particularly critical of the claims made for commercially produced ultrasonic devices
and of the standard of experimental testing in this field.Habitat and food manipulation
This is certainly the most elegant of control techniques because it does not have
to counteract density-dependent compensation within the pest population. The key
habitat elements are water and shelter. Red squirrels (Tamiasciurus hudsonicus) in
British Columbia lodgepole pine forests can be dissuaded from feeding on the stems
of very young trees by aerial spreading of sunflower seeds. This alternative food source
is preferred over the pines (Sullivan and Klenner 1993). This diversionary feeding
has possibly reduced predation by raptors on grouse chicks in Britain (Redpath
et al. 2001), and by small carnivores and corvids on artificial grassland bird nests in
Texas (Vander Lee et al. 1999). Supplemental food reduced predation by striped skunks
(Mephitis mephitis) on duck nests, but other carnivores increased their predation so
the results were equivocal (Greenwood et al. 1998). Where food is provided in local
concentrations at feeders (instead of distributed widely), the high density of carni-
vores may increase predation of ground-nesting birds (Cooper and Ginnett 2000).
Thus, the way food is presented is important to the outcome.The control of a pest species, in the sense of holding its density at a reduced level,
is essentially a sustained-yield operation where the yield is not used. Reduction in
density is not an end in itself: the success of the operation is measured not by the
number of animals removed but by whether the objective was attained, be it the increase
in density of an endangered species, an increase in grass biomass, or the reduction
of damage to fences. The logic of experimental design must be utilized to determine
whether benefits exceed costs, whether the treatment has a deleterious effect on non-
target species, and whether the targeted “pest” is really the cause of the perceived
problem.364 Chapter 20