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© 2011 Museum of Southwestern Biology. All rights reserved.

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Sampling Site Selection

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 map here).

 

Sites may:

· 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 sampling area.

 

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.

 

Target Species

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.

 

Supplemental Sampling

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 trappers.

 

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).