Bat Tree Habitat Key is a free web-hosted publication in three parts that was written by AEcol Principal Ecologist, Henry Andrews.

Bat Tree Habitat Key comprises:

  1. An account of how Potential Roost Features (PRF) form, why they form, where they form, why they form where they form, and approximately how long they can be predicted to last;
  2. An account of how bat species native to the British Isles use trees; and
  3. A dichotomous key to potential bat-roosts in trees for use in the formation of a hypothesis used to guide further survey effort, and also an interpretive tool to give a hypothesis of what might have been present, where conclusive evidence has eluded survey.

The book works through basic tree biology to illustrate how the different features that bats occupy form.

Each of the individual bat-roost features is described using the correct arboricultural nomenclature, with accompanying photographs and figures.

Accounts of the known tree-roosting ecology of our native bat species are provided, each in identical format so that what is unknown is also set out.

Accounts are also given for a variety of potential bat-predators and competitors.

Finally, a dichotomous key is provided, through which you can process unoccupied PRF to obtain a hypothesis of what might use each feature and for what purpose, thereby allowing you to target the best times to return and look again.

The 3rd Edition is currently available to download from, where you will also find the Bat Tree Habitat Key Database and Report.

If you’re on Facebook you can also search for the Bat Tree Habitat Key page and ask any questions you might have in an open forum that is seen by professionals, academics and amateurs in over 40 countries.

Finally, if you’re a professional ecologist and seeking training in tree-roost survey techniques for yourself or your consultancy, don’t forget that Henry Andrews provides reasonably-priced training to consultancies during the off-season, or can combine training with your survey commitments if you need advice on a difficult site. You can email Henry at for more information and a quote.

I have helped Henry work on this project by working on the database and carrying out various analyses on the data, in an attempt to understand better the relationship between bats and trees.