Don’t disturb the cockatoos on your lawn, they’re probably doing all your weeding for free



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Gregory Moore, The University of Melbourne

Australians have a love-hate relationship with sulphur-crested cockatoos, Cacatua galerita. For some, the noisy parrots are pests that destroy crops or the garden, damage homes and pull up turf at sports ovals.

For others, they’re a bunch of larrikins who love to play and are quintessentially Australian.

Along with other scientists, I had a unique opportunity during the COVID-19 lockdowns to study things that had intrigued me closer to home, perhaps for years. While isolating in the suburbs of Melbourne, I wanted to find out why cockatoos return to the same places, and what they’re after.

The answer? Onion grass, reams of it.

Onion grass is a significant weed, and I estimated in a recent paper that one bird gorges on about 200 plants per hour. A flock of about 50 birds can consume 20,000 plants in a couple of hours.

This significantly reduces the weed level and may make expensive herbicide use unnecessary. So if you have a large amount of onion grass on your property and are regularly visited by sulphur-crested cockatoos, it would be wise to let them do their weeding first.

When play verges on vandalism

Most of us see cockies whether we live in rural communities or major cities, but how much do you really know about them?

Two sulphur-crested cockatoos sitting on a branch
Sulphur-crested cockatoos nest in old hollow trees.
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In late winter and early spring in many parts of Australia, flocks of sulphur–crested cockatoos can be seen grazing on the ground. They’re usually found close to water, nesting in woodlands with old hollow trees, such as river red gums, Eucalyptus camaldulensis.

Where these forests and trees are being cleared, the number of cockies falls. But they are resilient and adaptable birds, and have spread their range to cities and the urban fringe, where numbers are increasing.




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The birds are known to play with fruits, hang upside down on branches or perform flying cartwheels by holding a small branch or powerline with their feet, flapping their wings as they do loop after loop.

Sometimes their play verges on vandalism as they follow tree planters, deftly pulling up just-planted trees and laying them neatly beside the hole.

While cockatoos feed on the fruits and seed of native species, they’ve adapted very quickly to the introduction of exotic species, such as onion grass from South Africa, which is plentiful and easy to harvest.

I observed flocks ranging from nine to 63 cockatoos at seven sites along the Maribyrnong River in Keilor last July and August. Onion grass was the only item on their menu.

A pest for humans, a feast for birds

Onion grass (Romulea rosea) is small and usually inconspicuous with grass-like leaves. It’s typically only noticed when it flowers in spring, producing pretty, pink and yellow-throated flowers.

Conspicuous onion grass with a small purple flower
Onion grass comes from South Africa, and is a big problem for native grasslands.
Harry Rose/Wikimedia, CC BY

Onion grass can be a serious weed that’s very difficult to control. It’s not only a problem for agricultural land, but also for recreational turf and native grasslands.

In some areas, there are nearly 5,000 onion grass plants per square metre. This is a massive number requiring costly control measures, such as spraying or scraping away the upper layer of top soil.




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Onion grass gets its name from its onion-like leaves. At the base is a small bulb, which works as a modified underground stem called a “corm”. The corm is what cockatoos will travel many kilometres for, to dig up and return to for days on end.

A brown bulb with small roots coming out
When cockatoos eat onion grass corm, it prevents the weed from regenerating.
Harry Rose/Wikimedia, CC BY

Their super weeding effort

Like other native parrots, sulphur-crested cockatoos are famously left-footed. So it was interesting to observe them primarily use their powerful beaks to pull onion grass plants from the ground and dig up corms, using their left foot only occasionally to manipulate the plant.




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The cockatoos fed for between 30 minutes and two and a half hours. At each feed, one or two sentry (or sentinel) birds, depending on the flock size, would keep watch and give raucous warning should danger threaten.

The cockies could remove a plant and corm from the ground in as little as six seconds, but sometimes it could take up to 30 seconds. They then removed and consumed a corm every 14 seconds on average in wet soil and every 18 seconds from harder, dry soil.

Eight cockatoos on grass, with autumn leaves
When flocks feed, one or two sentinel birds keep watch for danger.
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This means a flock of 63 birds could remove more than 35,400 onion grass plants in a feeding session lasting two and half hours. This is a super weeding effort by any standard!

Future partnerships

My further investigation revealed most of the corms were within 20 millimetres of the soil surface, so the holes left in the soil by the birds extracting the onion grass were shallow and quite small. This shouldn’t give seeds from onion grass any great advantage.

And they’re very efficient: the birds eat over 87% of the corms they lift, which then won’t get a chance to generate in future years. So, if we’re going to try to eradicate onion grass, it may be better to let the cockies do their work first before we humans take a turn.

We have a lot to learn about how our native species interact with introduced weeds, and more research might reveal some very useful future partnerships. They might be birdbrains, but sulphur-crested cockatoos really know their onions when it comes to, well, onion grass.




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The Conversation


Gregory Moore, Doctor of Botany, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Pulling out weeds is the best thing you can do to help nature recover from the fires



Australians are keen to help nature recover after a season of devastating bushfires.
Darren England/AAP

Don Driscoll, Deakin University

Many Australians feel compelled to help our damaged wildlife after this season’s terrible bushfires. Suggested actions have included donating money, leaving water out for thirsty animals, and learning how to help the injured. But there is an equally, if not more, important way to assist: weeding.

