Golden Eagles are now in the peak of their breeding season and over the past few weeks I've been visiting nests with my Scottish pals to ring the chicks, most of which are 4-6 weeks old. It has been brilliant to return to some familiar territories from my 2014 trip and see which sites the birds have chosen to nest in this year.
While a typical goldie nest is located on a cliff ledge, about 5% of the 440 breeding pairs in Scotland build their nests in tall trees, most of which are ancient and majestic Scots Pines (Pinus silvestris). Such nests, which consist of a mass of dead branches, heather and sprigs of pine and Birch (Betula pendula), are set near the top of the tree in a crown of wonderful, spreading, sturdy limbs. These provide good footholds and make working at the nests quite easy. Ewan Weston and I scaled to the nest shown above to weigh, measure and ring the single chick present, which was about 5-weeks old. As you can see, there was plenty of room in the canopy for both of us!
|Even as chicks, Golden Eagles have large yellow feet. This eyrie reared 'twins' in 2014.|
Two other tree-nesting pairs of eagles had also reared single chicks, but these were at locations where the nests were much higher and less accessible (even to barefoot free-climbers!), so we did the processing on the ground. At each site, after Ewan had climbed to reach the chick and lower it down in a handling bag, I helped Jenny Weston fit the rings while she showed me how to take measurements to accurately determine its sex. Jenny is a highly experienced bird handler and I was very fortunate to be able to watch her work and learn from her expertise.
|A 6-week old eaglet in the heather. Its bright yellow cere is a sign of good health.|
|Stainless-steel leg-rings are fitted using special pliers. Eagle feet make even large human hands look tiny!|
|A rivet-gun is used to secure the aluminium colour-ring in place on the bird's left leg.|
The metal colour-ring being fitted above is used to increase the chance of the bird being resighted at a later date, as the stainless-steel rings are not as easy to discern. Black has been chosen because a great deal of highland monitoring is being done with infra-red, motion-sensing cameras, which take black-and-white photos that clearly show the number. This ring appears tight, but the thick leg-feathers give the false impression it is closing on the leg when it is actually loose-fitting around the skin. Eaglet legs actually decrease slightly in diameter as they approach fledging because of the reduction in 'blood feathers' that are highly concentrated during development.
Even at this age, it is normally possible to tell by eye whether the bird is a male or a female, the latter sex being larger overall and having noticeably bigger feet. Ewan has found that the footspan, measured from the tip of the hind toe to the tip of the middle toe (with the foot spread open), is the most accurate way of sexing eaglets. Other measurements taken include the head, bill and wing lengths, and the size of the hind claw, as shown below:
This rear talon is a formidable weapon and care must be taken to ensure the eaglets don't do any damage to our soft hands! Eaglets have not yet had the opportunity to wear their talons down by grasping prey or perching on solid branches, so the tips are pin-sharp! When these birds fledge, this 'finger-dagger' will be close to 50 mm (2 inches) in length and used as the primary weapon to deliver fatal blows to a range of moorland vertebrates. While an adult goldie could easily drive a talon through a person's hand, their chicks are usually very placid and do not attempt to hurt you; they do not really yet know how to use their equipment! Instead, they sit quietly in the heather and lay flat, a natural instinct to hide from potential predators as they pass by.
After processing is complete, the eaglets are promptly returned to their nest. At this stage of the nesting period, the adult eagles are usually away hunting for much of the day, so visiting nests to conduct this research causes minimal disturbance to the birds. Eagle eyes may be watching, but with the extreme efficiency and excellent bird-handling skills of those involved, we are in and out in a flash and the birds can carry on as normal.
|In preparation to return an eaglet to its eyrie, Ewan hoists the handling bag back into the canopy.|
One particular nest in the northern highlands was set in some of the most spectacular scenery I've ever seen - remote, rugged country with deep gorges and ancient cliffs, adorned with heather, moss, ferns and occasional Rowan (Sorbus sp.) trees. This is a classic example of the habitat in which most of the Golden Eagle population lives, and it is both exhausting and exhilarating to traverse on foot. An 8-hour round hike took Stuart Rae, Adam Ritchie, his brother William and I to the nest cliff, which we were able to peer across to over a small gully.
|This eagle eyrie (centre left) has been built between an emergent Rowan tree and the ancient granite gneiss cliff.|
At first glance it was quite difficult to spot the eyrie, but when an eaglet's downy-white body moved, it instantly gave the location away. The chick was about a month old, the perfect age for ringing. While William stayed to take photos, Stuart, Adam and I zigzagged our way up the nearer hill, and traversed across the ridge until we were above the nest. I was very lucky to be offered the opportunity to descend to the nest and ring the chick, so I left my bag in the heather, put on my harness, attached myself to a climbing rope, and eagerly clambered past tufts of heather and gripped the bare rock on my journey down towards the nest.
|The month-old eaglet with fresh prey of Hooded Crow and Red Grouse on its eyrie.|
This was the first active cliff-eyrie I had been to in Scotland, and it was so interesting to take note of the difference between it and the tree-nests I'd seen recently. This one had the most wonderful assortment of construction material - heather, birch, woodrush, rowan, dead grass - all arranged in a sort of 'haystack' formation, and the varied colours of this vegetation, together with the flecks of white eagle down-feathers stuck to the surface, made it appear as some kind of alpine art-work, a simply wonderful structure. Nature really does create some truly incredible scenes! And as Stuart mentioned in his recent blog post about this site, the eyrie was enormous! It's sheer size only became apparent when I was on it - I estimated it was over 2.5 m across.
You can view a few more images of the eaglet at this site on my Flickr photostream. Once the ringing and measuring was complete, I quickly ascended the cliff face again and we promptly collected our gear and left the site, as quietly as we had arrived.
It's been a privilege to be able to visit these eagle nests and learn first-hand how some of the most long-term and highly important ornithological work on Britain's largest raptor is done. The knowledge I've gained from the people mentioned here has been invaluable and I already know much it will help with my Wedge-tailed Eagle work back in Australia. Everyone has willingly shared expertise, stories and laughs, and this has made me feel so at home, and a small part of what is a great family. Thanks Scotland, for some amazing eagle days. I'm looking forward to more already!
|I owe a great deal to Stuart Rae (centre), for first tempting me to Scotland, and fabulous friends of his like Adam Ritchie, another very knowledgeable ornithologist.|