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The Fossil Avifauna of Amsterdam Island.
Indian Ocean
ABSTRACT
The fossil avifauna of Amsterdam Island is described from
23,562 identifiable bones representing 2060 individuals from 30
sites. Twenty species of seabirds and one land bird are represented
by the fossils. This may underestimate the prehuman species richness
because two of the 10 indigenous species that now breed on
the island are not represented among the fossils. Lengths of bones
for all common species on Amsterdam are compared with those of
populations elsewhere. On Amsterdam, Great-winged Petrel
{Pterodroma macroptera (Smith)) and Grey Petrel (Procellaria
cinerea Gmelin) populations were composed of individuals of relatively
small mean size. The Macgillivray's Prion (Pachyptila
macgillivrayi (Mathews)) is shown to be specifically distinct from
the Broad-billed Prion (P. vittata (Forster)) and Salvin's Prion (P.
salvini (Mathews)), based on osteological measurements.
Introduction
Amsterdam (37°50'S, 77°31'E) and St. Paul islands lie 80
km apart in the middle of the Indian Ocean, more than 3,000
km from any continent (Figure 1); both islands are of volcanic
origin. Amsterdam is roughly circular, 9.2 km long and 7.4 km
wide, and rises to 881 m above sea level (a.s.l.). The western
coastal cliffs are spectacularly high (400-700 m), but cliffs are
20-80 m high over most of the remaining coastline. Average
air temperature varies between 11.2° C in August and 17° C in
February. The climate is windy and humidity is high, with rainfall
(annual mean 1114 mm) usually falling as a light drizzle on
239 days of the year (Jouventin, 1994). This high humidity and
frequent rain has promoted peat development over much of the
island.
Prior to human disturbance, lowland areas less than 250 m
that were above the coastal cliffs, and where the soil was wet
Trevor H. Worthy and Pierre Jouventin
Trevor H. Worthy, Palaeofaunal Surveys, 43 The Ridgeway, Nelson,
New Zealand. Pierre Jouventin, Centre d'Etudes Biologiques de
Chize, Centre National de la Recherche Scientifique, 79360 Beauvoir
surNiort, France.
39
and deep, were covered by a thick, six- to seven-meter-high
forest of the tree Phylica nitida (Rhamnacae). In the highlands,
and on the central plateau, peatlands were dominated by an association
of clubmoss {Lycopodium trichiatum) and a fern
{Gleichenia polypodioides), with some grasses, sedges, and
forbs {Uncinia brevicaulis, Poa fuegiana, Trisetum insulare,
Acaena seurguisarbae, and Scirpus aucklandicus) (Jouventin,
1994; Micol and Jouventin, 1995).
HISTORY OF EXPLORATION.—The island was discovered on
18 March 1522, but the first landing was not until 1696. Drawings
made then showed that 27% of the island was forested, but
by 1875 forest cover was reduced to 5%, and by 1990 only 12
ha, or 0.2%, remained (Jouventin, 1994). Deforestation was
caused by ships stopping en route from South Africa to Australia
to collect wood, and by repeated fires.
Fur seals {Arctocephalus tropicalis (Gray)) were harvested
in great numbers from about 1790, but they disappeared by
1893. A small colony was found in 1905 and is making a good
recovery (Jouventin, 1994). Other human visitors to the island
killed penguins, albatrosses, and petrels for food or for bait for
lobster pots. Many animals were introduced. The dog {Canis
familiaris Linnaeus), pig {Sus scrofa Linnaeus), and goat {Capra
hircus Linnaeus) died out, whereas the house mouse {Mus
musculus Linnaeus), Norway rat {Rattus norvegicus (Berkenhout)),
cat {Felis catus Linnaeus), and cow {Bos taunts Linnaeus)
remain (Jouventin, 1994; Micol and Jouventin, 1995).
Habitat degradation caused by repeated fires and cattle grazing,
plus predation by other mammals and active hunting by
people, combined to decimate the avifauna, which consisted
mainly of seabirds. The breeding fauna on Amsterdam at first
human contact has been estimated to include at least 20 species
(Jouventin, 1994), of which only the following 10 species remain
(Micol and Jouventin, 1995) (nomenclature for modem
avifauna discussed herein follows Marchant and Higgins,
1990). The Northern Rockhopper Penguin {Eudyptes chrysocome)
and the Yellow-nosed Albatross {Diomedea chlororhynchos)
are common. The Sooty Albatross {Phoebetria fused) is
rare, with about 240 pairs, and only about 20 breeding pairs of
the endemic Amsterdam Albatross {Diomedea amsterdamen-