Kiwis and pine forests

Forest and Bird, Volume 14, Issue 5, 1 February 1983, Page 15

Kiwis and pine forests

By

Wildlife Service

Brian Reid,

PRESS REPORTS in 1979 stating that Waitangi pine forest contained an estimated 400 kiwis and, furthermore, that kiwis were known to be present also in Glenbervie and other northern exotic forests triggered a series of inquiries to the Wildlife Service that are still continuing. Attitudes have ranged mostly from polite incredulity to hostile scepticism. How could these "barren monocultures’’, these ‘"‘biological deserts’, possibly cater for the requirements of such specialised birds that evolved with, and depend entirely on, the luxuriance of our native forests for their survival? To suggest that some plantations may have more birds per unit area than are believed to be present in many North Island indigenous forests was, to one irate correspondent, ‘misleading propaganda that should be discredited immediately".

SEVERAL WRITERS, though being pleased that our ‘‘national emblem’’ may have the versatility to adapt to pine plantations, expressed concern that if these provided suitable homes for kiwis, then another

argument against the conversion of our dwindling in-

digenous vegetation to exotics was weakened. A _ senior forester saw the situation entirely differently. He remarked, somewhat drolly, that "it would be ironical if a moratorium is placed on log-

ging in some plantations while their suitability as kiwi sanctuaries is assessed’’. This article examines briefly the requirements of kiwis, discusses the advantages and limitations of indigenous and exotic forest as habitat, and presents some findings from the joint Forest ServiceWildlife Service kiwi study at Waitangi. Needs for survival For survival kiwis need a fairly stable habitat that provides suitable cover for shelter and nesting, adequate immunity from predators and hazards (possum traps, poisons, fire, and the like), water, and sufficient accessible food (mainly earthworms, insects, and other invertebrates, supplemented with berries and foliage) throughout the year. Kiwi habitat Native forests We can only speculate about the probable great abundance of birdlife throughout the North Island in 1840, when predator-free and virtually unmodified forest (93 percent rich lowland forests and 7 percent montane forests) covered about 82 500 sq km (72 percent) of the land. About 75 percent of lowland forests and 10 percent of montane forests have now gone and today native forests (about 79 percent lowland and 21 percent montane) cover only 24 500 sq km (21.5 percent) of the island. Much of the remaining lowland forest is fragmented or persists as small pockets and though, perhaps, 80 percent can still = be. ‘classified ‘as ‘‘virgin’’, the luxuriance of the vegetation often conceals the sad truth that none remains pristine. This is often apparent only from the low numbers of birds present in seemingly bountiful habitats.

While traversing predominantly virgin North Island forests from bush-edge to bushedge with National Forest Survey parties between 1948 and 1954, I pitched camp at over 500 different sites and spent more than 600 nights under canvas in Coromandel, Taranaki, King Country, central plateau, and Urewera forests. Pigs were widespread and numerous over extensive tracts of bush, and hunting these with dogs was a national pastime. Goats, cattle, and deer locally were common, and evidence of possums, mustelids, rats, and, at times, cats was widespread. Diary entries, on the other hand, show that though kiwis were heard during most flycamping trips, the numbers that appeared to be present usually seemed only a small fraction of what the habitat should support. With few exceptions (some localities in Taranaki and the Ureweras), the frequency of calling indicated only sparse or moderate populations, and seldom did the rate of calling match that heard in the seemingly more austere habitats of the Waitangi plantation some 30 years later. The number of birds heard per unit of listening time at Waitangi also far surpassed the numbers recorded during brief 2- to 4-night kiwi surveys in several King Country and central plateau indigenous forests during 1976 and 1977. The reasons for generally low numbers of kiwis are not known. It is doubtful whether food and shelter were limiting factors, and of the environmental hazards present in the 1940s and 1950s pigs were probably the most devastating. Their enjoyment of flesh, keen sense of smell, and prodigious excavating skills, presumably, accounted for many birds, and the dogs that

were used to hunt pigs also killed kiwis. Thus the introduced disadvantages in many native forests today outweigh their natural advantages and it is questionable whether they can still be regarded as ‘‘natural habitat’’, for they no longer provide ideal conditions for sustaining high kiwi populations. For example, in 1967 one King Country possum trapper was reported to have already trapped more than 90 kiwis, and, more recently, the casual use of eee baits has taken a heavy toll. The highest kiwi density we have so far found, surprisingly, was in an isolated 130- to 140-ha remnant of cut-over/ second-growth at Tangiteroria, where (from plotting calling patterns and locations in 1976 and 1978) the population was estimated at between 35 and 43 pairs. As the number of birds is excessive for the food resources of the bush and they feed extensively in surrounding pasture land, it seems that predation here is of little or no consequence. Exotic forests For every 100 ha of native bush remaining in the North Island there are now 27 ha of exotic forests. These latter (48 percent private and 52 percent State owned) cover 6705 sq km, but few are known to contain kiwi. Many, in addition to sharing the shortcomings now apparent in native forests, also have other limitations that generally make them a poor second to our lowland forest. These may be related to their locations, climate and _ soils, their less diverse vegetation, their newness, some management practices, and the quick rotation (from seedling to logs) of their timber. Labelling them collectively as ‘‘biological deserts’’ is, however, more emotive than

