Australian Bird Count WHERE DO ALL THE BUSH BIRDS GO? In 1989 the RAOU embarked on one of the most ambitious bird counting projects undertaken in Australia – the Australian Bird Count. Now the analysis of the enormous volume of data is beginning to reveal the seasonal movements of our bush birds – including some surprises. by Michael F. Clarke, Peter Griffioen and Richard H. Loyn Supplement to Wingspan, vol. 9, no. 4, December 1999 ¢ ii Australian Bird Count The Australian Bird Count relied on the participation of a dedicated band of volunteers throughout the country. Photo by Jane Miller Inset: The ABC is helping to clarify the seasonal distribution of species that migrate southward from the tropics in summer, such as the Fairy Martin. Photo by Graeme Chapman EVEN A CASUAL OBSERVER KNOWS that the abundance of different bird species changes over time and space. What is less obvious is how changes at individual sites fit in with a continental picture of bird movements. By the early 1980s it was becoming increasingly clear that species and ecosystems could not be properly managed without an understanding of these movements. Thus it was that in the mid-1980s the RAOU’s best method to introduce in Australia.1,2 Four Research Committee decided to embark on an methods were selected for field testing,3 which ambitious Australia-wide project to gather bird showed that active methods (transects or area count data in a consistent and scientific manner. searches) detected more individual birds and species At that time there were already several monitoring in 20 minutes than stationary methods. A method schemes under way elsewhere in the world, and the known as active timed area-search4 was found to be Committee commissioned a review to determine the the most popular, and it was also the best-buffered Australian Bird Count iii Table 1 Major contributors against variations in counts due to time of day and Name Town State Number weather. This, then, was the method selected for of to the Australian Bird the project. surveys Count Responsibility for co-ordinating the project was Mrs K. Hastwell Kinglake VIC 2896 given to Dr Stephen Ambrose, initially from Sydney S. Telford West Armadale WA 2617 and then from the new Melbourne headquarters of The Wardens Norseman WA 1957 Birds Australia, where he was appointed as Research D. Latham Armidale NSW 1400 and Conservation Manager. Funding for initial work R. Watson Coffs Harbour NSW 1169 was obtained from the Federal Government through F. Ormsby Bondi Junction NSW 1018 the Australian Nature Conservation Agency (now Mrs S. Rooke Nambour QLD 951 D. Lockwood Clayton South VIC 848 Environment Australia), and BP Australia R. Canning Mt Barker SA 755 generously offered a major sponsorship amounting J. Gleeson Evatt ACT 649 to $250,000 over five years. With funding secured, N. Cruickshank Tea Gardens NSW 608 the field project began in 1989, and the Australian J. Bannister Alice Springs NT 579 Bird Count – the ABC – was born. C. Whiteoak Coolum Beach QLD 538 J. Lacey Red Lion via Talbot VIC 532 P. Slack Nelson Bay NSW 532 THE COUNT F. Bigg Bribie Island QLD 526 Between January 1989 and August 1995, 952 C. Hall Paynesville VIC 450 observers carried out 78,938 standard surveys at Mrs H. Wilson Winnellie NT 432 1681 different locations throughout Australia B.L. Schmidt Hawthorndene NSW 407 Mrs C. Clarke Annandale NSW 406 (Figure 1). Others took part intermittently, or R. Swaby Malvern QLD 400 helped with initial testing; altogether, over 2000 J. Morrison Albany WA 387 sites were surveyed by 1020 people. Observers were Miss M. Pywell Irymple VIC 380 asked to select groups of three sites each of about S. Lloyd Birralee TAS 371 3 hectares, close to each other and in a similar broad S. Waddell Stanmore NSW 371 habitat type. Birds were counted regularly on those D. James Forrestdale WA 360 sites by 20-minute area-search at least twice a year (summer and winter), but monthly if possible. Forms were used to record the basic details of the location and habitat at each site. Simpler forms were used for submitting count details. Birds observed off-site were recorded, but not included in the main data base. Survey locations were predictably biased towards areas close to human population centres. As a result, the eastern half of Australia and the south-west of Western Australia received the most intensive coverage. But observers, like some of the birds they admire, are somewhat migratory. Northern and inland parts of the continent were surveyed more often during the cooler, drier months of the year than during the summer wet season. Surveys in these remote locations by intrepid observers during the wet season thus became particularly valuable. Many observers took up the challenge of surveying their