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lens or smaller. However, the risk of handshake increases with the focal length of
the lens, so if you are using a 100 mm lens then you would need a shutter speed of
1/100th s to eliminate the risk of handshake, and a shutter speed of 1/500th s to
eliminate handshake using a 500 mm lens etc. We must also attempt to freeze the
movement of the birds which, in flight, can be more demanding. As a general rule,
setting the shutter speed at 1/500th s will be fast enough to still the movement in
most flocks of birds: only the Starling murmuration in the case studies below used
a higher shutter speed than this, at 1/640th s.
In summary, if you set the camera at ISO 400, with the f-stop at f11 and the shutter speed at 1/500th s, this should suffice to capture well-lit, well-defined images
with a good depth of field: images with these characteristics are ideal for carrying
out counts in ImageJ.
Capturing the Images
There are two basic alternatives for capturing images of bird flocks:
• Vertical images of feeding or breeding birds taken from light aircraft or
Unmanned Aerial Vehicles (UAVs); and
• Oblique images of cliff-based breeding colonies or flocks of birds in flight, typically taken from the ground, but also potentially by UAV.
Capturing Vertical Images of Feeding or Breeding Birds
Until recently, the only practical option for collecting vertical images of birds was
by light aircraft, similar to the four-seat Cessna used to capture the flamingo images
in Case Studies 3 and 4. This is no longer the case and the potential for using UAVs
to capture vertical images of birds is increasing rapidly. Although there are limitations to the area that UAVs can cover during one flight, which is often in the region
of 1 square km, this would be sufficient to capture images of many feeding hotspots
or breeding colonies. Furthermore, there is always the option of using more than
one UAV or carrying out more than one flight.
Vertical images of birds feeding on the ground or in water offer the best chance
for accurate counts, because the birds are all the same distance from the camera:
making it possible to differentiate different species by size as well as plumage. It
also means that we do not need to set a large depth of field on the camera, so an
f-stop of f8, or even f5.6, might be sufficient to provide adequate images for counts.
Another advantage of vertical images is that, whether breeding or feeding, birds
often prefer to have their own personal space: this space can be clearly visible on
vertical images but is less obvious on oblique images (see Fig.1).
Improving the Accuracy of Bird Counts Using Manual and Automated Counts…
lens or smaller. However, the risk of handshake increases with the focal length of
the lens, so if you are using a 100 mm lens then you would need a shutter speed of
1/100th s to eliminate the risk of handshake, and a shutter speed of 1/500th s to
eliminate handshake using a 500 mm lens etc. We must also attempt to freeze the
movement of the birds which, in flight, can be more demanding. As a general rule,
setting the shutter speed at 1/500th s will be fast enough to still the movement in
most flocks of birds: only the Starling murmuration in the case studies below used
a higher shutter speed than this, at 1/640th s.
In summary, if you set the camera at ISO 400, with the f-stop at f11 and the shutter speed at 1/500th s, this should suffice to capture well-lit, well-defined images
with a good depth of field: images with these characteristics are ideal for carrying
out counts in ImageJ.
Capturing the Images
There are two basic alternatives for capturing images of bird flocks:
• Vertical images of feeding or breeding birds taken from light aircraft or
Unmanned Aerial Vehicles (UAVs); and
• Oblique images of cliff-based breeding colonies or flocks of birds in flight, typically taken from the ground, but also potentially by UAV.
Capturing Vertical Images of Feeding or Breeding Birds
Until recently, the only practical option for collecting vertical images of birds was
by light aircraft, similar to the four-seat Cessna used to capture the flamingo images
in Case Studies 3 and 4. This is no longer the case and the potential for using UAVs
to capture vertical images of birds is increasing rapidly. Although there are limitations to the area that UAVs can cover during one flight, which is often in the region
of 1 square km, this would be sufficient to capture images of many feeding hotspots
or breeding colonies. Furthermore, there is always the option of using more than
one UAV or carrying out more than one flight.
Vertical images of birds feeding on the ground or in water offer the best chance
for accurate counts, because the birds are all the same distance from the camera:
making it possible to differentiate different species by size as well as plumage. It
also means that we do not need to set a large depth of field on the camera, so an
f-stop of f8, or even f5.6, might be sufficient to provide adequate images for counts.
Another advantage of vertical images is that, whether breeding or feeding, birds
often prefer to have their own personal space: this space can be clearly visible on
vertical images but is less obvious on oblique images (see Fig.1).
Improving the Accuracy of Bird Counts Using Manual and Automated Counts…