male antechinus Die en masse After mating From lethal levels of hormones

Nestled in the forests and woodlands of Australia, a peculiar group of small, mouse-like creatures scurry about in search of insects and other small prey.

These are the Antechinus, a genus of small marsupials native to Australia. Despite their resemblance to mice or shrews, these unusual little animals are more closely related to quolls and Tasmanian devils.

Physical Characteristics and Taxonomy

Antechinus are small marsupials characterized by their short, dense fur, which can vary in color from grayish to brownish depending on the species. They have thin, tapering tails that range from slightly shorter to slightly longer than their body length, and their heads are conical with small to medium-sized ears. Some species have a relatively long, narrow snout, giving them a shrew-like appearance.

There are currently 15 recognized species of Antechinus, with numerous subspecies. These species are divided into four main clades based on their geographic distribution and phylogenetic relationships. The most well-known species include the Agile Antechinus (A. agilis), the Brown Antechinus (A. stuartii), and the Dusky Antechinus (A. swainsonii).

Sexual dimorphism is present in most Antechinus species, with males typically being larger and heavier than females.

Adult Antechinus can range from 12 to 31 cm in length and weigh between 16 and 170 grams, with the Agile Antechinus being the smallest and the Dusky Antechinus being the largest.

Habitat and Distribution

Antechinus are found throughout the eastern coast of Australia, primarily along the Great Dividing Range, with some species extending into southern Western Australia and northern Australia. They inhabit a variety of habitats, including forests, woodlands, rainforests, heaths, and grasslands.

Antechinus are most commonly found in stringybark forests on the Fleurieu Peninsula and Central Mount Lofty Ranges regions. If you live in the Fleurieu Peninsula or the Adelaide Hills region (as far north as Para Wirra Conservation Park), there’s a possibility that the “mouse” in your house could be an antechinus.

In their natural habitat, antechinus typically reside in fallen timber and tree hollows.

To encourage them to move out of your house and take up residence outside, it’s essential to preserve these natural structures in your backyard or paddocks.

Most species are arboreal and nest communally in tree hollows, although some larger species, such as the Dusky Antechinus, are completely ground-dwelling. The microhabitat and foraging techniques vary between species, with smaller species like the Brown Antechinus being more scansorial and hunting in trees, while larger species forage in the leaf litter on the ground.

Diet and Foraging Behavior

Antechinus are primarily insectivorous, with their diet consisting mainly of beetles, insect larvae, and spiders. They also consume other invertebrates, such as amphipods, millipedes, and centipedes, and occasionally small vertebrates like skinks and feathertail gliders. The exact composition of their diet can vary depending on the species and habitat.

These marsupials are generally classified as dietary generalists and opportunists, as they eat a wide variety of prey and feed on most of the prey available to them. However, they do show preferences for certain prey items, especially when they are not food-stressed.

Antechinus have been observed employing various hunting strategies, such as jumping between branches to catch flying insects or scraping slugs on rocks to remove mucus and make them more palatable. As they age, Antechinus become more efficient hunters, learning which prey are the best to eat.

Sex, Death and Cannibalism

One of the most fascinating aspects of Antechinus biology is their unusual reproductive system. Females are synchronously monoestrous, meaning they have a single breeding season per year, with mating occurring over a short three-week period. The timing of the breeding season varies between species and populations, typically occurring in winter or early spring (July to September).

What sets Antechinus apart is the phenomenon of male semelparity, or male die-off, after the breeding season. During the intense mating period, which can last up to 12 hours for some species, males experience a surge in stress hormones (corticosteroids) that suppresses their immune system and causes gastrointestinal ulcers. This ultimately leads to the death of nearly all males shortly after mating, with survival being extremely rare. They are then feasted on by the surviving females.

The evolutionary advantages of this synchronous mating and male die-off are not entirely clear, but it is thought to ensure that as many matings as possible occur during the short breeding window and that males can focus all their efforts on a single breeding season. It may also help overwhelm predators with a large number of offspring after weaning.

Females often mate with multiple males, resulting in litters with multiple paternity. The gestation period varies between species, ranging from 25 to 35 days, and the offspring are independent after about 90-100 days, which is a relatively long development period compared to other similarly-sized marsupials.

Torpor: An Energy-Saving Adaptation

Antechinus employ an energy-saving strategy called torpor, which involves periodically lowering their body temperature and metabolic rate to reduce energy consumption. Unlike hibernation, which is long-term and largely dependent on ambient temperatures, Antechinus undergo daily torpor that lasts for a few hours and can occur even on warm summer days.

