Assessment of Short-Term Effectiveness of Artificial Resting

Home , European pine marten, Western spotted skunk

ASSESSMENT OF SHORT-TERM EFFECTIVENESS OF ARTIFICIAL RESTING

AND DENNING STRUCTURES FOR THE HUMBOLDT MARTEN (MARTES

CAURINA HUMBOLDTENSIS) IN HARVESTED FORESTS IN NORTHWESTERN

CALIFORNIA

Matthew S. Delheimer

A Thesis Presented to

The Faculty of Humboldt State University

In Partial Fulfillment of the Requirements for the Degree

Master of Science in Natural Resources: Wildlife

Committee Membership

Dr. Micaela Szykman Gunther, Committee Chair

Dr. Matthew Johnson, Committee Member

Dr. William Zielinski, Committee Member

Keith Slauson, Committee Member

Dr. Yvonne Everett, Graduate Coordinator

July 2015

ABSTRACT

ASSESSMENT OF SHORT-TERM EFFECTIVENESS OF ARTIFICIAL RESTING AND DENNING STRUCTURES FOR THE HUMBOLDT MARTEN (MARTES CAURINA HUMBOLDTENSIS) IN HARVESTED FORESTS IN NORTHWESTERN CALIFORNIA

Matthew S. Delheimer

The Humboldt marten (Martes caurina humboldtensis) is a habitat specialist that requires large, old woody structures such as live trees, snags, and logs to provide suitable resting and denning locations. Many timber harvesting practices remove these woody structures and harvested forests typically have a poor availability of suitable resting and denning locations for martens. Artificial structures (“marten boxes”) may increase the availability of resting and denning locations for martens in harvested forests by acting as surrogates for natural woody structures. Increasing the availability of resting and denning locations may improve suitability of harvested forest stands and thereby accelerate marten recolonization of harvested forests. In 2013, I deployed 55 marten boxes among three study sites in northwestern California. I monitored animal visitation and animal use with remote cameras at 43 boxes for approximately 12 months and detected 10 mammalian species. Douglas squirrel (Tamiasciurus douglasii) was the most common small mammal species and fisher (Pekania pennanti) was the most common carnivore species visiting boxes. Animal use of boxes (i.e., entering the box) was rare but was documented for four species, including marten. Track plate surveys conducted ii

prior to box deployment indicated that the Goose Creek and Mill Creek study sites were not marten-occupied; however, naïve occupancy estimates at the two sites were significantly different for three out of five other carnivore species detected. Habitat transects revealed that Pecwan Creek, the marten-occupied site, had a significantly higher density of potential resting structures for martens than the Goose Creek or Mill Creek sites. Differences between study sites in terms of box visitation, species occupancy, and potential resting structure availability may be the result of different animal species assemblages, dominant forest types, forest management histories, or other processes. My data demonstrate visitation and use of boxes by martens; however, longer-term monitoring of boxes will likely be necessary to better understand their effectiveness as a conservation tool for the Humboldt marten.

iii

ACKNOWLEDGEMENTS

This project was made possible through the collaboration, guidance, and support of numerous agencies, organizations, and individuals. First off, I would like to thank my committee members: Dr. Micaela Szykman Gunther, for taking me on as a student and guiding me through process; Dr. William Zielinski, for his enthusiasm, accessibility, and thoughtful input; Dr. Matthew Johnson, for his insightful ideas; and Keith Slauson, for developing the marten box project, allowing me to execute it, and continuing to provide feedback and support.

In addition to my committee members, there is a long list of folks who deserve recognition for their efforts. Thanks to Travis Langer at the USDA Forest

Service/Redwood Sciences Lab (RSL) for being the marten box construction foreman, and for truly getting the project off the ground. Ric Schlexer at RSL and Brenda Devlin at Six Rivers National Forest provided logistical support. Amber Transou and Jay Harris at California State Parks provided field equipment and knowledge of the Mill Creek watershed. Anthony Desch at Humboldt State University allowed me to raid the Wildlife stockroom of some of its best cameras and a lot of batteries. Keith Hamm and Desiree

Early at Green Diamond Resource Company provided logistical support at the end of the project. Dan Barton and Tim Bean at Humboldt State University offered valuable input on the occupancy component of the analysis.

The assistance of interns, volunteers, and undergraduate students was invaluable to the success of this project. Special thanks to Nalani Ludington, for putting up with me iv

for my entire first summer of field work. Matthew Fountain and Gary Sousa provided integral assistance during the occupancy surveys. Rachel Guinea, Riley Gorman, Rachel

Nypaver, and Abby Rutrough aided in the most difficult part, getting the marten boxes off the ground.

Many thanks to the Save-The-Redwoods League for initial financial support. The

USDA Forest Service/Redwood Sciences Lab contributed additional financial support, as well as logistical support, remote cameras, field equipment, field vehicles, and much else.

California State Parks provided the raw redwood material for the marten boxes and a number of remote cameras. California State Parks and Redwood National and State

Parks, Green Diamond Resource Company, and the Yurok Tribe graciously allowed me to travel across and work on their lands. And last but not least, thanks to all of the individuals, organizations, and agencies involved in the Humboldt Marten Conservation

Group for their continuing dedication to protecting and restoring the Humboldt marten throughout its historical range.

TABLE OF CONTENTS

ABSTRACT ...... ii

ACKNOWLEDGEMENTS ...... iv

LIST OF TABLES ...... vii

LIST OF FIGURES ...... viii

LIST OF APPENDICES ...... ix

INTRODUCTION ...... 1

STUDY AREA ...... 9

MATERIALS AND METHODS ...... 12

Marten Box Deployment ...... 12

Track Plate Surveys ...... 14

Marten Box Monitoring ...... 16

Habitat Transects ...... 18

RESULTS ...... 22

Track Plate Surveys ...... 22

Marten Box Monitoring ...... 24

Habitat Transects ...... 28

DISCUSSION ...... 32

MANAGEMENT IMPLICATIONS AND CONCLUSIONS ...... 39

LITERATURE CITED ...... 43

APPENDICES ...... 56

LIST OF TABLES

Table 1. Naïve occupancy of five carnivore species at the quadrant (n=40 per site) scale at the Goose Creek and Mill Creek study sites in northwestern California, July to September 2013...... 23

Table 2. Density (mean number of structures per hectare) of resting structures for the Humboldt marten at the Goose Creek, Mill Creek, and Pecwan Creek study sites in northwestern California, July to October 2014. Includes standing structure density, ground-based structure density, and total structure density (combined standing and ground-based structure densities). Standard error (SE) estimate in parentheses...... 29

Table 3. Density (mean number of structures per hectare) of standing resting structures for the Humboldt marten at the Goose Creek, Mill Creek, and Pecwan Creek study sites in northwestern California, July to October 2014. Includes live conifer density, live hardwood density, live tree density (combined live conifer and live hardwood densities), and snag density. Standard error (SE) estimate in parentheses...... 31

vii

LIST OF FIGURES

Figure 1. Study area including land ownership boundaries and marten box locations at three study sites in northwestern California...... 10

