Figure 2. Illustration of the four isolation categories.

(A) open site, grassland or parking lots, with only single shrubs/trees, no forest or high buildings as flight barriers within 100 m (0 isolation points), (B) single houses or allotments with built structures or few shrubs/trees as low flight barriers within 100 m (one isolation point), (C) dense forest and scrub (two isolation points), (D) row of high buildings as flight barriers (three isolation points).