Bilby Blog

I've been really lucky over the past couple of years to be involved in conducting targeted searches and monitoring for the Greater Bilby. And even more lucky to have had some success in finding them! They truly are a bizarre and unique looking animal, one of Australia's most iconic species. In one incredible moment, I was fortunate to observe a true wild Bilby, in what was, and still is one of my greatest wildlife moments. I've also been lucky to have been involved in unexpectedly catching one in a large Elliot trap (trigger plate box trap with bait), so have actually felt and held one, a true honour! But to find Bilbie's, you don't look for animals, you look for their evidence...

The Greater Bilby (Macrotis lagotis), is called the Greater Bilby, because just 50 odd years ago, there used to also be a Lesser Bilby (Macrotis leucura). Smaller, but otherwise similar in resemblance and ecology, the Lesser Bilby was last seen in the 1960's in remote South Australian deserts. The Lesser Bilby unfortunately falls in to what is termed the Critical Weight Range mammal group, a group of arid dwelling Australian mammals between approximately 35-5500 grams, that have made up the majority of the 30 mammal extinctions since european settlement (the worst mammal extinction rate in the world, by the way). The reasons are generally attributed to introduced predators (cats and foxes), increased competition from feral species (rabbits), habitat degradation from farming and cattle, and changed fire patterns. I've always found it almost incomprehensible that so many species have gone extinct, literally within one or two generations. I distinctly remember looking through my dads "The Mammals of Australia" text book, and having a genuine sadness and confusion about page after page of illustrations (because there are no photos) of extinct mammals, and that pale blue range map that illustrated the vast areas they used to occupy. That same feeling still sticks inside me.

But no point dwelling on the past too much ey! The Greater Bilby certainly hasn't escaped unscathed, they have undergone a serious range contraction. They are now restricted to two disjunct populations, one in south-west Queensland, and the other throughout the Tanami and Sandy Deserts of NT and WA, west to the Pilbara and north to Dampier Peninsula near Broome. What is hard to consider is that Bilbies used to be present right where I live now, in the Jarrah and Wandoo woodlands of the darling scarp near my home of Perth. And where i grew up as a young fella down in Bridgetown represents just about their former south west range limit. In what is unlikely to be a coincidence, their range now appears to almost directly resemblance where foxes are absent. This range contraction and continued threatening processes has led to the Greater Bilby being listed as Vulnerable under the Environmental Protection and Biodiversity Conservation Act (1999), Australia's federal threatened species protection law.

Previous and current Greater Bilby distribution

The Greater Bilby is part of the family Thylacomyidae, of which there are just the two species (Greater and Lesser). They are most closely related to the bandicoots, and exhibit a number of similar features. They are of course marsupials, giving birth to poorly developed babies which develop in a pouch. They loooove to dig, and in a classic evolutionary adaptation, have a backwards opening pouch, to prevent all that pesky sand getting in your pouch as you dig your burrows. They are purely nocturnal, sheltering in their burrow during the day. Individuals may utilise up to 12 burrows at once. They are an opportunistic omnivore, feeding on seeds, bulbs, fruits, fungi, invertebrates and their larvae and small vertebrate fauna. They have long, pointed noses, for nosing around, and large ears for seeing well... wait... thats not right, what do they use those ears for?? (hint: read on).

So how do you find Bilbie's? This rare and cryptic species doesn't give itself up easily. Unlike many other mammal species, they are unreliable to trap. They are either too trap shy, or bait just doesn't appeal to them. So it is unusual to capture one in a trap, even when you know individuals are present (although not impossible, as proven below). So you need to look for diagnostic signs instead. In order of most commonly encountered, signs you are likely to encounter are; diggings, followed by tracks (depending on soil substrate), scats and finally burrows. 

