Owl Boxes

Over the past few weeks I've been lucky to be involved in a nest-box project for my friend Mike Lohr, who is currently conducting a PhD project researching the impacts of habitat fragmentation on one of our most beautiful nocturnal birds, the Gookamit or Southern Boobook Owl (Ninox boobook). Part of Mike's research is looking at the availability of nest hollows, which, in our highly modified landscape of housing estates, parks, cleared agricultural land and farm buildings, are becoming an increasingly scarce resource for many animals.

Mike checks a newly installed owl nest-box in a typical patch of remnant native vegetation in the WA Wheatbelt region, which completely lacks old-growth trees (click to image to enlarge).

 
With diverse native plants and a suite of insects as a potential food source, many patches of bushland at two of Mike's study sites (the Perth metropolitan area and the Wheatbelt region, near Kellerberrin) are potentially suitable to support pairs of breeding boobooks, but the lack of tree-hollows large enough for owls to nest in may be the limiting factor. To test whether the addition of nest-boxes might encourage boobooks to breed at sites where previous surveys have failed to detect them, Mike kindly engaged me to supply and install 30 owl boxes - 15 for each study area. I spent much of January designing boxes, based the measurements of some natural tree-hollow nests from my local area in the Perth Hills, and over the past week it's been great to get out and install them!

The above photo shows a typical installation site for an owl-box at the Wheatbelt site. This York Gum (Eucalyptus loxophleba), which is only a very young tree and one that will not form suitable owl-sized hollows for several hundred years, has now had its life increased substantially with the addition of a nest-box!

Each box is installed using a length of multi-strand, galvanised wire, threaded through a piece of old garden hose to protect the tree's bark. A loop is twisted in one end of the wire, and the other end is pushed through holes drilled in the back of the box, and passed around the trunk above a forked branch. Then the loose end can be threaded through the loop and twisted to secure it in place, and finally tucked away into the hose. This method follows the idea of Alan and Stacey Franks whose book 'Nest Boxes for Australian Wildlife: A Practical Guide' has been a valuable reference to me since I began building boxes as a teenager, and as I have found over years of nest-boxing since, there are many benefits of using it. It is quick and easy, requires only a few basic tools, ensures virtually no damage to the tree is caused, and it allows the box to be moved or taken down easily if necessary. Alternative methods used to mount nest-boxes which involve drilling and bolting into the sapwood are short-term, because as the tree trunk thickens, the box is gradually pushed outwards and will eventually fall off. These practices also cause unnecessary damage to our precious trees, which are already under enough pressure with climate-stress, disease and insect attacks.

Once the box is in position, it is easy to observe some of the design features I used for this particular batch of boxes. The entrance diameter is about 200 mm and the length of hollow branch (sourced from firewood piles) is relatively short - only about 150 mm.

The natural Gookamit nest-hollows I've recorded have all been quite shallow and with a mostly horizontal orientation, so while constructing these boxes, I decided to keep the depth of the nest-chamber less than 150 mm. This will hopefully assist deterring unwanted species like Galahs, which prefer a deeper, vertically-oriented nest chamber. Once installed, the inside floor of each box is filled with a natural substrate (mostly decayed bark or termite excreta, and a few leaves) gathered from the base of the nest tree. As with all nest-boxes, coarse, well-drained material is best as it closely replicates the substrate inside a natural tree-hollow.

Most of the Wheatbelt sites we visited were composed almost entirely of stands of very young trees (like the one mentioned above), but there were some places with several mature eucalypts. Although large enough and having the potential to have lost limbs and hollowed out, however, these trees still either lacked large hollows, or had a few smaller ones that were being aggressively defended by Galahs.

One spectacular stand of Salmon Gums (E. salmonophloia) was particularly memorable as the trees were so tall and captivating! Mike and I chose the above specimen for the owl-box, and it was beautiful to see the the box's hollow front (made from a faded piece of Wandoo E. wandoo) matched the stunning pink of the Salmon Gum's bark perfectly. It was obviously meant to hang here!!

