THIS winter the UK witnessed the largest invasion of rare hawfinches ever recorded. Hawfinches enjoy a near-mythical status among birdwatchers, since they are among the hardest of all British birds to spot. The UK resident population is a paltry 1,500 and the bird is registered as endangered on the RSPB red list.

So this winter’s influx of birds, believed to be migrants from Europe’s Eastern Bloc, was very exciting.

When I heard of a flock at the Yorkshire Arboretum, a botanical tree garden affiliated with Kew Gardens and part of the Castle Howard estate, I promptly went to see these rare birds for myself.

When I arrived the place was bustling with bird watchers. There were still quite a few leaves on the trees, which meant that in places it was hard to get a clear look at the birds, and the hawfinches were very skittish and shy. But the noise they made as they cracked open the hard hornbeam seeds gave them away. Hawfinches are notable for their unusually large beaks and strong jaws. The avian equivalent to a fireman’s hydraulic cutter, these beaks can shear open plum, cherry and even damson stones.

I held up a telescope to examine a male as it perched on a branch of a hornbeam and was taken aback by its beauty. A hawfinch’s plumage is a warm autumnal colour, drawn out by an iridescent “sail” along its secondary wing feathers.

I decided I need to get closer and approached the arboretum to see if I could put up a hide while they were closed to the public for the winter.

I was delighted when they agreed and spent the next week shut in my workshop building a hide to watch them from. It included a 12ft infinity pool and elevated bird table.

By the end of November it was ready to go up in situ at the Yorkshire Arboretum. I scattered a mixture of seeds, including some extremely expensive hornbeam seeds I had bought online, on to the ground near the hide.

Some chaffinches and greenfinches quickly found the food. So did nuthatches and a variety of tits. But it was some time before any hawfinches appeared. Then one rainy morning I thought I heard one. A hawfinch makes a high pitched slightly spitting “pix” sound – which seems out of character for such a bulky, powerful bird. Before long there was a flash of black and white wings and a hawfinch landed in the leaf litter alongside greenfinches and chaffinches.

It wasn’t until I saw it next to its smaller cousins that I really appreciated how big this finch is. It is twice the size of a greenfinch and has a huge head that makes it look top-heavy.

Before long two more hawfinches appeared. I noticed the third bird was eating sunflower seeds. So much for the expensive hornbeam seed I had bought.

Now that the birds had found my food supply, I needed to persuade them to feed from the table I had built.

As I was driving home that evening I passed through North Grimston and noticed a line of yew trees at the side of the road. Hawfinches, incredibly, can crack open yew stones and eat the seeds that are highly poisonous to mammals inside. Other bird species only ever ingest these seeds and then eject them whole.

I drove back the next day and filled two big log baskets with the sweepings off the path. I sifted out the stones, dried them out on my boiler and put them on the table along with the hornbeam seeds I had bought and a mixture, including rowan berries and sunflower hearts.

Then one day in mid-December, a male hawfinch landed on the edge of the pool I had built. But it was very wary and within seconds it was gone. I decided to minimise any changes to my hide and to leave the shutters open all the time.

Then I built some “false” camera lenses out of painted plant pots – I placed a piece of black Perspex on one end to mimic the glass of a real lens - and left these poking out of the hide.

A week later I had six hawfinches feeding on the table. I stopped leaving seed for them on the ground and by Christmas Eve I started getting the sort of shots I wanted.

There was never a dull moment. The arboretum is home to more than 1,600 different tree species and these had attracted a bonanza of woodland birds. Alongside hawfinches there were nuthatches, goldfinches, chaffinches, siskins, bramblings, fieldfares, woodpeckers, greenfinches, long tailed tits, blue tits, coal tits, willow tits and great tits.

By mid-January I had 30 hawfinches feeding on my table. It was incredible and the photographs and video that I got were worth every moment.

l Robert Fuller will be exhibiting his hawfinch photographs and video footage alongside a new painting inspired by his sightings at the Yorkshire Arboretum visitor centre from February 10 to March 17 . The display will also be on show at his gallery in Thixendale throughout the period.

l The arboretum is open from 10am to 4pm daily and The Robert Fuller Gallery is open from 9.30am to 4.30pm on weekdays and from 10.30am to 4.30pm on weekends.