Sampling strategy and design for the Tongass is consistent with methods used to
collect similar data in previous years on the Tongass and in large inventory projects
elsewhere in Alaska to facilitate regional application of results. The sampling
strategy employs judgement-based sampling across the diversity of terrestrial habitats
within biogeographic units (Subregions maphere).
· represent under-sampled areas (knowledge “gaps”),
· possess a high probability of capturing the diversity of species,
· are located within representative habitats,
· reflect important resource management issues (e.g., hot spots of diversity; hot
spots map here),
· are accessible for current operations and long-term monitoring, and/or;
· possess other noteworthy characteristics such as important ecological processes,
unique communities, or biogeographic features (e.g., linkage areas, dispersal corridors
By evaluating the list of candidate sites, 3 to 5 “core” sampling sites are identified
from which to establish a base of operations and to conduct inventories. Between
10 and 15, 100-500 m transects are sampled per site. The area of the site is defined
be the maximum walking distance of crew members thereby limiting the scope of the
Using maps and local knowledge of selected sites, we evaluate the feasibility of
operating at selected sites. In instances where the site is unsuitable, the closest
site within a 1-km radius is selected. If no suitable sites can be located within
that radius the next alternative site is selected.
Capture and Collections
Standard and non-standard belt-transects (traplines) are used to document the occurrence
of small mammal species. Transects are established across the range of habitat types
present. We concentrate sampling effort in edge and patchy habitats (e.g., the margins
of ponds and streams, beach fringe, talus slopes, and blow-down areas) and elevational
gradients to maximize diversity of species collected.
Small mammal trapping is usually conducted from mid-July to August when populations
are at their peak and the ability to detect and capture less common species is greatest.
Field surveys consist of both targeted and opportunistic sampling that employs different
trapping techniques. While conducting field inventories, a primary focus of all
efforts is to document the full diversity of species present.
Removal sampling methods is used to document species occurrence, relative abundance,
and investigate genetic differentiation. To minimize trap bias, a variety of capture
devices may be used including museum special snap traps, pitfall traps, rat traps,
conibears, snares, and leg-hold traps. All specimens collected are preserved and
archived for future research and museum use.
Specimen-based inventories, which are recognized as essential to good science, require
large sample sizes through removal sampling for the following reasons:
· Various shrews and small rodents are difficult or impossible to identify without
specimens in-hand. Close examination of tooth pattern, body measurements, and other
characteristics is necessary to differentiate Alaska’s shrews. Microtus voles can
also be especially difficult to differentiate. Microtus oeconomus and M. pennsylvanicus,
in particular, are so similar that positive identification requires examination of
molars under magnification.
· Many captures of the most common and widespread species may be necessary in order
to document rare and uncommon ones.
As noted by Reynolds et al. (1996), the number of animals removed from a population
has no biological significance unless it is related to the total number of animals
in the population and their rate of replacement. Alaska’s small mammals are short-lived
and prolific, with reproductive potentials more than sufficient to accommodate low
levels of removal found in this inventory project.
Shrews, Voles, Mice, Lemmings. Shrews, voles, mice, and lemmings are surveyed using
standardized methods developed in previous inventories. Standard belt transects (trapline)
are established using of 20 to 40 trap stations. Transect length is typically 100m
and trapping stations are placed approximately 8m apart. At each station, either
2 museum special snap traps or 1 snap trap and 1 pitfall trap (primarily for shrews
and lemmings) are set within 2 m of each station point. Snap traps are baited with
a mixture of rolled oats and peanut butter. Pitfall traps are unbaited and buried.
Traplines are operated continuously for 2 or more nights depending on trapping success.
Traplines are checked twice daily for captures.
Squirrels. Sciurids (flying squirrels, red squirrels, marmots, and arctic ground
squirrels) are taken opportunistically using shotguns or by establishing special
transects in conjunction with shrew-vole traplines. In forest habitats, standard
transects are used with baited rat traps tied upside-down in trees to capture flying
and red squirrels.
Bats. Bats species are typically rare to uncommon. In general, bats are difficult
to collect and identify out of hand (Nagorsen and Brigham 1993). Bats are usually
captured with mist nets placed in strategic areas or hand-captured at roosts. To
identify potential sampling sites (e.g., outbuildings, mines, etc.), we routinely
contact people having local knowledge. Bats are collected opportunistically.
Hares. Lagomorphs, like squirrels, are taken opportunistically by trap or shotgun.
Wire snares set along trails are effective for capturing snowshoe hares.
Small Carnivores. Specimens of ermine and least weasels are most frequently documented
as incidental captures by furbearer trappers during the winter months. Box traps
set in suitable habitat occasionally work, as do rat traps. Weasels are occasionally
collected with a light load shotgun.
Opportunistic sampling of various species is conducted through shrew-vole traplines,
rat traps, mist nesting, wire snares, shotgun or rifle sampling, and collateral take
by trappers or some combination of these methods. Emphasis is placed on documenting
the full range of species using these methods.
When feasible, we coordinate small mammal trapping efforts with the activities of
other inventory studies (e.g., vascular plant inventory).
Collateral take is the acquisition of target specimens through secondary or indirect
means, such as purchase from trappers.Specimen acquisition through collateral take
may be conducted as an alternative to opportunistic shotgun or rifle sampling to
document squirrels, marmots, hares, pikas, and mustelids. This is achieved by working
closely with wildlife managers the winter preceding fieldwork to identify interested
Carcasses of these species obtained from trappers are acquired with locality and
date information. However, it is unlikely that these specimens will be associated
with detailed habitat information.
What about Inventories of Plants, Birds and other Organisms?
Much of the biotic diversity of southcoastal Alaska remains poorly documented. Plans
are being developed to see more multidisciplinary monitoring and inventory efforts
that incorporate other organisms in addition to mammals. We now, for example, routinely
collect samples of amphibians, ground beetles, and snails during the course of our
field work that are then loaned to researchers with expertise in these groups (e.g.,
land snails to malacologist Robert Forsyth in Smithers, British Columbia; ground
beetles to UAM, Fairbanks).