Movements and cumulative range size of the platypus (Ornithorhynchus anatinus) inferred from mark–recapture studies

Abstract

The extent of mammalian movements often varies with size, sex and/or reproductive status. Fyke nets were set along streams and rivers near Melbourne (southern Victoria) from the mid-1990s to 2007, and in the Wimmera River catchment (western Victoria) from 1997 to 2005, to assess how far platypus of different age and sex classes travelled between captures and over longer periods. The mean distance between consecutive captures of adults did not vary significantly as intervals increased from 1–3 months to >3 years, suggesting that most individuals occupied stable ranges. However, adult females travelled, on average, only 35% as far between captures as males in southern Victoria, and 29% as far in the Wimmera. Up to half of this difference may be explained by variation in size-related metabolic requirements. Immature males and females respectively moved 61% and 53% as far, on average, as their adult equivalents, although two young males dispersed >40 km. Adults incrementally occupied up to 13.9 km of channel in the case of a male (based on six captures over 67 months) and 4.4 km of channel in the case of a female (based on five captures over 127 months).

Novel use of in-stream microchip readers to monitor wild platypuses.

“…Suggested causes of failure to recapture certain individuals during longitudinal live capture studies have focussed on a likely high degree of mobility of certain individuals, including individuals with large ranges, individuals with a nomadic or roving breeding strategy, nonbreeding individuals unable to find a vacant home range, and transient occupation of an area (Grant, 2004;Bethge, 2009;Serena & Williams, 2013). Such explanations would be consistent with certain platypuses not being detected in this study.…”

“…Importantly, during the 13 months of the study, the detection rates of platypuses microchipped at the monitoring sites (72% of the platypuses microchipped in 2011-2012 and 43% of those microchipped in [2007][2008] were similar to the recapture rates achieved during repeated live capture studies performed by Grant (2004) over ~30 years and Serena & Williams (2013) in two areas over ~8 and 12 years. The results of the direction of movement investigations, the absence of a significant effect of length of monitoring on the number of platypus observations at each site and for each individual platypus, and the regular and frequent observations from two platypuses further reinforce our conclusion.…”

“…Secondly, radiotracking has shown platypuses using certain parts of their home ranges more frequently than others (Gardner and Serena 1995;Gust and Handasyde, 1995). Lastly, a long-term mark-recapture study found that the home ranges of male platypuses were significantly larger than those of females (Serena and Williams, 2013). The variation of frequency of observations for those individuals that were detected in this study (Fig.…”

“…At the time of writing the use of acoustic transmitters has not been reported in detail, however, each of the other listed methods of monitoring platypuses has limitations (Grant 2009;Gust and Griffiths 2010). For instance, while live capture studies provide detailed information on individuals, they are very labour intensive and often have low recapture rates -36% of 271 males and 51% of 429 females over ~30 years in the Upper Shoalhaven River reported by Grant, (2004), and 58% of males and 73% of females over ~12 years near Melbourne and 38% of males and 31% of females over 8 years in the Wimmera River reported by Serena and Williams (2013 A variety of techniques have been used to monitor platypus populations to assess the impacts of the threats they face, but each technique has limitations. In this study we investigated the novel use of in-stream microchip readers, to remotely monitor the movements of microchipped wild platypuses.…”

Insights into platypus population structure and history from whole-genome sequencing

“…These observations are consistent with an underlying pattern of limited dispersal of (at least some) relatives. This is somewhat surprising given that previous studies using mark-recapture approaches in the Shoalhaven River (Grant, 2004b;Bino and Grant, 2015) and other streams (Serena, 2012;Serena et al, 2014) have reported the dispersal of a high proportion of juveniles, especially males, few recaptures of adult males, and the continued capture of unmarked males and females. Of all the pairs of relatives we sampled at the same site, most were female-female or male-female, and not male-male (there are only three male-male relative pairs in Table S4), which is consistent with male-biased dispersal.…”