the future? Because they nest on the mainland and adjacent islands, tawaki are susceptible to introduced predators such as dogs, stoats and cats. Nests are also attacked by weka which occur throughout Fiordland.

Tawaki are sensitive to disturbance by people, and increasing pressure by tourists to see wildlife (especially penguins) is of concern. The oft-discussed road from Jackson Bay to the Hollyford River would pass close to hundreds of tawaki nests.

All three of the world's rarest penguins have their problems. It makes no difference which species is the least abundant. All suffer from a limited distribution, low abundance, and unceasing human encroachment on their domain. Awareness about tawaki has climbed to unprecedented levels as a result of the work of the University of Canterbury, Southern Heritage Tours and DoC. Hopefully, our sensitivity to the needs of this unique penguin will continue to increase.

lan G. McLean is a lecturer in the University of Canterbury's Department of Zoology.