The field biology of the platypus, Ornithorhynchus anatinus , was first studied by a number of expatriate biologists who visited the Australian colonies to collect specimens in the 1800s. Their work was followed in the early to mid–1900s by a group of resident natural historians and later by an increasing number of academic biologists. All of these workers contributed significantly to the current understanding of the field biology of this unique Australian species. The platypus occupies much the same general distribution as it did prior to European occupation of Australia, except for its loss from the state of South Australia. However, local changes and fragmentation of distribution due to human modification of its habitat are documented. The species currently inhabits eastern Australia from around Cooktown in the north to Tasmania in the south. Although not found in the west–flowing rivers of northern Queensland, it inhabits the upper reaches of rivers flowing to the west and north of the dividing ranges in the south of the state and in New South Wales and Victoria. Its current and historical abundance, however, is less well known and it has probably declined in numbers, although still being considered as common over most of its current range. The species was extensively hunted for its fur until around this turn of this century. The platypus is mostly nocturnal in its foraging activities, being predominantly an opportunistic carnivore of benthic invertebrates. The species is homeothermic, maintaining its low body temperature (32°C), even while foraging for hours in water below 5°C. Its major habitat requirements include both riverine and riparian features which maintain a supply of benthic prey species and consolidated banks into which resting and nesting burrows can be excavated. The species exhibits a single breeding season, with mating occurring in late winter or spring and young first emerging into the water after 3—4 months of nurture by the lactating females in the nesting burrows. Natural history observations, mark and recapture studies and preliminary investigations of population genetics indicate the possibility of resident and transient members of populations and suggest a polygynous mating system. Recent field studies have largely confirmed and extended the work of the early biologists and natural historians.

Field biology of the platypus (Ornithorhynchus anatinus): historical and current perspectives

While the diet of the platypus (Ornithorhynchus anatinus) is known to include a wide range of benthic macro-invertebrates, little is known about how the animals distribute their feeding behaviour along a waterway. This radio-tracking study aimed to determine whether the spatial distribution of platypus foraging activity varied in relation to habitat attributes and/or the amount of food present along a southern Victorian stream. Five O. anatinus were tracked nocturnally for a total of nearly 95 h in March and April 2000. Attributes of the channel and bank were described both in the area used by the animals and adjoining unused sections of stream, and macro-invertebrates were sampled quantitatively in six substrates that varied in abundance in the used and unused areas. Eleven habitat variables showed a significant positive relationship with the occurrence of platypus activity (including the number of medium and large Eucalyptus, Acacia and Populus trees growing along the bank; presence of gravel, pebbles, cobbles, large rocks and coarse particulate organic matter in the channel substrate; amount of riffle habitat; amount of large woody debris in the channel; and amount of undercut banks). Six habitat variables showed a significant negative relationship with platypus activity (including the number of medium and large Salix trees growing along the bank; the presence of silt, solid clay and Salix roots in the channel substrate; the amount of pool habitat; and the maximum channel depth). Substrates that were relatively abundant in the area used by O. anatinus (gravel/pebbles, Eucalyptus litter, Populus litter) did not consistently support more macro-invertebrates than substrates that dominated the unused area (silt, Salix roots, Salix litter). This may reflect the fact that the platypus population was not food-limited (and hence not under pressure to optimise foraging) at the time of the study, that platypus feeding patterns were influenced by habitat features that were not considered in relation to invertebrate abundance, or that the choice of foraging areas by O. anatinus may be influenced by factors other than the total abundance of food items, e.g. the nutritional quality and/or accessibility of prey.

Effect of food availability and habitat on the distribution of platypus (Ornithorhynchus anatinus) foraging activity

Live-trapping surveys recorded populations of the platypus, Ornithorhynchus anatinus, in 73% of 45 reaches in the Dandenong Creek and Werribee, Yarra, Maribyrnong, Bunyip, and Lang Lang River catchments near Melbourne, Victoria; however, many populations occurred at low density. Our study investigated the relationship between population status and water and sediment quality along 28 stream reaches, including 17 reaches supporting a population of O. anatinus and 11 reaches lacking a resident population. Stream attributes included surface water-quality variables (summer concentrations of dissolved O2, total P [TP], NOX, total Kjeldahl N [TKN], dissolved organic N, NH4-N, and 50th, 75th, and 90th percentiles of suspended solids [SS]), concentrations of sediment toxicants (Zn, Pb, Cd, As, Cr, Cu, Hg, Ni), extent of catchment urbanization (as indicated by % imperviousness), and daily discharge. Reaches supporting a medium-density population (mean number of ≥0.5 adults or subadults captured per pair of ...

