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Bird and Bat Survey of Beech Working Circle 4,
Maruia Valley, North Westland,
By Rhys Buckingham
for Timberlands West Coast Ltd
This document describes the results of a baseline bird and bat survey carried out in forest areas owned by Timberlands West Coast Ltd (TWC) in the Maruia Valley, Murchison-Springs Junction district, between April 1996 and January 1997. The survey was requested by TWC as part of an ecological assessment required for sustainable beech management planning.
Species distributions, relative abundances and diversities on a local, regional and national scale are discussed. The document describes the predicted impact of logging on indigenous birds and bats (with emphasis on rare or endangered species), and offers recommendations for reducing these impacts.
Previous bird surveys were carried out by New Zealand Wildlife Service (NZWS) and Ecology Division, Department of Scientific and Industrial Research (DSIR) in the Maruia and upper Grey Valleys during the 1970s. These surveys were carried out in response to a scheme, proposed by the New Zealand Forest Service (NZFS), to harvest approximately 240,000 ha of lowland beech and podocarp forest in North Westland. Extensive five-minute bird count trials were carried out in the Maruia Valley between 1974 and 1979 (Best & Harrison 1976, Morse 1981). In addition, smaller scale bird surveys were carried out in the upper Grey Valley, Lake Daniells, Lewis Pass and Victoria Range areas during the 1980s (Buckingham 1983; Graeme Elliott, pers. comm. June 1996).
Parakeets, like kaka, have specialised habitat requirements. ODonnell & Dilks (1986) recorded parakeets on fewer plants than most other forest bird species. In podocarp/beech forests, the most frequently used tree species was rimu, while silver beech and Southern totara were also important (ibid). Also like kaka, parakeets had a preference for large diameter trees (40% of parakeet observations in rimu were at trees >80 cm dbh) (ibid).
Only two extant species of endemic bats occur in New Zealand, the short-tailed bat and the long-tailed bat. Both species have declined significantly since the arrival of humans, and their distribution is now discontinuous (ODonnell &Sedgeley 1994). Current research aims to identify factors that are limiting bat populations, and is being carried out mainly in the central North Island (for short-tailed bat), and in Fiordland (long-tailed bat). Recently, short-tailed bats have been found in the South Island, at Karamea (Kahurangi National Park) and the Eglinton Valley (Fiordland National Park).
Due to overlap in call frequencies of the two species of bat, problems have occurred in identifying bats using automatic detection equipment (ODonnell 1997b). Until further information on bat vocalizations, and their regional variations is known, interpretation of bat survey information should be treated with caution.
It is not known to what extent logging may impact long-tailed bat populations in Maruia SF, or elsewhere. Determining these impacts by experimental logging on bats, given current knowledge, would pose unacceptable ecological risks (Colin ODonnell, in litt., 15/8/1997). It is known, however, that long-tailed bats favour trees that are usually targeted for logging, i.e. trees with an average dbh of 118 cm (usually 400-600 years old). Long-tailed bats also use dead standing trees for roosting. In the Eglinton Valley (Fiordland beech forest), 59% of bat roosts found were in red beech, and 34% in standing dead trees (Colin ODonnell, in litt., 15/8/1997).
Radio-tracking studies of long-tailed bats carried out in the Eglinton Valley have found that bats highly prefer tree roosts, that are more commonly found in low altitude than high altitude forest (Sedgeley & ODonnell, in press; Colin ODonnell, in litt., 15/8/1997). Preliminary results of these studies indicate that long-tailed bats are highly selective in choosing roost sites (Sedgeley & ODonnell, in press). Bats were found to prefer tall trees with large trunk diameters, dead trees, trees with large numbers of holes, and trees with low canopy closure. Roost sites were generally used for only one day, and had a low frequency of reuse (16%). These results imply that long-tailed bat populations require large numbers of suitable trees covering large areas of unmodified lowland forest (ibid).
Kaka are regarded as habitat specialists, with seasonal preferences for specific forest types and altitudes (ODonnell & Dilks 1986). Habitat use studies in South Westland found kaka to most frequently use large silver beech and kamahi throughout the year, while rata and rimu were seasonally very important (ibid). Over 85% of kaka sightings were made in only eight species of plant (silver beech, kamahi, rimu, rata, Southern totara, mistletoe, miro, fuchsia), and dead trees. Kaka have a strong preference for large diameter trees, with 55% of kaka observations in rimu being at trees >80 cm dbh (ibid).
Many studies (e.g. Onley 1983, Spurr 1985, ODonnell & Dilks 1987) have indicated that kaka are adversely affected by traditional logging methods (e.g.clear felling, coupe logging). It is not known to what extent, if any, the proposed group tree logging will impact kaka in this area. ODonnell & Dilks (1987) predicted, however, that the removal of even small proportions of preferred habitat trees (e.g. rimu, silver beech, rata, dead trees) would have detrimental effects on kaka and parakeet, because of their specialist niche requirements.
South Island kokako
At least two relatively recent reports of kokako are known from Station Creek (Robin Inch, pers. comm. April 1996, Neil Taylor, pers. comm., May 1996). The reports include descriptions of unusual birds seen, and resonant bell-like, or organ-like calls heard. Details of possible kokako sign (including a sighting), found on the present survey, are given in Appendix 3.
The predicted impact of group tree logging on South Island kokako (if they still exist) is difficult to determine, as their behaviour and habitat preferences are largely unknown. South Island kokako may have quite different habits and habitat requirements to North Island kokako, the ecology of which is well known (Hay 1984, Best & Bellingham 1991, Innes & Hay 1995). Logging, including selective logging has impacted populations of North Island kokako by removal of preferred food plants (Heather & Robertson 1996). However, the main threats imposed on kokako are almost certainly competition and predation by introduced mammals (particularly possum, stoat and European rats) (Leathwick et al. 1983, Innes & Hay 1991, Brown et al. 1993, King et al. 1996).
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