I checked now and again on the pair during their 38 day incubation. Every time I crept carefully through the dense trees to my hideout, I always expected to find an empty nest with both adults soaring high above or perched together nearby indicating their usual failure. But every time, I could still make out that familiar sandy-coloured head of a sitting bird on the nest. I had to be so careful and quiet, any snap of a twig underfoot and she or he might come off. On one occasion, I startled a red deer hind in the forest and she galloped away and burst out of the trees right by the nest. The sitting bird was suddenly very alert but she must have realised it was just a running deer, nothing to be alarmed about and she settled down again. This was nerve fraying stuff.

A day or two after I'd calculated they should have hatched - if they were going to - I crept back to my vantage point, almost on hands and knees through the wet, peaty mud. I couldn't believe it. There was no bird on the nest. It had all gone wrong again. I looked down in disbelief at my soaked boots, then looked up again and back at the nest, thinking how best I could check the nest contents and retrieve the egg shell remains. There was an adult on the nest! I nearly fell over. It was the female. She was looking down into the nest, turning her head, this way and that, as if to say: "What on earth is that?"  Then I noticed she had a small item of prey in one foot. She steadied herself and started to feed, first herself and then slowly and carefully, she bent deep into the nest cup, out of my view, with a tiny morsel of food - and she came up without it. She was feeding a chick! Fantastic. They had got this far. Now only another 3 months to go... After a few minutes of watching her tender care, she clenched her sharp talons together to protect her young and then settled down over it or them to brood, rocking gently side to side, to get comfortable, just like a broody hen.

And so it continued. Visit after visit, they were still there. The chick getting bigger each time. We got passed the four weeks when their other chick had died. It changed from having a covering of creamy white down to a grey down and then by six weeks old, tiny dark brown feathers started to emerge. It grew from Day 1, when it would have been small enough to sit in the palm of your hand to a fully grown young eagle at Day 70 - just 10 weeks old. I held my breath every time I went to check. Once or twice, the nest had seemed empty but as I watched, a head would slowly look up or a growing wing would stretch out and I could breathe again. The parents fed the single chick well on fish, gulls, auks, sea duck, rabbits and hare. At Week 8, we had visited the nest, under special licence, to check the chick over, weigh and measure him (his small size suggested he was a male), ring him and fit his special wing tags which would help us follow him in the years ahead - if he survived that long. He was 'Yellow E' and he was a miracle.

Finally, at week 12, I visited again. After three months of checking on his progress every few days, this was the moment of truth. But this sunny morning, the nest really was empty. Could he have fledged already or had he been blown or fallen out as has happened to other chicks? I waited. No calls. No adults. After an hour, I couldn't stand it anymore and crept out of the forest and down the side of the burn opposite the nest. We must have seen each other at about the same time because there was 'Yellow E' glaring back at me, standing proudly on the top of the river bank a few hundred metres down stream. His dark chocolate plummage making him hard to spot. With a double bob of his head, he turned away from me and launched off confidently from the ground, flew a few more hundred metres and landed, rather clumsily, in the top of a big spruce tree. He was on his way. Nothing much I could do to help him now. I turned and headed back the way I'd come, leaving him to settle safe and sound in his new lookout. Both adults must have been away hunting so they never even knew I'd been there. I glanced across at the abandoned nest, now flattened (from the chick jumping up and down getting ready to fly) and littered with flecks of down, feathers and old prey items. What a different scene to what I usually find at the deserted nest of Territory 19 each year. For the first time in their lives, they had a miracle chick on the wing to care for. He'd be with them for many months yet. As ever, even though I'd played no part in their success, I left them with a happy heart and a warm glow inside. A coffee back at the landrover was going to taste very good this morning.

Update: Yellow E was still with his parents the following January. They were seen by a local Forestry Commission Ranger, all feeding together on a red deer carcase. And best of all, he has been seen back on Mull this summer, now aged two. Happy birthday and many happy returns!

Tomorrow: As the 'Big Cat Live!' team prepare for their first live broadcasts from Kenya (BBC One 6.10pm), for one night only, I'll be  swapping Mull for the Masai Mara and our big birds for some big cats. Join me on location as a 'spotter' for the leopard team during my RSPB sabbatical - the trip of a lifetime.

Dave Sexton RSPB Scotland Mull Officer

1800hrs