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Relationship of sediment toxicants and water quality to the distribution of platypus populations in urban streams

The platypus (Ornithorhynchus anatinus) is one of the world’s most evolutionarily distinct mammals, one of five extant species of egg-laying mammals, and the only living species within the family Ornithorhynchidae. Modern platypuses are endemic to eastern mainland Australia, Tasmania, and adjacent King Island, with a small introduced population on Kangaroo Island, South Australia, and are widely distributed in permanent river systems from tropical to alpine environments. Accumulating knowledge and technological advancements have provided insights into many aspects of its evolutionary history and biology but have also raised concern about significant knowledge gaps surrounding distribution, population sizes, and trends. The platypus’ distribution coincides with many of Australia’s major threatening processes, including highly regulated and disrupted rivers, intensive habitat destruction, and fragmentation, and they were extensively hunted for their fur until the early 20th century. Emerging evidence of local population declines and extinctions identifies that ecological thresholds have been crossed in some populations and, if threats are not addressed, the species will continue to decline. In 2016, the IUCN Red Listing for the platypus was elevated to “Near Threatened,” but the platypus remains unlisted on threatened species schedules of any Australian state, apart from South Australia, or nationally. In this synthesis, we review the evolutionary history, genetics, biology, and ecology of this extraordinary mammal and highlight prevailing threats. We also outline future research directions and challenges that need to be met to help conserve the species.

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The platypus: evolutionary history, biology, and an uncertain future

This study examined the occurrence, relative abundance and condition of platypuses in the upper catchment of the South Esk River, in north-east Tasmania, Australia, and the impact of past forestry activities on the occurrence of platypuses in first order headwater streams. The main trapping sites were in twenty first order streams, eight second-fourth order headwater streams and one fifth order stream reach. Additional trapping was also undertaken in the South Esk River and farm dams. Sites were trapped during late spring/mid summer and early autumn. A total of 78 individuals were caught in the study area. Platypuses were caught at all sites trapped in the second-fourth order and fifth order stream reaches and in nine of the twenty first order streams. Catch success was greatest in the fifth order stream reach and lowest in the first order streams. There was a trend toward a higher proportion of juvenile/subadult males in the lower order stream sites. For the higher stream orders, a higher proportion of individuals was caught during the summer, however for the first order streams, a higher proportion was caught during the autumn trapping period.
Information collected on the body mass, body length and condition of individuals indicated smaller individuals with a higher tail fat index in the lower order streams.
There was a trend toward a lower occurrence of platypuses in the first order streams, which had been disturbed 15 years previously by forestry operations compared to first order streams with relatively undisturbed catchments. Differences in occurrence of platypuses were related to differences in the 'in-stream' and riparian characteristics of disturbed streams compared to undisturbed streams. Headwater streams form a large proportion of a river system. Although they provide more marginal habitat for the platypus than larger river reaches, their disturbance may be an important land management issue in the conservation of this species, particularly in river catchments where the species is impacted by other environmental changes or disease.

The platypus Ornithorhynchus anatinus in headwater streams, and effects of pre-Code forest clearfelling, in the South Esk River catchment, Tasmania, Australia

Bryant (1993) collected extensive data on the habitat preferences of the platypus (Ornithorhynchus anatinus) measured in 36 pools in the upper Macquarie River system. Platypus presence or absence in these pools was measured on three occasions. Detailed modelling of the factors affecting pool preference was complicated by the scale of response being ordinal due to the inability of the observer to distinguish between repeated sightings of the same animal and several different animals. Initial modelling using logistic regression on a presence/absence index, collapsed from the ordinal response, discounted time of day and seasonal effects. These temporal simplifications allowed a binomial analysis of success rate based on the three visits, which identified an additional habitat factor not identified in the original analysis. Finally, a full ordinal regression of the proportions falling into each ordered category is presented as the ultimate modelling of platypus pooI preferences. The analysis indicated that length and depth of pools and the presence of overhanging vegetation were positively related to the observed presence of platypuses.

B.A. Ellem

Papers

Statistical Modelling of Platypus, Ornithorhynchus anatinus, Habitat Preferences Using Generalised Linear Models.