Figure 2. Example of marten box distribution at the Mill Creek study site in northwestern California. Each grid was 1-km2 in size and was divided into four equal 0.25-km2 quadrants. Each quadrant received one marten box (red squares)...... 13

Figure 3. Percent of marten boxes visited by five small mammal species and five carnivore species at three study sites in northwestern California, June 2013 to October 2014...... 25

Figure 4. Mean number of visits at marten boxes by five small mammal species and five carnivore species at the Goose Creek, Mill Creek, and Pecwan Creek study sites in northwestern California, June 2013 to October 2014. Bars represent standard error (SE) estimate...... 26

viii

LIST OF APPENDICES

Appendix A: Marten box construction and installation methods including structural and design modifications to the Vincent Wildlife Trust marten “den” box, as well as suggestions for future marten box deployment and additional box modifications...... 56

Appendix B: Marten box design schematic (Messenger et al. 2006), box structural components, box deployment, and examples of animal visitation at boxes in the Pecwan Creek study site in northwestern California...... 60

Appendix C: Complete results from track plate surveys to assess carnivore species occupancy at the Goose Creek and Mill Creek study sites in northwestern California, July to September 2013. Includes number of track plate boxes surveyed at each study site and across study sites (n) and number of track plate boxes surveyed that a given species was detected at each study site and across study sites (detected)……………...…...………...61

Appendix D: Complete marten box monitoring results, including visitation and use at by 10 mammal species at the Goose Creek, Mill Creek, and Pecwan Creek study sites in northwestern California, June to October 2014. Includes total number of marten boxes (n); total number of boxes visited by a given species (visited); total number of visits at marten boxes for a given species (total); and whether or not a given species was documented to enter a marten box (use)…………………………………………………62

Appendix E: Complete results of habitat transects for standing resting structures at the Goose Creek, Mill Creek, and Pecwan Creek study sites in northwestern California, July to October 2014. Includes mean diameter at breast height (DBH) and DBH range of hardwood and conifer live trees and snags, and number of structural element types (branch platform, broken top, cavity) within each standing structure type……………...63

Appendix F: Review of previous literature documenting nest box use by mammals. Carnivore species are in bold lettering…………………………………………………...64

Appendix G: Review of previous literature concerning carnivore species documented to use tree cavities for resting or denning purposes………………………………………...65

INTRODUCTION

The loss of suitable habitat has been identified as one of the primary processes threatening species persistence (Lindenmayer and Fischer 2006). Habitat loss can take many forms, including landscape conversion, habitat fragmentation, and encroachment from human development. Timber harvesting may result in habitat loss for forest- dependent wildlife by reducing overhead forest cover, fragmenting forest stands, and removing large, old, and complex forest structures. Restoration of harvested forest stands to suitable conditions may take decades or centuries to occur. In the short-term, it is critical to understand the mechanisms that allow for wildlife species to persist in harvested forests and to develop management strategies to mitigate the effects of forest management on habitat loss.

Martens are carnivores and are medium-sized members of the weasel family

(Mustelidae); North American martens include the American marten (Martes americana) and the recently-recognized Pacific marten (M. caurina; see Dawson and Cook 2012).

Martens in the western United States are typically associated with structurally complex, late-seral and old-growth coniferous forests (Buskirk and Ruggiero 1994). Marten populations are characterized by low densities, low reproductive rates, habitat specialization, and relatively large spatial habitat requirements (Buskirk and Ruggiero

1994). As habitat specialists, martens are considered to be indicators of healthy forest ecosystems (Zielinski and Kucera 1995).

Martens experienced significant range contractions in the coterminous United

States during the 20th century (Laliberte and Ripple 2004). Decreased distribution of coastal marten populations in the Pacific states is of particular cause for concern, where the Humboldt subspecies (M. caurina humboldtensis) of the Pacific marten has been extirpated from the majority of its historical range in Oregon and northwestern California

(Zielinski et al. 2001). This decrease has been dramatic for the California population of the Humboldt marten, which appears to currently occupy <5% of its historical range

(~400 km²) and to number <100 individuals (Slauson and Zielinski 2004, Slauson et al.

2009).

The initial population decline of the Humboldt marten in California is likely attributable to unregulated fur trapping prior to the 1930s (Twining and Hensley 1947); however, legal trapping for martens in California ended in 1946. The continued absence of the Humboldt marten from large portions of its historical range is likely due to a reduction in suitable forest habitat as a result of timber harvesting (Zielinski et al. 2001).

Large areas of forest in the historical range of the Humboldt marten in northwestern

California are privately-owned and intensively harvested for timber production; for example, Fox (1996) estimated that <5% of the original forest cover in the redwood region remains unharvested. This has resulted in a largely structurally-simplified, early- to mid-seral (<100 years old; Thornburgh et al. 2000) landscape in harvested forests. The largest amounts of remaining old growth and late-successional coastal forests are found on public lands (USDA Forest Service 1992).

Grinnell et al. (1937) originally described the Humboldt marten in northwestern

California as occurring in a “narrow northwest humid coastal strip, chiefly within the redwood belt”, from sea level to ~1000 m; Slauson and Zielinski (2007) noted that >80% of historical records occurred in coastal redwood (Sequoia sempervirens) and Douglas fir

(Pseudotsuga menziesii) forests within 25 km of the coast. However, the extant population of Humboldt martens in northwestern California appears to be largely absent from redwood forests, with the contemporary distribution of the Humboldt marten occurring primarily in two distinct habitat types: Douglas fir dominated forest in old growth and late-seral stages; and to a lesser extent “serpentine” habitats, typified by mixed-conifer forest in various developmental stages with extensive shrub cover, and occurring on serpentine soils (Slauson et al. 2007). More recently, there is limited evidence that Humboldt martens will use harvested forest stands in earlier seral stages that appear to have relatively high retention of live and dead conifer and hardwood structures (K. Slauson, pers. comm.).

Martens appear to exhibit habitat selection at four spatial scales: microhabitat, forest-stand, home-range, and landscape (Bissonette et al. 1997). At the microhabitat scale, martens use specific structures for resting and denning (“rest sites”) that provide thermoregulatory benefits, refuge from predators, and protection for females raising kits.

Rest sites are comprised of a resting structure and a resting location (Slauson and

Zielinski 2009). The resting structure is the specific habitat element, such as a snag or log, in which a marten rests; the resting location is the specific microsite within a habitat element, such as a cavity within a snag, in which a marten rests.

Martens select particular types of rest sites on a daily basis, in response to daily and seasonal variability in weather conditions. The majority of studies (e.g., Raphael and

Jones 1997, Slauson and Zielinski 2009) have shown that martens use the largest diameter live and dead woody structures (e.g., live trees, snags, and logs) available as resting and denning sites. Female martens are particularly selective of natal den sites.

Bull and Heater (2000) noted that natal den sites (compared to rest sites) of female martens in Oregon were: (1) more secure, drier, and better insulated; (2) inaccessible to any predators other than another marten; and (3) most common in large-diameter structures including live trees, snags, and logs. Other habitat structures that may provide functional resting or denning sites include stumps, rock piles, slash piles, root balls, and dense shrubs (Buskirk and Ruggiero 1994).

