Prof Don Bradshaw presented a talk on this tiny, rare WA mammal that is neither a possum nor a devourer of honey.
Professor Don Bradshaw, Chair of Zoology and Senior Honorary Research Fellow at the School of Animal Biology at UWA, presented a talk on Honey Possums to a well-attended meeting on April 8. Both Don and his wife Felicity have been involved in many years of Honey Possum research.
This illustrated talk presented some aspects of this tiny, rare Western Australian mammal that is neither a possum nor a devourer of honey. Unique to Western Australian Banksia woodlands, the Honey Possum has an ancient lineage dating back over 40 million years and is not related to any other Australian marsupials. Although the Honey Possum is classed in a separate family, the Tarsipedidae, DNA evidence traces it to a small marsupial called the Monito del Monte (Dromiciops gliroides) found in Chile. Its origins are considered to have been in South America when it was part of Gondwana, with the migration of its forebears to Australia occurring via the early Antarctic continent.
The Honey Possum was first named in 1842 as Tarsipes spenserae but it was discovered that the first published description of this animal shortly predated this event. It had been described and named Tarsipes rostratus by French naturalists Gervais and Verreaux and their written account—also in 1842—took precedence. The original specimen is preserved in the Natural History Museum in Paris. The Honey Possum features in an illustration by Gould in 1863.
Originally found north of Perth and east of Esperance, the Honey Possum is now found principally in south-west WA, such as at the Scott and Fitzgerald River National Parks.
The Honey Possum is a very small mammal weighing about 4mg at birth, the smallest birth weight of any mammal known and attains a weight of up to 10g at maturity. The female is larger than the male and is more aggressive and promiscuous; the male has a lifespan of about one year and has some unique accoutrements—the largest testes (relative to body size) and the largest sperm of any mammal. Mating takes place within 24 hours of the female giving birth and the female exhibits embryonic diapause.
Feeding exclusively on the pollen and nectar of flowers, a Honey Possum is well adapted to this specialist diet and feeds using its long bristled tongue (left). It is also an important pollinator in areas where species from the groups Proteaceae, Myrtaceae and Ericaceae have established. Honey Possums spend quite a bit of time on the ground and laboratory work is conducted on individuals caught in pit traps. Once caught, the animals go into a state of torpor and can even be kept in the refrigerator. Following various tests, the animals receive an energy boosting meal and are released unharmed.
Research work covers many aspects: the choice of preferred flowers, the amount of nectar that is ingested, determining how pollen is digested and the amount required for nutritional needs, and assessing the balance of their apparently high carbohydrate-rich diet. Some of this research involves the use of oxygen, nitrogen and sodium isotopes as tracers: O₁₈ measuring energy intake, H isotopes to measure water intake, hydrogen (deuterium and tritium) and sodium (Na₂₂) are used to measure nectar intake. Pollen intake is then measured by subtracting nectar intake from the daily total. From these data the field metabolic rate can be deduced. As an example, a 9g individual consumes on average 7ml of nectar and 1g of pollen per day. The field metabolic rate is smaller than that of small insectivorous mammals, averaging 30 kilojoules per day.
Pollen as a foodstuff is high in carbohydrate and has a protein content of between 36 and 42 per cent, but has been previously considered indigestible. The minimum daily requirement of nitrogen has been calculated as 2.8mg per day for a 9g Honey Possum. Results have shown that the 1g average weight of pollen per day actually consumed provides approximately 30mg of nitrogen, an amount far greater than required. Studies of pollen grains from the animals’ digestive tract (scats) can identify the primary source food species as well as the chemistry of how pollen is digested.
For research into the activities of the Honey Possum, radio collars are used for tracking. These collars weigh less than 1g although they appear relatively massive when seen on a tiny mammal. Evidence shows that they travel quite large distances (about 0.5km), with some males occupying an area of about 0.8 hectares and when food sources are scarce they may journey several kilometres. By contrast, female Honey Possums are more sedentary.
Honey Possums have no means of protection and being largely ground dwelling they are highly vulnerable. Factors that threaten them include fire, habitat changes caused by declining rainfall and die-back, and predation by birds and feral animals such as foxes and cats. In spite of set-backs and ongoing environmental changes the endearing and diminutive Honey Possum is not listed as endangered.
Both Don and Felicity are prolific authors having published a prodigious list of scientific papers, many featuring aspects of their research work on Honey Possums. Felicity is also author of a beautifully illustrated children’s book: A Tale of Two Honey Possums, featuring a factual yet adventurous story about Honey Possums. A copy is in the WANats (JNR) library.