Tree hollows[1]:

How hollows are formed

-         Take up to 120 or150 years to form (p.2). For large species sometimes need trees to be 220 years old (p.34). But can start from young age e.g. some as young as 35-30yrs (p.47).

-         Trees needs to be stressed or injured e.g. by fire, logging damage, bored by insects (p.35). Heartwood must be in decay (often by termites or fungi); often when a branch breaks and exposed heartwood is decaying a hollow will form (p.34). Some species e.g. parrots, cockatoos will contribute to faster rate of hollow formation but will not create a hollow in a healthy tree (p.38)

-         Tree hollows have to be managed on public lands. E.g. in Vic the loss of hollow-bearing trees in native forests has been listed as a threatening process in the Flora and Fauna Guarantee Act. Regional plans and agreements refer to protecting populations of hollow-using fauna. Hollows are being lost to silviculture, firewood collection, dieback, grazing and land-clearing for agriculture or other intensive resource use. (p.1) Fire tends to temporarily reduce but then increase presence of hollows.

o       But there is little data that adequately describes the distribution and abundance of hollows in natural or managed landscapes. Managed landscapes tend to have 10-50% less hollows than natural areas (p.151).

Usage

-         Used by fauna for shelter , rearing young (i.e. seasonal), feeding, thermoregulation, to facilitate ranging behaviour (e.g. nocturnal roost sites p.10) and dispersal. Many hollow-dwelling species are threatened.

o       About 15% of all birds, 10% reptiles, 31% mammals (p.4), 13% frogs (amphibians) (p.6), 66% bats (mammals, as diurnal roosts (ie during the day) and maternity colonies p.15)

o       An estimated 303 native vertebrate species use tree hollows

-         For many species there are no alternatives (p.1).

o       Opportunistic users include Common Ringtail Possums, Sugar Gliders, Long Eared Bats (p.5) but this is habitat and climate dependent. E.g. in cold climate such as Snow Gum areas possums seem to have no alternative (p.6); Peregrine falcons use hollows in River Red Gum woodlands (p.6).

-         Native fauna face competition from Myrna birds, Common Starlings, House Sparrows, Tree Sparrows and Mallards (p.10) and European honeybees (p.2) as do native Galahs, Little Corellas and Common Brushtail Possum (p.2).

-         Some species prey on eggs and species in hollows e.g. Currawongs prey on eggs and nestlings in hollows (p.10), a Forest Raven has been observed taking a Feather Gliders, Grey Butcherbird has been seen taking a Kookaburra (p.10).

-         If tree hollow numbers suddenly decline, this can lead to increased predation (p.151).