11.8 Disturbance
If studying disturbance is necessary to relate the level of disturbance to the ecology
of the species. A major difficulty is that there are numerous categories, for example,
bird of prey, car, tractor, hunter, person on horse, person walking, or person
walking with dog. With numerous categories it is then difficult to relate the impact
on the birds to any one category. One approach is to measure each separately but
combine similar groups in the analysis. Disturbance is usually measured by either
scan counts or focal counts. In scan counts the number of disturbers is counted in
each of a series of the observer’s fields of view as if a series of non-overlapping
photographs had been taken. For example, by moving from field to field and
recording the disturbance at the first instance at which the entire field can be seen.
If individuals then arrive or leave they are ignored. Scan counts can be repeated, for
example, by measuring the number of disturbers at snapshots every 10 min. In
focal counts an area is watched for a given period (e.g. an hour) and the number of
potential disturbers counted. It is then often common to assess the impact on the
birds by measuring some of number disturbed, distance at which disturbed, time
disturbed for, and whether the birds resettle in the same area or elsewhere.
Acknowledgements
We thank Aldina Franco and Ian Newton for useful suggestions.
References
Aebischer, N.J., Robertson, P.A., and Kenward, R.E. (1993). Compositional analysis of
habitat use from radio tracking data. Ecology, 74, 1313–1325.
Ausden, M. (1996). Invertebrates. In Ecological Census Techniques, ed. W.J.Sutherland,
pp. 139–177. Cambridge University press, Cambridge.
Bakken, G.S., Buttemer, W.A., Dawson, W.R., and Gates, D.M. (1981). Heated taxidermic
mounts: a means of measuring the standard operative temperature affecting small birds.
Ecology, 62, 311–318.
Bowden, C.G.R. and Green, R.E. (1994). The Ecology of Nightjars on Pine Plantations in
Thetford Forest. RSPB, Sandy.
Bryant, D.M. (1975). Breeding biology of the house martin Delichon urbicain relation to
aerial insect abundance. Ibis, 117, 180–215.
Chamberlain, D.E., Hatchwell, B.J., and Perrins, C.M. (1999). Importance of feeding
ecology to the reproductive success of Blackbirds Turdus merulanesting in rural habitats.
Ibis, 141, 415– 427.
Davenport, I.J., Bradbury, R.B., Anderson, G.Q.A., Hayman, G.R.F., Krebs, J.R.,
Mason, D.C., Wilson, J.D., and Veck, N.J. (2000). Improving bird population models
using airborne remote sensing. Int. J. Remote Sens., 21, 2705–2717.
Flaspohler, D.J. (1998). A technique for sampling flying insects. J. Field Ornithol., 69, 201–208.
266 |Habitat assessment