24th May 2022

Updated guidance for use of night vision aids for bat surveys

We recently published an Interim Guidance Note about the role of night vision aids for professional bat roost emergence surveys.

In the last few years, night vision and infrared cameras have become much more accessible to ecologists. Without them we must rely solely on our eyes and on bat detectors! This can be effective for spotting bats immediately after sunset before it gets really dark or where the night is illuminated by a full moon or artificial lighting. However, it is much more challenging for later emerging species, species that use quiet echolocation calls, or where roost exit points are overshadowed and the night is dark. For this reason, the existing bat survey guidelines for professionals (3rd edition) recommends that emergence surveys are combined with dawn re-entry surveys, where bats sometimes swarm around entrance points prior to entry and may be better observed than when they flit out and disappear at dusk.

The use of night vision aids can vastly improve the detection of bats as they emerge from their roostsand video recordings provide solid evidence of bats emerging from their roosts. The Interim Guidance Note specifies that all professional surveys should be supported by night vision aids and the rationale provided in reporting if they are not used. This is a step up from the existing bat survey guidelines (3rd edition), which specifies only that night vision aids can be used as a complementary technique.

By using night vision aids to improve emergence surveys, we can reduce the need for dawn re-entry surveys, which have been brought into question by research that suggests that many bats return to their roosts early. Reducing the need for night work provides a real health benefit for ecologists too!

The Interim Guidance Note has been prepared by Bat Conservation Trust (BCT) and discussed and agreed with the Statutory Nature Conservation Body (SNCB) mammal specialists. It supersedes the bat survey guidelines for professionals 3rd edition. Separate, more technical guidance on the use of infrared cameras for bat surveys is also in preparation.