Journal of the Royal Society of Western Australia, 87:101-108, 2004 
Land Birds on Barrow Island: Status, Population Estimates, 
and Responses to an Oil-field Development 
S Pruett-Jones 1 and E O'Donnell 2 
1 Department of Ecology and Evolution, University of Chicago, 1101 East 57 th Street, Chicago, Illinois 60637. USA. 
2 Department of Evironmental Biology, Adelaide University, Adelaide, South Australia 5005. Australia. 
EE3 pruett-jones@uchicago.edu 
(Manuscript received October 2003 ; accepted June 2004) 
Abstract 
A census of land birds on Barrow Island, Western Australia was carried out during September 
and October 2001. A total of 178 transects was conducted in six major vegetation zones, with 777 
individuals of 16 species of birds recorded. The six most common species, in order of their 
abundance, were Spinifexbird ( Eremiomis carteri), White-winged Fairy-wren (Malurus leucoptems), 
Singing Honeyeater (Lichetiostomus virescens), White-breasted Woodswallow ( Artamus leucorynchus), 
Zebra Finch (Taeniopygia guttata), and Welcome Swallow ( Hirundo neoxena). Our total population 
estimates for these species were generally comparable to those of a survey of Barrow Island in 1976 
(Sedgwick 1978), but some differences existed for these and other species. In an analysis of habitat 
preferences, more complex vegetation zones supported more species. The density of both 
Spinifexbirds and Singing Honeyeaters was significantly correlated with the number of emergent 
shrubs. Also, across vegetation zones, the number of different bird species was correlated with the 
maximum height of vegetation in a habitat. Species richness and numbers of individuals were 
compared between natural areas, areas surrounding oil pads, and along roadsides. There was no 
significant difference in species richness across these three areas, but there was a significant 
increase in number of individuals along road sides. This latter result occurred because disturbed 
areas along roadsides were colonized by a large species of spinifex, Triodia angusta , which 
supported greater numbers of birds than other species of spinifex away from roads. The oil-field 
development on Barrow Island occupies approximately 4% of the land area on the island and 
appears, at present, to have had a relatively minor impact on the populations of land birds. This 
conclusion is qualified in that several species of insectivorous birds have declined in numbers over 
the last 25 years, and the reasons for these declines are not yet known. 
Keywords: birds, Barrow Island, oil-field development, species diversity 
Introduction 
Barrow Island is the second largest island (after Dirk 
Hartog Island) in Western Australia. Barrow Island 
experiences a tropical arid climate, and its vegetation is 
dominated by spinifex (Triodia sp.). The ecosystem on 
Barrow Island is interesting because it has been relatively 
unimpacted by the negative consequences of human 
activity and development, a situation unique in Australia 
and elsewhere. Barrow Island was designated as a Class 
A Reserve in 1910, which greatly limited human activity. 
In 1964 an oil-field development began on the island (by 
Western Australian Petroleum (WAPET), and continues 
with Chevron Inc. Despite this, however, there are no 
introduced animal species on the island, the fauna has 
never been persecuted or hunted, and the terrestrial 
vertebrates are extremely common. 
The avifauna on Barrow Island was surveyed three 
times during the 20th century: by F. Lawson Whitlock in 
1917 and 1918 (Whitlock 1918, 1919), by D. L. Serventy 
and A. J. Marshall in 1958 (Serventy and Marshall 1964), 
and by E. H. Sedgwick in 1976 (Sedgwick 1978). 
Additionally, W. H. Butler has made extensive and long¬ 
term observations of the avifauna on Barrow Island 
© Royal Society of Western Australia 2004 
beginning in 1964 and continuing to the present. During 
this collective work, a total of 113 bird species has been 
recorded (110 species listed by Sedgwick (1978) plus 
three additional species recorded by Butler (pers. comm.), 
and 32 species have been recorded breeding there. 
Additional work on the avifauna of Barrow Island 
consisted of an analysis of the diet of insectivorous birds 
(Wooller and Calver 1981) and a study of breeding 
chronology (Ambrose and Murphy 1994). 
Given the approximate 25 years since the survey by 
Sedgwick (1978), we sought to conduct a current survey 
of land birds on Barrow Island, with three objectives: 1. 
to quantify the occurrence and abundance of species; 2. 
to document any changes in the avifauna since the survey 
of Sedgwick (1978); and 3. to quantify the effects of the 
oil-field development on the island's land birds. Our 
focus on land birds differs from the complete avifaunal 
survey of Sedgwick (1978), and this earlier research 
remains the primary source for a list of all bird species 
recorded on the island. We focused on land birds because 
our time on the island was limited and we wanted to 
obtain an accurate estimate of population densities. We 
acknowledge that oil-field development can have both 
direct and indirect consequences for water birds and sea 
birds as well as land birds but our focus here is only with 
the island's land birds. 
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