A Bat Survey in Norfolk
Love ‘em or hate ‘em – bats are one of those marmite species groups that either cause shudders of pain or coos of delight. I fall firmly into the latter camp, and doing bat surveys in Norfolk is very often, I think, one of the most intimate of wildlife experiences.
While some of my more experienced colleagues are licensed experts, being qualified to handle bats amongst other things, my own experiences are limited to arm’s length surveying techniques, such as using bat detectors. As we routinely record all bat sounds using these devices, surveys can be undertaken by ecologists with a relatively low skill base. Some bats are not heard on survey, but only discovered lurking on the sound recording on analysis the day after. The bat species recorded on our Norfolk surveys are often quite predictable.
The commonest species are almost always the two pipistrelles, common and soprano. These bats forage widely in the East Anglian countryside, and are often encountered hawking for insects along hedgerows remote from any potential roosting site. Their distinctive echolocation signals also make them easy to identify, with common pip registering at 45KHz and soprano registering at 55KHz, and they will frequently fly very close to observers, perhaps mistaking you in the dark for a small tree or insect-attracting farm animal.
Larger bats are generally scarcer in Norfolk, but because they are wide ranging do often get recorded on surveys as a single fly-through. Noctule, serotine and Leisler’s bats fall into this category. Being larger, they also echolocate at a lower frequency, though if close the calls can be almost deafening through the bat detector. Brown long-eared bat, though a relatively common species, rarely gets picked up on bat survey transects due to its short echolocation range. The other group of frequently encountered bat species in Norfolk are the Myotis bats – especially Daubenton’s and Natterer’s. These species have distinct habitat preferences, with Daubenton’s preferring to forage over water, and Natterer’s preferring woodland. Daubenton’s fly in a distinctive manner, skimming low over the water with an immobile body, and fast fluttering wings. Their echolocation is broadband, and has often been likened to a marble bouncing on a mirror.
The last group of bats is the rares, the ones that make the hair stand up on the back of your neck. Barbastelle is the ascendant among these, thinly distributed in East Anglian woodlands, but there are also other species such as Brandt’s and whiskered bats and Nathusius’s pipistrelle about which very little is known in Norfolk. There are no doubt concentrations of these species in Norfolk, Suffolk and Cambridgeshire awaiting discovery.
Rob
Robert Yaxley