Document ID: chunk:federal_register_of_legislation:F2024L00482:reg:1:p4
Version: federal_register_of_legislation:F2024L00482
Segment Type: reg
Provision Reference: reg 1 (pt 4/16)
Character Range: 19652–22444

be between 60 and 338 individuals (Olah et al. 2020) noting that Ne is a parameter commonly used in population genetics to quantify loss of genetic variation in populations and it is often smaller than the census population size (Nc) (e.g. Wang et al. 2016).
While the current population size is uncertain, recent research has shown it is likely undergoing dramatic declines due to predation by Sugar Gliders (Heinsohn et al. 2015). Sugar Gliders are an introduced species to Tasmania (Campbell et al. 2018), and their impacts on Swift Parrots compound and add to other known threats including habitat loss and degradation. Stojanovic et al. (2014) found that Swift Parrot nests failed at a very high rate on the Tasmanian mainland, compared to no failure on offshore islands where Sugar Gliders were absent. Most cases of glider predation resulted in the death of the adult female, and always involved the death of either eggs or nestlings.
Heinsohn et al. (2015) constructed a population viability analysis (PVA) using demographic data gained from the Sugar Glider predation study and population monitoring (Stojanovic et al. 2014; Webb et al. 2014). Five scenarios were considered in the PVA. The first scenario was based on field data from Bruny and Maria Islands, which are both Sugar Glider free. This scenario estimated growth rates in the absence of Sugar Glider predation and projected a substantial increase in numbers over time. Four other PVA models were tested which accounted for Sugar Glider predation but used different generation times for Swift Parrots.
The mean decline over the four scenarios that included Sugar Glider predation was projected at 86.9 per cent (range over the four models was 78.8 to 94.7 per cent decline) over three generations. The preferred model by Heinsohn et al. (2015) projected that Swift Parrots would undergo an extreme decline of 94.7 per cent within a three-generation period. This model used a generation time of 5.4 years, which was obtained through expert elicitation (Garnett et al. 2011).
While research has found that that breeding success is much higher on Sugar Glider free islands (Stojanovic et al. 2014), this greater success was insufficient to buffer the population against collapse under the modelled scenarios (Heinsohn et al. 2015). More recent evidence shows that high predation by Sugar Gliders at some breeding sites has resulted in a change to the Swift Parrot mating system due to the rarity of adult females, resulting in even worse projected population declines based on PVA (Heinsohn et al. 2019).
Figure 1 Indicative distribution of the Swift Parrot in Australia
Figure 2 Potential breeding range of Swift Parrot in Tasmania
Note: Swift Parrot Important Breeding Areas (SPIBA) are known or suspected to have supported