ECOLOGY & LEGISLATION
If planned works have been identified as having the potential to disturb bats or their roosts, then activity surveys will have to be carried out to identify any roosts, what bat species are present, and roost numbers.
This element of the survey looks at all structures, whether it be a building, bridge, tunnel etc. Any structures are inspected internally as well as externally where safe to do so, during the day to assess their suitability for use by bats and whether any field signs are visible.
Trees are inspected externally from the ground. This involves the use of a range of equipment such as ladders, torches and an endoscope where necessary. In the case of buildings, walls, roofs, attic spaces, basements, cellars and all outbuildings including sheds and leant to’ s are examined. The features that are looked for, but not limited to include gaps in stonework and tiling, under fascia and roofing felt as well as the following field signs;
- Bat droppings, for example, on building or ground
- Polishing, scratching or staining resulting from bats entering or exiting the buildings
- Live or dead bats
- Any insect remains which may indicate feeding
In a tree survey we are looking for features that may be suitable for bats to roost. These vary from rot holes, woodpecker holes and cracks to loose bark and tears or rips from fallen or broken limbs. The field signs we look for are exactly the same as in a building survey.
This part of the survey can provide valuable information in relation to potential roost sites, as well as evidence of an existing roost however activity surveys in the evening when bats are at their most active and easier to observe are usually also required as it is at this time of the day that bats are active and easiest to find.
EMERGENCE & RE-ENTRY SURVEY (DUSK & DAWN)
The emergence survey, also called a dusk survey is carried out to look for bats exiting a roost. This requires surveyors to be in fixed positions around the structure so that every aspect of a building, bridge or tunnel etc can be observed. Bat detectors are used to listen for bats echo locating either whilst exiting the structure as well bats that come into the area to feed. Surveyors are in position at least 30 minutes before dusk and for around 90 minutes or so after dusk. This survey should be carried out twice preferably over the months of May, June, July and August.
Bats are highly mobile and although you may find bats on one visit you may not on subsequent visits as they can move from roost to roost depending upon the internal conditions or if there has been any external interference. This explains why the survey is carried out on two to three separate occasions over the active season. This helps build up a picture of how the structure might be used.
The re-entry survey, also called a dawn survey is carried out in a similar way to the emergence survey. Surveyors are in place 90 minutes before dawn and cease surveying at dawn. During this survey distinctive bat behaviour such as swarming is looked for. This is where the bats come together prior to re-entering their roost. This survey is generally carried out once, however this can change depending upon each project.
During the winter months’ emergence and re-entry survey cannot be carried out as this is considered to be a sub-optimal survey period as bats may be inactive or hibernating. Structures can still be assessed for their suitability and whether any field signs are present A desk study can also be carried out. If works are not planned for a site until the spring and summer, then a full survey including emergence and re-entry survey will usually be required.
Trees can be surveyed at any time of year by climbing and inspecting them. This means features that are visible from the ground, can be checked and if no field signs are found, they can be blocked to prevent future use by bats. Blocking may only last a short time as it can be removed by birds and squirrels or even the weather if left over time.
Wild Surveys has seven qualified and experienced tree climbers, four of whom have a bat licence.