field methods influence and alter each other, and they will in turn influence and
potentially alter the survey objectives (Figure 2.10). For example, if the required
survey method for a particular species, or habitat, is labor intensive, this might
dictate that a smaller number of census plots could be covered. Equally, if the
sampling strategy dictated that survey effort needed to be spread across several
potential habitats because of uncertainty over the true habitat requirements of
a scarce species, this might lead us to re-define and simplify our survey objectives.
There are some general issues to consider in planning fieldwork:
- The season and the time of day the survey is to be carried out.
- The size of the survey plots.
- The number of visits to be made to each sample plot or area (commonly
around 10 visits for territory mapping, 2–4 for transects, see below). - The recommended search effort, for example, walking speed (this is particu-
larly important for line transects) or count duration (for point counts), and
general counting protocol for the observers. - The recording units and behavior of the birds to be noted (ages, sexes, nests,
singing, calling males, etc).
The three most common field methods are mapping, and line and point tran-
sects; each of these is discussed in turn below.
2.3.1 Mapping
During the temperate zone breeding season, many individual birds are restricted
to relatively small areas, actively defending a territory or spending much time
around a nest. If a number of visits are made to an area, and the exact location of
birds plotted on maps, it becomes possible to identify clusters of sightings and so
to estimate directly the total number of pairs or territories of each species present.
36 |Bird census and survey techniques
Survey objectivesSampling strategyField methodsSurvey designFig. 2.10Feedback loops operating in survey design between the survey objectives,
sampling strategy, and field methods.