The active part of a bat’s year starts in mid to late March when they start to emerge from winter hibernation.  This time of year is spent foraging and replacing fat reserves loss during hibernation.  Female bats that mated in the autumn,carry the male’s live sperm inside the the uterus throughout the winter months and will  ovulate in spring and become pregnant. This method of delayed implantation is quite unusual and helps bats in temperate zones cope with seasonality.

By the early summer female bats start to move to maternity roosts where females of the same species conregate together to have their young which is often a single pup. These roosts can very in number between species from 10 to over 1000 bats.

This maternity season is taken from May to August and during this time bats are extremely susceptible to disturbance.  Depending on the species these maternity roosts can be found in buildings, under bridges and in trees. During the autumn, male bats start to increase their intensity of mating calls to attract females to their mating roosts. A single male bat will mate with several females during this time.

This time of year is also associated with an increase in feeding to build up fat stores for winter hibernation that will start around the end of November.

Bats leave their roost between sunset and up to 90 minutes after sunset so emergence surveys reflect this, starting at sunset and continuing for up to an hour and a half. Pre-dawn re-entry surveys commence an hour or so before sunrise and record the species of bat and number entering the roost.

Bat Building Surveys can be undertaken at any time of year but should evidence of bats or potential be found and further surveys are required then under the survey guidelines recommended by the Bat Conservation Trust (link to this website), evening emergence and dawn re-entry surveys must be undertaken during the main active season of May to August. The type of development, size of roost, species of bat etc will determine the number of surveys required but often sufficient information can be gathered from 2-3 surveys.

If the scheme includes the removal or management of trees then Corylus Ecology can undertake ground and climbing inspections to assess a tree’s potential and to look for evidence of bats. We have fully trained and bat licensed tree climbers within our Devon and Kent office.

Larger sites may also require information relating to bat activity across the Site and we are finding these surveys becoming more and more relevant with planning applications.

Actvity surveys involve surveyors walking a pre-determined transect around the Site stopping at transect points for 3-5 minutes.  Every bat pass is recorded during the survey with the aim of identifying key foraging, commuting and swarming habitats. This information helps us to prepare an impact assessment and mitigation can be designed into the scheme with the aim to conserve and enhance the local bat assemblage.

All bat species within the UK are protected by law and details of the legislation can be found here. The law protects bats against death and injury but also protects the strutures they use for rest and shelter.

Therefore if you are planning a scheme to demolish or renovate a building the local planning authority may request a survey to determine if bats are present.

This initial survey is referred to as a Bat Building Survey and will involve experienced surveyors looking for evidence of bats such as droppings, feeding remains and bats themselves during the day.  This survey also looks for potential for bats to roost in that structure.  Often evidence is not obvious as bats roost in different locations such as under roof tiles, hanging tiles and wall cavities for example.  So if evidence of bats is found or the structure supports features suitable for bats then evening emergence and/or dawn re-entry surveys may be recommneded to determine the number of bats, species, status of roost and emergence points.