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ScienceWise - Winter 2010

The drumming parrot

Article Illustration
A nesting-pair of palm cockatoos change over incubating duties for the day, otherwise known as nest-exchange. Female on left, male on right. Males incubate during the day, females at night. Lockhart River, Cape York Peninsula, far north Qld. Photo by Martin Willis and Christina Zdenek
Article Illustration
Christina Zdenek takes notes in the field. Photo by Roland Seitre
Article Illustration
Male Palm Cockatoo drums with a fashioned drum-tool during his territorial display on a trunk-sheared hollow. Lockhart River, Cape York Peninsula, far north Qld. Photo by George Gornacz and Christina Zdenek

The extraordinary behaviour of Cape York’s palm cockatoos

Palm Cockatoos (Probosciger aterrimus) are large smoky-grey parrots that can grow up to 60cm tall and weigh in at over one kg. They’re native to Papa New Guinea and the Cape York Peninsula of northern Australia. We do not know the size or age-structure of the population on Cape York, and loss of habitat from mining and inappropriate fire management are possibly threatening these incredible animals.

Christina Zdenek is a Fulbright Postgraduate Fellow undertaking a graduate degree at the Fenner School of Environment and Society. She’s studying Palm Cockatoos with aims to conserve the species, but the wider project aim is to ensure conservation benefits for the whole of Cape York Peninsula.

“It’s really important to be able to track individuals within a population in order to do effective conservation,” Christina says. “Palm cockatoos, and parrots in general, are very long-lived species and because of this, any impact on the species could be masked for decades by a persistent, but aging, population. Exacerbating this problem is the fact that palm cockatoos are very slow breeders and also have low reproductive success, so recovery would be slow, if even possible at all. So if we just monitor the number of individuals, without knowing their age or how many are breeding, we could easily be missing a big part of the story. So what I’m looking to do is develop a way to identify individual birds without harming them or interfering with their normal lives in any way.” 

With some species this can be a relatively simple thing to do – trapping them and putting a coloured leg-band on them or fitting a temporary tracking collar. However this doesn’t work well with parrots in general and especially with palm cockatoos because they are very difficult to catch and become highly over-stressed when they are caught.
“Palm cockatoos are quite sophisticated birds. They have an enlarged forebrain, compared with other birds, which presumably gives them enhanced cognitive abilities. This may explain why they react so poorly to trapping and tagging.” Christina explains. To avoid such problems, she is developing a non-invasive identification technique based on the calls of individual birds.

 “Palm cockatoos are socially complex and their vocal repertoire reflects this,” she says. “On Cape York, Palm Cockatoos have a vocal repertoire made up of various syllables that are mixed and matched in different combinations. This mixing and matching of syllables in their vocal repertoire may be unique among the cockatoo family. Their calls are also not raucous, harsh calls like other cockatoos (picture the Sulphur-crested Cockatoo calls), but instead are pleasant-sounding whistles. Palm cockatoos even appear to mimic two other local bird species- something that is common in captivity but has rarely been noted for parrots in the wild. One of my favourite Palm Cockatoo calls sounds almost exactly like a human saying ‘hello.’”

Just like human voices, it is likely that each individual palm cockatoo has its own specific way of making each sound. The differences may be subtle but the variation in the way a particular bird makes a call is likely to be unique enough to recognize individuals.

Christina spends up to six months of each year living in a 2-walled shelter-shed “humpy,” adjacent to the rainforest in the remote wilderness of the Cape York Peninsula. The remote sites are only accessible during the dry season with a 4-wheel drive vehicle (or a motor-bike, which she will use for next field season). In the wet season the rivers swell their banks and the dirt tracks are frequently washed away or under metres of water. “One of the things I had to learn before beginning this project was how to handle a large four wheel drive in rough off road conditions.” she says, “That was pretty fun.”

Christina tracks the cockatoos and records their calls with a sophisticated directional microphone and digital recorder. Then back at base she analyses these sounds using software that maps the frequencies, amplitudes and timing of each call. She is using nesting birds over time to build a library of bird-calls to use for a non-invasive identification method with which to study palm cockatoos.

Although the cockatoo’s calls are interesting, they are not the only way these birds use sound to communicate. 
Palm cockatoos have a habit of drumming. On occasion, male palm cockatoos use their powerful beaks to fashion a drum-tool from a live tree branch. They then fly over to a tree hollow and beat on its edge, making a distinctive sound that can be heard 100m away or more. This behaviour makes palm cockatoos particularly unique among wildlife in that they create a tool for a purpose other than eating as the end goal. “Although drumming was first described by G.A. Wood in 1984, today, 26 years later, we still can only hypothesise why they do it. Perhaps they drum to get a clue of the quality and durability of the hollow. They could be doing it to mark their territory, or maybe even to show off their cognitive abilities to a prospective mate.” This wonderful mystery is something that Christina hopes to solve.

“Even though this parrot is very interesting and charismatic, we still know relatively little about them.” she says, “We still don’t know how long they live in the wild or when they first reproduce, which are two key factors in our understanding of their conservation status and risk to extinction. They may be threatened by bauxite mining on Cape York, but since palm cockatoos live for so long, even a major reduction in good quality nesting trees (and therefore their opportunity to replace themselves into the future) could go unnoticed until it is too late.”

Aside from mining, a major threatening process is inappropriate fire regimes. Late dry season burns are typically more intense and widespread than early season pre-scribed burns because they have a higher fuel load that is also cured. This kills more trees than early season burns and even releases more carbon into the atmosphere. These late dry season burns may also lead to declines in termite populations, which are a key part of the nesting hollow-formation process. Over the course of decades, termites eat out the middle of a tree, and this forms a mud-gut that eventually gets washed out, thereby creating a possible nesting hollow. And since palm cockatoos are obligate hollow-nesters, the amount of good quality hollows determines the amount of nesting birds there can be in the population.

However, in the world of tree hollows though, not all hollows are equal. Palm cockatoos prefer to nest in slightly off-vertical hollows of live trees, as opposed to vertical hollows in dead, but still standing, trees. Presumably, a hollow in a living tree would have better and longer-lasting structural integrity than a hollow in a dead one. This would make them more immune to both fire and cyclones, which are both a part of life on Cape York.

Although now based in Australia, Christina did her undergraduate degree at the University of California Irvine, where she funded her studies with a professional basketball scholarship. “I still enjoy playing basketball but just at this point in my life my focus is on the environment and I want to devote all my energies to this. I think it’s really important that we understand the issues facing natural ecosystems because it’s not just wildlife that depends on them, but us too. We really need to come to grips with the science so that we can be sure that the management strategies we make for preservation achieve maximum effectiveness,” she explains.

“Although my specific research is focused on identification of individual palm cockatoos, what I am most passionate about with this project is the big picture of conservation across all of Cape York. Palm cockatoos are an iconic species and they can be a great flagship species to raise awareness, funding and public interest for the benefit of all the flora and fauna of the region.”

As with so many environmental issues, it’s only possible to make effective conservation decisions once the background science is properly understood. For example, the landscape of Cape York is a mosaic of rainforest and woodland savanna. Although Palm Cockatoos generally forage in the rainforest, they almost always nest in the adjacent woodland, where the hollows are. Knowing this enabled Christina and her colleagues to confidently recommend for the boundaries of the bauxite mines on Cape York to be at least 1 ½ kilometers before the rainforest edge, as opposed to being right at the edge of the rain forest itself. If this recommendation is taken, it would mean this ecotone would be protected, and crucial breeding habitat would be maintained for the future survival of palm cockatoos in Australia.

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