The call playback technique is also used for presence/not detected (possible) surveys. Measures of relative abundance using call playback can be calculated if call playbacks are conducted from call playback stations where birds are evaluated as the number of observations per point, or along transects, where birds are evaluated as the number of observations within a given length of fixed-width transect (or some other index of abundance). For details on call playback techniques, refer to the description of Call Playback surveys within the Presence/Not Detected section.
Refer to the Sampling design and sampling effort section and the General considerations section above for consideration of using Call Playback for obtaining measures of relative abundance. For comparing measures of relative abundance using call playback methods, it is especially important to ensure that the equipment and the use of that equipment (e.g., volume and direction) are consistent between call playback stations.
This technique is also used for presence/not detected (possible) surveys. For details on how to conduct this type of survey see Wildlife Tree/sign surveys under the Presence/Not Detected section. Similar methods of measuring the distance from the transect line or point to a wildlife tree or woodpecker activity area are used for measures of relative abundance. The methods as described in the Presence/Not Detected section, combined with changes in study design and data analysis are used for obtaining measures of relative abundance.
A generalized method for conducting wildlife tree/sign surveys involves using simple encounter transects and distance sampling methods. Surveyors walk at a relatively slow pace along transects, recording information about woodpecker sign and species encountered en route. To obtain measures of relative abundance of woodpecker sign, distance sampling procedures such as the widely used Point-to-object and Nearest neighbours methods as described in Buckland et al. (1993; pp. 292-294) should be considered. Refer to the Sampling design and sampling effort (3.4) section above for further reference.