factual, as native birds known to live in or utilise some pine forests include robins, tits, fantails, whiteheads, grey warblers, silvereyes, riflemen, cuckoos, moreporks, falcons, and even tuis, bellbirds, and pigeons. Some pine forests which appear to cater for all their needs have contributed significantly to the preservation and spread of several insect-eating native birds, including a few species that are now relatively uncommon or, possibly, absent from some bush areas where once they were abundant. None of these forests, as far as we know, have the capacity to sustain entirely populations of native nectar-, leaf-, and fruit-eaters. The survival of these birds may depend on a richer understorey of native and other broad-leaved plants than many plantations have, or on the presence of adequate patches of native bush nearby. In the latter case the exotic stands may provide a secondary — but important — supplementary feeding area. Even the vast 125 000-ha Kaingaroa plantation has been shown to support greater densities of some species of native birds than are believed to be present in many native forests. Before afforestation the elevated, exposed, and bleak Kaingaroa plains boasted no finer covering than tough, stunted heath land shrubs and tussock grasses. The planting of pines thus converted an extensive tract of previously barren country into acceptable habitat for a considerable number of birds, both native and introduced species. How widespread are kiwis in pine forests? Like Kaingaroa, many exotic forests are on waste land traditionally lacking kiwis and these can hardly be expected to have birds today unless liberations were made and afforestation created an

‘oasis’? as far as the kiwis’ needs are concerned. A bird identified as a kiwi was heard calling in Kaingaroa in 1965, but this was probably a mistaken identification, as no further supporting evidence has been reported. It is more likely that Kaingaroa still lacks kiwis, as the low numbers inhabiting native forests to the east are under no pressure to abandon their traditional homes, and even if they were, any colonisation of this plantation would be hampered by farm land and water barriers of the intervening Rangitaiki River. Unlike the extensive central plateau plantations, those at Glenbervie and Waitangi are on previously forested land that contained kiwis. Reports from Forest Service field staff that kiwis were still present and appeared to be utilising exotic as well as_ cut-over/second growth bush areas of these forests suggested some _ interesting ecological relationships that should be investigated, as it seemed that site preparation, planting, and subsequent management of maturing pine stands need not result in a total loss of birds from areas chosen for afforestation. Joint Forest Service-Wildlife Service studies to assess the relative contributions of pine and indigenous components for sustaining a kiwi population were started at Waitangi in 1978. The Forest Service, which funded this work, wished to confirm the ‘‘kiwi-pine relationship’’ and then ‘‘relate kiwi population trends with various developmental, management, and utilisation phases in the life of an exotic forest’’ to help ‘‘determine what changes may be required in management techniques’’ to safeguard kiwis.

The Wildlife Service defined the nature and sequence of the investigations necessary to meet these requirements, and the Entomology Division of DSIR contributed to the discussions on some methods and field techniques. The three men to whom all credit for intensive and thorough field work is due were Harold Corbett in 1978-79 and Rogan Colbourne and Ruud Kleinpaste in 1981-82. Studies at Waitangi Two features about Waitangi conveniently explained the presence of kiwis for the sceptics. They contended that this 2900-ha forest between Waitangi and Kerikeri provided an ‘‘island refuge’’ in an expanse of residential, orchard, and pasture land. It could be regarded as a geriatric refuge for birds displaced from the surrounding developed lands. Secondly, as only two-thirds is in exotics (1900 ha in pines and 100 ha in other species), it is the remaining 900 ha, consisting of scrub, bush, and swamp pockets, that alone sustains the kiwis. The first contention is difficult to substantiate. Before European settlement Waitangi was clothed in kauri forest, but by 1840 the area was in scrub. Until exotic afforestation began in the 1930s successive attempts at farming were made, with numerous burnings and subsequent reversions to scrub land, and for about 100 years the kiwi population suffered a series of severe setbacks. With such a history it seems that though some of the Waitangi kiwis may be immigrants, the present high population is composed largely of individuals bred within the forest. Data collected since 1978 mainly in exotic stands certainly indicate a healthy population with all age classes appropriately represented.