When I'm in the field looking for Bilbie's, it almost feels like I'm trying to crack some criminal case. You need to build the evidence. First you will find a digging, but is it a Bilby? If it is, you need to search more and compile the evidence. Expand the search radius, diggings will become more frequent as you hone in on its key home range. Search for scats in the spoil heaps of diggings, if you can find their diagnostic scats, then you have confirmation. If you keep looking and the soil substrate is right, then you might be lucky to find some tracks. Then burrows start appearing. The final step is setting up motion cameras on the burrow and hoping to capture a photo. But it is important not to confuse the secondary evidence of Greater Bilby with other species, so below are some tips.

Diggings
Diggings are the most frequent form of evidence you will find, but can easily be confused with other species. The main confusion species include varanids (goannas), macropods (kangaroos and wallabies) and echidnas. Tips to separate from these species include:

• Varanids (goannas): Typically Bilby diggings are more frequent and higher density, so single and isolated diggings lean towards varanids. Varanids leave a similar pointy, conical shape, but often have a peak in the middle of one side of the burrow rim. This is because varanids dig by excavating with their legs in a sweeping motion either side of the body, opposed to Bilby which is more compact in their digging action (more like a rabbit).
• Macropods (kangaroos and wallabies): Generally a larger and messier digging, done in isolation or lower frequency in the immediate area.
• Echidnas: Can produce very similar small conical burrows. If you compare the noses of the two species, you can understand why as they are very similar. However, typically diggings are shallow and don't extend below nose length, compared to Bilby which often excavate much deeper diggings. Echidna diggings can also be far more messier, and its common for an entire square meter or more of ground surface will be disturbed, this would be unusual for Bilby.

Another hot tip to separate Bilby from the rest is if the digging is located at the base of shrubs. If you find diggings at the base of shrubs investigate further, if the digging goes in to a root and you can feel or see the root has been opened up, then you are 99% on to Bilbies. More on this in the habitat section.

Bilby digging at the base of an Acacia setallaticeps shrub. If you find diggings like these at the base of a shrub in to the roots, it's almost certainly a Bilby

Single isolated Bilby digging and scat. Scat is not always this easy to find.

A confusion species digging. This was done by an Echidna, typified by more 'messy' diggings over a larger area.

Scats
The scats of Greater Bilby are diagnostic and unlikely to be confused with any other species, so try hard to find them. They are small to medium in size, smooth and dense and cylindrical in shape. They can consist of a single pellet, or can be part of a string of pellets (sometimes joined). They are most commonly found in association with diggings (but you may have to search 60+ diggings first). Confusion species include macropods, but these are usually squarer and have a small point on one side, and also typically contain vegetation and are much lighter. Bilby scats are mostly dirt so are denser and heavier. I've heard Spectacled Hare-wallaby scats are quite similar, but are more laterally compressed. Don't think there is too much more out there to confuse with.

Greater Bilby scat. This one contains multiple pellets but single pellets may be found. Scats are cylindrical, smooth, and relatively dense as they contain lots of dirt.

Tracks
The tracks of the Greater Bilby are typical quadrapedal gait which includes all other dasyurids (carnivorous marsupials), that means their two back legs stay together but front feet overlay one in front of each other (slightly offset). Because they are larger then all other native species left in their range, their size distinguishes them from the rest. However, that wascilly wabbit (introduced European Rabbit) happens to exhibit very similar tracks in size and shape. If the soil substrate is soft then you can not distinguish between the two species, so you need to search for more evidence. If the substrate is firmer, then Bilby will leave a narrower foot pad in the track, and you may be able to see the diagnostic toe structure of the Bilby, compared to the softer and wider foot pads of Rabbits. In good tracking soil substrate, you should be able to track an individual some distance, hopefully leading you to their burrow.

Very fresh Bilby tracks from the night before in river sand after rainfall showing excellent track detail. You can clearly see the toe details in the hind and front feet, The tracks lead to the right.

Bilby tracks in soft sand showing no toe detail. These tracks could potentially belong to the European Rabbit, so if both species have potential to occur at the location you need to search for more evidence. Bilby heading to the right.

Sequence of tracks of Bilby in soft river sand. Bilby is heading to the left.

