Counting Birds

Method categorization
Quantitative	Qualitative
Inductive	Deductive
Individual	System	Global
Past	Present	Future

In short: Territory mapping, point counts and line transects are key methods for counting birds. They are suitable for many different groups and species of birds. Additional methods can be found in Sutherland (1996).

Table 1. The use of the methods territory mapping, point counts and line transects for different groups of birds (modified after Sutherland 1996). These methods were selected because they can be applied to most bird species. *=method usually applicable , +=method often applicable.

	Territory Mapping	Line transects	Point counts
Waterbirds	+	+	+
Seabirds		*	+
Wading birds	+	+
Raptors	+	+
Gamebirds	+	+
Near passerines	+	+	+
Passerines	*	*	+

1. Territory Mapping

1.1 What the method does

1.1.1 Creating a map of all sampling points for each occasion

Territory mapping is a method used to study populations of territorial breeding species such as some ducks, gamebirds, raptors and most passerines. These species are territorial during the breeding season. Males sing in their territory and defend the borders of their territory by disputes. Therefore, the breeding territory is used as a census unit. Territory mapping determines the number of territories of each species in a given area. Multiple species can be mapped during one visit (1). In the first step, the land cover of the study plot is mapped at a scale of commonly 1:2500. Then, obvious features of the plot, such as houses, isolated trees, hedges, ponds etc. are marked on the map. In closed habitats such as temperate woodlands plot sizes of 15-20 ha are often sufficient. In a tropical forest, even half of this area could already be suitable. However, in more open habitats, an area of 60-80 ha is needed (1).

The length of the plot borders should be kept as short as possible by not selecting a long, thin area. This is because many bird territories would be overlapping if the plot boundary was long. To determine if a territory belongs to the plot or not might be difficult in some cases. Therefore, round or square plots should be preferred. Species-rich features such as hedges should also not be located at the plot boundary (1). In temperate woodlands, 10 sampling visits per breeding season are recommended. In temperate open habitats, 5 visits may already be sufficient. To cover both early and late breeding species, the visits should be equally distributed throughout the whole breeding season. For songbirds, the census should usually be started after the first hour of dawn and continue no longer than midday. The first hour after dawn may commonly be omitted because most birds are then singing, which might be confusing in areas with high bird densities. After midday, most birds stop singing which usually makes this time frame unsuitable as well. Each visit to a plot can be completed during a morning (1).

In practical terms, in the beginning of the breeding season, several plot maps are produced, one for each visit. The map is attached to a clipboard that can be covered with a large polyethylene bag in case of rain. By walking at a slow pace, the plot is covered with several routes in parallel with a 50 m distance in between the routes. Each bird that was heard or observed is marked at the location with a species code. Comments are made for evidence of nesting such as nests or birds carrying nesting material (1).

If only a certain group of birds, such as raptors, is censused, the same area can be covered much faster by ignoring all other species and mapping at a bigger scale (e.g., 1:10.000 (2)).

1.1.2 Analysis of maps

After the end of the breeding season, the results for each species in each single-visit map are transferred to a species map covering all visits. This is done by marking each observation for visit 1 with an A on the species map, for visit 2 with a B, and so on. After the map is finished for each species, circles are drawn around clusters of observations. Each cluster should contain at least two registrations for 5-7 visits and at least three for 8-10 visits. Each nest is automatically considered to be a cluster. There are different methods to deal with edge territories (1). We suggest considering a cluster to be within the plot if more than 50% of its registrations lie within the plot.

1.2 Strengths and challenges

Territory mapping is a very work-intensive method, that requires good skills in bird identification by the observer. It cannot be applied to species that are colonial or live in loose groups. However, due to the longer time spent in the field compared to line transects and point counts, there is a lower impact of environmental variation such as the weather or the time of visit (1).

The author of this entry is Anna-Lena Rau.

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