Slauson and Zielinski (2009) investigated rest site use by Humboldt martens in northwestern California. The majority of structures used by Humboldt martens consisted of large woody material, including snags (37% of total structures), logs (23%), and live trees (17%), with a mean diameter for standing woody structures (e.g., snags and live trees) of >90 cm. Additionally, mean age of 24 woody structures used as rest sites was

339 years (Slauson and Zielinski 2009). These factors support the idea that similar to martens elsewhere, Humboldt martens typically select the largest, oldest structures available as rest sites.

Availability of suitable resting and denning structures may be an important limiting factor for marten populations (Ruggiero et al. 1998), yet these structures are relatively rare in harvested forest stands due to the removal of large live trees, snags, and

5 downed logs during timber harvest (Cline et al. 1980). For example, Slauson et al.

(2010) found that large diameter trees and snags with suitable resting locations were extremely depauperate in harvested forests in northwestern California. Birks et al. (2005) proposed that a scarcity of arboreal cavities led to use of sub-optimal resting locations by the European pine marten (M. martes) in Scotland.

Young (i.e., early- to mid-seral) harvested forests are generally considered to be low-quality marten habitat (Buskirk and Ruggiero 1994). Harvested forests typically lack the structural complexity that martens require, such as large downed woody debris, understory vegetation (particularly dense shrub cover), and large live trees and snags

(Payer and Harrison 2003). Structural complexity in the form of large, cavity-bearing trees and snags are particularly critical in forest ecosystems, not just to martens, but many other species as well. Cavities have been described as “keystone vegetation structures”

(Tews et al. 2004), and may be inhabited by birds, mammals, insects, and amphibians.

Cockle et al. (2011) estimated that 10-40% of bird and mammal species worldwide use cavities for nesting or roosting. In interior British Columbia, Canada, 44 vertebrate species (approximately 30% of total forest vertebrates), including 12 mammalian species, were identified as cavity-nesters (Martin and Eadie 1999).

Large trees suitable for cavities may take more than a century to develop in

Douglas fir forests (Franklin et al. 2002), and western red cedar (Thuja plicata) and western hemlock (Tsuga heterophylla) forests (Stevenson et al. 2006). Cavities typically form through two primary processes: (1) natural decay, which may include interactions between mechanical wood breakage or wood damage (e.g., a broken branch or a lightning

6 strike), temperature and precipitation, as well as fungal and invertebrate activity; and (2) excavation, where cavities are created or enlarged by primary cavity-nesting species, particularly woodpeckers (Remm and Lohmus 2011).

Many forest ecosystems worldwide are characterized by an increasing loss of large cavity-bearing trees, failure to recruit a new cohort of large cavity-bearing trees, or both (Lindenmayer et al. 2012). The loss of cavity-bearing trees worldwide is largely the result of timber harvesting, but has also been caused by altered fire regimes, domestic livestock grazing, and other human-induced processes. Timber harvesting directly affects cavity availability through removal of large trees and snags, and may also indirectly affect cavity availability by exposing remaining structures to increased wind and other disturbances (Edworthy and Martin 2013). Additionally, timber harvesting rotations are typically shorter than the amount of time required to recruit new cavity-bearing trees

(Stevenson et al. 2006, Gibbons et al. 2010).

Restoring large, decadent forest structures such as cavity-bearing trees and snags to harvested forests will minimally take one to two centuries to occur naturally. In the mean time, artificial structures may act as surrogates for natural forest structures and thereby improve short-term habitat suitability of regenerating forest stands for martens and other cavity-dependent species. Artificially creating snags by girdling trees, topping trees, or applying herbicides may accelerate cavity creation (Bull and Partridge 1986), and artificial cavities have been created by inoculating holes drilled into trees with decay- causing fungi or by using chainsaws to bore chambers (Carey and Gill 1983). However,

7 these methods involve killing or damaging trees, are often expensive and time-consuming to conduct, and are generally unproven in their efficacy (Kilgo and Vukovich 2014).

Artificial structures (“nest” or “den” boxes) provide an alternative for creating cavities without damaging or killing trees. Nest boxes have been demonstrated to be an effective conservation tool for a suite of avian and mammalian species. Nest boxes have been used for more than 50 years in ecological studies of birds (Czeszczewik et al. 2008);

Fokidis and Risch (2005) deployed nest boxes for southern flying squirrels (Glaucomys volans) in South Carolina; and Lindenmayer et al. (2009) assessed nest boxes as an alternative to cavities for the endangered Leadbeater’s possum (Gymnobelideus leadbeateri) in southeastern Australia.

Of particular relevance, the Vincent Wildlife Trust (VWT) provided surrogate den boxes for wild European pine martens on commercial forests in Scotland (Messenger et al. 2006). The study indicated that 40% (n=8) of den boxes showed clear evidence of marten use after 14 months, and that 10% (n=2) of boxes had been used by reproductive female martens to raise kits. Den boxes are currently deployed for martens in Scotland,

Ireland, England, and Wales (http://www.pine-marten-recovery-project.org.uk/), and are also commercially available in the United Kingdom (http://www.nestbox.co.uk/Pine-

Marten-Den-Box-PIN.html).

Artificial structures may fulfill a similar purpose for Humboldt martens on harvested forests in northwestern California. A comprehensive plan for Humboldt marten conservation is currently under development (Slauson et al. in prep); broad measures of this plan include increasing population size, number of populations, and

8 geographic distribution. Long-term conservation actions to achieve these measures include re-establishment of marten occupancy in currently unoccupied areas, habitat protection and restoration, and re-establishment of habitat connectivity. In the short- term, artificial resting and denning structures may partially address these measures, by increasing availability of resting and denning locations, and thereby improving habitat suitability and accelerating marten recolonization of harvested forests.

The primary goal of this study was to assess the short-term effectiveness of artificial structures (hereafter, “marten box”, or simply, “box”) as surrogates for natural resting and denning structures for martens in harvested forests. To address this goal, I developed three main research objectives and three corresponding predictions. The first objective was to investigate marten occupancy of harvested forest stands where marten boxes would be deployed, with the prediction that boxes were more likely to be visited and used in marten-occupied forest stands than in forest stands not occupied by martens.

The second objective was to evaluate visitation and use patterns of marten boxes in harvested forest stands by marten and other cavity-dependent wildlife species, with the prediction that martens and other cavity-dependent wildlife were more likely to visit and use boxes than species that do not use cavities. The third and final objective was to assess availability of natural resting structures in harvested forest stands, with the prediction that marten-occupied forest stands had a higher density of natural resting and denning structures than forest stands not occupied by martens.

