4 Things I Learned About Hawfinches During a UK Hawfinch Invasion

Hawfinches are a rare sight here in the UK. So when reports came in of an invasion of migrants from Eastern Europe, I headed to the Yorkshire Arboretum at Castle Howard where several flocks were feasting on the seeds of the hornbeam trees that grow there. From a hide next to a makeshift bird table, I watched these beautiful finches for days. Read on to discover what I learned.

1. It's the largest native finch

At roughly 18cm long, a hawfinch is twice the size of a greenfinch. This makes it almost big enough to be able to square up to a blackbird!

But it wasn't until I saw the hawfinches feeding alongside their smaller cousins that I appreciated how big they are.

2. Their autumnal plumage is perfect camouflage

As an artist I feel particularly drawn to the autumnal plumage of these finches. They have orange-gold feathers on their heads which is complemented by a duller brown on their backs and a softer grey-brown on their bellies. At the tips of their secondary wing feathers is an iridescent black. These wings are unusually short and slightly curved which could be the reason that they fly a little awkwardly. Once the seeds have fallen from the trees, they tend to forage on woodland floors for seeds and are perfectly camouflaged against the leaf litter here.

3. They eat yew seeds 

The most striking feature of a hawfinch is that its head is unusually big for its body, giving it a prehistoric, top-heavy look. This is to accommodate a huge over-sized beak that is remarkably strong. The avian equivalent to a fireman’s hydraulic cutter, it can shear open tough cherry or damson stones. Scientists have measured the crushing force of a hawfinch bill and found it to exceed 50kg. This is quite extraordinary might for a bird that weighs only 0.05kg. Powered by strong jaw muscles, this ferocious bite gives a hawfinch an advantage over any other finch since there are few stones it can't break.

Even more incredible is the way it uses this huge beak. All finches will lodge seeds in a gap between the cutting edge and the inner ridge of their beaks and pierce the husk with the 'teeth' in their lower bill, rolling the seed with their tongues to peel off the husk. But hawfinches have the added advantage of a bony, serrated protuberance at the back of both upper and lower jaw to clench on a seed from four angles at once.

Amazingly hawfinches eat the seeds inside cherry, plum, yew, elm and hornbeam stones. It would take just three yew stones to kill a human and other bird species only ever ingest them and then eject whole - yet hawfinches consume them like confectionary.

In the summer, surprisingly, hawfinches seem to put aside the power of their famously strong beaks and feed instead on insects. 

4. Their song is surprisingly gentle

The hawfinch song is soft, halting and unmusical - so quiet and unobtrusive this lack of a distinctive song is partly what makes it so difficult to find hawfinch in its natural woodland habitat. Many birds use their song to attract mates but this doesn't seem to be a requirement between hawfinches. Similarly the male hawfinch's display is quite subtle. It involves the males ruffling their plumage, then drooping and spreading out its wings. The hawfinch call note is easier to pick out against the chatter of other woodland species once you know what you are listening for: a distinctive contact ‘whistle’ and a loud ‘tic’ similar to a robin or song thrush.