PDF (Lo-Res) - Smithsonian Institution Libraries

The History of the Chatham Islands' Bird Fauna
of the Last 7000 Years—A Chronicle of
Change and Extinction
ABSTRACT
Over the past 150 years, thousands of fossil bones of extinct and
living species of birds have been collected from the Chatham
Islands, an isolated island group some 860 km east of New
Zealand. Recent field research (1988-1993) has dramatically augmented
the earlier collections and has provided, for the first time, a
sound stratigraphic and radiometric chronology for this rich subfossil
avifauna. Most of these bones have been found naturally
deposited in the buried soil horizons of coastal sand dunes or in
limestone caves, but some are of archeological origin, deposited
by human agency in coastal dune middens or, occasionally, in
dwelling caves. Most, if not all, of the avian remains are of early
Holocene or younger age, as indicated by a series of some 65
accelerator-mass-spectometry radiocarbon dates ranging from ca.
7000 yrs BP to ca. 300 yrs BP. The Holocene fossil record for, and
patterns of evolution and extinction within, the Chatham Islands'
avifauna are documented and discussed. Taxonomic studies indicate
that several taxa, all extinct, can no longer be considered
inseparable from their mainland counterparts; among these are as
yet undescribed species of Eudyptes, Tadorna, Mergus, and Nestor.
Introduction
Dune sands and cave sediments on the Chatham Islands (Figure
1) have yielded thousands of Holocene fossil bones of extinct
and living species of birds (Forbes, 1892a, 1892b, 1892c,
1893a, 1893b; Andrews, 1896a, 1896b; Scarlett, 1955; Dawson,
1957, 1958, 1959, 1960, 1961a, 1961b; Simmons, 1964;
Olson, 1975, 1984, 1990; Sutton and Marshall, 1977; Sutton,
1979,1982; Millener, 1981, 1991, 1996; Tennyson and Millener,
1994). The Museum of New Zealand, Wellington, for example,
holds more than 250,000 Chatham Islands fossil speci-
Philip R. Millener
Philip R. Millener, Geology Department, University of Tennessee at
Chattanooga, 615 McCallie Avenue, Chattanooga, Tennessee 37403-
2598, United States.
85
mens, whereas extensive additional material is housed at the
Canterbury Museum, Christchurch, and in the Natural History
Museum, London. The diversity of this fossil avifauna, which
included many endemic land birds (among them several flightless
forms), numerous waterfowl, and colonies of breeding
subtropical and subantarctic seabirds, contrasts markedly with
that of the present. The total number of bird species, living and
extinct, recorded from the Chatham Islands is more than 100.
The majority of them, some 60 species, are marine birds;
among them are albatrosses, petrels and shearwaters, penguins,
cormorants, waders, and gulls and terns (see Table 1). Only
about 25 of these marine species currently breed in the
Chathams, although formerly perhaps as many as seven more
did so (Bourne, 1967). The remaining seabirds are summer migrants,
occasional visitors, or vagrants. The rest of the birds
(those of terrestrial and freshwater habitat) can be divided into
three groups: (1) those present prior to first human contact; (2)
those that self-colonized more recently, some of them within
the historic period (e.g., Welcome Swallow {Hirundo tahitica),
White-faced Heron {Ardea novaehollandiae), Spur-winged
Plover {Vanellus miles)); and (3) those that have been deliberately
introduced by Europeans (e.g., Black Swan {Cygnus atratus),
Weka {Gallirallus australis), House Sparrow {Passer domesticus),
Blackbird {Turdus merula), Song Thrush {Turdus
philomelos), Starling {Sturnus vulgaris)). This paper is primarily
concerned with the composition of the prehistoric Chatham
Island avifauna, so the recent self-colonists and the deliberately
introduced species are not considered further. Nomenclature
for species' binomials and English names of modern birds follows
Turbott (1990) unless otherwise noted.
METHODS
Radiometric ages quoted in this paper were determined by
the Rafter Radiocarbon Laboratory, Institute of Geological and
Nuclear Sciences, Gracefield, New Zealand, using accelerator