Crossing With the Tide: Our Night Among the Reeds on the Tees Estuary

There's a particular pleasure in doing a survey the hard way. Anyone can drive to a nature reserve, park up and switch on a bat detector at dusk. But when the only way to your survey site is the last ferry of the evening across the Tees, the night starts feeling like an adventure before you've even unzipped the equipment bag.

Six of us from Cleveland Bats gathered at the landing in late June, rucksacks stuffed with detectors, thermoses and enough snacks to see us through to sunrise. The ferryman gave us a look that said he'd seen stranger cargo, and we chugged out into the broad brown water just as the light began to fail.

A River With a Working Past

The Tees Estuary doesn't pretend to be pretty. Everything about it is functional and industrial — the bulk carriers riding at anchor, the chemical plants glowing on the far bank, the gulls squabbling over whatever the tide has turned up. But that's precisely why we were here. Working rivers are often the most underrated wildlife habitats in Britain, and the strips of reedbed that have colonised the estuary's margins are some of the richest bat habitat on Teesside.

Daubenton's bats are the reason we make this trip each summer. These are the water specialists — small, chestnut-brown bats that skim low over the surface of rivers and lakes, scooping up insects with their big hairy feet. On a calm night, watching a Daubenton's work a stretch of water is one of the great free spectacles of British wildlife. It looks like a tiny hovercraft trailing ripples across the surface.

Reading the Water by Ear

By half past ten, we'd split into three listening stations along the reed fringe. Daubenton's echolocate around 40–50 kHz on a frequency-modulated call — a dry, rapid tick-tick-tick through the detector that's unmistakable once you know it, quite different from the wet slapping rhythm of a pipistrelle.

The first pass came at 22:47. Then another. Then, gloriously, two bats working the same channel of open water between the reed stands, criss-crossing each other's flight paths like figures skaters who'd never been introduced.

Over the next four hours we logged consistent activity at every station. That matters. Daubenton's are fussy about water quality — they need water with plenty of insect life, which means water that isn't too polluted. A healthy count on the Tees Estuary is a quiet vote of confidence in a river that spent most of the twentieth century written off as a chemical highway.

What Else the Night Gave Us

The reeds kept giving. A noctule boomed overhead — deep, nasal, audible to some human ears — on what must have been a commute line between roost and feeding ground. Common pipistrelles hawked around the light spill from the industrial estate. And at some ungodly hour, a water rail shrieked from the reeds with such force that two of our volunteers nearly abandoned the survey entirely.

By the time the sky went pale, we'd recorded over ninety Daubenton's passes across the three stations, plus at least four other species. For a site that most Teessiders drive past without a second glance, that's a remarkable haul.

Try It Yourself

You don't need a ferry to start appreciating what our rivers do after dark. Pick a warm, still evening, find a stretch of slow water — the Tees at Yarm, the Leven, any mill pond — and be in position by sunset. Sweep your detector slowly across the water's surface. That dry ticking low over the ripples? You've found your first Daubenton's.

And if you fancy joining us for next year's estuary count — thermos and wellies essential — we're always looking for new ears. The river, it turns out, is very much alive.