Trevor H. Worthy

Palaeofaunal Surveys, 2A Willow Park Dr., Masterton

Abstract

The distribution and relative frequency among anatids of Brown Teal (Anas chlorotis) in Holocene fossil deposits on the North, South, and Stewart Islands of New Zealand are reviewed. Brown teal remains representing 641 birds are reported from 73 widely distributed sites throughout New Zealand. The fossil sites indicate the prehistoric use of a large range of palaeohabitats including coastal sites, lakes, swamps, and forests as diverse as wet podocarp and beech forests up to 700 m altitude. There is often no direct association of these forest sites with aquatic habitats such as rivers or ponds indicating that Brown Teal were foraging often at considerable distances from such features while in forests.  In the seasonally drier eastern regions Brown Teal were confined more to aquatic habitats, though this may have been the result of competitive exclusion with Finschs duck which dominated terrestrial habitats, rather than habitat incompatibility.

Introduction

The Brown Teal (Anas chlorotis) is a small duck endemic to the main islands (North, South, Stewart, and associated islets) and the Chatham Islands of New Zealand. It is recognised as a distinct species as originally described following Oliver (1955), Kennedy & Spencer (2000), and Holdaway et al. (2001). Its nearest relatives are flightless congeners on Auckland and Campbell Island.

 Brown teal were abundant historically throughout the North and South islands. It was common in kahikatea (Dacrycarpus dacrydioides) forest swamps and most commonly found by day sheltering beneath overhanging vegetation in quiet waterways, and was known to feed by night in a variety of habitats including lakes and in drains e.g. Buller, in Turbott (1967). However, within 40 years of Buller’s 1888 account, Brown Teal were noticeably declining in numbers, a trend that was related to loss of habitat (Oliver 1955, Turbott 1967). The wide variety of habitats used is summarised by Marchant & Higgins (1990), but includes, estuaries, tidal flats, beaches, rivers, hill swamps, gully-heads, mountain lakes, pasture, and forest.

 The decline in numbers of Brown Teal has continued until the present day (Oliver 1955, and references in Williams 2001), a decline described most recently as ‘arguably, more dramatic than any other of New Zealand’s endemic birds’ (Williams 2001). At present (2002), the species exists in the South Island as a very few birds in Fiordland, and in the North Island by small and declining populations in Northland. Even the population on the apparent stronghold of Great Barrier Island is declining, with all population in imminent danger of extinction.

 The aim of the present report is to clarify the prehistoric distribution of Brown Teal and the broad habitat (plant/landscape) characters with which remains have been associated throughout New Zealand, through an examination of fossil evidence. From these data I comment on the habitat preferred by Brown Teal prehistorically.

 Methods

 The fossil distribution is only assessed for the main islands of New Zealand (North, South and Stewart islands): records from Chatham Island are not assessed. Figure 1 shows the distribution of fossil sites, which were assessed for the presence of Brown Teal.

 Data on the frequency and distribution of Brown Teal and other anatids were extracted from a database maintained by Palaeofaunal Surveys. Constituent data are derived from all published literature, particularly Worthy (1997a, b, 1998a, b, c, d); Worthy & Holdaway (1993, 1994, 1995, 1996, 2000); Worthy & Swabey (in press), Worthy et al. (in press) and unpublished theses and reports, particularly Millener (1981) and McGovern-Wilson (1986). All major sources are listed in the references. Archaeological data are based on Worthy (1999) and all the references cited therein.

 Data from all sites (Appendix 1) are compiled into regional categories for the following selected anatids to show their relative abundance as fossils in each region (Table 1): Finsch’s duck (Chenonetta finschi), formerly in the endemic genus Euryanas, but recently referred to the Australian wood duck genus Chenonetta (Worthy & Olson 2002), grey teal (Anas gracilis), grey duck (Anas superciliosa), blue duck (Hymenolaimus malacorhynchos), scaup (Aythya novaeseelandiae), and merganser (Mergus sp.). The Auckland Island merganser (Mergus australis) was known historically only from the Auckland Islands. Fossil Mergus bones of Holocene age from Chatham Island have been suggested to be from a distinct taxon (Millener 1999), but no comparative study of the available material has been completed yet. Mergus bones of Holocene age from widespread sites in mainland New Zealand have not been studied, and so may be referable to M. australis, the Chatham form if it is indeed distinct, or a third distinct taxon.

 In order to better associate fossil localities with palaeohabitats the analysis was restricted so far as practical to sites known or likely to be of Holocene age, as then palaeovegetation is much easier to reconstruct. Sites or faunas (if there are discrete faunas in a single site), known to be older than 10,000 years were not included.  However, as surface collected bones from some caves may include older material because time averaged deposits are common in New Zealand caves (Worthy & Swabey in press), undated individual bones/skeletons that are actually older than 10,000 years may be included.

Table 1. Frequency of selected anatids in fossil sites by region in New Zealand. Sites which are known to be exclusively older than Holocene in age are excluded. Data from Palaeofaunal Surveys database, and available on request.

Notes to Table 1.

Brown teal have been recorded from 11 North Island, 16 South Island, and 1 (Old Neck) Stewart Island archaeological sites in addition to the natural fossil sites (Worthy 1999) (Figure 3).Grey teal (Anas gracilis) – In addition to the natural sites listed in Appendix 1, this species has been recorded in archaeological sites as follows: Taranaki (Kaupokonui, P21/3; Ohawe, N129/77); Coastal northern South Island (Marfells Beach P29/2; Haulashore Island, Nelson O27/56); North Canterbury (Redcliffs, S84/76; Whalers Bay Cave, O31/12); South Canterbury (Gooseneck Bend, H39/16, 1); North Otago (Pleasant River; Shag Mouth, J43/2); Southland (Riverton, D46/35; Tiwai Point, E47/13; Lee Island S131/4). Most if not all these records need to be treated with caution as the basis on which they were separated from Brown Teal was not given, and it is now known that the wing elements of both taxa widely overlap in size and are generally not distinguishable.

 Merganser (Mergus sp.) – Additional records of this taxon are known from archaeological sites in the Hauraki Gulf (Ponui Island N43/1), Wellington coast (Paremata N160/50), Marfells Beach P29/2, North Otago (Kakanui J42/4, Shag Mouth J43/2), and Old Neck on Stewart Island.

 Scaup (Aythya novaeseelandiae) – some of the Waitomo karst and Northland dune records require reassessment as Millener (1981) often confused scaup with Brown Teal (THW pers. observ.).

 Blue duck (Hymenolaimus malacorhynchos) – Archaeological records for this species include at least one site in Central Otago (Hawksburn).