Monday, 27 October 2014

Hanging near Home

The last time we heard about Kuyurnpa, she had just completed a giant journey from the Pilbara region of WA, into South Australia, then back to the centre of WA again. Her life since then has continued to be filled with high adventure! After crossing the Great Victoria Desert for the second time, Kuyu headed north again, and settled down on Roy Hill station in the Pilbara. We don't know if she 'met someone' or just stayed in an area of good food supply (perhaps with other young eagles of similar age), but the Roy Hill area and surrounds became her home for the next 10 weeks. Her tracking data showed a concentration of points with a total area of just over 10 000km2 (about 2.5 million acres). Here's a map (click to enlarge):

As if it was in her diary to be 'gone by the end of the month', Kuyu left Roy Hill on 1st October, and once again headed homeward, roosting just 10km south of the south-eastern Matuwa boundary, 40km from her natal nest. She didn't stop there though, and continued eastwards as far as Lake Carnegie, where she has mostly remained for the past 3 weeks. However, it looks as though Kuyurnpa has made a couple of 'attempts' to get closer to home, with two roost sites being just 10km east of Matuwa's eastern boundary, and a few day fixes have shown her soaring over Matuwa itself. Below you can see the most up-to-date map of this amazing young eagle's movements.

Kuyurnpa's latest GPS fix is the point near the north-western extremity of Lake Wells.

In a few days it will be a year ago that Kuyurnpa left her nest for the first time, and 7 months ago that she left her parents' home range. Since fledging she has now travelled 14 800km around 2 states of Australia! It has been an incredible journey, both for the eagle herself, and for us as we've eagerly tagged along for the ride! I hope you've enjoyed follow her as much as I have. Where will she fly to next?

Friday, 17 October 2014

Cute Chicks

Wedge-tailed Eagles are now well into their breeding season at Lorna Glen, and over the last few days we have been checking nests for breeding success. So far five nests have had large chicks! The one pictured above is the same chick shown at the start of the previous blog post, just 6 weeks later - isn't the change incredible!? To gather data on their dispersal I am ringing/banding the eaglets with coloured and numbered leg rings. This will hopefully make them recognisable in the field when the eaglets fledge and leave their natal territory, and give us information on where these young birds disperse. 

Kuyurnpa is an eagle chick that was fitted with a satellite tracker in 2013, and while ringing cannot provide as much detail as satellite tracking, it does at least create an opportunity for a re-sighting at some stage in the future.

Lowering down an eaglet from a particularly small Wedge-tailed Eagle nest. Don't worry - I'm harnessed in!

To fit the rings, eagle chicks are removed from their nests and lowered to the ground in a closed bag. They are then placed gently on a folded sheet where they sit quite happily as they are processed. I followed the same methods used by Golden Eagle researchers Ewan Weston, Rab Rae and Stuart Rae in Scotland, whom I accompanied on several ringing forays in the highlands earlier this year. This method allow for efficient processing and minimal impact to the birds.

Neil Hamilton holds an eagle chick as I attach the leg rings.

Once on the ground, the first step is to fit the rings to the eaglets' legs. An Australian Bird and Bat Banding Scheme (ABBBS) band is fitted to the right leg, then a unique colour band (right) is placed on the left leg. Bands do not harm the bird in any way - they have been designed to fit the leg comfortably: loose enough so they don't cause damage, but tight enough so they don't come off or get caught on vegetation. Furthermore, all banding conducted at Lorna Glen is licensed under the West Australian Wildlife Conservation Act and has been approved by an Animal Ethics Committee. The colour bands I am using are also the same design as those being used by my friends in Scotland. I am hoping they will be visible enough to be seen by any keen bird-watchers or photographers who can report sightings to me once these eaglets take to the air and leave home!

After the ringing is done, several measurements are taken from the bird, including weight, head length, wing, leg and talon length - these can be used to age and sex the eagle at a later date.

An eaglet aged ~7 weeks sits calmly as it is fitted with an ABBBS band.

The head-bill measurement is taken after fitting both leg bands (you can see the blue colour band on the eaglet's left leg.

When the banding and measuring are complete (the whole process takes about half an hour), the eaglet is placed back in the handling bag and hoisted back up to its eyrie. Here it sits and waits for its parents to return to the nest, hopefully with food. The adults have more than likely been watching the whole process from somewhere up high, but our presence at the nest does not significantly alter their behaviour. At this stage of the nesting period it is common for the parents to spend most of the day off the nest and away hunting. Their chick sits on the nest, keeping to the shade when it can, and watches over the surrounding Mulga shrubland, honing its skills at spying moving objects, and occasionally standing for a practice at wing-flapping.

Removing an eaglet from the handling bag to return it to its nest.

Several days after ringing each wedge-tail chick, I returned to check up on their progress, to ensure their parents had returned with food since the disturbance, and to check the rings were still in the right place. All were doing well. This one, the smallest (probably male) eaglet, was sitting up waiting to greet me as I poked my head over the edge of his eyrie.

