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Trip to Castle Howard July 22nd 2003 (Bat Evening)

About a dozen members plus a couple of guests turned up on a glorious summer evening to try and see some of the bats around the lake at Castle Howard. The trip was led by Michael Thompson who was a fount of knowledge on these fascinating animals.

Unfortunately because it was getting dark I do not have any photos of this trip...

We began our trip with some bird-watching. It was interesting to see cormorants nesting on an island in the lake in a rather sick-looking willow tree. Ruddy ducks and great crested grebes were seen on the lake along with many mallards (and farmyard crosses), tufted ducks, pochard, coot, moorhen and Canada Geese (large raft). House Martins were flying overhead, but few swallows and no swifts were seen over the lake. And the bats? 1 noctule was seen, at least 2 others picked up on the bat-box (a Bat Box III); Pipistrelle 55s (according to the box) also known as Soprano Pipistrelles were flying and feeding along the path on the far side of the lake, and Daubenton’s bats were flying low over the water – only glimpsed as they came out late when the light had more or less gone, but confirmed by the box.

We learned many fascinating things about bats, which I have tried to summarise:

Female pipistrelles (weighing c. 6gm) must eat half their body-weight in insects (say 1000+ midges) every night when lactating, so usually nursing colonies are close to good rich feeding areas – it is not cost-effective to fly more than 5km. Breeding colonies are composed of related females, often well over 100 together. The young are placed in a “crèche” to keep them warm while the mothers go hunting. Males are not part of the colony, lead solitary lives and seem not to live as long as the females who can reach 11+ years, rather surprisingly for such a tiny mammal. Winter hibernation quarters are different from the summer roosts, and the bats leave them in March or April to go to their nursery colonies. Fascinating mating cycle: females will mate in the autumn but delay fertilisation of the eggs till the following spring, and the whole colony synchronise births. The females seem to have some control over the length of the pregnancy depending on conditions (wet weather will reduce insect numbers, so they may delay the births till the weather improves).
The young are more or less independent at 3 weeks of age, and they must gain weight rapidly in order to survive their first winter. Pipistrelles more or less fill the swallow/martin niche after dark. Now known to be (at least) two species, separated by their echo-location frequency – 45kz and 55kz. It is not yet known whether they co-exist, and if so whether they compete for food and roosts. Brown long-eared bats have quieter echo-location than other species and have super-sensitive dish-like ears to compensate. This is so the moths can’t hear them coming so easily: moths have primitive ears on the thorax, and can only pick up bats within about 35° of a line running transversely through the body. If they hear a bat they simply close their wings and drop to the ground. The long-eared bats have learned to approach moths from underneath to catch them in their dropping behaviour.
Daubenton’s bats almost always hawk over water, either lakes as here or rivers (e.g. the Rye at Nunnington) or canals. They are after mayflies and the like. They scoop them up with their big feet, then transfer them up into the inter-femoral pouch before flying to a perch to dismember and eat the catch, although sometimes the insects are consumed on the wing.
Noctules are the biggest British bat, and more or less replace the swifts at night, flying relatively high among the swarms of insects above trees etc. The bat-box reveals that they have a very distinctive echo-location call, with a marked final trill as they close in on their prey. Natterer’s bats are relatively uncommon in Ryedale, but have large winter roosts in the Ryedale Windypits around Helmsley, and also in places such as churches (Ellerburn Church has a problem here in that it has a colony of these bats, which the congregation want rid of...).

Gill Smith July 2003, revised August 21st, with thanks to Michael Thompson.

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© Ryedale Natural History Society 2003
Page last modified 28th August 2003