“Species share roosts sites, but segregate spatially within” & “Large influxes of species into roosts (especially little red flying-foxes) can displace other species” & “Species roost at different heights”
The range of black flying-foxes underwent a phase of rapid southern expansion in the late 1990s and early 2000s, increasing the area of overlap with grey-headed flying-foxes (Roberts et al. 2012a). As the two species co-occupy roosts where their distributions overlap, this process has substantially increased the number of roosts occupied by both species, and thereby increased the pertinence of understanding the structure of mixed species roosts. There has been relatively little formal documentation of species overlap and segregation within roosts. Ratcliffe (1932) noted that sections of roosts were occupied by different species - specifically, that little red flying-foxes and black flying-foxes occupied different areas. Some horizontal separation has also been noted by Nelson (1965b) and Klose et al. (2009), and notes of displacement by little red flying-fox have been described in Birt and Markus (1999). We contribute quantitative, spatial information on the extent and overlap little red flying-fox, black flying-fox and grey-headed flying-fox, extending on the predominantly anecdotal observations underlying management documents to date. Findings from our data support common understandings of flying-fox roost structure: species commonly showed preferences for discrete areas of roosts, and even more commonly, preference for occupation of separate trees. We also observed segregation of species by roosting height, with black flying-fox foxes showing the highest roosting, followed by grey-headed flying-foxes and little red flying-foxes. These findings flag the importance of species monitoring of roost sites prior to management interventions. It cannot be assumed, for example, that species occupy areas of the roost uniformly, and management actions need to consider areas that may be more or less important to vulnerable species, like the grey-headed flying-fox. These results also give interesting insights into understanding disease transmission dynamics within roosts, relating to the extent of mixing of primary host species (e.g. black flying-foxes for Hendra virus) and other species presumed to be incidental hosts (e.g. grey-headed and little red flying-foxes).