This team is responsible for monitoring the small mammal community on the restored areas.

The small mammal community is an important component of biological diversity in most ecosystems.  Small mammals act as seed dispersal agents, their burrowing disturbs soil and creates microsites for seedling development.  Small mammals also provide a prey base for higher trophic level consumers.

Small mammal populations will be sampled by using the methods developed by (Hallett and O’Connell 2009) removal by trapping on a 9 x 5 grid centered at each sample point and 12 meter spacing.  Trapping will be conducted for three consecutive nights yielding a total of 270 trap nights per sample point.  Data recorded for each specimen include:

• trap location
• date of capture
• species
• standard body measurements
• sex
• reproductive condition

Positive species identification will based on skull morphology and DNA.

References:

Hallett, J. G. and M. A. O’Connell.  2009.  Analysis of Terrestrial vertebrate and vegetation response to ecological restoration.  Upper Columbia United Tribes Wildlife Monitoring and Evaluation Program (UWMEP) – project #2008-007-00.  Report of Progress from 2009 ISRP Wildlife Categorical Review.

The Clark Fork River Delta Restoration Project

Small Mammals Inventory and Monitoring

August 2014

Report by IDFG Wildlife Technician Jerry Hugo

Small Mammals Inventory Team:  IDFG Staff Mitigation Biologist Kathy Cousins, BLM Panhandle Idaho Wildlife Biologist Carrie Hugo, IDFG Wildlife Technician Kate Crowell-Walker

Restoration Plan

The Clark Fork River Delta is located at the mouth of the Clark Fork River where it empties into Pend Oreille Lake in northern Idaho. A mosaic of islands was formed here long ago as the river slowed when confronted by the lake and released its suspended substrates. Annual spring runoff once separated the islands into the classic alluvial fan delta landscape and provided a very valuable habitat for many wildlife species for thousands of years. The subsequent damning of Pend Oreille Lake has caused overall lake levels to rise and fluctuate unnaturally.  This has contributed to severe erosion to (or complete loss of) these valuable islands over time.  An effort is now underway to rebuild, bolster and re-vegetate this delta complex back to its near original glory for the good of both wildlife and mankind.

Objectives

Our first objective was to inventory and survey small mammal populations on those islands that are planned to be physically restored and historic vegetation re-established.  Methods were designed to detect what species are there, determine what habitat types they occupy, and obtain an initial relative abundance index for those species.  Our second objective was to continue to survey and monitor the change in relative abundance (trends) of those species (and new species detected) with a catch per unit effort analysis over a five year period. We also made an effort to detect the presence of larger mammals inhabiting the delta and will monitor their use here over the five year period as well.

Methodology

Area 3 of this island delta complex was chosen to undergo the initial restoration efforts, so we chose the most representative segments of Island 3 to kick off our small mammal surveys. We chose two segments of Island 3 separated by open water; Island 3 North and Island 3 West. Both island segments are dominated by Reed Canarygrass (Phalaris arundinacea), Black Hawthorne  (Crataegus douglasii) and Black Cottonwood (Populus trichocarpa).  Four main habitat types were observed: 

1. Wetland/Canarygrass(no overstory)
2. Dry land/Canarygrass(no overstory)
3. Hawthorne/Canarygrass
4. Cottonwood/Canarygrass  

Museum Special small mammal snap traps were chosen to capture small mammals inhabiting the wetland and terrestrial habitats. This trap not only has the trigger sensitivity to capture light weight shrews, but it is also designed to not destroy the skull due to its lighter spring. Often, the only way to properly identify these small mammals is by close inspection and measurements of the skull and teeth with optical aids and use of a key. Victor rat traps were chosen to capture the larger ground inhabiting small mammals AND arboreal small mammals inhabiting the overstory trees. Arboreal rat traps were drilled on one end and nailed to a tree. A mixture of peanut butter and rolled oats was used as bait for all traps.

Reconyx, Moultrie and Browning motion cameras were also deployed on Island 3 North, Island 3 West and Island 7 in an effort to detect larger mammals inhabiting these islands. A skunk tincture based scent lure was used to attract mammals to each camera trap.

A linear deployment of Museum Special traps was the chosen survey method.  This method allows for the most thorough survey of each island segment and its four main habitat types, but also ensures that traps will intersect a maximum number of small mammal runways and ecotones that small mammals regularly use, especially voles. August was also chosen as the month to conduct these surveys due to our knowledge that multiple litters per summer are produced by small mammals and that their populations peak by the end of each summer.

A GPS location of the starting point for the line transect was taken and a site chosen and scarified for each trap.  A Museum Special trap was baited, then set and placed every 10 feet or 3 paces thereafter. A small piece of colored flagging was affixed over each trap. A Victor rat trap was baited, a site chosen, then set and placed off either side of the transect line every 10 Museum Special traps. A GPS location was taken every 30 Museum Special traps thereafter.