Below you can see an ~8-week old eaglet with its new rings. This was the oldest chick we banded and it had quite large wings and very well-developed body feathers compared to the others. It should be easily recognisable with the blue colour band '005'. Where in WA will this young wedge-tail turn up next?

Thanks to Neil Hamilton, my 'eagle handling mentor', for overseeing the process of eaglet ringing. I would also like to thank John Angus, Pam Cherriman, Gill Basnett, Mark Jeans, Ayla Wilson, Bruce and Kaye Withnell and Tammy Elliott and her family for their assistance during the past few weeks.

Friday, 10 October 2014

Nest Failures

Smashed eggs! Never a nice thing to find on any bird's nest that you have been monitoring with the hope it will soon house an eagle chick. However, such findings are to be expected and teach us a great deal about the both the bird and its environment.

This photo was taken on Wedge-tailed Eagle Nest 2 at Matuwa (Lorna Glen). You can read more about the discovery and its implications on my personal News blog here.

Monday, 6 October 2014

Wallu After 16 Months

As the sun began its decent late this afternoon, I drove along the edge of a dry salt lake past 'Rabbit Ridge', and was extremely excited to see Wallu and Wurru launch from among the samphire! The pair had been on the ground only 50 m from the road and caught me completely by surprise. I suspected they'd been hunting rabbits from within the dense cover at ground level. Although unusual, I've seen this behaviour a couple of times before. Eagles are quite capable of running along the ground to catch prey if they manage to surprise it, and what better way to get a rabbit than meet it face to face?

It was brilliant to see Wallu in good health and capture a fleeting shot of him bearing his PTT, which can be seen the above photograph. Wallu only flew a hundred metres before alighting on the ground once again. Was he determined to get a rabbit?

Wallu alights in the samphire about 100m from where we flushed him.

He might've been hungry for himself, but we know he wasn't after prey to feed a chick. Unfortunately we discovered last week that Wallu and Wurru had another unsuccessful breeding season this year. When looking at the tracking data in June and July (nesting season), I started noticing a pattern in Wallu's daily movements. He would often be at Rabbit Ridge at dawn, then at mid morning we would see one or two fixes at his nest site.

Here are some maps (click to enlarge):

A day in the life - Wallu has travelled just over 25 km and roosted at two favoured hunting sites.

This map shows Wallu beginning his day at the eastern edge of a salt lake ('Rabbit Ridge' - cluster of red dots, centre right), and flying to his nest at 11am. He then soars to about 1000m above sea level and remains at this altitude for the middle of the day, drifting from the far western end of his territory (green circle) to the far east (yellow circle), and back to the middle. By sunset he has gone to roost at another favoured hunting spot, near an old farm well just north-east of Rabbit Ridge. The total distance covered was about 25km - not a bad day's work!

Another day, Wallu roosted much closer to 'home' on two consecutive nights - the green circle around the red dots reveals the spot, just 1.3km from his nest (see map below). At 6am he was at roost, but by 7am he was on the nest, at 8am he sat in a tree high on the ridge 800m to the north. At 9 and 10am Wallu was back on the nest, then as the clock struck 11am, he was airborne, cruising at 30km/h above Rabbit Ridge (as shown by the blue arrow). He spent from noon until 2pm sitting in his perch tree only 50m from the nest, headed off 'rabbiting' again from 3-5pm, and by 6pm, Wallu roosted back at the same spot again (green circle).

This data is consistent with Wallu delivering prey to his incubating female, 'guarding' her from a nearby perch, and, on occasions where he spent more time at the nest, taking on an incubation shift while Wurru has a break, perhaps to feed or stretch her wings.

In August I was thrilled to visit their nest (Nest 57) with Neil Hamilton and make an exciting discovery, confirming that Wurru had laid eggs. As we neared the nest tree  we crept through the bush, making every effort to keep a dense thicket of mulga trees between us and the nest. A stiff breeze ruffled the foliage, and through a few fine gaps I could make out the shape of Wurru sitting on her nest. She was incubating!! We retreated quickly as to not disturb her, our movements being concealed by the quivers of surrounding vegetation constantly in motion from the wind. Such conditions are good for remaining 'camouflaged' to an eagle's eye, which on a still day detects even the slightest movement from a long distance.

I arrived back at Lorna Glen last week (late September), excited to return with the strong hope that our inaugural satellite-tagged eagle would become a father for the first time. My Mum was accompanying me as a volunteer to help with my fieldwork. However, we were both disappointed to find Nest 57 empty (right). It contained fresh Eucalypt leaves and a slightly flattened nest cavity, but no eggshell, which almost certainly means the eggs had hatched but the chicks had not survived past their first week or so. Why?

Food is the ongoing factor which influences raptor breeding success, and although Wallu hunts regularly at several active rabbit warrens, and has access to other prey (kangaroos, monitor lizards) in his home range, he still has to supply plenty to a growing family, and this isn't easy in the arid zone. There are several other factors which also influence breeding success, and you can read about these here.

October now marks the 16th month we have been tracking Wallu by satellite, and even after this time we are still learning new things. It is only through satellite tracking that we are able to have such detailed insights into the lives of these magnificent eagles.