Burrows
Bilbie's live in burrows, and due to their large size can be the most conspicuous form of evidence to find. However, typically it takes longer to locate a burrow then other evidence if there is a Bilby in the area. Other burrowing species to confuse with are usually varanids (goannas) and rabbits. A Bilby burrow is almost perfectly round, and if anything is vertically elongated. Goannas in contrast, like all reptiles, have a horizontally compressed burrow entrance. Rabbits are more similar, but tend often be more trenchy, where as Bilbies are a nice hole leading straight in to the ground. Bilby burrows also often curve to the side once inside the entrance. DO NOT stick your hand down a burrow, I have seen many other fauna species (via motion cameras) such as venomous Mulga Snakes entering Bilby burrows, so use a spinifex seed head or similar if you want to poke something down the hole to see if it is open. When looking for burrows (and diggings) a useful give away is looking for a change in soil colour. The soil that has been excavated from sub-surface is typically a different colour, so it can be seen for some distance through vegetation that otherwise obscures a burrow. 

Active Bilby burrow from the Kimberley. Note the change in soil colour at the entrance of the burrow, a useful feature to look for whilst scanning through vegetation.

A very recently constructed Bilby burrow from the Pilbara. This one is at the base of a termite mound.

Motion cameras
One of the great technological advancements in biological studies of recent times has been the development of infra-red motion cameras. Even though once you have found Bilby evidence and an active burrow and therefore confirmed their presence, topping off the evidence with a motion camera photo is always nice. Below is a selection of photos and videos of some Bilby action from motion cameras that have been set up on active burrows.

This big male Bilby was captured on a burrow appropriately named "Big Hole"

A smaller Bilby (female or juvenile) from "Big Hole"

A large Bilby re-entering the burrow. Interestingly this photo was captured during twilight hours of 5:26 am. The Bilby is regarded as strictly nocturnal so this photo challenges that to some degree.

Habitat associations
One of the really important components of finding Bilbies is recognising and identifying suitable habitat. My experience is restricted to the Pilbara and Kimberley, so can't speak for the inland sandy desert regions. But in the areas I am familiar with, I am now very confident in identifying suitable habitat. Its typical of being able to find many threatened species, get your eye in for their specific habitat requirements, target those areas and consequently your success rate in detecting threatened species will go up. The other critical component is hard yakka! You need to put in the effort to find these guys, that means getting out there and walking. Some days I do well over 20 km stomping through potential habitat, and I'm definitely convinced the more ffort you put in, the more reward you get.

Being a burrowing species, soil substrate is a critical habitat attribute. Soil needs to be soft enough (typically sandy) to facilitate ease of digging, but not completely lose so a burrow won't hold its structure. In the Pilbara region, I have found a strong association of Bilby occurrence with minor drainage systems with fringing sand plain habitats. A dominant and key plant species at these locations is Acacia stellaticeps. Whilst in the Kimberley, I've had strong success in detecting Bilbies within stands of mature Acacia tumida woodlands. Although these two habitats don't appear overly similar, they provide similar structures. Firstly, a relatively open ground surface is available, I believe this allows the easy locomotion of Bilbies, so tehrefore is preferable. I have never found Bilbies in areas that contain dense spinifex or other grasses. Next, some aerial protection is provided by the canopy. Although not obvious in the below photo, Acacia stellaticeps is a shrub narrow at the base which spreads out providing an open ground layer with closed in canopy in dense growth areas. Finally, the presence of Acacia spp. shrubs are always present....

Classic Bilby habitat from the Pilbara, sandplain adjacent to minor drainage line with Acacia stellaticeps shrubs

Classic Bilby habitat in the Kimberley. Dense Acacia tumida woodland.

After a while of finding a strong correlation of Bilby diggings and Acacia species shrubs, the curiosity was building as to what the food source was. Was it the roots, or a fungi association, or some sort of insect larvae? Feeling around in the diggings showed the roots had been pried open, with a hollow cavity left inside the root itself. Then it was observed some funny insect shell casings were seen at the base of some of these shrubs. I needed to know more! So we started digging at the base of some of the shrubs and in one glorious moment all questions were answered, when we extracted the biggest, juicest, most ridiculous Witjuti grub I had ever seen. In that one fleeting moment it all became so obvious, Bilbies eat Witjuti grubs, and lots of them. And when you see the size of these things, its really not surprising why! Check out the size of that grub!

