REPRODUCTION
The reproductive characteristics of bandicoots and the bilby are such that, depending on favourable environmental conditions, they are able to achieve rates of reproduction greater than any other marsupial group.
All species are polyoestrous and capable of breeding throughout the year. The stimulatory influence of food availability and rainfall on breeding activity has been described for temperate zone and wet-dry tropical zone bandicoot species (Heinsohn 1966; Friend 1990). In the wet tropics where rainfall is more reliable, however, lengthening photoperiod seems to be the primary cue for initiating breeding (Vernes and Pope 2009). The oestrous cycle of bandicoots and the bilby is relatively short, ranging between 12 and 37 d. The length of the gestation period is also extremely short, ranging from 12 to 16 d (Jackson 2007). Despite the short gestation period, bandicoot and bilby young are born at a relatively advanced stage, compared with other marsupials, because of the nutrient exchange efficiency of their placental structure (Tyndale- Biscoe 2005). In the bilby, females separated from males were shown to be acyclic, despite olfactory and auditory contact (Ballantyne et al. 2009). Elevated progesterone levels and development of pouch glandular structures were noted within 5 d of introduction of the male. It is unclear whether luteal activity was subsequent to or preceding coitus. Plasma progesterone peaked in the bilby within 3 d of birth and although declining slightly was maintained at elevated levels throughout lactation (Bal- lantyne et al. 2009). In contrast, plasma progesterone concentration in the northern brown bandicoot declines to a basal level 19 d after parturition (Gemmell 1979).3.
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