Bats in Trees
Most of the bat species in the UK commonly roost in trees. They do not construct their own roosts but utilise features such as loose bark, rot holes, cracks, splits and woodpecker holes. These Potential Roost Features (PRFs) are usually found in veteran trees which are often mature although younger trees can be veteranised by fungal infection, structural damage or other condition. Bat roosts have been observed in trees with a diameter of as little as 10cm. Oak, beech and ash trees are particularly suitable for bat roosts but bats are also found roosting in many other tree species. It is therefore important that any trees that are to be impacted by a development are assessed for the potential of bat roosts.
The initial assessment is a Ground Level Tree Assessment (GLTA) where surveyors look for PRFs from the ground often using binoculars, a powerful torch and a ladder to assist. An endoscope may also be used if PRFs are accessible from the ground or a ladder. A GLTA may be carried out at any time of year but is optimal outside of the summer months when PRFs may be obscured by leaf cover.
If PRFs are observed then further survey will be necessary if the tree is to be impacted by development.
Dusk/dawn emergence surveys may be carried out on trees as they would be on a building. This technique is particularly suitable if a tree cannot be climbed due to structural features or fungal infection making it unsafe. Emergence surveys can only be carried out in the active bat season between May and September.
Tree climbing surveys for bats are a cost-effective and reliable method of assessing PRFs. At Just Mammals we have a professional, fully qualified tree-climbing team able to undertake this work using ropes and specialist climbing equipment. PRFs can be assessed at close quarters using a torch and endoscope to determine roost characteristics.
