Filling in the Gaps - PsittaScene May 2001

PsittaScene, May 2001

2/1/02

12:50 PM

Page 2

Filling in the gaps The breeding biology of Palm

Cockatoos on Cape York Peninsula

Editor Rosemary Low, P.O. Box 100, Mansfield, Notts., United Kingdom NG20 9NZ

by STEVE MURPHY As I sat in the tropical savanna of far northern Queensland, sweat beading on my brow, I knew it wouldn't be long before the show would start. Even though I'd been working in the area since midmorning, I hadn't yet heard so much as a peep. But then, right on time, something went whooshing by above my head. Something that sounded like someone narrowly missing me with a big leafy branch. And then, there in front of me, on the rim of a hollow in a huge paperbark, landed a magnificent male Palm Cockatoo. I had been watching this particular tree hollow for the past week in an attempt to piece together the behaviour leading up to a breeding attempt. The male sat there whistling, wing spreading and stomping his left foot. Shortly after, a female arrived and the pair bowed their heads to one another, presented their brilliant scarlet cheek patches and synchronised their calls in an impressive courtship display.

Within the next few minutes, several more males arrived in the area and all started trying to outdo one another with more earsplitting calling. This was obviously too much for the resident male who promptly attempted to round up all his rivals. One clash with a particularly stubborn interloper ended in a cloud of black feathers as the two males tumbled to the ground. Once the last of the intruders was seen off, the resident rejoined his female and got down to business again.

Although I had seen male-male conflict before, this particular afternoon turned out to be one of the most impressive of these displays that I have ever seen.

And yet despite the amount of activity that went on, it could be another year or so before an egg appeared in the nest hollow. These are the sort of encounters that reinforce my suspicions that, for

CONTENTS Palm Cockatoo................2-3 Echo Parakeet..................4-5 Golden Conure Fund..........6 Buffon’s Macaw Fund..........7 Grey Parrots..................8-10 Palm Cockatoo Fund Launch..............................11 Breeding for Conservation ..............12-13 Carnaby’s Black Cockatoo13 Lilac-crowned Parrot ..14-15 Psitta News..................16-17 Members List....................18 WPT Info Page..................19 Parrots in the Wild ..........20

Cover Picture Once again we are indebted to Roland and Julia Seitre for an outstanding photo on our front cover. We had thought there were simply no good shots of Palm Cockatoos in the wild, but the Seitres had it covered!

The World Parrot Trust does not necessarily endorse any views or statements made by contributors to PsittaScene.

It will consider articles or letters from any contributors on their merits.

Anyone wishing to reprint articles will need permission from the author, must state that it was copied from PsittaScene, and notify WPT. All contents © World Parrot Trust

actually started with the first rains of the wet season. I think that this lack of concordance is due to a small number of observations of what can be a protracted breeding season. This arises from a long incubation and nestling period (about four months) and the ability of pairs to lay again after a failed attempt. I have found that Palm Cockatoos are loosely seasonal breeders, with most laying occurring around August, but because individuals can re-attempt after nest failure, breeding can trickle on throughout the year. This accounts for the fact that I have detected breeding in every month of the year on Cape York.

Like breeding seasonality, the preferred breeding habitat of these cockatoos was also debated.

Some thought that breeding

Palm Cockatoos, breeding involves an extremely long lead up time of complex courtship displays and never-ending vigilance for potential rivals. Even then, after all the lead-up time, it seems that the odds are stacked against them....

Our knowledge about Palm Cockatoos in the wild has suffered from a large and enigmatic void for a long time.

Even the most basic biological information, vital to our understanding and future management of these threatened birds, is surprisingly poor. Take the question of breeding season.

In the past nobody could agree on exactly when these cockatoos breed in the wild. Some thought that young usually left the nest by the beginning of the wet season (around December). By contrast, others suggested that breeding

A pair of Palm Cockatoos in full display.