Two methods of deploying our arboreal Victor rat traps on trees were used. Arboreal trap sites were chosen on Island 3 North simply by those trees most likely to inhabit arboreal small mammals. Arboreal trap sites were chosen on Island 3 West by selecting trees most likely to inhabit arboreal small mammals only along and just off of the linear transect trap line. A GPS location was taken for every arboreal small mammal trap placed.

All traps were checked, captured animals collected, and traps were re-baited and reset each morning. A trap night is defined as one trap, baited and set to catch small mammals over night – whether anything was caught or not by morning. Trap trips and/or trap re-baits with no captures were NOT corrected for as ½ trap nights.

Victor rat trap nailed to tree to capture arboreal small mammals.

Island 3 North

A total of 182 Museum Special traps were set on Island 3 North and caught small mammals over three nights. The total Museum Special trap night effort for Island 3 North was 546 trap nights. 18 ground Victor rat traps were set on Island 3 North and caught NO small mammals over three nights. The total ground Victor rat trap night effort for Island 3 North was 54 trap nights. Eight arboreal Victor rat traps were set in trees on Island 3 North and caught NO small mammals over three nights. The total arboreal small mammal trap night effort for Island 3 North was 24 trap nights.

The overall total trap night effort for small mammals on Island 3 North was 624 trap nights.

Island 3 West

A total of 182 Museum Special traps were set on Island 3 West and caught small mammals over two nights. The total Museum Special trap night effort for Island 3 West was 364 trap nights. 18 ground Victor rat traps were set on Island 3 West and caught NO small mammals over two nights. The total ground Victor rat trap night effort for Island 3 West was 36 trap nights. Eight arboreal Victor rat traps were set in trees on Island 3 West and caught NO small mammals over two nights. The total arboreal small mammal trap night effort for Island 3 West was 16 trap nights.

The overall total trap night effort for small mammals on Island 3 West was 416 trap nights.

The entire trap night effort for capturing small mammals in area 3 was 1, 040 trap nights. When attempting to capture all species present and obtain a relative abundance index for small mammals in a given area – a goal of 1,000 trap nights will give optimal confidence that the data collected accurately represents reality. Therefore we feel that we now have a solid initial index of small mammal relative abundance in area 3 and this index will be useful in long term population trend analysis as this area is restored.

Results

The following three small mammal species were captured in Area 3 in Museum Special traps. NO small mammals were captured in any of the ground or arboreal Victor rat traps.

The Vagrant Shrew (Sorex vagrans) – insectivore
The Meadow Vole (Microtus pennsylvanicus) – herbivore
The Deer Mouse (Peromyscus maniculatus) – granivore/omnivore

Island 3 North
Vagrant Shrews captured – 7
Catch per trap night effort for Vagrant Shrews is 7/ 546 = .013 or a shrew caught per every 78 trap nights

Meadow Voles captured – 12
Catch per trap night effort for Meadow Voles is 12/546 = .022 or a vole caught per every 45.5 trap nights

Deer Mice captured – 15
Catch per trap night effort for Deer Mice is 15/546 = .027 or a d. mouse caught per every 36.4 trap nights

Island 3 West
Vagrant Shrews captured – 5
Catch per trap night effort for Vagrant Shrews is 5/364 = .014 or a shrew caught per every 73 trap nights

Meadow Voles captured – 8
Catch per trap night effort for Meadow Voles is 8/364 = .022 or a vole caught per every 45.5 trap nights

Deer Mice captured – 5
Catch per trap night effort for Deer Mice is 5/364 = .014 or a d. mouse caught per every 73 trap nights

Our crew mantra of “No trap left behind” was upheld except for one arboreal small mammal Victor rat trap that was absconded by a Black Bear (Ursus americanus). Therefore, we were able to check all traps set each day during the survey, except one. We assume the bear preferred the peanut butter/oat mix alone instead of an arboreal small mammal.  Evidently our bait mix is very attractive to banana slugs as well? We caught 64 banana slugs during the survey in our Museum Special traps. We saw and heard ONE Red Squirrel (Tamiasciurus hudsonicus) on Island 3 West in a very small grouping of coniferous fir trees.  We saw elk and white-tail deer tracks and raccoon and coyote scats.

Summary
Area 3 of the Clark Fork River Delta currently has a very limited array of vegetative diversity. Reed canarygrass is the dominate vegetation and out-competes many important native plants, shrubs and trees that could support a greater diversity of small mammals. Therefore, it is not surprising to only find evidence of four small mammal species (Vagrant Shrew, Meadow Vole, Deer Mice and Red Squirrel) inhabiting this area. It is also not surprising that these small mammal species are present at such relatively low population levels. It appears that on these delta islands, small mammal diversity is strongly linked to habitat diversity.

• Deer Mice were most often associated with dry, terrestrial woody debris sites under the Hawthorne and Cottonwood over stories.
• Meadow Voles were most often associated with wetland or dry land reed canarygrass in the more open over story habitats.
• Vagrant Shrews were most often associated with dry land reed canarygrass habitats in the more open over story habitats AND in the ecotones of dry land reed canarygrass up against hawthorne or black cottonwood overstory groves.
• Red Squirrel sighting and sign was only associated with the very small number and groupings of coniferous fir trees.