“Individual roosts have distinguishable seasonal patterns of abundance and occupation”
All roost sites in our empirical dataset were occupied continuously throughout the year by adults and juveniles/sub-adults of both sexes. This type of roost occupation has been noted from 1981 onwards (Puddicombe 1981; Parry-Jones 1985) and has become common in recent decades (e.g. Aston 1987; Eby 1991; Larsen et al. 2002; Van der Ree et al. 2006). This pattern of occupation contrasts to the ‘summer’ and ‘winter’ pattern described historically by Nelson (1965a) and Nelson (1965b) and cited in the Flying-fox Roost Management Guideline for Queensland, where ‘summer roosts’ of reproducing individuals would form between ~September/October and April/May, and ‘winter roosts’ of dispersed animals would form between April/May and September (Ratcliffe 1931; Nelson 1965a; Nelson 1965b; Parry-Jones & Augee 1991; Parry-Jones & Augee 1992). For these roost types, overwintering animals at summer roosts were rare, and when present, were documented as being predominantly juveniles or lone adult males (Nelson 1965b).
While seasonally occupied colonies are still observed (e.g. Kloseet al. 2009), an increasing number of roosts are now consistently occupied year around, particularly in urban areas (Parry‐Jones & Augee 2001; Tait et al. 2014). The cyclic patterns of summer aggregation and winter dispersal were originally thought to reflect social drivers and availability of resources (Parry-Jones & Augee 1992). Specifically, territory formation (from January) and conception (from ~March) (P. poliocephalus and P. alecto ) (Welbergen 2005) coupled with abundant flowering of native flora in these months (Nelson 1965a), were understood to drive and support aggregative living in summer/autumn, while decreased food availability and the cessation of mating from ~May triggered the animals to disperse and adopt a less-gregarious living style in winter (Parry-Jones & Augee 1992). This ecology has changed in more recent decades, where continuous availability of exotic foods in urban areas has reduced the need for migratory behaviours and allows aggregate groups to remain year round (Parry‐Jones & Augee 2001; Williams et al. 2006).
Policy documents containing only historical information on flying-fox occupation patterns (including the most recent Flying-fox Roost Management Guideline for Queensland: State of Queensland Department of Environment and Science (2020)) are of concern, as recommendations based on historical usage patterns may be inconsistent with current usage patterns, particularly in urban areas where occupation patterns have changed the most (Larsen et al. 2002; Tait et al. 2014), and where human-bat conflict is often the highest (Kung et al.2015). Roost monitoring prior to management actions should encompass every season, and not assume that bats will disperse in winter. Similarly, contemporary overwintering roosts commonly contain individuals from all age and sex groups and may be consistently utilised through time (Larsen et al. 2002; Tait et al. 2014).