Detecting area sensitivity: A comment on previous studies

Several studies have reported that some grassland birds are area sensitive; they exhibit a nonrandom avoidance of small fields. The methods used to te st for area sensitivity, however, differed among studies. Some investigator s sampled fields with sampling effort proportional to field size, whereas o thers used equal sampling effort in all fields. We created a simulation mod el with the same number of fields and field sizes as those examined in earl ier studies to determine if birds that select habitat randomly would displa y area sensitivity if fields were sampled in proportion to their size. The three species that we modeled to settle randomly, upland sandpiper (Bartram ia longicauda), Henslow's sparrow (Ammodramus henslowii) and eastern meadow lark (Sturnella magna), had positive relationships between occurrence and h eld size when a complete census or proportional sampling was used, and ther efore, would have been considered area sensitive by the methods used by som e previous authors. When equal-effort sampling was used, these species show ed no relationship between occurrence and field size. Future studies on are a sensitivity that use proportional sampling should compare results to a nu ll model. Otherwise, conclusions made about area sensitivity may be erroneo us because the response is a sampling artifact.