An army of volunteers is needed to help land owners with judicious weed removal. This will help burnt habitats recover more quickly, providing expanded, healthy habitat for native fauna.

Other emergency responses, such as culling feral animals and dropping emergency food from aeroplanes, are obviously jobs for specialists. But volunteer weeding does not require any prior expertise – just a willingness to get your hands dirty and take your lead from those in the know.

Volunteer weeding will help burnt habitats recover more quickly.
Silje Polland/Flickr

Why is weeding so critical?

The recent bushfires burned many areas in national parks and reserves which were infested with weeds. Some weeds are killed in a blaze, but fire also stimulates their seed banks to germinate.

Weed seedlings will spring up en masse and establish dense stands that out-compete native plants by blocking access to sunlight. Native seedlings will die without setting seed, wasting this chance for them to recover and to provide habitat for a diverse range of native species.




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This mass weed germination is also an opportunity to improve the outlook for biodiversity. With a coordinated volunteer effort, these weeds can be taken out before they seed – leaving only a residual seed bank with no adult weeds to create more seed and creating space for native plants to flourish.

With follow-up weeding, we can leave our national parks and reserves – and even bushland on farms – in a better state than they were before the fires.

Bush regeneration groups are well placed to restore forests after fire, but need volunteers.
Flickr

Weeding works

In January 1994, fire burned most of Lane Cove National Park in Sydney. Within a few months of the fire, volunteer bush regeneration groups were set up to help tackle regenerating weeds.

Their efforts eradicated weeds from areas where the problem previously seemed intractable and prevented further weed expansion. Key to success in this case was the provision of funding for coordination, an engaged community which produced passionate volunteers and enough resources to train them.




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Following recent fires in the Victorian high country, volunteers will be critical to controlling weeds, particularly broom (Scotch broom and related species), which occurs throughout fire-affected areas .

Fire typically kills these woody shrubs but also stimulates seed germination. Without intervention, broom will form dense stands which out-compete native plant species .

However, swift action now can prevent this. Mass germination reduces the broom’s seedbank to as low as 8% of pre-fire levels, and around half of the remaining seeds die each year. Further, broom usually takes three years to flower and replenish its seedbank. So with no new seeds being produced and the seedbank low and shrinking, this three-year window offers an important opportunity to restore previously infested areas.

Scotch broom, a native shrub of Western Europe, has infested vast swathes of Australia.
Gunter Maywald-CSIRO/Wikimedia

Parks Victoria took up this opportunity after the 2003 fires in the Alpine National Park. They rallied agencies, natural resource management groups and local landholders to sweep up broom . Herbicide trials at that time revealed that to get the best outcome for their money, it was critical to spray broom seedlings early, within the first year and a half.

Broom management also needs to use a range of approaches, including using volunteers to spread a biological control agent.

Plenty of work to do

Parks Victoria continue to engage community groups in park management and will coordinate fire response actions when parks are safe to enter. Similar programs can be found in New South Wales, Western Australia, South Australia, Queensland, Tasmania, the Northern Territory, and the ACT.

A wide range of weeds expand after fire and warrant a rapid response. They include lantana, bitou bush, and
blackberry.




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Managing weeds after fire is currently a high priority at many sites. At the edges of the World Heritage Gondwana rainforests of southwest Queensland and northern and central NSW, there is a window to more effectively control lantana. In many forested areas in NSW, Victoria and South Australia, fire has created an opportunity to address important weed problems.

State government agencies have the mapping capacity to locate these places. Hopefully they can make these resources easy for the public to access soon, so community groups can self-organise and connect with park managers.

A koala badly injured during the Canberra bushfires before it was returned to the wild.
ALAN PORRIT/AAP

All this needs money

Emergency funding is now essential to enable community-based weed control programs at the scale needed to have a substantial impact. Specifically, funding is needed for group coordinators, trainers and equipment.

While emergency work is needed to control regenerating weeds in the next 6-18 months, ongoing work is needed after that to consolidate success and prevent reinfestations from the small, but still present, seed bank.

Ongoing government funding is needed to enable this work, and prepare for a similar response to the next mega-fires.

Want to act immediately?

You can volunteer to do your bit for fire recovery right now. In addition to state-agency volunteer websites, there are many existing park care, bush care and “friends of” groups coordinated by local governments. They’re waiting for you to join so they can start planning the restoration task in fire-affected areas.

Contact them directly or register your interest with the Australian Association of Bush Regenerators who can link you with the appropriate organisations.




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If we do nothing now, the quality of our national parks will decline as weeds take over and native species are lost. But if you channel your fire-response energy and commitment to help manage weeds, our national parks could come out in front from this climate-change induced calamity.

By all means, rescue an injured koala. But by pulling out weeds, you could also help rescue a whole ecosystem.


Dr Tein McDonald, president of the Australian Association of Bush Regenerators, contributed to this article.The Conversation

Don Driscoll, Professor in Terrestrial Ecology, Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.