Based on platypus mark-recapture studies in Victoria and acoustic-tag tracking studies in New South Wales, adult males typically travel around three times farther than adult females over times periods ranging from a few weeks to more than a year (Serena and Williams 2013; Bino et al. 2018). Up to half of this difference may reflect the fact that males generally weigh more than females and so have to find food in larger areas to meet their energy needs (Serena and Williams 2013). An adult male is also undoubtedly motivated to include two or more female home ranges within his own home range to improve his prospects for mating (Gardner and Serena 1995; Serena and Williams 2013). Though adult males appear to try to avoid coming into direct contact with each other, especially just before and during the breeding season, male home ranges often overlap to some extent (Gardner and Serena 1995; Gust and Handasyde 1995). Female home ranges also typically overlap, in a well-ordered manner that ensures that each female has enough room to raise her offspring successfully (Serena 1994). To date, the longest platypus home ranges have respectively measured 18.8 kilometres in the case of a male (Bino et al. 2018) and 6.0 kilometres in the case of a female (Griffiths et al. 2014) in length.
The size of a platypus’s daily foraging area can vary in different places, presumably in response to how food resources are distributed and the amount of competition for food. Individual daily activity areas in a subalpine Tasmanian lake (Lake Lea) comprised 3 to 35 hectares for males (up to 25% of the total surface area) and 2 to 58 hectares for females (up to 41% of the surface area) (Otley et al. 2000). By comparison, daily foraging areas used by animals occupying a small stream in the Yarra catchment in southern Victoria (Badger Creek) comprised 0.4 hectares on average (Serena 1994). A platypus has been known to travel up to 4.0 kilometres (in the case of an adult female) or 10.4 kilometres (in the case of an adult male, including backtracking) along a creek or river channel in a given activity period (Serena et al. 1998).
Juvenile dispersal is believed to be an important mechanism for repopulating vacant platypus home ranges and promoting genetic exchange. It’s been well established through both mark-recapture and genetic studies that young males move farther on average as compared to young females (Furlan et al. 2013; Serena and Williams 2013). Young females are also much more likely to settle near the place where they grew up (Grant 2004; Serena et al. 2014).
The number of juveniles captured in live-trapping studies in Victorian streams drops quite sharply in late autumn, suggesting that many juveniles initiate dispersal at this time of year (Serena and Williams 2012). Young dispersing males have been documented to travel at least 43 kilometres in the Yarra River system and nearly 45 kilometres in the Wimmera River system, and undoubtedly may sometimes venture much farther (Serena and Williams 2013).
Photos courtesy of L. Berzins (top), B. Catherine (bottom)
LITERATURE CITED
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