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Vris, Tjitte de. / The Galapagos hawk: an eco-geographical study with special reference to its systematic position
(1973)

Introduction,   p. 2


Page 2


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       INTRODUCTION
       The Galapagos Islands are situated in the Pacific Ocean, under the
 Equator, some 600 miles (1000 kilometres) off the coast of Ecuador, to
 which country the Archipelago politically belongs.    The total land-
 area consists of 7800 square kilometres, half of which comprises the
 island Isabela.    Four other islands are in the range of 500-1000 km
 eight are from 500-5 km2, six from 5-1 km2, forty smaller than 1 km2, the
 rest (some 45) are considered exposed rocks (see Table 1 for further
 details, and English and Spanish names of the islands).    The waters
 between the islands cover some 40.000 km2.    The distance from the most
 northern island, Darwin, to the most southern island, Espalola, is 350 km.
 The highest volcano is 1700 metres.
      Oceanic islands are in an outstanding position when compared with
 continental conditions, since such isolated islands have relatively simple
 ecosystems.    The presence of only one resident diurnal bird of prey in
 the Galapagos provides an unique opportunity to study the ecological niche
 which the hawk occupies here, particularly in relation to the other, main-
 ly nocturnal avian predators, the Short-eared Owl Asio flammeus galapa-
 goensis and the Barn Owl Tyto alba punctatissima.    There are no indi-
 genous land predators in the Galapagos.
      Detailed food observations were undertaken and breeding cycles
followed over several years (1966-1970) in order to obtain information
on the variety of prey taken and on the relative importance of the various
prey species to decide on the ecological place of the Galapagos Hawk.
This ecological part of the study was mainly undertaken on the four islands
Santa Fe, Espafiola, Pinz6n, and Santiago.
      The Galapagos Islands, which are geologically speaking of recent
volcanic origin (the oldest exposed rock sofar known dates back some two
million years, in the Pliocene, Williams 1966), must have been colonized
by
hawks coming somewhere from the American continent.     The Galapagos Hawk
is obviously the result of a process of geographical species formation, but
its direct relative on the American continent is not apparent and there-
fore unknown.     Facts on food and hunting habits in conjunction with
comparative plumage studies may demonstrate the similarities and distinc-
tions with regard to other species of Buteo.    The scanty data on conti-
nental species of Buteo are included for comparison and an attempt is made
to link this endemic species with mainland forms.
      There is a certain confusion regarding the common names of Buteo
species.     In this paper the established name Galapagos Hawk is used,
which is considered a synonym for Galapagos Buzzard.
      MATERIAL AND METHODS
      The Charles Darwin Research Station at Academy Bay on Santa Cruz
served as headquarters during my five years stay (October 1965 - February
1971) in the Archipelago.     The square-rigged motor vessel Beagle II,
local yachts and fishing boats made inter-island transportation possible.
Base camps were made ashore, at times it was necessary to establish ad-
ditional camps further inland; these have always been made outside the
territory of the pair of hawks under study at the time.
      Some of the field observations were made with the aid of binoculars
of 8 x 30, 10 x 50 or a telescope of 30 x   magnification.     A hide was


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