Photo: Roland Seitre

2 ■ PsittaScene Volume 13, No 2, May 2001

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PsittaScene, May 2001

2/1/02

12:50 PM

Page 3

Could scrub pythons be responsible for Palm Cockatoo nest failures? Here, a large and bulging python is caught inside a Sulphur-crested Cockatoo nest. Photo: Steve Murphy

Bamaga chick. Even at this quite advanced age Palm Cockatoo chicks can be predated.

Photo: Steve Murphy

snug 18x20cm! A tight squeeze for a bird that can weigh up to 1kg, is 56cm long and has a wingspan of over 1m. Compare this to the largest active nest found so far, a spacious 80x35cm, and you begin to get some idea of the variation. Equally varied is the depth of the nest from the rim of the hollow to the nesting platform, which can be anything from 43cm to over 2m.

The nesting platform is very interesting, as Palm Cockatoos are the only parrots that go to such extraordinary lengths to ensure that their chicks and eggs remain high and dry during the long wet season of tropical Australia.

Throughout the year, pairs maintain several hollows in their territory and build platforms of splintered twigs which can be anything from a few centimetres to well over two metres deep.

Given the huge amount of effort that goes into preparing each site, there should be little wonder why males don't tolerate each other near their nest hollows. It may have also been the mechanism that drove the evolution of the flamboyant wing spreading and drumming displays for which these Cockatoos are renowned.

Perhaps the most alarming statistic to emerge from the study to date is the high rate of nest failure. Over the past two breeding seasons I have monitored 21 active nests, and of these only 4 have successfully fledged young cockatoos. Eggs and chicks seem equally likely to go missing, and even quite advanced chicks have mysteriously vanished. The culprits are likely to be large varanid lizards, like Gould's monitors Varanus gouldii, and scrub pythons Morelia

Palm Cockatoo prefer, those that have openings that face upwards seem to be the norm. But don't be fooled into thinking that large bird equals a large nesting hollow.

While it is true that some pairs don't like to feel cramped and crowded while incubating and brooding (which is understandable with incubating shifts that can exceed ten hours!), others obviously prefer that cosy feeling. In fact, the record for smallest internal dimensions of an active nest so far is a remarkably

occurred in the rainforest while birds foraged in the savanna, while others suggested that it was the exact opposite. The truth is, that on Cape York, breeding occurs in the savanna as well as the rainforest, although most of the breeding that has been detected has been in the savanna.

This more reflects observer bias (i.e. nests are easier to find in the more open savanna), although nest hollows superficially seem to be more common in the savanna.

As for the type of tree hollows

Steve and Paul Igag (par rot researcher from Papua New Guinea) prepare to climb an active nest tree.

Photo: Sarah Legge

amethistina. This is especially likely given the fate of some of the local Eclectus Parrot and Sulphur-crested Cockatoo chicks.

For example, in one Eclectus nest that researchers Rob Heinsohn and Sarah Legge were monitoring, a disastrous exchange of hollow occupancy occurred. One day, instead of finding two healthy and quite advanced chicks, the hollow was full of coiled up and contented serpent. Several days later the snake moved on, only to leave a couple of large scats which contained the leg bands of the nestlings. Sure proof if ever there was any doubt!

Although this gives me some idea of what might be happening to all those Palm Cockatoo chicks and eggs, I have a sneaking suspicion that sometimes it can be a lot more sinister. A couple of times I have found eggs crushed but uneaten in the nest. This seems unlikely behaviour for a predator. Maybe rival pairs are responsible? Birds fight tooth and nail (or beak and claw?) to chase off rivals during courtship. But what would happen if rivals visited an active nest and they couldn't be chased off?

More and more the gaps in our understanding of Palm Cockatoo biology are being filled. It's challenging work and it's far from over. There are still a few big questions that need to be answered, like how often do pairs attempt to breed, and what really is happening to all those missing chicks and eggs? I'm also trying to find out what defines good breeding habitat, and then there's the question of whether birds move between the different subpopulations in Australia, and .....well, let's just say that I'd better get back to it...

PsittaScene Volume 13, No 2, May 2001 â– 3

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