A beak shaped by sheoaks?

Two Glossy Black-cockatoos peer down at me from a sheoak tree, both busily munching seeds from a sheoak cone held in each left foot. Gentle gurgles and chortles pass between the two – it’s a male and a female, maybe mates for many years now. A patter of sheoak cone fragments sprinkle down from the tree. Each bird finishes eating the seeds from its cone, drops the ‘ort’ (the chewed cone) and reaches for another.

Glossy Black-cockatoos feed almost exclusively on the seeds of sheoak trees (Allocasuarina and Casuarina spp.)(BirdLife International 2022). Each day they spend many hours extracting seeds from woody sheoak cones –  that much I knew. What I didn’t know, until I looked closely at the skull and beak of a Glossy Black-cockatoo, is exactly how their beak is beautifully shaped for the task of extracting a sheoak seed and eating it.

I’m currently studying how the shape of parrot beaks (especially cockatoos) is related to what they eat. This project has been made possible by the collections and the support of the Queensland Museum. I’m planning to publish the detailed findings in a series of scientific papers, but I’m bursting to tell you about the amazing Glossy Black-cockatoo beak, because I know this gorgeous bird is loved by so many people. The Glossy Black-cockatoo is also threatened with extinction – and its highly specialized beak is part of the reason why.

Perhaps the easiest way to explain how a Glossy-black Cockatoo beak seems to be shaped by sheoaks is to compare it to another Black-cockatoo. Below I’ve drawn a comparison between the beaks of the Yellow-tailed Black-cockatoo (discussed in a previous blog) and the Glossy Black-cockatoo.

Above: Comparison of two cockatoo beaks: Yellow-tailed Black-cockatoo (top), Glossy Black-cockatoo (bottom). a) Skull and beak from front; b) Lower beak / mandible from front; c) Inside upper beak tip; d) Inside lower beak tip; e) Skull and beak from side.

Both the upper and lower beak of the Yellow-tailed Black-cockatoo have a single narrow and sharp tip. These birds use their beaks like pincers to chew into the wood of branches to extract wood-boring insect larvae (below):

They also use their beaks to open woody Banksia cones, Hakea cones, and more recently, the cones of exotic Pine trees, to get at the seeds:

They break the seeds into smaller fragments by slicing/crushing them between their upper and lower beak tips:

(At this point I’d like to say a very BIG thankyou to all of the photographers out there who take amazing high-resolution photos and videos of birds in the wild, and share them online. Without your work and generosity I would not have been able to look closely at how different species of parrots feed on different food items. Thank you so much!)

The upper beak tip of both Black-cockatoos is similar, and both species use it against their lower beak to pierce and break open woody fruits (see drawing of Glossy Black-cockatoo below):

However, their lower beak tips are wildly different. The lower beak tip of the Glossy Black-cockatoo is divided into two points, and between these points is a thickened, blunt, convex ‘saddle’. The scooped shape of this lower beak seems to be well-suited for holding the barrel-shaped cones of sheoaks. Sheoak cones can vary in size – both between and within species – but they are always roughly barrel-shaped. No other cockatoo I’ve looked at so far has a lower beak like this.

When I started looking closely at videos of Glossies eating, I noticed another remarkable thing. Like many other cockatoos, Glossies tend to be left-footed. That is, they seem to nearly always hold their food in their left foot when eating. But remember those pointed lower beak tips on each side of the ‘saddle’? It appears that the Glossies use one tip only – the right tip – to crush or dehusk each individual sheoak seed against the inside of their upper beak:

If you watch closely when a Glossy eats, you’ll see it take a bite of the sheoak cone, by driving the tip of its upper beak into the cone. They deftly manoeuvre a seed with their tongue, and then rub the seed between the right lower beak tip and the inside of the upper beak. Either to crush it and/or to dehusk it, or maybe remove the wing of the seed. (Here’s a terrific video example: https://macaulaylibrary.org/asset/482266 Thank you Sarah Dzielski Cohen for taking this footage and sharing it!)

At least that’s what I’ve observed – in many photos and videos. (Please let me know if you see them using their left lower beak tip!). Left foot, right lower beak tip. Why is this so? I really don’t know.

However, it seems that this highly specialised beak would make it hard for Glossy Black-cockatoos to eat anything else but sheoak seeds. It also takes them a long time to eat these seeds, as it seems that each seed is carefully processed, one by one. Even more strangely, the thickened ‘saddle’ in the middle of the lower beak might mean that Glossies can’t use their beaks like narrow, pointed forceps or chopsticks…. Yet this way of using a beak is arguably the most widespread and useful beak function used by all birds – not just parrots – worldwide. Losing the ability to use your beak like forceps seems to be a huge price to pay, in exchange for a specialised sheoak-seed-processor.

You might think this is a crazy strategy – this high degree of specialisation for eating sheoak seeds. But don’t forget that sheoaks recently (~200 years ago) covered vast areas of Australia before European settlement, and over geological time. Sheoaks have been part of the Australian biota for tens of millions of years – just like cockatoos. Sheoaks don’t release their seeds soon after fruiting, but instead store them in those woody cones in their canopies for some time (serotiny). Sheoaks are nitrogen-fixers, and their seeds are highly nutritious. Birds of the Glossy Black-cockatoo lineage have probably been spending their time munching sheoak seeds for tens of millions of years before humans even evolved.

Above: Critically endangered sheoak grassy woodlands on Eyre Peninsula, South Australia. Left: fenced area with Drooping Sheoak Allocasuarina verticillata and a native grassy understorey; Right: unfenced area subject to grazing by kangaroos, rabbits and horses. 

However, sheoak forests and woodlands in many parts of Australia have suffered massive declines in the last 200 years, and at least one of these vegetation communities is critically endangered (Department of Agriculture, Water and the Environment (2022). This decline has been caused by vegetation clearing, changed fire regimes, and over-grazing by domestic, native and feral animals.

The decline and threatened status of the Glossy Black-cockatoo mirrors this loss. The relationship between this gorgeous and intriguing bird, and the equally beautiful sheoak trees, has blossomed over millions of years. It’s our job to make sure it can continue for many years to come.

This is the third blog post in a series of stories about the amazing cockatoo beak, featuring new scientific research and original illustrations. Subscribe to my blog (black ‘subscribe’ box on bottom of the page) or email newsletter (green box top of page, or pop-up) to get these stories delivered straight to you inbox.

References:

BirdLife International (2022). Species factsheet: Glossy Black-cockatoo Calyptorhynchus lathami. Downloaded from https://datazone.birdlife.org/species/factsheet/glossy-black-cockatoo-calyptorhynchus-lathami  on 22/05/2026

Department of Agriculture, Water and the Environment (2022). Conservation Advice for the Drooping sheoak grassy woodland on calcrete of the Eyre Yorke Block Bioregion. Canberra: Department of Agriculture, Water and the Environment. Available from: http://www.environment.gov.au/biodiversity/threatened/communities/pubs/172-conservation-advice.pdf. In effect under the EPBC Act from 26-Feb-2022.