sites on a monthly basis, or even more frequently. Some even provided series of long- term counts from before the ABC. Table 1 shows the observers who contributed the most number of Figure 1 surveys to the count. enormously by the fortuitous return to Australia of Peter Griffioen, from a computer programming career in California’s Silicon Valley. Figure 1 Locations of the PUTTING THE DATA TO WORK Peter wanted to use his skills to build a new sites at which ABC surveys With any large data set it is never easy to interpret career in conservation, and was quickly introduced were made. data and present it in an easily digestible form. to the project and Mike Clarke of La Trobe Modern computer technology has helped University as an academic supervisor. Together they immensely, but special skills are needed to make the have cleaned up the data base and developed some best use of these new tools. The project benefited powerful visual tools for viewing it, including iv Australian Bird Count For flocking species such as animated graphics of seasonal movements. In this species in the region, as recorded by ABC surveyors. the Straw-necked Ibis, a article we are unfortunately confined to stationary Many bird surveys such as the Atlas of Australian change in reporting rate is graphics, but some animated versions can be viewed Birds collect data on a presence/absence basis, with not a good predictor of a change in abundance. via links on the Birds Australia website: no measure of numerical abundance at each site. Photo by Graeme Chapman www.birdsaustralia.com.au. Measures of ‘reporting rate’ (the proportion of surveys in which a species is detected) are sometimes Reporting rate vs abundance taken as approximate measures of regional Two of the major strengths of the ABC data are the abundance, but how reliable is this? For example, if intensive repeated surveying effort observers put in at Rufous Whistlers were recorded in 75 of 100 fixed sites over several years, and the collection of summer surveys within the catchment of the numerical information. This makes it possible to see Murrumbidgee River, and in 10 of 100 winter how well changes in the ‘reporting rate’ of a species surveys in the same region, it might be concluded in a region reflected changes in abundance of that that there were more Rufous Whistlers in this region in the summer – but perhaps they were simply more widespread in summer and more concentrated in winter. We really need to estimate the relative number of individuals present during each period. The ABC surveyors did this, and so created a unique data set with which to examine the strength of this relationship between reporting rates and a species’ regional abundance. Peter Griffioen’s analyses revealed that, for most species, there was a very strong relationship Figure 2 The relationship between the reporting rate and the abundance of between reporting rate the species in the region, as reported by the ABC and mean abundance Figure 2a contributors. (The average correlation coefficient (birds detected per hectare for 512 species sampled was 0.81 ± 0.17, calculated in a 20-minute survey), using the method of Nachman.5) The relationship based upon ABC data, for (a) Red Wattlebird, and was strong for most species examined, such as the (b) Straw-necked Ibis. Red Wattlebird (Figure 2a). The red lines represent 95 per cent confidence intervals. In other words, we can be 95 per cent certain that our estimate of this species’ abundance for a particular reporting rate lies between the two red lines. But the confidence intervals for species that can form large flocks (such as the Straw-necked Ibis, Figure 2b) are much further apart, so changes in reporting rate will not be a good predictor of changes in that Figure 2b species’ abundance. Australian Bird Count v Regional changes in abundance Thanks to the sterling efforts of thousands of Information about the timing of movements is volunteers, Birds Australia and affiliated rarely obtainable from large-scale bird-banding. ornithological organisations possess some In a country the size of Australia, the chance of a extraordinarily large data sets. These include the bush bird that has been banded in one location first Atlas of Australian Birds, the NSW Atlas, and the Canberra Ornithologists Group’s data base. being recaptured (or the band recovered) in another With the computerisation of these data bases, they location is very small, since there are few people can now be combined to provide a very powerful and the area needing to be covered is immense. research tool. The core of this power lies in the For example, by 1995 about 270,000 Silvereyes huge number of surveys it represents – more than had been banded in Australia,6 but only 458 4.5 million records.