A platypus will starve in the absence of sufficient surface water in which to feed. However, animals can survive dry periods in an isolated refuge pool, as long as the pool is large enough to provide enough food in the form of aquatic insects and other invertebrates. If a pool continues to shrink, a platypus will have to weigh up the risk of starving versus the risk of being killed by a predator if it chooses to walk across land to find another place to live.
Adequate water flow also contributes to platypus breeding success both in urban and rural water courses, as shown by research conducted in streams near Melbourne (in Victoria) and in the upper Shoalhaven River (in New South Wales) (Serena et al. 2014; Serena and Grant 2017):
- In both study areas, reproductive success was positively related to the amount of rainfall or water flow recorded in the five months prior to mating (March to July).
- Virtually the same proportion of adults died each year in stable and declining platypus populations near Melbourne during the Millennium Drought. Population resilience was determined by reproductive success: in stable populations, the number of adults lost annually was matched by the number of new juvenile recruits to replace them.
- The most resilient population monitored near Melbourne during the Millennium Drought (Olinda Creek, in which 16 resident animals were lost and replaced by 17 new residents from 1997 to 2007) benefited from a reliable environmental flow of about 2 megalitres per day throughout the period.
Floods can harm platypus populations either directly (when animals drown) or indirectly (by damaging their habitat). The main direct mortality risk is to juveniles occupying nesting burrows, especially in the weeks soon before and immediately after the time that young animals first emerge from a burrow (Serena and Williams 2010; Serena et al. 2014; Serena and Grant 2017). Floods can degrade platypus habitat in a number of ways, notably by eroding banks and depositing unconsolidated sediment in the channel (as shown at right).
Photos: APC
LITERATURE CITED
Serena M and Grant TR (2017) Effect of flow on platypus (Ornithorhynchus anatinus) reproduction and related population processes in the upper Shoalhaven River. Australian Journal of Zoology 65, 130-139.
Serena M and Williams GA (2010) Factors contributing to platypus mortality in Victoria. The Victorian Naturalist 127, 178-183.
Serena M, Williams GA, Weeks AR and Griffiths J (2014) Variation in platypus (Ornithorhynchus anatinus) life-history attributes and population trajectories in urban streams. Australian Journal of Zoology 62, 223-234.