Figure 3. Large patches are better than small. As a general rule, bigger patches tend to have more species. Many species, such as some forest songbirds, primarily live in interior habitat during the breeding season. Generally, interior habitat will begin to appear in a circular preserve when it reaches 8 acres [c. 3 ha] in area (the point at which a circle exceeds 328 feet [c. 100 meters] in radius). How much of a patch is considered edge? Estimates vary, but an edge is estimated to extend 50–100 meters into a patch of habitat. Essentially, microclimatic conditions (soil moisture, temperature, etc.) are different on edges vs. interiors. At 90 acres [c. 36 ha] a circular reserve would contain as much interior as edge habitat. Nevertheless, patch size requirements vary according to factors such as species and natural community type. Even conserving a collection of small patches can help threatened and endangered species.