Despite the difference in vegetation composition at Mike's Perth metropolitan area study sites, being patches of Jarrah (E. marginata), Tuart (E. gomphocephala) and Marri (Corymbia calophylla) among the Swan Coastal Plain's beautiful Banksia woodland, the theme of younger trees lacking hollows was consistent. Local Jarrahs, whose particularly hard 'termite resistant' timber was extensively logged during the 20th century, are still in the process of recovery and maturation following the cessation of logging. Research has shown that it takes more than 500 years for a Jarrah to form a hollow with an internal diameter of 300 mm, so many individuals remaining in our bushland are a long way from becoming habitat trees.

This large Jarrah tree was the ideal site for an owl box.

It was therefore a wonderful feeling to know that the artificial hollows Mike's study was providing would be very useful habitat for wildlife in general, not necessarily just the boobooks we were targeting. As I like to emphasise in my nest-box building workshops, the provision of any box in an area lacking tree hollows will create habitat for some wildlife, even if it is not a conspicuous vertebrate like an owl. It is easy to assume that a box has not worked if the target species doesn't use it - however, with this 'inside the box' thinking, we tend to forget it will still likely benefit smaller wildlife like skinks, geckoes, cockroaches, moths and spiders, all of which play a role in keeping our environment healthy.

Mike will be monitoring the owl boxes during the breeding season later in the year to check their occupancy. To keep track of the project, please visit his Boobook Research Facebook page. I can't wait to see who (hoo, hoo!) takes up residence! :-)

What's a Wambenger?

At the end of a guided bird tour I took in the Perth Hills recently, I was chatting to some participants in the group over a hot cuppa when one of them pointed behind me and said, "Look, there's a possum on the roof!" I glanced around quickly and suddenly found myself leaping across the lawn towards the roof in one of the greatest moods of excitement I've ever experienced. The animal in my torch-beam was no possum - it was a WAMBENGER!!

'Wambenger’ is an Aboriginal word for a small Australian marsupial known as a Phascogale (pronounced ‘fas-koh-gale’). This name means ‘pouched weasel’, and was used by early European settlers because of the animal’s similarity to the tenacious carnivore of the northern hemisphere. Phascogale is used both as a common name and a scientific genus name. There are two different species of Wambenger: the Brush-tailed (Phascogale tapoatafa) and the Red-tailed (P. calura), both of which occur in Western Australia. The Brush-tailed variety, however, prefers forest and woodland, and is the only species to occur in the Jarrah forest of the Perth Hills.

A Wambenger's black ‘bottlebrush’ tail has hairs as long as a matchbox (50mm).

While I was totally thrilled to have (for the first time in more than 25 years of being a naturalist in the Mundaring area) seen a live, wild Wambenger, and I thoroughly enjoyed sharing my excitement with all members of that evening's bird walk, I was in no position to take any decent photos. The blurry shot I managed to take with my iPhone 4s (which, incidentally, at ~150 - 200g, weighs about the same as the subject!), were enough to prove this sighting of what is quite a rare species, but that was about it. I immediately began planning a return nocturnal visit in the hope for better images, but my chances were quite slim. Several walks with a head torch over the past few weeks left me with no luck. But last night, after more than 3 hours of waiting in some bushland not far from the original sighting, my patience paid off.

A Brush-tailed Wambenger forages for invertebrates on the bark of a Jarrah tree.

The individual I spotted, which was moving rapidly along the limb of a Jarrah tree about 10 m above me, was surprisingly unafraid of my torch beam, and I watched with delight as it behaved completely naturally, going about its nocturnal foraging business. As I observed the Wambenger's behaviour, I thought about what I knew of their biology, and felt so totally filled with excitement to know that an animal so rare was right THERE!!

Wambengers live in very low densities, with individual females having a home range of about 50 ha (~10% of the area of Perth’s CBD), and males requiring more than twice this. Their cryptic behaviour, low numbers, and the fact that many are eaten by cats, foxes, owls and goannas, means Wambengers are very difficult to glimpse. Emerging from the safety of their tree-hollow home well after dark, they spend most of the night in the canopy, climbing expertly through the branches and catching insects with their sharp teeth. Prey consists mostly of spiders, crickets, centipedes and even bull-ants, but they will also feed on nectar and sometimes small birds. What struck me was how easily the animal could scurry up and down branches, cling to the underside and remain hidden, and I even saw it run up one limb and leap nearly 2 metres to the next tree!