The first part of the study was made in 1978. Its aim was to estimate the population size and establish whether birds lived in all areas of the forest and then to relate relative kiwi densities with the different habitats (vegetation types, age of the stands, modifications resulting from various management practices, and the like). One hundred and twelve listening stations were located at vantage points throughout the forest and these allowed the position of vocalising birds to be approximately determined. Then daytime follow-up searches for ‘‘sign’’ (mainly feeding probe holes) permitted a more precise plotting of territory sites. Each station was manned for about 13 minutes on six nights. Ground configuration and vegetation at times distorted acoustics and 37 substations were used to fix the positions of ‘‘problem’’ birds. A preliminary analysis of the population survey data prepared mainly by Peter Thode, the district forester at Kaikohe, whose drive and curiosity launched the investigations, shows: ¢ Kiwis were generally found to be more numerous in native bush than in pine stands. The population density in the latter varied from less than 10 percent to about 45 percent of the density estimated for the compartment of bush at the west of the forest, which was proclaimed a kiwi sanctuary by the Forest Service in March 1978. e The greatest densities of kiwis, however, occurred under previously thinned and/or pruned exotic stands that contained a dense ground cover of slash. These were estimated to contain between 10 and 35 percent more birds per unit area than were present in typical bush

areas. Slash provides shelter and darkness without the need to burrow, and rotting logs, presumably, are rich in invertebrates for food. © Though kiwis were found in pines of all ages (from 3 to 40 years), they were estimated to be up to six times more numerous per unit area in older stands, particularly in those that had a thicker (up to 10 cm) ground cover of pine needles. e The relationship between kiwis and undergrowth was inconclusive, mainly because much of the shrub layer consisted of gorse, which is widespread in several compartments and holds little attraction for the birds. This preliminary analysis provisionally placed the total adult population at 450 to 520 kiwis. A reassessment of the data indicates that this is a very conservative estimate. My calculations suggest that the adult population at Waitangi numbers at least 760 and may exceed 1000 kiwis. A similar estimate (between 800 and 1000 birds) was also made by Messrs Colbourne and Kleinpaste from data obtained during their assignments in 1981-82. Conclusions Native forests, besides providing berries and foliage of value for food, also probably contain considerably greater varieties and quantities of soil and litter invertebrates than occur beneath pine stands. The value of some pine forests over some bush land for kiwi habitat is therefore believed to be due to the disadvantages that the former lack. At Waitangi, where the hazards likely to be encountered in bush and pine blocks are similar, kiwis are generally more plentiful in bush areas and reach similar, or greater, numbers in pine stands only after pruning or thinning. This suggests that the time span when a compartment (manage-

ment area) of pines can match lowland forest in providing high density kiwi habitat is linked to the duration of rotting slash and, therefore, is relatively short. The fact that kiwis are up to 10 times more numerous in native bush than in pines at Waitangi probably exaggerates the relative differences in habitat quality of these two environments. Whereas the indigenous pockets occur mostly in damp gullies with more penetrable soils, the pines are planted mainly on drier, less favourable hill sites more susceptible to droughts. Mature pine stands in better low-lying areas are believed to contain sufficient food to sustain large numbers of kiwis. One 90-ha area of 23- to 28-year-old pines contained an estimated 16 or 17 pairs. The main disadvantages of pine forests for kiwis (particularly those forests planted for wood-pulp) are the short lives of their stands — often shorter than the life span of a kiwi — and the destructive and highly disruptive operations associated with the beginning and end of each production cycle. Depending on the age of the stands, kiwis in one part of the forest may be at increased risk while, simultaneously, those in another part are benefiting from a different management procedure. Though management may cause fluctuations in the number of kiwis and the safety of individual birds cannot be guaranteed, the population within an exotic forest can be adequately maintained and safeguarded. Rogan Colbourne has reported similarly high numbers of kiwis in Puhipuhi exotic forest (now in its second production cycle) and Waipoua kauri forest, and the density of birds at both forests is believed to equal, or exceed, the density in Waitangi.

Birdlife in exotic forests could be increased by planting suitable broad-leaved species along compartment margins, but this action would not provide a valid argument for those wishing to clear-fell and replace native bush with pines. Native forests have their own intrinsic values and notwithstanding any reduced worth as

habitat for indigenous fauna, their floristic character alone justifies their preservation. Furthermore, there is no guarantee that exotic forests at present supporting high populations of kiwis and other birds will remain immune from the large numbers of vermin that have contributed to the decline in birdlife in many bush lands.