STUDY AREA

The study took place in Del Norte and northern Humboldt Counties in northwestern California. The study area covered a total area of approximately 600 km2; elevations ranged from approximately 150 to 1000 m. The study area consisted of three study sites: (1) the Goose Creek watershed on Six Rivers National Forest lands, (2) the

Mill Creek watershed on Del Norte Coast Redwoods State Park lands, and (3) the

Pecwan Creek watershed on private timberlands owned by the Yurok tribe (Figure 1). I chose these study sites because: (1) they are proximal geographically (e.g., similar forest habitat associations and elevation profiles), (2) they have all been intensively managed for timber production, and (3) they are either currently marten-occupied (Pecwan Creek, as determined by an ongoing study of radio-collared martens at the site; K. Slauson, pers. comm.), or are of unknown marten occupancy but are directly adjacent (<5 km) to areas where martens have been detected in recent years (Goose Creek and Mill Creek; K.

Slauson, pers. comm.).

The study area is located within the Klamath Mountain and Northern California

Coast Range sections of the California Coastal Steppe, Mixed Forest, and Redwood

Forest Province (USDA Forest Service 2007). The climate of this region in northwestern

California is characterized by moderate annual temperatures, distinct wet and dry periods of the year, and high precipitation amounts in the winter (Jimerson et al. 1996). Annual temperatures average between 7 and 15° C, and annual precipitation averages between

750 and 3000 mm (USDA Forest Service 2007). Precipitation typically falls as rain at

Figure 1. Study area including land ownership boundaries and marten box locations at three study sites in northwestern California.

11 the lower elevations (<700 m), and rain or snow at the higher elevations (>700 m) in winter months.

The study area is dominated by tanoak (Notholithocarpus densiflorus) and

Douglas fir forest associations in the eastern portion, with redwood-dominated forest associations becoming more common in the western portion. Other common tree species found throughout the study area include golden chinquapin (Chrysolepis chrysophylla), red alder (Alnus rubra), bigleaf maple (Acer macrophyllum), Pacific madrone (Arbutus menziesii), western hemlock (Tsuga heterophylla), Port Orford cedar (Chamaecyparis lawsoniana), and western red cedar (Thuja plicata). Additionally, sugar pine (Pinus lambertiana), lodgepole pine (P. contorta), and western white pine (P. monticola) occur at higher elevations on serpentine soils. Dominant shrub types include salal (Gautheria shallon), rhododendron (Rhododendron macrophyllum), evergreen huckleberry

(Vaccinium ovatum), and huckleberry oak (Quercus vaccinifolia).

MATERIALS AND METHODS

Marten Box Deployment

I built marten boxes between January and June 2013 (see Appendix A for box construction and installation methods and Appendix B for box design schematics). I deployed 55 boxes between June and November 2013 in the Goose Creek (n=20), Mill

Creek (n=19), and Pecwan Creek (n=16) study sites. Boxes in the Goose Creek and Mill

Creek sites were deployed in areas determined to be unoccupied by martens. Boxes in the Pecwan Creek site were deployed within the home ranges of ~10 radio-collared martens (K. Slauson, pers. comm.) to assess whether or not martens would visit boxes in areas of known marten occupancy.

I distributed marten boxes at each study site within four or five grids of 1-km2; each grid was divided into four quadrants of 0.25-km2 and each quadrant received one box (Figure 2). Grids were sized similar to mean home range size of male Humboldt martens (K. Slauson, pers. comm.), with the intent of providing four boxes for each marten home range-sized area. I attempted to place a marten box at the center of each quadrant. I relocated the marten box ≤100 m from the original placement at the center of the quadrant if: (1) the habitat was unsuitable (e.g., in the middle of a clear-cut), (2) the placement was <50 m from a road, or (3) the placement was ≤25 m from a natural resting or denning structure.

To diversify marten box placements, I defined habitat as either riparian or upland, with each grid receiving two boxes within riparian habitat and two boxes within upland habitat. I defined riparian as habitat ≤50 m from a perennial stream (Knutson and Naef

1997, Everest and Reeves 2007). I defined upland as habitat >200 m from a perennial stream using a combination of aerial photos, vegetation and stream layers in a geographic information system (GIS), and ground-truthing.

Track Plate Surveys

Prior to marten box deployment, I conducted track plate surveys to determine whether or not quadrants selected for box deployment were marten-occupied and to assess baseline carnivore species occupancy of selected quadrants. These surveys were conducted from July – September 2013 and only at the Goose Creek and Mill Creek sites.

Track plate surveys were not conducted at the Pecwan Creek site, as marten occupancy had been recently verified there (K. Slauson, pers. comm.). I followed previously established methods used for Humboldt marten population surveys (Slauson et al. 2009).

I distributed track plate boxes at the Goose Creek and Mill Creek study sites using an experimental-control design. At each site I paired 1-km2 grids selected for marten box deployment (“experimental” grids; n=5 per site) with adjacent 1-km2 grids that did not receive marten boxes (“control” grids; n=5 per site). Each 1-km2 grid was separated into four 0.25-km2 quadrants and each quadrant received one track plate box (i.e., n=4 track plate boxes per grid, or n=40 track plate boxes per site). In experimental quadrants, track plate box placements were at the same location as expected marten box placements. In

15 control quadrants, track plate box placements were placed approximately at the center of each quadrant.

Track plate boxes were constructed of corrugated plastic (Coroplast®, Dallas,

TX) with dimensions of 60 cm length x 25 cm height x 25 cm width. I placed an aluminum track plate with carbon soot on one half and sticky paper (Con-Tact® Brand,

La Mirada, CA) on the other half to collect tracks. I baited track plate boxes with chicken (one drumstick) and applied an olfactory lure (Gusto®, Minnesota Trapline

Products, Pennock, MN) nearby. I checked each track plate box six times on approximately 4-day intervals for a roughly 4-week-long sampling period. At each return check, I replaced bait, re-applied the olfactory lure, and collected and replaced Con-

Tact® paper if any tracks were present. I identified the majority of animal tracks to species-level using methods described by Taylor and Raphael (1988). I identified chipmunk (Tamias sp.), mice (Peromyscus sp.), and weasel (Mustela sp.) tracks to genus, as I was unable to distinguish to species.

For statistical analysis of track plate survey data, I summarized naïve (i.e., not adjusted for detection probability) carnivore species occupancy for the Goose Creek and

Mill Creek sites at the quadrant (n=40) scale. I then used Fisher’s exact test and a significance level of α=0.05 to compare species occupancy between quadrants at the two study sites. I chose not to use an occupancy modeling approach, which adjusts occupancy estimates by allowing for imperfect detectability of a given species (see

MacKenzie et al. 2002), as the scale of my sampling units did not meet the assumption of spatial independence for several of the carnivore species I detected. I did not summarize

16 naïve occupancy of small mammal species detected, as track plates may not provide reliable estimates of small mammal species occupancy (e.g., Long et al 2008).

Marten Box Monitoring

I monitored animal activity at 43 marten boxes (out of 55 total deployed) for ~12 months between June 2013 and October 2014, depending on date of box installation. I monitored a subset of boxes at the Goose Creek study site (n=8), and all boxes at the Mill

Creek (n=19), and Pecwan Creek (n=16) sites. I was unable to monitor or revisit 12 boxes (i.e., three grids) at the Goose Creek site for the duration of the study, due to access restrictions to control the spread of Port Orford cedar root disease (Phytophthora lateralis).

