A Critical Review of the Effects of Marking
35
were restricted to a particular sex, implying that not all animals are equally vulnerable to negative effects. However, the prevalence of toe clipping as a tool for
marking small (and some larger, e.g., Andelt and Gipson 1980) mammals
necessitates that additional studies address its potential effects. Other forms of
mutilation include freeze branding, tattooing, and fur clipping (Hadow 1972;
Cheeseman and Harris 1982; Fullagar and Jewel 1965; Stewart and Macdonald 1997), but in most cases effects of these markers have not been evaluated.
However, Stewart and Macdonald (1997) did show that European badgers
(Meles meles) could be effectively marked via fur clipping and that the mark has
no effect on badger body condition. However, the applicability of this technique in colder climates, where loss of guard hairs may affect thermoregulation, requires further study.
radiotransmitters Radiotelemetry of mammals can involve either
external or internal attachment of packages. We found that small mammals
had received more attention than other groups in marker evaluation studies
and that only recently (Cypher 1997; Creel et al. 1997) had terrestrial carnivores received consideration for potential transmitter effects. Most studies we
surveyed failed to find significant effects of transmitters (table 2.4), but discrepancies among studies performed on the same species were noted. For
instance, the meadow vole (Microtus pennsylvanicus) was subjected to four
evaluation tests: Bertaux et al. (1996) did not find a negative effect of transmitters (6.7 to 9.0 percent of body weight) on vole energetics, but other studies (Hamley and Falls 1975; Webster and Brooks 1980; Berteaux et al. 1994)
showed that transmitters affected vole activity patterns. The fact that differential activity of radiomarked voles was not detected as higher energy expenditure (Berteaux et al. 1996) highlights the difficulty associated with attempting
to generalize study results. It also has been shown that effects of radiotransmitters on small mammal behavior and movements often are either short-term
(Wolton and Trowbridge 1985; Henderson and Johanos 1988; Mikesic and
Drickhamer 1992) or specific to a particular sex (Daly et al. 1992), but the
potential demographic implications of such marker effects have not been
assessed.
CRITIQUE OF MARKER EVALUATION STUDIES
A primary shortcoming of many marker evaluation studies is experimental
design. Sometimes this is manifested as a lack of appropriate controls (i.e.,
unmarked animals) to which marked animals can be readily compared. The
35
were restricted to a particular sex, implying that not all animals are equally vulnerable to negative effects. However, the prevalence of toe clipping as a tool for
marking small (and some larger, e.g., Andelt and Gipson 1980) mammals
necessitates that additional studies address its potential effects. Other forms of
mutilation include freeze branding, tattooing, and fur clipping (Hadow 1972;
Cheeseman and Harris 1982; Fullagar and Jewel 1965; Stewart and Macdonald 1997), but in most cases effects of these markers have not been evaluated.
However, Stewart and Macdonald (1997) did show that European badgers
(Meles meles) could be effectively marked via fur clipping and that the mark has
no effect on badger body condition. However, the applicability of this technique in colder climates, where loss of guard hairs may affect thermoregulation, requires further study.
radiotransmitters Radiotelemetry of mammals can involve either
external or internal attachment of packages. We found that small mammals
had received more attention than other groups in marker evaluation studies
and that only recently (Cypher 1997; Creel et al. 1997) had terrestrial carnivores received consideration for potential transmitter effects. Most studies we
surveyed failed to find significant effects of transmitters (table 2.4), but discrepancies among studies performed on the same species were noted. For
instance, the meadow vole (Microtus pennsylvanicus) was subjected to four
evaluation tests: Bertaux et al. (1996) did not find a negative effect of transmitters (6.7 to 9.0 percent of body weight) on vole energetics, but other studies (Hamley and Falls 1975; Webster and Brooks 1980; Berteaux et al. 1994)
showed that transmitters affected vole activity patterns. The fact that differential activity of radiomarked voles was not detected as higher energy expenditure (Berteaux et al. 1996) highlights the difficulty associated with attempting
to generalize study results. It also has been shown that effects of radiotransmitters on small mammal behavior and movements often are either short-term
(Wolton and Trowbridge 1985; Henderson and Johanos 1988; Mikesic and
Drickhamer 1992) or specific to a particular sex (Daly et al. 1992), but the
potential demographic implications of such marker effects have not been
assessed.
CRITIQUE OF MARKER EVALUATION STUDIES
A primary shortcoming of many marker evaluation studies is experimental
design. Sometimes this is manifested as a lack of appropriate controls (i.e.,
unmarked animals) to which marked animals can be readily compared. The