USGS - science for a changing world

Northern Prairie Wildlife Research Center

  Home About NPWRC Our Science Staff Employment Contacts Common Questions About the Site

Point Counts of Birds: What Are We Estimating?1


Example of a breeding range of a bird
Figure 1 - Left: Simplified example of a breeding range of a bird, partially filled with territories. Top right: Simplified example of a rectangular study area containing portions of four territories. Bottom right: The same study area in which three stations for point counts (located at the x's) have been established.


Location and hypothetical paths of birds within the study area
Figure 2 - Top: The location of birds within the study area at one particular instant. Bottom: Hypothetical paths of birds in the study area taken during a period of time.


Cumulative detection zone for a bird
Figure 3 - Left: The area in which a bird can be detected by the observer at a particular instant is called the detection zone. Right: The cumulative detection zone for a bird by an observer during the period of counting.


Detection zones of the same bird for a highly skilled observer and a less-skilled observer
Figure 4 - Cumulative detection zone of the same bird for a highly skilled observer (left) and a less-skilled observer (center). Right: Cumulative detection zone of bird increases with longer duration of counting period.


Using playbacks to increase detection zones
Figure 5 - Cumulative detection zones can be increased from the normal (left) by using playbacks of calls or other attractors (center), but such devices may also induce birds from beyond the study area to move into it (right).


Stations too close together may double count the same bird
Figure 6 - If stations are too close together, relative to the movement patterns of a bird, the bird may be double counted. The x's indicate stations at which the bird, whose path is shown, is counted.


Roads may increase a bird count
Figure 7 - Compared with an area lacking roads (left), a road, indicated at the bottom of the area, may increase the count either by increasing the cumulative detection zones of birds (center) or by increasing the actual number of birds present (right), or both.