Hibernacula Surveys

Fall Swarm Trapping

Harp trapping is limited to fall and spring, when bats are entering, exiting, or socializing at hibernacula. Fall is preferred because it is fairly well known when specific species will swarm these sites, so trapping for specific species, (the Indiana bat) can be accomplished much more easily. There is a limit to the amount of data that can be infered from harp trapping. Some bats that swarm a site may not actually hibernate there, they may just be mating at that site or examining the site in case a disaster makes their primary hibernacula inaccessible or unsuitable. It is mainly used at sites where internal surveys are not safe and it does give us a good idea of importance of the site, based on number and species of bats caught. Costs vary depending on location, size, number of portals, and number of trap nights. All threatened or endangered species are photo-documented.

Winter Site Surveys

While bats are hibernating, stable sites can be entered and the hibernating bats identified and counted. This is the best way to get a count of and determine the species of the bats that are hibernating in a site. In the northeast we prefer to do these surveys in January, Feburary, and early March to ensure that all species of bats that use the site are present. Some bat species come in later or leave earlier than others so surveys in December or May may not give a acurate picture of site use. Internal surveys do disturb the roosting bats, we move as quickly and quietly as possible to minimize disturbance. Few methods of inventorying and monitoring are as accurate, inexpensive, or good for locating problems (campfires in the hibernacula, human destruction of bats, etc....). Monitoring every other year is accepted as a appropriate hibernacula survey frequency. Aqueducts, railroad tunnels, caves, mines, large water mains, abandoned subways, all can hold significant hibernating bat populations. Internal conditions can often indicate what species the site is suitable for, and show disturbances to the site.

Temperature Monitoring

Different bat species prefer different temperature ranges. Hibernacula can be managed (via entrance modification) to achieve specific temperature ranges. Using temperature data, entrance modifications can be made to achieve ideal temperatures for hibernating bats. We only advocate temperature modification in manmade sites (mines, railroad tunnels, and aqueducts). Monitoring is also useful at any site where long-term management is planed. Temperature data can be invaluable when unraveling disappearing bat scenarios, a entrance that was not known to connect to the cave system may have a huge impact on the temperature ranges and stability of your site. This is a long term but relatively inexpensive project where either we can monitor and provide reports to you, or we can train your personnel in data retrieval and interpretation.