Photo: A veteran tree that is a prime example of a high potential bat roost site (photo by: Simon Huguet [via Wikimedia Commons])
Trees are an essential aspect of bat ecology, with three quarters of UK bats species know to roost within trees, some using the exclusively for roosting purposes and others during parts of the year. However all species are known to forage within and surrounding woodlands. Any tree has the potential to be provided roost sites for bats and it is important in being able to recognise the signs and assess the likelihood of a tree to be a roost site.
Certain features within trees can indicate the potential for harbouring a roost. The features that are indicatory of ‘High Potential’ are:
Once these features have been identified the presence of bats can be identified from evidence surrounding the potential roosts. Things to look for include: Staining surrounding the hole from the natural oils with bat fur, staining beneath the hole from urine, excrement/droppings can also be found beneath a hole, scratch marks from their claws, insects flying around a hole can indicate the presence of wildlife and bats emerging from the features at dusk and retuning during dawn.
During the surveys, trees should recorded for feature, descriptions and location using our bat survey sheet. Assessing the surveys outcome and indicating the trees bat potential will offer clues in the best management options for those trees.
Prior to conducting tree work it is important to check local record centres, statutory nature conservation organisations (SNCO) or local councils for any known bat roosts or other significant species. A survey is then recommended to be carried out to look out for bat potential and other evidence (this survey can be carried out at the same time to tree safety surveys). Assessing the data will highlight the trees potential as a roosting site; taking pictures will help analysis later on. Alert the contracted tree workers on the ‘high potential’ roost trees and take account of this. A tree is deemed to have ‘high potential’ will not stop work nor will the presence of bats, but this does mean that advice should be sought on how to complete works legally. It may be easier to recruit the assistance of an experience ecologist to survey the trees within an area to prevent undue delays in the work.
Best practice indicates that where possible retain ivy, dead and dying trees unless the tree is a cause for concern. Depending on the results of the survey acquiring appropriate permissions and licences may be required especially for carrying out work on high potential trees. Leaving wood on site for a 48hour period after cutting will provide an opportunity for bats potentially roosting in a felled tree to escape, whilst leaving the wood indefinitely proves another important habitat for invertebrates and other species. If bats are found during works than all work should cease immediately and an appropriate license acquired from Natural England.
Habitat improvement works can be implemented on sites where significant habitat loss of change has occurred. For example placing bat boxes, leaving deadwood, planting native trees can all assist in compensating habitat loss and improve the local environment for all users.
You should record the presence of protected species on a national database. This can done by contacting the local Statutory Nature Conservation Organisation (SNCO). Alternatively you can record online at the National Biodiversity Network. You should also alert the appropriate land owner, council and or management body to the presence and location of this species.
If you encounter or believe that there are bats present on a site where work is being conducted contact the Bat Conservation Trust or your Local Bat Group for advice and guidance on what should be the next steps you take.