Much of my walk to and from work is spent on paths alongside the rivers and streams which pass through the town. When I'm not keeping my eyes peeled for inconsiderate cyclists, I like to observe the activities of our feathered friends.

As I go about my daily routine, so they go about theirs. In the morning, the mallards are active, chasing the females both in the water and out. I love the way they land in the water after a labour-intensive flight. They raise their orange feet and splash to a halt in the water. They then glide off, looking graceful and effortless, but a closer look reveals those same orange feet flapping away just beneath the surface. Among the mallards is a single, pure, white duck, who seems to have bagged himself a female. They glide around together, rummaging around at the riverbank and upending themselves regularly.

On my walk home, the mallards are preparing for nightfall, bagging the best spot and settling down, turning their heads, hiding beaks in feathers and standing on one leg.

The blackbirds are active at the moment, chasing their females around and singing their sweet and complex melodies. I often see a songthrush just to the left of the path. I expect him to fly away as I approach, but he freezes and watches me pass, only about a metre away. I always wonder if it's the same one.

One day I saw a heron. More recently, a kingfisher. I recognised his shape first as he sat on a branch. The electric blue flash when he flew off was unmistakeable.

For the past couple of days, there's been a new bird on the block, preening himself and stalking the mallards. A handsome fellow, he looks for all the world like an oversized mallard with a sepia filter applied. He doesn't have the classic green head or yellow beak - his head is blackish brown, his beak greyish green. I texted Big, excitedly:

"I've just seen a big duck - like a mallard but considerably bigger, with a brown head and tan body. What do you think it is?"

"I can't think what it could be. Mallards are pretty much the biggest wild ducks. It must be a goose"

I shook my head at my mobile phone as I read his response. I'm no bird-watcher, but I was sure this wasn't a goose. My mystery duck doesn't have the delicate, pinched beak of a goose and it had the same shape and proportions as a mallard, just bigger. It was surely a duck.

When I got home, I scoured Big's bird books but could find nothing close to what I'd seen. I began to wonder if I'd dreamt the whole thing. But when I saw it again this morning and this evening, always in the same location, I stopped to confirm my observations and took a low quality photograph with my low quality phone-camera-phone, ensuring that there was a male mallard in the shot to demonstrate the size difference.

Despite extensive Googling, I'm no closer to finding out exactly what he is beyond being some sort of hybrid, but I'm quite excited about my mystery duck. I shall look out for him each time I walk past.

I wonder how long he'll stick around...