3. Protocol

Interest in woodpecker field surveys has increased over the last decade. The interest is primarily a response to habitat alterations caused by widespread forest fragmentation, simplification of forest structure through even-aged stand management, and reduction in certain forest habitat components such as wildlife trees. There is great variation, however, in the amount of study effort expended on different species. While Pileated Woodpeckers have been extensively investigated (especially in the United States), few studies have been conducted on most of the other species. Surveys of woodpeckers as a subgroup of cavity-nesting birds (e.g., Raphael and White 1984; Sedgewick and Knopf 1986; Lundquist and Mariani 1991) are more common than investigations of individual woodpecker species or genera. Most surveys have been conducted during the spring/summer or breeding season. Winter surveys are rare and may be important as habitat requirements during this period may be more restrictive (Raphael and White 1984; Galen 1989).

The recommended protocols are based on information obtained from: (i) a monitoring workshop for Pileated Woodpeckers and other cavity-nesters in February 1992, organized by The Wildlife Society, Oregon chapter, (ii) direct communication with active woodpecker researchers in the Pacific Northwest; (iii) methods outlined in various woodpecker studies; (iv) a wildlife tree/woodpecker research project in the interior of British Columbia (Steeger and Machmer 1995; Steeger et al. 1996); and (v) a subsequent review of optimal survey design and statistical techniques (Integrated Ecological Research 1998). An excellent critical review of methods for censusing diurnal forest birds (including woodpeckers) is given in Manuwal and Carey (1991).

For all survey methods, the following general assumptions must be met if conclusive, accurate, precise, and statistically valid results are to be obtained (from Manuwal and Carey 1991; see also RIC Species Inventory Fundamentals manual):

• Birds are correctly identified;
• Sampling effort is sufficient and adequately timed to detect presence of species or to obtain the desired precision for comparative purposes;
• Differences among observer survey ability are insignificant or can be accounted for;
• Differences among species detectability are insignificant, can be accounted for, or are unimportant;
• Differences in species detectability among habitats or survey periods are insignificant or can be accounted for.

Design and evaluation of woodpecker inventory methods must take species-specific characteristics and local ecological conditions into consideration. The following points are worth considering:

• There is potentially great variation within and between forest stands in vegetation density and terrain features. The probability of detecting and identifying individual woodpeckers, their nests and territories can vary accordingly.
• Woodpeckers with relatively large home ranges or territories (e.g., Pileated, Black-backed, or Three-toed Woodpeckers) are not very numerous. Surveying such species usually involves sampling an area proportional to the species-specific home range or territory size.
• During non-breeding seasons, most woodpeckers are solitary, quiet and therefore difficult to detect. They are, however, year round residents in British Columbia and may be surveyed throughout the year.
• Occurrence of woodpeckers within any given area is variable in space and time and closely linked to the availability of suitable nesting, feeding and roosting trees. Woodpecker aggregations and population irruptions are periodically observed in burns and areas of epidemic bark beetle infestations (Yunick 1985, Murphy and Lehnhausen 1988, Hutto 1995, Machmer and Steeger 1995).
• As occurrence and abundance of woodpeckers is highly dependent on the availability of wildlife trees, surveyors are encouraged to collect data on trees used by woodpeckers (e.g., nesting, roosting, feeding trees). Such information is important for assessing woodpecker habitat use and quality.