Learning about Australia’s largest bird of prey

The magnificent wedge-tailed eagle is Australia’s largest bird of prey, but it’s endangered in Tasmania. There are a few regulations in place to try and help the species, but not much science to determine if the regulations are working. My research has been looking at how effective current regulations are and also how the population is doing and if there are any unrecognised threats.

Over the last few years we’ve made some grim findings – evidence of widespread rat poison and lead exposure in wedge-tailed eagles in Tasmania.

Over the last few years we’ve made some grim findings – evidence of widespread rat poison and lead exposure in wedge-tailed eagles in Tasmania.

Our research tried to find a link to the source of the rat poison exposure, but this is difficult in Australia because the amount of poisons sold is not recorded. We were able to link exposure to human population densities, and also the amount of agriculture in the areas around where each bird was found.

The link with agricultural area was particularly interesting, because normally we think that rat poison exposure in wildlife is due to people buying it in the supermarket and putting it around the house. But we had lots of eagles exposed to a specific type of rat poison called flocoumafen, which you can only buy from agricultural suppliers in Tasmania.

The high levels of rat poisons we found in Tasmanian wedge-tailed eagles was also particularly concerning as they don’t normally eat rats. Our results suggest that rat poisons may be moving through the food chain. Rats that eat the poison could be eaten by other predators, which in turn could be eaten by eagles, which is very concerning.

Lead exposure is a different question. Around a million macropods (wallabies and pademelons) and half a million possums are shot annually in Tasmania, mostly using lead bullets. The problem is that when the lead bullets hit the animals, they can fragment. The animals are usually left where they’re killed, so when wedge-tailed eagles come down to feed on the dead animal, they end up eating some of these fragments.

Both the rat poisons and the lead poisoning will eventually kill a wedge-tailed eagle at high enough levels, but it’s difficult to know what that level is. We’re just as worried about how lower levels affect their behaviour – for instance, wedgies can end up crashing into power lines or fences because they’re not well.

We’ve been using a bunch of different methods to try to understand the wedgies’ behaviour, including GPS tracking. For my PhD, I focused on young birds, because a lot of the birds we find dead in Tasmania are young. We wanted to find out more about what they do, how long they stay with their parents, and what are the rates and causes of mortality.

We were expecting over half of the birds to die in the first year, yet we still have over half the birds flying around sending us data every day. So the survival of our younger wedgies has been better than expected.

To fit a tracking device to a young eagle, we needed to catch the birds just before they left the nest. We climbed up to their nest, which can be 50 metres up, then brought the chicks down to the ground, where we fitted the transmitter to the bird. The transmitter is fitted like a little backpack, and it gives us a GPS fix every 15 minutes.

We’re still tracking most of these birds five years after we first caught them, because the units are solar-powered and can last a number of years. One of the main things we’ve found has been good news. We were expecting over half of the birds to die in the first year, yet we still have over half the birds flying around sending us data every day. So the survival of our younger wedgies has been better than expected.

For the last couple of years we’ve been working with adult eagles. We have to use a different technique to catch them, luring them in with a carcass to a feeding station and using a trap to capture the feeding birds.

I’m very lucky to do what I do.

The GPS transmitters we are fitting to the adults are giving us very detailed information, sending us a GPS fix every six seconds. This is really important data for us: two big issues for wedge-tailed eagles and also birds of prey worldwide are collisions with power lines and wind turbines. We’re working on models to predict where birds are going to fly at certain heights, so that we can help manage the risk of collisions.

We are out in the field at the moment and we caught a bird to fit a tracker a few days ago. Every time you see one up close it’s such a huge privilege. Wedge-tailed eagles are usually so far away, just a dot on the horizon or in the sky, so being face-to-face is pretty special.

I’m very lucky to do what I do.

As told to Graem Sims for Cosmos Weekly.

Follow James Pay on Twitter @JamesMPay and see the remarkable results of his tracking.