Bat listening results: October - December 2010
Analysis by Bob Bullen, BAT CALL WA Pty Ltd.
Photo by Terry Reardon.
The White-striped bat (Tadarida australis) is one of the largest insectivorous microbats in Australia. It is a fast flyer that forages in the open space above the tree canopy. It was chosen as a ClimateWatch indicator species because its foraging behaviour is limited by high night time temperatures. On an annual cycle it expands its range to the northern regions of the continent in April for the cooler winter months and then contracts to the south in October for the hotter summer months. It has been shown to be restricted to areas where the mean monthly minimum overnight temperature is 20°C (Bullen and McKenzie 2005). By understanding its distribution through the year scientists will therefore gain an insight into how this species is responding to our changing climate. This in effect is an early warning system that other subtle ecological changes are likely to be occurring.
The White-striped bat's echolocation call is powerful, distinctive and audible to human hearing making this species ideal for monitoring by Citizen Scientists. ClimateWatch, in association with the Citizen Science Program of the Conservation Council of WA, has begun to monitor the presence and absence of this species across Australia. A call to ClimateWatchers to listen out for the White-striped bat from 23rd October to 5th December 2010 was made and the results of this pilot project are presented here.
Results and Discussion
A total of 30 observations for the White-striped bat were recorded during the period 23rd October to 5th December 2010 (see Figure 1 below). These included 21 from WA, 8 from Victoria and 1 from NSW. Of these, 16 were recorded in the metropolitan areas of Perth, Melbourne and Sydney while 14 were recorded in rural areas. The daily rate of records received show an initial surge during Western Australia’s Conservation Week (23rd to 30th October 2010), followed by a steady rate of collection through November.
Figure 1. Daily rate of observations recorded for T. australis. The data show an initial surge during Conservation Week, 23-30 Oct, followed by a steady rate of data collection throughout November.
The presence and absence data collected during October and November of 2010 are presented in Figure 2 below. There are 16 presence records and 14 absence records in the data set. All data collected, with the exception of a single presence record from the Pilbara region of WA, are within the latitude that the species is expected during these months. These data, while preliminary in nature, show that the method of data collection employed by ClimateWatch can provide a viable method of monitoring the effect of temperature change on species such as T. australis.
The Pilbara record has been independently confirmed. It was taken at a site close to a meteorological station that has recorded overnight temperatures of 20°C during late October and early November. This bat is believed to be one that is late in departing for the south, probably associated with mild overnight temperatures, averaging 18°C at Newman, during October 2010.
Figure 2. ClimateWatch presence and absence data for the White-striped bat, T. australis during October and November of 2010. All presence data lie south of the latitude that the species would be expected to inhabit during these months, represented by the dotted line with the exception of a single, independently confirmed record taken in the Pilbara region of WA. This record was collected during October when the minimum overnight temperature at the site was 20°C.
Figure 3 below presents the monthly average minimum overnight temperature for the location where T. australis presence records were recorded. Temperature data are taken from the closest Bureau of Meteorology recording station to the presence record. These are all at or below the 20°C limit expected for the species.
Figure 3. Monthly average minimum temperatures for each of the presence records recorded for T. australis.
In summary, the observations collected through ClimateWatch for the White-striped bat from 23rd October to 5th December 2010 were successfully recorded. Over half of the records were recorded in the major cities of Perth, Melbourne and Sydney. To fully develop the potential of this monitoring program, it should be widely promoted in rural communities that are spread across the country.
ClimateWatch would like to thank Bob Bullen for the analysis of the data.