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Any time anyone's discussing a threatened species, the same question always comes up: How many are there?
There's a good reason for this. A species' global population size gives some indication of just how close to extinction it might be. Population numbers naturally go up and down - regardless of any other threats they might be experiencing - and a species of just a few hundred remaining individuals is at a much more immediate risk of snuffing out than one that's several tens of thousands strong. Population size is a key factor when a species is being formally assessed for threatened status. On top of that, this information helps you figure out the implications of a venture that might be of great social or economic value but might put, say, five individuals at risk.
In the case of the Tasmanian wedge-tailed eagle, we actually don't know how many there are.
To be honest, it's a difficult question to address for most species. Everyone tries, but the estimates are often very approximate. For Tasmanian wedge-tailed eagles, we've never had really solid information, but the best guess has been at fewer than a thousand birds.
But this brings us to the other common - and equally important - question about any threatened species: how are they doing? A population of several tens of thousands might actually be at immediate risk of extinction if it's disappearing fast. A count of just a few hundred might not be quite such a worry if it's now flourishing.
Where Where Wedgie calls for everyone's eyes to help count eagles, and - over the years - follow how the numbers are changing. The more the merrier - not only because it's a big job, but also because mass participation is the best possible way to share what's discovered. Most Tasmanians live, work or play in the bush at least occasionally - we can all affect the prospects of this species. If everyone has good information on what it needs, we're in the best position to make sure our impacts are positive.
If we simply record every time we see an eagle, then over the years we’ll end up with a map of Tasmania completely covered with dots. Eagles can move huge distances, and they fly all over Tasmania, though they spend much more time close to their nest sites.
This is great in terms of understanding that eagles use the whole of Tasmania, but it doesn’t tell us how many there are!
We might consider doing an intensive effort, trying to count every single eagle in just one part of Tasmania - but food and shelter availability can vary a lot - from rainforest to paddock to buttongrass... It’s unlikely that the numbers are spread out evenly across the state.
For the Where Where Wedgie survey, we’re doing a ‘snapshot survey’ over a single weekend (25th-27th May). The idea is that as many people as possible get outside all across Tasmania, everyone makes a similar effort to see an eagle (at least six 10-minute surveys in a 4 km x 4 km square), and records whether they see an eagle, or not. The ‘not’ is extremely important: we need also to know where eagles were looked for but still weren’t seen.
In areas where we didn’t see an eagle, this could be because there wasn’t one there, or because we just didn’t happen to see it. We have some clever ways of figuring out how likely it is that we missed one - if we know this, then we can make a reasonable estimate of how many eagles there are overall. Check out theto find out more about this.
We’ve prioritised squares that are widely spaced apart, so that we have a good chance of getting an idea of what’s happening all over the state, and to reduce the chances of picking up the same eagle in more than one survey square.
While our target is the wedge-tailed eagle, we’ll see if we can get information on other birds of prey at the same time. Find out more in the
There is a lot being done at the moment to try to help our eagles recover from their threatened status. But there’s plenty to tackle.
The Threatened Species Link profile for wedge-tailed eagles describes the numerous ways we can inadvertently cause problems for eagles in our every day activities - including -
If you’re interested in helping eagles recover, it’s well worth getting familiar with the various issues described on the Threatened Species Link. You might be quite surprised at the ways we can all help or hinder both of Tasmania’s eagle species, with the best will in the world. Individual birds vary a lot, but, for example, breeding may fail after a visit by a photographer - even on the ground, hundreds of metres away - let alone someone using a drone in the area!
It’s hoped that population numbers will increase if nest protection is more effective and unnatural mortality rates are reduced.
Where Where Wedgie will track those population numbers to see how successful our efforts are.
The Tasmanian wedge-tailed eagle Aquila audax fleayi occurs only in Tasmania, and is distinguished by its size - it’s Australia's largest bird of prey - and its wedge-shaped tail.
We’ll be posting more information on the biology of eagles and other birds of prey shortly, both here and within the.