A bit of research shows Witjuti (also spelt Witchetty, but i like the indigenous spelling) is the larvae of the Australian Wood Moths, belonging to the genus Endoxyla. There are many species throughout the arid regions of Australia, which occur in association with various Acacia species shrubs. The hit rate of Bilbies per grub appears incredible. I reckon every digging i investigate at a shrub reveals the tell tale sign of root excavation and the cavity inside the root where a grub has been extracted. Remember those big ears? I reckon they must be used for listening for Witjuti grubs at night time, as they slowly bore and grind wood from inside the roots. Must be like the dinner bell ringing in their ears I reckon. I have confirmed Witjuti grub and Bilby diggings at the following shrub species; Acacia stellaticeps, Acacia bivenosa, Acacia trachycarpa, Acacia orthocarpa, Acacia collei and Acacia tumida. And if you want my opinion, those grubs actually taste pretty good....

Shell casing of a Witjuti grub that has exited from the shrub and metamorphosed  in to a Wood Moth

A seriously large and juicy Witjuti grub extracted from an Acacia trachycarpa shrub (below). No wonder Bilbies love these things, check out the size of it!

Acacia trachycarpa which the above Witjuti grub was extracted from

DNA scats analysis
An interesting development I have been recently involved in is the collection of Bilby scats, which consequently undergo DNA extraction and analysis, allowing for individual Bilby identification. One of the challenges with Greater Bilby is that they are completely unreliable to entice in to a trap. I can confirm the ineffectiveness of trapping, I've had cage traps all over a site that has multiple Bilbies present, confirmed through motion cameras and DNA analysis (as below), with zero captures! Thats not to say they are impossible to trap...


Anyway, the DNA scats analysis method has proven invaluable in being able to determine exactly how many individuals are present. Activity alone is a poor indicator of population numbers, as individual Bilbies can occupy up to 12 burrows within their home range. What I've found interesting is that the scats analysis is generally showing more individuals are around then you would expect. 

Bilby encounters

Finally, the really good part of the blog, actually seeing a Bilby! We were lucky enough to actually trap a Bilby a few years ago. It was completely unexpected, and had managed to cram itself inside a large elliot trap. Thankfully, she was unharmed. After taking some morphology measurements, a tissue sample from the ear and numerous photos, she was released. I was surprised at how soft and silky their fur is. 

The trap capture was good, but spotlighting one and watching it go about its business was better. In fact it is right up there with the best wildlife moment I've ever had. Never had I really thought I would ever see a real wild Bilby, so when it happened it was a surreal, but incredible moment. We had motion cameras set up on a burrow, whilst checking the camera during the day a Bilby had entered the burrow early morning, and appeared to have not come out, so we were confident there was one in the burrow. So we staked it out at dusk. 

The stake out was ridiculously short. I felt we got there too late and I was flustered, thinking we should have been there 30 minutes earlier prior to sunset, to allow our disturbance to settle. Regardless, we sat down and no more then 5 minutes later out popped a Bilby, unbelievable! I'm very thankful I had my new Canon 650D with me and chose to video the moment, because it allows me to relive the moment whenever I want. However I wish I had have bought a tripod at the same time! The combination of holding a headtorch, camera and trying to take it all in resulted in a slightly Blair Witch feel to it all, but I still enjoy it and hope you do to, I will never forget that moment!

ps I've had to chop the videos down in length to get under 100 mb...

An unexpected trap capture, a female Greater Bilby. A unique and slightly odd looking animal no doubt, but an absolute pleasure to hold and a great experience.

Getting to process a Bilby, very lucky chap!

One of my greatest wildlife moments, the pleasure to see and observe a wild Greater Bilby. I only took three photos, as I was focussed on video and taking in the moment. I''m glad this pic turned out the way it did :D