A piercing whistle whirls across the damp air from the far bank of the River Devon. I know it is an otter but as I peer through a tangle of alder and willow branches, I see no movement. Another whistle, even louder this time, and then I spot the otter running along a carpet of golden, tumbled leaves by the bank edge.

The otter slips into the water and swims upriver leaving a V-trail in its wake, continually calling all the while – a whistle with a pitch of such intensity that there was an air of desperation to its tone. This might have been a mother looking for a lost cub, or perhaps a male seeking out a mate, but whatever the case, the animal did not seem unduly perturbed by my near presence, despite eyeballing me several times.

Indeed, after swimming a hundred yards upriver, the otter then turned around and swam straight back down again, passing close by me before disappearing in among a twisted mass of alder roots by the bankside. The whistling had stopped, the otter was gone, and the only sound permeating the air was the gurgle of rushing water – beautiful and hypnotic music drawn from the very depths of the river.

Normally, dawn and dusk are the best times to see river otters, but this encounter was in the early afternoon, which underlines that when it comes to wildlife spotting, always expect the unexpected.

I wandered on, disturbing a diminutive wren that churred its annoyance as it swept up on brown-blurred wings from a thick stand of twisted bramble stems. Wrens are one of our most ubiquitous birds, equally at home by a riverbank or on high windswept moors, or in thick gorse by the coast. The name ‘wren’ derives from the middle English ‘wrenne’, meaning ‘little tail’.

Another whistle permeated from across the water, but rather than an otter, it was a kingfisher streaking just above the river’s surface in a bolt of electric-blue. It has been a good year for kingfishers on the river, the low rainfall in the early part of the breeding season suiting their requirements perfectly for seeking out minnows in the languid pools.

Down by my feet, a scrap of black velvet caught my eye. It was a dead water shrew, the black upperparts contrasting starkly with the white belly and chest. It is the largest of our shrews, a capable swimmer that can dive to depths of two metres in search of aquatic invertebrates.

Finding the corpse reminded me when as a boy I had found a dead water shrew by a burn that tumbled into Loch Earn, and as I cradled its velvety body in my hands, I wished it were possible one day to glimpse a live one. Since then, I have seen a living water shrew on only two occasions – but that is enough for my dream to have come true, providing a fleeting insight into their mysterious and secretive lives.