Brown antechinus: peak cuteness

Names: Brown antechinus (Antechinus stuartii), marsupial mouse

Size: Length around 10cm; weight 35g (males), 20g (females)

Diet: Insects, spiders, sometimes other small animals, occasional fruit

Habitat/range: South-eastern Australian forests

Conservation status: Least Concern

Superpower: Where do we start? Antechinus are extraordinary in almost every way. They are agile, acrobatic tree-climbers with fast reflexes and the fighting skills to subdue large spiders and centipedes. Their ankle joint rotates backwards, allowing them to run easily down tree trunks head-first – in a cage they will even run in a mouse exercise wheel upside down. They travel long distances each night, and share nests in tree hollows in groups that change location and composition each day.

Brownantechinus2 brett vercoe via inaturalist
Brown antechinus. Credit: Brett Vercoe via iNaturalist

Antechinus have an astounding life cycle that is unlike any other mammals other than their close relatives the phascogales, and another dasyurid, the kaluta.

Most of their life is spent feeding and growing as juveniles. They spend early September until Christmas as a nursing infant, five weeks in the pouch (yes, they are marsupials) then three months in the nest. By January the litter of eight weighs four times as much as their mother. Time for the young to be weaned, although they are far from adulthood at this stage – they won’t mature until June.

This is when the first strange event happens to males. They make sperm, store it in the epididymis, but then a month before the July mating season they stop making any more. With the clock ticking, a brief, intense mating season begins. Males don’t fight each other – they just go all out to impregnate females and limit their rivals’ . . . opportunities. Mating sessions can last for 12-14 hours. By prolonged mating, the male effectively blocks rivals’ access to the female, giving his sperm a head start. Males are constantly active and have astounding endurance.

The next peculiar event in the male life cycle? Strap yourselves in: this is when testosterone levels increase, while the feedback system that normally prevents the escalation of stress hormones fails. While male effort to win at sperm competition is dramatic, it’s the females that call the shots. Females have only one litter in a year, and they intensify male competition by having a brief, synchronised mating period.

Antechinus litter and nest box. 850
Brown antechinus litter. Credit: Diana Fisher

Males that have the most competitive sperm also father young that survive best, so females gain by mating with many males to promote sperm competition. But as circulating stress hormones continue to rise in the males, their immune systems collapse – fur falls out, skin disintegrates, and males inevitably die of internal bleeding and infections at eleven and a half months old, having competed for fertilisations at the expense of their own lives. Females store this sperm for two weeks, so there are no males at all in some populations – not even embryos – for two weeks after all males are dead. Only then do females conceive.

Things can be tough even for the newborns: because females give birth to more young than the number of teats, only the eight newborns that attach to a teat will survive.

Antechinus are sometimes confused with common house mice, but they don’t generally thrive in urban environments. Out in the bush they might build a spherical leaf nest in one of your cupboards. Put away that poison! They’re endearing little animals – cuter than any Disney cartoon creations! And definite candidates for Australian Mammal of the Year.

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