Writer Rose Rouse is on an adventure – not in Cuba, Bali or the Outer Hebrides but in Harlesden where she lives. Every month, she walks and talks with friends, neighbours around busy NW10 and meets people you may have heard of living on your doorstep. As part of her Not On Safari In Harlesden project, she went on a bat walk with Roy Beddard at the Welsh Harp.

Did you know there is an annual bat walk at the Welsh Harp?

As soon as I found out, I booked my place.

So one Wednesday evening, I found myself in Cool Oak Lane looking for Roy, our batwalk leader. I spotted a large gentleman with binoculars on the bridge and concluded wrongly that this must be Roy, our leader it wasn’t. It was Derek, a veteran birder and ‘batter’ who has been visiting the Welsh Harp since 1960. However, Roy and Derek are a bit of a comedy duo.

There’s an initial assessment of the night insects. “There are a lot around tonight,” says Roy, “which means it should be a good night for bats because they eat them.

Apparently the common pipistrelle (our most common bat) can eat up to 3,000 insects per night. In fact seven varieties of bat have been seen at the Welsh Harp.

I am – no surprise here – a bat detector virgin. And intend to stay that way.

We head off into the darkness and pick up the small group already on a viewing platform. They’ve already seen a common pipistrelle – the UK’s smallest bat, its body is the size of a pound coin.

As we come out into a clearing, our eyes are trained on the late dusk skies. I hear a sound that I think is a woodpecker at first, it’s kind of violent knocking. Of course, it isn’t a woodpecker, it’s a bat detector picking up a noctule, one of the bigger bats.

At this point, I actually see the shadowy flicker of what I take to be a common pip.

We’ve just missed a fish owl in flight across the lake. Roy is standing still, his detector aloft. Derek makes an interesting observation. “Listen, did you hear a kind of raspberry, that is the pip eating an insect, they do a little loop round,” he tells us.

Now that is incredible. Experiencing a pip feeding via a frequency. Who would have thought it.

A longer version of this walk can be seen at roserouse.wordpress.com