I monitored marten boxes with remote-sensing cameras (Bushnell Trophy Cam®,

Bushnell, Overland Park, KS, and Reconyx HC500, Reconyx Inc., Holmen, WI ), with one camera at each box. I mounted cameras at ~2 m height on a tree bole upslope and <5 m distance from the box. Due to the orientation of cameras (facing downslope towards the box) relative to box entrances (facing the box mounting tree), cameras had a clearer view of the upslope box entrance than the downslope box entrance (see Appendix B for examples). I applied an olfactory lure (Gusto®) ≤10 m from the marten box to attract animals to the vicinity of each marten box.

I set Bushnell cameras to video mode for a 15-second capture period with no delay interval between capture events. I set Reconyx cameras to 10 rapid-fire photograph capture bursts with no delay between capture events. I used video and rapid-fire

17 photograph settings to document animal activity at marten boxes. I considered two types of animal activity at marten boxes: animal visitation and animal use. I defined visitation as a video or photographic capture event of animal presence at a box with no evidence that the animal entered the box (e.g., animal on top of the box, investigating the box entrance but not entering, or on the bole of the box mounting tree). I defined use as a video or photographic capture event of an animal entering a box and not exiting the box within the same capture event.

I revisited all marten boxes monitored with remote cameras (n=43) on 6- to 8- week intervals from July 2013 to October 2014. At each revisit I visually inspected boxes for signs of use, such as scats at the base of the marten box tree or on the roof of the marten box. I also inspected boxes for evidence of attrition, such as major damage from weather events or black bears (Ursus americanus). I refreshed the olfactory lure at each revisit.

I serviced remote cameras while inspecting marten boxes. I assessed cameras for functionality, including proper mounting, external damage, or moisture damage. I verified camera settings, including appropriate date/time stamps, video lengths or photo capture bursts, and intervals between photo/video events. I replaced batteries when necessary and replaced memory cards if any new video or photo events were present. I reviewed all video and photograph events for animal visitation or animal use of marten boxes. I identified the majority of animal visitation and use events to species. For a subset (<10%) of small mammal visitation events, I was only able to distinguish to family-level (Sciuridae).

For statistical analysis of marten box monitoring data, I compared all study sites individually with respect to: (1) total number of boxes visited per species, and (2) mean number of visitation events per box per species. I then pooled data across study sites and used linear regression to investigate potential correlations between frequencies of marten box visitations by small mammals versus frequency of box visitations by carnivores. I also summarized mean latency to box visitation (i.e., average number of days from box deployment to first visit occasion) for all species, and minimum latency to box use (i.e., minimum number of days from box deployment to first use occasion) for all species documented to use boxes. I chose to omit black bear visitation event from the analysis, as bears are too large to use boxes.

Habitat Transects

I conducted 42 habitat transects between July and October 2014 at the Goose

Creek, Mill Creek, and Pecwan Creek study sites to compare availability of naturally- occurring resting structures between marten-occupied areas and marten-unoccupied areas. At the Pecwan Creek site, I conducted transects in all quadrants that were marten- occupied (n=14); I defined marten occupancy as any quadrant that had a marten detection at a marten box camera. I conducted the same number of transects (n=14 per site) in marten-unoccupied quadrants at the Mill Creek and Goose Creek sites.

I followed methods for belt transects established by Bate et al. (1999) for fragmented forest stands, and similar to variable-width transects used by Slauson et al.

(2010) for harvested redwood forests in northwestern California. I considered the marten

19 box as center of a 500 m transect, with half of each transect (“sub-transect”) extending

250 m in opposing directions from the center. I used a random number generator including numbers up to 360 to determine the starting orientation, and conducted a 250 m sub-transect at that orientation. I then returned to the marten box (i.e., center of transect) and conducted a second 250 m sub-transect at the opposite (i.e., 180 degree) orientation.

I used the random number generator to chose an alternate orientation if I determined that a transect would: (1) cross another transect, (2) travel across impassible terrain (e.g., a cliff face), or (3) follow a road for a large proportion of the transect.

I determined forest seral stage (Jimerson et al. 1996) and transect width at the beginning of each transect and at each change in forest stand. Transect width was based on detectability (i.e., maximum estimated visibility) of potential resting structures from center of transect. I estimated transect width separately for arboreal versus ground-based structures, as arboreal structures were typically visible at further distances than ground- based structures. I used a laser rangefinder (Bushnell, Overland Park, KS) to determine maximum visibility.

I estimated density of potential resting structures along each transect. I defined suitable resting structures following Slauson and Zielinski (2009) and considered the five most common resting structures used by Humboldt martens in northwestern California, including: (1) live trees with defects, (2) snags, (3) large logs and log complexes (≥2 large logs stacked together), (4) large rock piles, and (5) large slash piles. I defined resting structures as either standing (live trees, snags) or ground-based (logs/log complexes, rock piles, slash piles).

Within each potential resting structure I documented a specific structural element, which a marten could use for resting. Within standing structures, structural elements were defined as cavities, broken top platforms, or large branch platforms. All ground- based structural elements were defined as chambers. All structural elements must have been easily identifiable (i.e., visible to the naked eye or with binoculars).

I documented standing structures ≥60 cm diameter at breast height (DBH) and

≥15 m height (Slauson et al. 2010). For each standing structure, I recorded distance on transect, distance from transect, species, DBH, decay class, height, and type of structural element. For each ground-based structure, I recorded distance on transect, distance from transect, decay class of logs, maximum breadth, and type of structural element. I determined distance from transect using a laser rangefinder, used a standard metric tape

(Forestry Suppliers, Jackson, MS) to measure DBH, and determined tree and snag decay class following guidelines from Maser et al. (1979).

For statistical analysis of habitat transect data, I pooled habitat data separately for each study site. I used a hierarchical approach to compare potential resting structure densities at multiple scales. At each scale, I first used ANOVA and a statistical significance level of α=0.05 to compare densities across study sites. I then used Tukey’s

Honest Significant Difference (HSD) to compare all pairwise combinations of study sites.

I investigated: (1) total resting structure density, (2) total standing structure density (i.e., combined live tree and snag density), (3) total ground-based structure density (i.e., combined log, slash pile, and rock pile density), (4) individual standing structure density

(live tree, snag), and (5) individual live hardwood and live conifer tree density.

I also compiled summary statistics by study site for: (1) total and percent availability of each structure type; (2) total and percent availability of each structural element type; and (3) percent of total transect length in each forest seral stage. Finally, I summarized live trees and snags at each study site with respect to mean DBH and DBH range.

RESULTS

Track Plate Surveys

I did not detect marten at either the Goose Creek or Mill Creek study sites during the track plate surveys. However, I detected four other carnivore species at the Goose

Creek site, including fisher (Pekania pennanti), Mustela sp., ringtail (Bassariscus astutus) and western spotted skunk (Spilogale gracilis). At the Mill Creek site, I detected three carnivore species, including fisher, gray fox (Urocyon cinereoargenteus), and western spotted skunk.

In addition, I detected five small mammal species at the Goose Creek site, including Douglas squirrel (Tamiasciurus douglasii), dusky-footed woodrat (Neotoma fuscipes), northern flying squirrel (Glaucomys sabrinus), Peromyscus sp., and Tamias sp.

