Bats and Birds

More on bats - but first the birds:

 Several days later and more fine weather, another look at bats.  Tuesday 25th September was another fine day. House Martins were circling in groups over the river, with varying but large numbers seen all morning, then more again towards evening when the air cooled.

The reason they were visiting the river was clear - abundant food was available in insect form, concentrated over the water.

The House Martins will be migrating soon and large numbers were already being seen on the south coast. Those seen today would soon be joining the migration as the hours of daylight diminish fast.

Dappled sun and shade on the warm river water and bank-side mud  brought out the insects

which could be seen low over the surface and high in the air over the river course.

House Martins quickly picked up the clouds of insects  over the tree canopies and were flying high and low following them. They won't go hungry on autumn migration this year, at least for the first few days.

What is good for house martins is also good for bats. Day-flying insects gave way to night-flying insects in large numbers. Covering the adjacent stretch of the river,  at dusk the sky was still bright in the west, as before, and bright enough to see bats flying rapidly, erratically across from one large oak to another, diving low over my head then up into the canopies, they can change direction much faster than birds - they are flying with their fingers - an exhausting process which means a continuous supply of food is needed. Common Pipistrelle and Soprano Pipistrelle bats were in the majority but Natterer's bats could be heard too. The bat detector was detecting numerous comings and goings in the dark of the trees. Echolocation was used as well as eyesight at first. It was clear that most bats were emerging from local tree cavity roosts and starting to forage immediately. Moving out from the tree margin however onto the short sterile grass of the recreation field at first no bats could be detected under the clear sky - but taking just a few steps closer to the overhanging trees bats were soon picked up. One or two were even audible flying across the corner, taking a short cut.

A large bat was seen to fly downwards over tree canopies from the evening sky, then very loud sounds on the bat detector  revealed that it was a Noctule, the largest bat encountered in this area.

After a slow start, bats seem to be doing well this year. They should survive in good numbers provided that their traditional roosts (both summer and winter) are protected - by conserving old trees in their natural state with holes and cracked branches and bark and natural understorey  vegetation with the local riverine ecology preserved. 

Bats need water as their unique physiology demands high levels of moisture intake from their insect food as well as the availability water in rivers, ponds or lakes.