In this issue:
On Rosellas
Brushtails win again
The Glossies of Kangaroo Island
| The Chatterbox #10 December 2005 |
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| ON ROSELLAS
Our local rosella is the pale-headed and, where we live, it is in serious decline. Over the last 15 years it has slumped from visiting our yard for 10 months in every year to just a couple of times a year. This article speculates on why that might be so. The obvious explanation is that the decrease is in response to an increase in possums, especially brushtails. Brushtails are obligate hollow-users, they find the space needed by the typical rosella family of four chicks to be very comfortable and they are almost impossible to budge. This explanation also satisfies an oft-mentioned characteristic – that rosellas move into a newly installed nestbox, often within days, breed immediately but never again. They may return in subsequent years but their activities never result in breeding. Recently we have become aware of an entirely different possibility. The Europeans have observed, at least since 1956, that hole-nesting birds tend to prefer new nestboxes over ones that are a few years old, even though the latter are often still in very good condition. The reasons for this were investigated in Latvia using data collected over the 20-year period to 2000 (Vilka, 2003). The number of nestboxes surveyed ranged from 530 to 1400 per year. The author considered the following possible causes:
Only the last item—internal brightness, correlated with usage and this correlation was more pronounced with one species than a second. As can be seen from this local photo of rosella chicks in a new box, the ply is very light in colour with lots of light bouncing around. It darkens naturally with age. To translate the behaviour of Latvian
flycatchers and tits to Australian rosellas is speculative, to say the
least. But in the absence of any local research, it remains a
possibility, as does the next item, also drawn from overseas. |
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| Years ago we recovered a
nestbox that had been used occasionally by brushtails, dumping it in
the workshop with other gear from the day’s activities. Before night
had completely fallen that box had attracted a possum into the
workshop (this had never happened before) to investigate the new
smell. That possums use smell to maintain their territory is no secret—it
is this desire to leave their scent in every possible den that makes
them so frustrating if one is trying to attract birds.
Conventional thinking is that birds generally have a very poor sense of smell. But perhaps not. A British researcher (Roper, 2003) has just completed the world’s first study into the sense of smell of any parrot species (using a lorikeet from Indonesia) and he found that they had no trouble distinguishing one smell from another. |
Photo courtesy Tracey Hopkins |
While this does not prove that rosellas can smell, it does offer yet another possibility for why rosellas breed initially but not again, even though possum numbers may not be high. Note that possums are implicated in each of the above, either through their physical presence, through the oils from their fur that darken the insides of box or through the scent that they leave. But possums are very, very good. |
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Most issues of The Chatterbox have
carried stories on our (always futile) attempts to deter possums from
boxes where they are not wanted. This years effort stemmed from the
observation that most possums approach a box entrance via the lid. |
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Enter the "bed of nails" lid, totally covered with upturned gangnails. Logic: if you can’t sit on the lid, you won’t access the entrance. From this exercise we have learned that possums possess a coat remarkable in its durability and that a lid embellished with nails elevates a simple grooming session to something approaching ecstasy. They loved it. |
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THE GLOSSIES OF KANGAROO ISLAND Glossy-black cockatoos are an endangered species with the South Australian subspecies being the subject of a formal Recovery Program, part of which involves the use of nestboxes on Kangaroo Island in South Australia. The 2005 census has revealed that, for the first time, successful nestings in artificial hollows has exceeded that in natural hollows (17:12). This is a sad situation. The future of these lovely birds is now in the hands of a small, dedicated group of volunteers who maintain the boxes (these are large boxes, mounted very high and subject to problems from possums and bees). Maintenance will be required for decades. |
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