I detected four small mammal species at the Mill Creek site, including Douglas squirrel, dusky-footed woodrat, Peromyscus sp., and Tamias sp. (see Appendix C for complete track plate survey results).

The Goose Creek site had a greater carnivore species richness (four species) than the Mill Creek site (three species). However, the Mill Creek site had significantly higher naïve occupancy than the Goose Creek site at the quadrant scale for all three carnivore species detected there, including fisher (p<0.001; Table 1), gray fox (p=0.025), and western spotted skunk (p<0.001). The Goose Creek and Mill Creek sites were not significantly different for naïve occupancy of Mustela sp. or ringtail.

Table 1. Naïve occupancy of five carnivore species at the quadrant (n=40 per site) scale at the Goose Creek and Mill Creek study sites in northwestern California, July to September 2013. Species Goose Creek Mill Creek

Fisher 0.10 0.50a

Gray Fox 0.00 0.15a

Mustela sp. 0.10 0.00

Ringtail 0.03 0.00

Western Spotted Skunk 0.03 0.38a

a: Denotes significantly higher than Goose Creek study site at significance level of α=0.05

Marten Box Monitoring

Animal visitation of marten boxes was much more common than use (see

Appendix D for complete summary of animal activity at marten boxes). Across all study sites, five carnivore species visited boxes, including (in order from greatest number of boxes visited to least number of boxes visited): fisher (n=27, 63% of total boxes; Figure

3), marten (n=15, 35%), ringtail (n=3, 7%), raccoon (Procyon lotor; n=2, 5%), and western spotted skunk (n=1, 2%). Martens visited 88% (n=14) of boxes in the Pecwan

Creek (i.e., marten-occupied) study site. A marten visited a single box on a single occasion in the Mill Creek study site in late September 2014; this is the first time a marten has been documented in Mill Creek since the Mill Creek parcel was acquired by

California State Parks in 2002 (A. Transou, pers. comm.).

Five small mammal species visited marten boxes across all study sites, including

(in order from greatest number of boxes visited to least number of boxes visited):

Douglas squirrel (n=38, 88% of total boxes; Figure 3), northern flying squirrel (n=28,

65%), Tamias sp. (n=11, 26%), western gray squirrel (Sciurus griseus; n=7, 16%), and dusky-footed woodrat (n=2, 5%).

Fishers visited boxes at all three study sites and were the most frequent carnivore species to visit marten boxes with 1.86 ± 0.48 (mean ± SE) visits per box (Figure 4). At the Pecwan Creek site, martens were the carnivore species that most frequently visited boxes (4.19 ± 1.07 visits/box). Ringtails visited boxes at all study sites but were uncommon (0.16 ± 0.12 visits/box). Raccoons and western spotted skunks each visited

100 90 Goose Creek 80 Mill Creek 70 60 Pecwan Creek 50 40 30

% of Boxes Visited Visited % of Boxes 20 10 0

Species

Figure 3. Percent of marten boxes visited by five small mammal species and five carnivore species at three study sites in northwestern California, June 2013 to October 2014.

18 Goose Creek 16 14 Mill Creek 12 Pecwan Creek 10 8 6 4 Mean # of Visits (SE) Visits # of Mean 2 0

Species

27 boxes at a single study site and were also uncommon.

Douglas squirrels visited boxes at all three study sites and were the most frequent small mammal species to visit marten boxes (9.58 ± 1.33 visits/box; Figure 4). Northern flying squirrels also visited boxes at all study sites and were relatively common (3.65 ±

0.82 visits/box). Western gray squirrels visited boxes at all three study sites but were less common (0.49 ± 0.27 visits/box); Tamias sp. visited boxes at two of three study sites

(0.91 ± 0.37 visits/box). Dusky-footed woodrats were visited boxes at a single study site and were uncommon.

Animal use of marten boxes was rare across all study sites; I documented animals entering boxes on nine separate occasions at four (9% of total) boxes. Box use was documented for four animal species, including Douglas squirrel (n=4 occasions), dusky- footed woodrat (n=1), marten (n=3), and northern flying squirrel (n=1). Across study sites (n=43 boxes), there was a significant positive correlation (t42=4.982, p<0.001, r2=0.3619) between frequencies of marten box visitation by small mammals compared to frequency of marten box visitation by carnivores.

Mean latency to first visit in terms of number of days for carnivore species at marten boxes across study sites includes: fisher (116 ± 22 days; mean ± SE), marten

(143 ± 25 days), raccoon (118 ± 105 days), ringtail (142 ± 19 days), and western spotted skunk (277 days). Mean latency to first visitation event for small mammal species at boxes across study sites includes: Douglas squirrel (88 ± 17 days), dusky-footed woodrat

(144 ± 67 days), northern flying squirrel (103 ± 20 days), Tamias sp. (150 ± 41 days), and western gray squirrel (101 ± 67 days). Latency to first use of marten boxes across

28 study sites includes: Douglas squirrel (194 ± 125 days), dusky-footed woodrat (141 days), marten (152 days), and northern flying squirrel (26 days).

Habitat Transects

Across all sites, live trees (47%), snags (29%), and logs (15%) were the most common potential resting structures (see Appendix E for complete summary of standing structures). Large slash piles were completely absent from the Goose Creek and Mill

Creek sites but were relatively common at the Pecwan Creek site. Rock piles were present at the Mill Creek and Pecwan Creek sites but were rare, and were absent from the

Goose Creek site. Within resting structures, cavities (36%), broken top platforms (28%), and chambers (23%) were the most common structural elements.

The Pecwan Creek site had the highest mean density of total potential resting structures with 4.0 ± 0.40 (mean ± SE) structures per hectare, followed by the Goose

Creek site (2.09 ± 0.17 structures/ha) and the Mill Creek site (1.54 ± 0.42 structures/ha).

Density of total resting structures (i.e., combined standing and ground-based structures per hectare) differed significantly between the three study sites (F2,39=11.63, p<0.001;

Table 2). Total resting structure density was significantly higher at the Pecwan Creek site than both the Goose Creek (p<0.001) and Mill Creek (p=0.003) sites; there was not a significant difference in total resting structure density between the Goose Creek and Mill

Creek sites (p=0.56).

Standing 1.69 (0.28) 1.25 (0.37)a 2.24 (0.35)

Ground-Based 0.40 (0.13)a 0.29 (0.13)a 1.76 (0.28)

Total 2.09 (0.17)a 1.54 (0.42)a 4.00 (0.40)

a: Denotes significantly lower than the Pecwan Creek site at α=0.05

The Pecwan Creek site had the highest mean density of standing structures (2.24

± 0.35 structures/ha), followed by the Goose Creek site (1.69 ± 0.28 structures/ha) and the Mill Creek site (1.25 ± 0.37 structures/ha). The Pecwan Creek site had significantly higher standing structure density (p=0.047) than the Mill Creek site. There was not a significant difference in standing structure density between the Goose Creek and Mill

Creek sites (p=0.57) or between the Goose Creek and Pecwan Creek sites (p=0.42).

