Territory Size in the White- Crowned Sparrow (zonotrzchza Leucophrys) : Measurement and Stability

The problems involved in reliably measuring bird territories and estimating their stability have often been ignored by ornithologists. Observers frequently use the same technique to measure territories as that used by Noble (1939) and other pioneers. Typically, the observer carries a map into the field and notes where a subject bird flies, sings, or has aggressive encounters during a given period of time (e.g., Ralph and Pearson 1971). This method provides intuitively satisfying results because the birds are interacting without human interference. However, it is often time-consuming, and owing to the rarity of interactions on some territorial boundaries it may not be feasible to wait for these interactions to occur. To avoid some of these problems, Wiens (1969, 1974) proposed a method of mapping territories that he termed the “territory flush” procedure. With this method, an observer approaches a singing male until it flushes from its initial position, and then maps both the flight path and the landing location. In another method, Dhondt (1966) presented Great Tits (Parus major) with a stuffed conspecific model and a recording of their territorial song at different locations in the territory. By noting where the subject responded to the stimulus, he soon defined all of the territorial boundaries in a given area. Some investigators (e.g. Krebs 1971, Howard 1974) have used both approaches interchangeably and have combined the data from them. The methods should be evaluated by using both the standard mapping procedure and the stimulus procedure, and comparing the results as to territorial boundaries. In this study, we used both methods to delimit territories and to estimate their stability throughout a breeding season.