At 250mm, a Wambenger’s tail can be longer than its body. Sharp claws and highly flexible ankle joints allow them to climb down tree limbs as though gravity doesn't exist.

 

My mind went back to a fauna survey I was assisting with several years ago, during which time we had caught Wambengers in traps designed for possums and bandicoots, and this research had created an opportunity to observe some of their features close up. One fascinating insight was seeing underneath a Wambenger's foot, and observing the tiny ridges or keels on the foot pads, a special adaptation which help it grip to the bark while climbing.

The underside of a Wambenger's foot showing the finely keeled foot pads.

I mentioned above that this was the first time I'd seen a wild live Wambenger. You might remember my blog post from 2013 which described a dead (road-killed) male, and at the time I was excited to use the opportunity to write about this animal. I've since recorded another road-killed Wambenger close to Mundaring, an indicator that this species is obviously still surviving in some suburban parts of the Perth Hills. 

HOW CAN YOU HELP?

While many Australian’s have probably never heard of a Wambenger, they are an important part of what makes the our landscape unique. In Western Australia they are classified as ‘Vulnerable’, meaning they can be threatened with extinction if factors affecting their survival (habitat loss, altered fire regimes, and in particular, predation by cats (especially roaming pet ones), are unmanaged. They can also be a natural form of pest control, eating many of the spiders, ants and cockroaches we humans find annoying. The main thing these cute animals need to survive is habitat (that is, native vegetation with large, hollow-bearing trees), so you can help them by supporting the protection of bushland in your local area. In the Perth Hills, EVERY tree is vital, and the increasing number of Jarrah and Marri trees we are seeing felled in the Mundaring Shire of late is of great concern. This has direct impacts on the survival of all local animals, including Wambengers. Nest boxes designed for Wambengers can also help, and be a useful way to determine the species presence and abundance if boxes are monitored regularly. Wouldn't you love to share your space with this magnificent creature? :)

Cockatoos - Who's Chews?

Can you imagine gnawing into a box of Weetbix made of solid wood, using only your mouth, and finding just four small biscuits inside the bottom, then repeating this 150 times to get your daily nutrition? Welcome to a Black Cockatoo's daily routine.

When you are out bushwalking, you might have discovered dozens of ‘honkey nuts’ (the fruit of our native Marri trees, Corymbia calophylla) dropped on the floor, sometimes all over a track or firebreak. This ‘mess’ (which is actually an important part of bushland ecology) was likely left by one of the three species of Black Cockatoo unique to Western Australia’s south-west. But if the birds aren’t there, how can you tell which species is responsible?

Foraged Marri fruit dropped by Carnaby's and Forest Red-tailed Black Cockatoos.

When you pick up a ‘honkey’, the first thing you will notice is multiple chew-marks, where the cockatoo’s beak has damaged the fruit’s skin. As shown in the above image, these marks might be fresh, with the flesh still being green, or quite old, where the flesh has faded to a brown or grey colour. Such information is useful in establishing how recently the birds have been there, and how frequently different species visit that particular food source. As well as damaging the rim and neck of the fruit (i.e. the top), all Black Cockatoos leave lower mandible (beak) impressions at the base or bowl of the fruit (near the stalk), because their gape (the size of their open mouth) is large, unlike that of smaller parrots.

Now, have a closer look at the fruit. If you are holding a Black Cockatoo-foraged ‘honkey’, it will fall into one of the following three categories:

‘The Surgeon’ – Baudin's Black Cockatoo (Calyptorhynchus baudinii), one of the white-tailed species, has a long upper mandible specially adapted to probing into Marri fruit and extracting the seeds, leaving little damage (Picture 1B, below). The rim and neck are sometimes slightly frayed, with obvious puncture marks in the centre where the seed chamber has been perforated and the seeds expertly hooked out. Chew marks, however, never extend deeply into the rim. The base of the nut has numerous small ‘V’ shaped marks (from the corners of the lower mandible), or narrow, ‘square U-shaped’ marks (~5mm across), from the whole lower mandible’s impression.