The Pecwan Creek site had the highest mean density of ground-based resting structures (1.76 ± 0.28 structures/ha), followed by the Goose Creek site (0.40 ± 0.13 structures/ha) and the Mill Creek site (0.29 ± 0.13 structures/ha). Ground-based resting structure density was significantly higher at the Pecwan Creek site than both the Goose

Creek (p<0.001) and Mill Creek (p<0.001) sites. There was not a significant difference between the Goose Creek and Mill Creek sites for ground-based structures (p=0.91). For individual standing structures, the Pecwan Creek site had significantly higher snag density (p=0.03) and live hardwood density (p=0.02) than Mill Creek (Table 3). There was no significant difference between the Goose Creek, Mill Creek, and Pecwan Creek sites for any other pairwise comparisons of individual standing structures.

All three study sites were dominated by early-seral, pole, and shrub forest conditions with >90% of total transect length occurring in these seral stages. Mid-seral and late-seral forest stands cumulatively accounted for <6% of total transect length across all study sites and were typically found in riparian buffer zones. Old-growth forest conditions accounted for 1% of total transect length across study sites and occurred in a single section of transect at the Goose Creek site in a previously burned riparian area.

Live Conifer 0.65 (0.17) 0.88 (0.27) 0.81 (0.17)

Live Hardwood 0.36 (0.17) 0.00 (-)a 0.57 (0.17)

Live Tree 1.01 (0.19) 0.88 (0.27) 1.39 (0.29)

Snag 0.68 (0.23) 0.37 (0.16)a 0.85 (0.14)

a: Denotes significantly lower than the Pecwan Creek site at α=0.05

DISCUSSION

This is the first study in North America to specifically investigate the effectiveness of artificial structures as surrogates for naturally-occurring resting and denning structures of a carnivore species. The results of this study indicate that: (1) the

Pecwan Creek study site was the only marten-occupied site; (2) at the Pecwan Creek site, martens were the most frequently detected carnivore species at marten boxes, and were the only carnivore species documented to enter boxes; and (3) marten occupancy at the

Pecwan Creek site may be influenced by forest structural complexity, specifically a higher density of naturally-occurring resting and denning structures than at the two marten-unoccupied sites (Goose Creek and Mill Creek).

The Pecwan Creek study site was the only site known to be marten-occupied for the majority of the study; although a marten was detected at the Mill Creek site at the end of the study, it was likely a dispersing juvenile rather than a resident individual.

Encouragingly, martens were the most common carnivore species at the Pecwan Creek site with respect to both total number of marten boxes visited and total number of visit occasions. Additionally, one box was documented to have marten use during the study; this occurred on three occasions in November and December 2013, and appeared to be the same female individual on each occasion (based on body size, presence of a radio- collar, and radio-telemetry locations in the box vicinity; K. Slauson, pers. comm.).

Although I designed and constructed marten boxes specifically to fit the needs of martens, the animal species community response to the boxes was of great interest as

33 well. Box entrances were sized with the intent of excluding fishers, and despite being the most common carnivore species detected at boxes across all study sites, no fishers were documented to enter boxes. This may provide evidence that fishers are unable to enter the boxes. This is an important result, as fishers entering boxes could preclude use by other species (e.g., a marten may not enter a box that a fisher has used), and fishers could also kill other species (such as martens) that are using the boxes.

Douglas squirrel and northern flying squirrel were by far the most common species detected at marten boxes across study sites, in terms of both total number of boxes visited and mean number of visits per box. Additionally, ~50% of box use events involved one of these two species. This is relatively unsurprising, as nest box use by

Douglas squirrels and northern flying squirrels in North America has been well documented previously, and both species have specifically been targeted for nest box research (e.g., Ransome and Sullivan 2004, Patterson and Patterson 2010).

A shared attribute of Douglas squirrel, northern flying squirrel, fisher, and marten is that they are all cavity-dependent species. Thus, they may be more likely to visit marten boxes than species that are not cavity-dependent; however, they may also have been relatively common species at the sites where they did occur. A number of other mammal species visited boxes less frequently or rarely, and the combination of likelihood of box visitation and relative commonness (or rarity) of each species may provide insight into why. For example, ringtails are known to use arboreal cavities (Myers 2010), but were infrequently detected at track plates and also infrequently visited boxes; they may simply have been a rare species in the study area. Western spotted skunks were

34 frequently detected at track plates, but infrequently visited boxes; they may have been a common species, but unlikely to visit boxes because they do not typically use arboreal cavities (e.g., Doty and Dowler 2006). Mustela sp. were infrequently detected at track plates and did not visit marten boxes at all; they may have been both rare and unlikely to visit boxes, as they also do not typically use arboreal cavities (e.g., Martin et al. 2004).

Differences in mammalian species assemblages between study sites may be mediated by habitat differences, particularly in respect to how forest management practices and forest composition influence habitat at each site. Habitat transects confirmed that potential resting structures for martens, especially ground-based structures, were more abundant at the marten-occupied site (Pecwan Creek) than the marten-unoccupied sites (Goose Creek and Mill Creek). Ground-based structural complexity not only provides protection for martens from predators in the form of rest sites (e.g., Ruggiero et al. 1998), but also increases marten foraging efficiency

(Andruskiw et al. 2008); Poole et al. (2004) suggested that large woody debris in the form of slash piles and large diameter logs is particularly important in maintaining marten populations in harvested forests. Higher ground-based structure density at the

Pecwan Creek site is likely the result of forest management practices that left relatively large amounts of downed woody debris (large logs, log platforms, slash piles) in situ.

The Goose Creek and Mill Creek sites, conversely, are better typified by forest management practices that either removed and/or burned large accumulations of downed woody debris.

The Pecwan Creek site also had a significantly higher density of snags and live hardwood trees than the Mill Creek site; this is likely a result of both forest composition and forest harvest practices. The Pecwan Creek site is largely Douglas-fir and tanoak- dominated, whereas the Mill Creek site is largely redwood-dominated; for example, large live hardwoods were a relatively common feature at the Pecwan Creek site, but were not documented at all at the Mill Creek site. The Pecwan Creek site is better typified by harvest practices where mostly large, merchantable trees (in this case, Douglas fir) were removed, and many non-merchantable trees (including hardwoods such as golden chinquapin, and softwoods such as western red cedar and western hemlock) and snags were left standing. Conversely, the Mill Creek site is typified by harvest practices where most or all standing structures (including both hardwood and softwood live trees and snags) were removed from a given stand. In addition, large live trees and snags at the

Pecwan Creek site were well distributed throughout the landscape, but were found almost exclusively in riparian buffer zones at the Goose Creek and Mill Creek sites.

Several researchers have suggested that young, post-harvest forest stands may be suitable for martens if sufficient structural complexity is retained (e.g., Baker 1992, Payer and Harrison 2003, Porter et al. 2005). Marten occupancy at the Pecwan Creek site compared to the marten un-occupied Goose Creek and Mill Creek sites may be influenced by: (1) higher retention of ground-based structures such as logs and slash piles, and (2) better spatial distribution of retained standing structures such as large live trees and snags. This indicates that where sufficient forest structural complexity is retained, martens may occur, and where martens do occur, they will visit and potentially

36 use marten boxes. If martens visit and use boxes, then boxes may increase availability of resting and denning locations in harvested forests and thereby improve habitat suitability for martens.

