“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).