‘The General’ – Carnaby’s Black Cockatoo (C. latirostris), the second white-tailed species, has a shorter upper mandible which causes much more damage to the rim and neck of the honkey nut (Picture 2A, below). Chew marks often cut into, or shave the skin from, the rim. The distinguishing feature of this species is the narrow, ‘square U-shaped’ lower mandible marks, virtually identical to those of the Baudin’s.

‘The Butcher’ – Forest Red-tailed Black Cockatoo (C. banksii naso), has a short and very robust beak which tears at and often completely removes the top half of the honkey nut, exposing the internal seed chambers. Several shallow dish-shaped marks (~10mm across) from the lower mandible’s impression are visible on the base (Picture 2B, below).

Click to enlarge any of the below images. Note: arrows point to low mandible impressions.

Picture 1: An unmarked honkey nut (A) and one foraged by Baudin's Black Cockatoo (B).

Picture 2: Carnaby's Black Cockatoo (A) and Forest Red-tailed Black Cockatoo (B) foraging debris.

Lately I've been building nest-boxes for a variety of birds, including cockatoos, and (as though the wildlife wants to be involved!), all three species of Black Cockatoo have visited to forage in a low Marri tree just above my workshop. This has provided some great opportunities for photographing the birds' behaviour and helps shed light on the different techniques used to extract precious seeds. 

I watched one female Forest Red-tail snip off quite a thick branch containing a bundle of honkey nuts, and 'hoist' it slowly up, using her bill to pull and her foot to grasp. She then held the branch with one toe of her right foot, then proceeded to pluck off one nut at a time to be held in her left foot for 'processing' (all cockatoos are 'left handed'!), all the while scanning the scene with her beady brown eyes to watch for predators.

The damage this 'Butcher' species causes to each honkey nut is evident in the above picture. By contrast, the 'Surgeon' leaves very little damage: below is a female Baudin's Cockatoo using her dexterous tongue and thin upper mandible to 'tweezer' out a single seed from a honkey nut. You can view more images of this species on my Flickr photostream here.

Do cockatoos visit your backyard or local reserve, and if so, which species are they? Next time you are on a bushwalk, remember it can be just as exciting to play ‘bush detective’ and work out who's who, without actually seeing the culprit! You can find further reference material about chewed Marri nuts on the WA Museum's 'Cockatoo Care' website.

Cocky-Boxing Success

When you last checked in for an update on the Ngolyenok (Carnaby's Cockatoo) nest-box in the Mundaring Shire a nearly 2 months ago, you might remember that it contained 2 eggs, something I found very surprising given my expectation on that day for the box to contain a large chick. The conclusion was that the first breeding attempt had failed, but the 2 eggs meant a second pair was still incubating and there was a strong chance for a favourable nesting event. Last week I scaled the tree, peered inside the nest-box, and was thrilled to discover the above sight - the eggs were gone, but in their place was a healthy, 6-week-old cockatoo chick! Today, a small community group including WA Museum ornithologists, revisited the bush reserve for the chick to be weighed, measured and banded.

With a special chick-wrangling 'net-pole' hanging from my harness, I ascended my rope to the nest box, a climb that by now was becoming quite a familiar routine! It didn't take long to lift the chick gently into the bag, tie it safely shut, and lower it down to my friends Jeff and Jo on the ground. Ron Johnstone and Tony Kirkby from the WA Museum kindly allowed me to band the chick, which involved placing a specially designed, uniquely numbered aluminium ring on the bird's leg for identification. There was then time for a few photos of the precious nestling before I returned to the canopy and placed him back inside the safety of his (artificial) hollow home.

The darkening bill and reddish eye-ring tell us this Carnaby's Cockatoo chick is a male.

When I returned to earth I paused for a brief moment to reflect on the situation: this nest box was installed less than 12 months ago and had cockatoos using it within 3 months. Now a beautiful endangered bird had successfully been reared, and another had fledged from a nearby natural tree-hollow that remained a secret until the nest-boxes inspired us to begin monitoring cockatoo behaviour during Kambarang (spring). Now, there was the start of a potential breeding population, right here in the magic Mundaring! What will this year's breeding season bring?

Visit this link to read the ABC's news story on this exciting day in the Perth Hills.