Point Counts of Birds: What Are We Estimating?1
Figures
![Example of a breeding range of a bird](images/fig1.gif) |
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](images/fig2.gif)
|
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](images/fig3.gif) |
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. |
|
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](images/fig5.gif)
|
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](images/fig6.gif) |
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](images/fig7.gif) |
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. |