138 
METHODS 
The procedure of automatic interpretation and count 
of game birds consists of three steps: 
1) Aerial photography 
2) Digitization of images 
3) Pattern recognition 
It is emphasized that the aerial photography itself 
is a very valuable tool in bird census even if the automatic counting 
procedure is not used. 
Aerial Photography 
The type of aerial photography to be used is dependent 
on the species to be photographed. The main aim is to pro 
duce clear, distinctive images of birds with the least amount 
of background noise. Black and white photography is most 
suited to work with white birds, like the Greater Snow Geese, 
Chen nyperbora . Color or spectrozonal photography has to be 
applied when the color of birds is more complex. For this 
reason a separate photographic technique has to be developed 
for each species. Another important factor is the scale of 
aerial photography. Large enough area has to be covered by 
a single frame but bird images still have to be separable. 
Our aerial photographic missions uses a two camera 
system. Photographs are taken simultaneously with the two 
cameras. Camera one, with a short focal length lens provides 
pictures covering a large area, while camera two has a long 
focal length lens providing an enlarged strip of the large 
area. The small scale aerial photographs are used for the 
total count of birds. The large scale photos give indication 
of the distribution and percentage of various species and of 
various classes of a species. 
Digitization of Images 
Images of birds are digitized using a scanning micro 
densitometer (Scandig, tech/ops). The transparent aerial 
photographic specimen is mounted on a rotating drum in the 
instrument. The maximum area of a transparency which can 
be scanned is 8" by 9 M . The sampling aperture can be set 
to 50, 100 or 200 micrometers. If the 100 micrometer aper 
ture is used ten point readings will be obtained along one 
millimeter on the transparency. Because of the edging effect 
it is desirable to choose the sampling aperture, such that at 
least 10 sample points will fall within one image.