Spot-mapping accurately delineates song-territory boundaries.
It has long been known that songbird home ranges are often much larger than song territories. However, Anich et al. (2009) found that telemetry-delineated song territories in one population of Swainson's Warblers were larger than spot-mapped song territories in other populations, suggesting spot-mapping underrepresents territory size in that species. We used telemetry and spot-mapping to delineate song territories for individual Golden-winged Warblers and found that territories are much larger and include much more mature forest than spot-mapping suggests. These results were recently corroborated in other populations of Golden-winged Warblers with work by Frantz et al. (in press, Studies in Avian Biology). Spot-mapping probably remains an excellent low-cost tool for identifying core-use areas within song territories and assessing abundance of breeding males within an area. However, the assumption that spot-mapping accurately delineates song-territory boundaries, and therefore accurately identifies areas of territory use vs. non-use, is not valid.