Geoscience Reference
In-Depth Information
use of fishers between his study, where he followed tracks in the snow, and
another nearby radiotelemetry study; he attributed the difference to error in
the telemetry system and consequent incorrect habitat categorization for ani-
mals near edges. Nams (1989) showed that simply discarding locations
because of large telemetry error, as is common practice, exacerbates bias; he
offered a procedure for circumventing it, but few studies have used it. Kufeld
et al. (1987) suggested using the habitat composition of error polygons formed
by the triangulation of radio bearings, but this would not alleviate bias.
Chapin et al. (1998) solved the problem a different way. In a study of habitat
use of American martens (
Martes americanus
), which have a documented affin-
ity for mid- to late-successional forests, they classified telemetry locations that
were outside small patches of forest but within telemetry error of the edge as
representing use of those forest patches.
Even if habitat use can be measured accurately, biases may result from sam-
pling or analytical procedures. Habitat use may vary by individual, sex-age
group, social status, time of day, season, and year, yet many (most) studies pool
individuals and do not sample adequately. Schooley (1994) reviewed habitat
studies published in the
Journal of Wildlife Management
and found that
most lasted only 2 years, and most pooled results across years without testing
for annual variation. He used results of a black bear (
Ursus americanus
) study
to show that habitat use can vary annually, and that the data pooled across
years can yield misleading results. Beyer and Haufler (1994) found that most
published studies that they reviewed collected data only during daylight hours;
in their study of elk (
Cervus elaphus
), habitat use differed between day and
night. Similarly, Arthur and Schwartz (1999) reported diurnal and nocturnal
differences in habitat use for brown bears (
Ursus arctos
) that fed at a salmon
stream that was used by people during the day; this difference was detected
with data from
GPS
collars, but was not apparent from conventional diurnal
telemetry data. Ostfeld et al. (1985) and Belk et al. (1988) observed sex-related
differences in habitats used by ground-dwelling rodents; Belk et al. remarked
that combining the two sexes would produce a false perception of habitat use.
Paragi et al. (1996) observed differences in habitat use of resident and transient
martens. Boitani et al. (1994) and Macdonald and Courtenay (1996) observed
individual differences in habitat use, apparently related to social status. Bow-
ers (1995:18) found that habitat use of eastern chipmunks (
Tamias striatus
)
varied significantly with distance from their burrows, a finding noticeable only
by considering the data on an individual basis. “It is time,” Bowers com-
mented, “that ecologists recognize that microhabitat selection and usage is a
process involving individuals, not species.”
