Wednesday 13 November 2019

Night of watching bats brings an otter encounter

Ireland is a stronghold for the Eurasian Otter.
Ireland is a stronghold for the Eurasian Otter.

By Jim Hurley - Nature Trail

I completed one of my annual bat surveys last Wednesday for the All Ireland Daubenton's Bat Waterway Survey organised by Bat Conservation Ireland. The exercise involves walking a one kilometre stretch of waterway at night and stopping every one hundred metres to monitor bat activity for a four-minute period.

It was a lovely late summer evening: dry, warm and with a light westerly breeze. A bonus was that the night was forecast to be the best ever for seeing the Perseid meteor shower with abnormally high levels of shooting stars.

To my surprise on arrival the water surface was totally blanketed in Gut Weed, an apple-green alga. Predominantly a summer annual, Gut Weed gets its name from the fact that its fronds are long, irregularly inflated tubes that look like animals' intestines or guts.

The Gut Weed blanket was wall to wall. My lamp showed very little insect activity. My bat detector tuned to 35 kilo Hertz specifically for Daubenton's Bat stayed disappointingly silent apart from the background hiss caused by the gentle rustling of Common Reed lining the waterway.

On the night in question, planet Earth was forecast to hurtle through the debris field of the Swift-Tuttle comet resulting in the annual display of shooting stars known as the Perseid shower. I doused both my lamp and my head torch and let my eyes adjust to the gloom.

The night was particularly dark as there was no moon and light pollution was low. However, the sky had clouded over so there were no stars shooting or otherwise. A flock of eight Mallard passed overhead followed by the lazy flapping of two Grey Herons

An Otter whistled in the darkness off to my right. These animals are common on my waterway. Suddenly there was a ferocious splashing immediately below me as if a child had fallen into the water. The sound was too loud for a Mink; too long-lived to be a Grey Mullet jumping. It must have been an Otter.

Then my bat detector cackled into life with the unmistakable series of rapid dry clicks of a passing Daubenton's Bat, its stream of echolocation calls reminiscent of the sound of a box of marbles being spilled on a tiled floor. I had to turn on my lamp to visually confirm the bat pass over the waterway surface but the light intrusion caused the Otters to fall silent not to be heard again that evening.

Wexford People

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