Torpor allows Antechinus to conserve energy and water during rest periods, especially when food is scarce. Smaller individuals, particularly females, are more likely to enter torpor and maintain lower body temperatures during torpor compared to larger males. Lactating females, however, do not enter torpor.

Antechinus have been observed increasing their use of torpor after intense bushfires, which destroy the dense undergrowth that provides them with shelter and food. By reducing their foraging needs, torpor helps them avoid predators and survive in the post-fire environment. Interestingly, smoke, ash, and charcoal serve as cues for torpor induction in these marsupials.

Conservation Threats and Status

Several Antechinus species, such as the Black-tailed Antechinus (A. arktos) and the Silver-headed Antechinus (A. argentus), are currently listed as endangered. The primary threats to these species, and indeed all Antechinus, are habitat destruction and introduced animals.

Deforestation and habitat degradation remove the complex understory vegetation that Antechinus rely on for protection from predators and foraging. The loss of senescent trees also reduces the availability of tree hollows, which are essential for nesting.

Introduced predators, such as foxes and cats, prey upon Antechinus, while introduced rats and mice compete with them for habitat and food resources. Pigs, cattle, and horses can also trample and degrade Antechinus habitats.

Climate change poses an additional threat, particularly to high-altitude species in northern Queensland, as it alters their habitat and food availability.

Antechinus or Mouse? How to Tell the Difference and Protect Native Species

If you’ve spotted a small, mouse-like creature scurrying around your home, take a closer look before setting up traps. While it might be a common house mouse, there’s a chance you could be dealing with a native yellow-footed antechinus (Antechinus flavipes). As a threatened species classified as vulnerable in South Australia, antechinus are protected under the National Parks and Wildlife Act (1972), and you must handle them differently than pesky mice.

Identifying Antechinus: Unique Physical Characteristics

At first glance, antechinus may resemble house mice, but upon closer inspection, several distinct features set them apart:

1. Snout shape – Antechinus have a much pointier, longer, and narrower snout compared to the round head and nose of a mouse.
2. Size – Antechinus are larger than mice, with a body length of up to 165 millimeters. They also have a tail that is approximately the same length as their body.
3. Facial features – Look for a white ring of fur around the eyes and double-lobed ears, which are unique to antechinus.
4. Coloration – Antechinus may have yellow feet, legs, and bellies, unlike the uniform coloration of mice.
5. Scent – While mice and rats produce a musky smell, antechinus have no lingering odor.
6. Scat appearance – Antechinus droppings are much larger and cylindrical in shape compared to mouse droppings.

Encouraging Antechinus to Relocate

If you’ve confirmed that your houseguest is indeed an antechinus, the next step is to gently encourage them to find a more suitable home outdoors.

1. Provide alternative shelter – Install a specially designed nest box in your yard, ensuring that it has the correct dimensions for antechinus. These marsupials require a vertically long nest box with a small entrance hole to prevent other animals from climbing in.
2. Maintain natural habitats – Preserve fallen timber and tree hollows in your outdoor spaces, as these provide essential shelter for antechinus and other native species.
3. Avoid using pesticides – Refrain from using harmful chemicals or traps that could injure or kill antechinus and other beneficial wildlife.

Fascinating Antechinus Facts

As you work to coexist with these unique marsupials, take a moment to appreciate some of their fascinating characteristics:

1. Antechinus primarily feed on insects, but they also consume flowers, nectar, spiders, cockroaches, lizards, small birds, and even mice, making them valuable for pest control.
2. Male antechinus have a remarkably short life span, dying by the end of the breeding season at about one year old.
3. Female antechinus can give birth to litters of up to 12 young at a time. The young drink milk and cling onto their mother’s “pouch” to survive.

Antechinus are a unique group of marsupials their unusual reproductive biology, with synchronous mating and male die-off, sets them apart from other mammals. Their ability to enter torpor showcases their adaptability to changing environmental conditions and resource availability.

Despite their remarkable adaptations, Antechinus face many threats, mostly from habitat loss and introduced species. Conservation efforts aimed at protecting and restoring their habitats, as well as controlling introduced predators and competitors, are crucial for ensuring the long-term survival of these intriguing marsupials.

As we continue to study and learn more about Antechinus, we gain a deeper appreciation for the incredible diversity and resilience of Australia’s unique fauna. By raising awareness about these small but significant creatures, we can inspire efforts to protect them and the ecosystems they inhabit for generations to come.