BLAGDON LAKE BIRDS

Nathusius's Pipistrelle Transects & Monitoring


Transect Walks

I have revised the transects beside the lake so that they fall in line with the National Bat Monitoring Programme protocol, even though I think that they start too soon after sunset. Each transect is one kilometer long and has been divided into ten sections. Recording will be continuous from the start to finish with 4 minutes spent at each point and during the walk between each one, making for a total duration of about 1 hour. In order to understand and reduce the bias that I think will occur because of the early start (20 minutes after sunset), I'm going to alternate the direction each month and, additionally, note the time and species of the first call recorded. My prime reason for walking the transects is to understand the level of Nathusius's Pipistrelle Pipistrellus nathusii activity throughout the year and find out how they are using the lakeside environment spatially. All bat echolocation calls will be recorded using my Wildlife Acoustics Echometer EM3+ (10 sec limit set on recording) and I'll keep the raw data. Analysis will be carried out by viewing spectrograms in Analook and Kaleidoscope. I will count all Nathusius's passes and note all other unusual recordings for possible identification, if not now, perhaps in the future. I expect the huge majority of recordings to be Soprano Pipistrelle Pipistrellus pygmaeus, but with 13 species identified at the lake to date, who knows what might turn up.

Transect Details

Transect 1 (Between the Dam south end and Long Bay)

Transect 2 (Between Green Lawn and Holt Copse)

Transect 3 (Between Hellfire Corner and Top End)

Transect 4 (Between Indian Country pines and Orchard Bay)

Transect 5 (Between the Dam south end and half way along Butcombe Bank)

If you've looked at the map of transects around the lake, you will note that I have not covered the area along North Shore around into Butcombe Bay. It has been our experience over the last two years that Nathusius's Pipistrelle's have tended to use this as a flight line from one area of foraging to another e.g. Butcombe to Rugmoor. Although we have recorded bats feeding at Spinney Copse, including Nathusius's Pipistrelles, the woodland edge going around the corner into Butcombe Bay has proved to be less well used than the opposite bank. So, in order to keep the workload manageable, I've elected to drop this walk for the time being.

Results

In preparation.

Irregular Walks

Aside from the regular transect walks, I carry out irregular autumn walks in villages around the lake to try and find ♂ 'advertising' sites using the Echometer EM3+. Apparently, it's normal for Nathusius's to roost within a couple of kilometres of foraging sites so I will, over time, look to survey likely spots targeting Blagdon, Ubley, Nempnett Thrubwell and Butcombe. As yet, I've not found any new 'advertising' sites, but I have recorded echolocation calls at the points shown below.

Map of recordings

Recordings made of Nathusius's Pipistrelle Pipistrellus nathusii during irregular walks © Nigel Milbourne, 2013

Passive Monitoring

We have been using my Wildlife Acoustics Songmeter SM2BAT+ to help understand the way Nathusius's use the environment around Blagdon Lake. Currently, we are monitoring the Bat House to see which species are investigating it with a view to roosting or hibernation since its conversion last spring. Nathusius's have used the roof as an 'advertising' site to try and attract ♀♀s for mating, especially during the months of August through October.

Bibliography (sources of information)

Russ, J. 2012. British Bat Calls A Guide to Species Identification. Pelagic Publishing, Exeter.


Updated 31 March, 2014