THE WEKA VICTIM OR VILLIAN

Forest and Bird, Volume 16, Issue 3, 1 August 1985, Unnumbered Page

THE WEKA VICTIM OR VILLIAN

Could the weka, one of our more endearing native birds, thanks to its cheeky, fun loving nature, be a risk to Kapiti’s little spotted kiwi population? The possibility was floated in the February issue of Forest and Bird. This article, by DSIR ecologist Ian Atkinson and Kapiti Island Lands and Survey Ranger Peter Daniel, challenges such a notion and the assumption behind tt.

I n recent years there has been an increasing tendency to treat the weka as if it were an introduced predator no different from the rat, cat or stoat. This prejudice is associated particularly with wekas introduced to islands where vulnerable species of birds, or their

eggs, are sometimes eaten by wekas. The prejudice is now appearing in print, as for example the articles in Parkscape December 1984 and the February 1985 edition of Forest and Bird. It has perhaps been stimulated by the campaign to rid Codfish Island of wekas, a campaign we fully support. In this instance there is proof that wekas introduced to that island threatened the survival of Cook’s petrels, a seabird known to breed on only one other island. The possibility of eradicating wekas from Kapiti Island has been raised by Mr Jim Jolly in the Forest and Bird article, as he believes they may threaten the survival of little spotted kiwis. In this case we think the argument is based on inferences and assumptions that should not go unchallenged. Wekas were introduced to Kapiti Island around the turn of the century. Little spotted kiwis were not introduced until 1912 — although Mr Jolly raises

the possibility that they had persisted there from the last ice age. This seems unlikely, for Maori informants of early writers about Kapiti apparently made no mention of kiwis having been there and Cockayne, who spent 14 days on the island in 1906, suggested that ‘‘flightless birds of various kinds’’ should be introduced. Whatever their origin, it is clear that little spotted kiwis, if present on the island before 1912, must have been present in very small numbers. Wekas were ‘‘everywhere’’ on Kapiti Island by 1924 when A. S. Wilkinson became caretaker of the island. Despite this presence of wekas, Wilkinson (1949) records that by 1924 little spotted kiwis had colonized the higher parts of the island above Rangatira and in the Te Rere and Kaiwharawhara basins. Since then both wekas and little spotted kiwis

have increased: a Wildlife Service survey in 1982 found little spotted kiwis inhabiting all suitable habitats, with a breeding population exceeding 1000 birds. Puzzling reference No studies of the numbers or breeding of little spotted kiwis on Kapiti Island were made until 1980, when Mr Jolly and his team began their work. It is difficult therefore, to understand the reference in the articles to a ‘‘disquieting trend’’ that has emerged ‘‘over the last five years’’ when earlier studies are lacking. The cause for his concern, however, is that two-thirds of the eggs produced by the 10 pairs of kiwis he studied have apparently been lost to wekas. It may be thought that eggs are a major food item of wekas because a little spotted kiwi egg eaten by a weka is pictured in the article and is described as one of many. A recent PhD study of wekas made on Kapiti Island by Mr A. J. Beauchamp failed to show any evidence of kiwi egg predation. No egg shell was found in stomachs or faeces and the diet consisted largely of invertebrates and various fruit from native trees. There is no doubt that some wekas eat some kiwi eggs but the question not yet answered is whether this happens often enough to adversely affect kiwi numbers. If two-thirds of the eggs were lost, what happened to the remaining third? Losses of eggs and chicks, caused by predators and other factors, are common in any population of breeding birds. These losses become important only when the number of young birds reaching adulthood falls short of the number of adults that die each year. In that case the population must decline. If we assume that a kiwi’s adult life averages 20 years and that we have a breeding population of 1000 birds, then 50 young birds must be added to the breeding population each year if the population is not to decline. Put another way, each pair need produce a grown-up offspring only twice in their lifetime in order to replace themselves. We have no evidence of a decline in the breeding population of little spotted kiwis on Kapiti Island. The 10 pairs of kiwis studied represent no more than 2 percent of a population of 1000 birds. It would be risky to generalize from such a small sample unless one was sure it was representative. There are two reasons why we doubt that it is. First, some kiwi burrows are more than 2 m in length while others are short. Eggs in short burrows are more likely to be found by wekas. This crucial point is not discussed in the article although in an earlier 1983 article Mr Jolly stated that ‘‘all egg losses have been from the part of the study area where burrows were shorter and presumably more accessible to the weka’’.

Second is the unavoidable effect of human disturbance on the birds studied. We know that the Wildlife Service team have taken great care to minimize this disturbance, but birds are caught, measured and weighed at all stages of the breeding cycle, transmitters are fitted, and video recorders set up outside nesting burrows. Wekas are highly inquisitive opportunists, and it is therefore possible that this human activity around the kiwis and their nesting burrows has increased the chances of wekas finding kiwi eggs. Kiwis vulnerable? The article implies that wekas probably attack kiwi chicks, because kiwis seem ‘"peculiarly vulnerable’ to wekas. There is evidence to the contrary. Mr Beauchamp’s study showed that although wekas often call at night, they are unlikely to kill birds then because they cannot see adequately in the dark. Kiwis and their chicks are active at night when wekas are less active and a wellcamouflaged chick may be difficult to find, either at night or during the day. At present, there is no evidence that wekas kill kiwi chicks. Furthermore, on several occasions little spotted kiwis have been seen chasing wekas at night. Because kiwi chicks were rarely, if ever, reported on Kapiti Island before the current intensive study began, one must accept that they are not conspicuous. The article states that in four seasons of all-night patrols only 17

chicks have been found. But how many hours have been spent in actual searching? And what are the chances of a small party, using only headlamps in sometimes thick undergrowth and rugged terrain, finding more than a fraction of the chicks present? We do not wish to belittle the importance of the research undertaken by Mr Jolly and his team. Nor should anybody underestimate the difficulty of studying a burrow-nesting nocturnal bird. As Mr Jolly pointed out, future research is designed to test these questions concerning the interaction between wekas and kiwis, and as we have pointed out, many questions remain. Wekas and kiwis are the only flightless predators among New Zealand native birds. Wekas belong to the rail family, a group that includes the banded rail, marsh crake and takahe. Most New Zealand rails are closely related to rails in Australia or the Pacific Islands. Wekas, however, like takahe, are flightless rails which have been long enough in New Zealand to diverge significantly from their flying ancestors. Not less than 6 species of flightless or near-flightless rail have become extinct in the South Pacific during European times. In the same period wekas have disappeared from eastern South Island, most of Stewart Island, and from almost all of the North Island except Gisborne. Thus some island populations of wekas will always be needed to safeguard the species.

Unique weka Wekas are among the most enjoyable of our native birds to watch, and there is no other place in the lower North Island where this is easier than on Kapiti Island. Their mammal-like behaviour, inquisitive nature, tameness in man’s presence, protectiveness shown to chicks and primaeval-sounding call combine to set the weka apart from all other New Zealand birds. These intrinsic values must be recognised, just as we recognise those of the kiwi. If it was shown that wekas threatened the survival of little spotted kiwis on Kapiti Island, removal

of wekas would need to be considered. But if kiwis are established satisfactorily on islands free of wekas, an option currently being pursued by the Wildlife Service, any threat posed to the kiwis by wekas on Kapiti Island would become less critical. We should not be trapped into managing an island nature reserve solely for one species of bird, unless this is the only way to save that species from extinction. Other birds and other values of the whole island system must be kept in mind when deciding our aims for management. we

Editor’s footnote: Since receipt of this article, we have heard of a 75 percent reduction in the weka population in the Gisborne area. As yet no cause has been determined for such a dramatic loss, although avian disease or the effects of the drought have been mentioned as possibilities. References Cockayne, L. 1907. Report on a botanical survey of Kapiti Island. Append. J. House Rep. (N.Z.) C8. Jolly J. 1983. Little spotted kiwi research on Kapiti Island: 1980-1982. Wildlife, A Review 12: 33-39. Jolly, J. 1985. Little spotted kiwi : paradise regained or paradise lost? Forest and Bird 16: 15-17. Wilkinson, A. S. Kiwi on Kapiti Island. New Zealand Bird Notes 3: 113. Wilkinson, A. S.; Wilkinson, A. 1952. Kapiti Bird Sanctuary. Masterton Printing Co., Masterton.