This research is part of a larger study (see Slauson et al. 2014) that is investigating the effects of cavity restoration on mammalian species across the redwood region, a study that is both broader in scope and longer in timeframe than my study. As part of the larger study, marten boxes are being monitored with remote-sensing cameras at the Mill Creek site (n=19 boxes) and the Pecwan Creek site (n=16 boxes) for a second year (summer

2014 to summer 2015), without the application of the Gusto® lure. As indicated by the positive correlation between small mammal detections and carnivore detections at marten boxes, carnivores may be attracted to marten boxes not only by the olfactory lure, but also by small mammal activity at boxes; further monitoring may provide additional insight into whether animal species are visiting marten boxes due to the olfactory attractant, are visiting boxes on a natural basis, or both.

Continued monitoring efforts at existing marten boxes may seek to investigate additional methods of assessing animal visitation and use at marten boxes, as estimates of visitation and use from this study are almost certainly conservative. For example, ~8% of visitation events of species in the Sciuridae family could not be identified to species, and were not included in the analysis. Cameras were mounted facing the upslope portion of the box and the box mounting tree, and may not have captured animal visitation on the downslope portion of the box mounting tree. Additionally, cameras appeared to perform well capturing animals entering boxes, but often triggered too slowly to capture animals

37 exiting boxes, resulting in a lack of information on how long animals stayed in boxes.

Certain additions or modifications, such as integrating a hair snare device into the box entrances (e.g., to passively collect genetic material from animals entering boxes), or inserting an endoscopic camera into the central box chamber (e.g., to investigate box contents for evidence of use; see also Appendix A) may improve the effectiveness of future monitoring efforts.

One of the original objectives of this study was to re-evaluate species occupancy in summer of 2015, one year post-deployment of marten boxes (summer 2014); changes in species occupancy of treatment grids versus control grids may be correlated with species use of marten boxes. However, due to a paucity of documented animal use of marten boxes, I determined that it was premature to conduct occupancy resurveys. A longer return interval (e.g., 5 years post-deployment of marten boxes) for occupancy resurveys will allow a greater amount of time for animals to find and potentially use marten boxes. This is especially important for boxes in the currently marten-unoccupied

Goose Creek and Mill Creek study sites. The process for martens to find and occupy these sites will likely require multiple juvenile dispersal events from adjacent marten- occupied areas, and could occur on temporal scales of several years to decades. Timing of future occupancy surveys conducted by the USFS and California State Parks should take this into consideration.

Several variables, in addition to density of potential resting structures, may influence marten occupancy throughout the study area. For example, while all three study sites are proximal geographically (within <30 km radius), the Pecwan Creek site is

38 directly adjacent to unharvested and less intensively-harvested USFS forest lands that contain the “core” Humboldt marten population in northwestern California, while the

Goose Creek and Mill Creek sites are separated from the core Humboldt marten population by both longer distances and more intensively-harvested forests. Similar to martens elsewhere, marten occupancy in northwestern California may be influenced by additional variables such as prey abundance (e.g., Buskirk and Powell 1994), predator abundance (e.g., Hearn 2007), and habitat components such as density of shrub cover

(e.g., Slauson and Zielinski 2007). Future studies concerning marten occupancy of harvested forests may be more informative with the inclusion of similar covariates.

Additionally, certain factors made estimating density of potential resting structures difficult. For example, the upper portions of large trees were typically obscured by vegetation, which may have resulted in underestimates of resting locations, due to an inability to detect them. Conversely, I did not climb potential resting structures, and therefore did not verify cavity depth, which could have resulted in overestimates of cavities of useful size to martens. In particular though, it was impossible to confirm that a marten would use a particular resting structure and location, without actually observing a marten in that structure and location. Future studies may further clarify the relationship between resting structure density and marten occupancy by comparing resting structure availability in marten-occupied harvested forests to marten-occupied unharvested forests, and assessing marten use versus availability of naturally-occurring resting structures in harvested forests.

MANAGEMENT IMPLICATIONS AND CONCLUSIONS

There is a long and rich history of research regarding use of artificial structures

(“nest boxes”) by avian species (e.g., Purcell et al. 1997, Lambrechts et al. 2012).

Additionally, small mammal nest box use has been well-documented worldwide (e.g.,

Czeszczewik et al. 2008, Madikiza et al. 2010, Warakai et al. 2013; see also Appendix F).

In North America, members of the Sciuridae family have often been targeted for mammalian nest box research (e.g., Carey 2002, Fokidis and Risch 2005), and at least 6 sciurids including Douglas squirrel, fox squirrel (Sciurus niger), northern flying squirrel, southern flying squirrel (Glaucomys volans), eastern gray squirrel (Sciurus carolinensis), and western gray squirrel have been documented to use nest boxes (McComb and Noble

1981, Ransome and Sullivan 2004).

Conversely, there is a paucity of information available concerning nest box use by carnivores. Much of the existing information has been gleaned incidentally, often when carnivores are documented using boxes intended for birds (e.g., Hakes 1983, Juskaitis

1999; see also Appendix F). Few studies have been specifically designed to investigate use of nest boxes by carnivores (e.g., Messenger et al. 2006), despite the fact that carnivore species exist worldwide that are partially or primarily dependent on arboreal cavities (e.g., Zielinski et al. 2004, Glen and Dickman 2006, Carvalho et al. 2014; see also Appendix G). However, interest in the application of nest boxes as a conservation tool for carnivores appears to be growing. The Habitat Conservation Trust Foundation and BC Hydro are currently investigating the effectiveness of boxes for reproductive

40 female fishers in British Columbia

(http://www.hctf.ca/communications/blog/entry/declining-den-sites-finding-cavities-fit- for-a-fisher); Southern California Edison is considering a similar approach for fishers in the southern Sierra Nevada range in California (S. Byrd, pers. comm.).

The loss of arboreal cavities is a global phenomenon; artificial structures such as nest boxes may have the potential to partially mitigate the effects of this phenomenon on carnivores and other mammal species. Yet use of boxes by martens and other arboreal- cavity using species, if it occurs, will take time. For example, Carey (2002) found that after nine months, only 10% of nest boxes were used by northern flying squirrels, but after 35 months, 80% of boxes showed use. Messenger et al. (2006) found no evidence of pine marten use of den boxes in Scotland after four months, but 40% (n=8) of boxes showed some level of use after 14 months; however, it’s worth noting that pine martens in Scotland were already accustomed to using a diversity of man-made structures for resting and denning activities, largely in response to a relative lack of suitable natural structures (Birks et al. 2005).

In this study, only 10 total use events occurred for all species over ~12 months.

The relatively low levels of animal use of marten boxes in this study, however, may be the result of a limited timeframe, rather than a true reflection of the boxes’ utility. Over time, boxes will become more integrated into the landscape, and more animals will have the opportunity to discover them and potentially use them. Response time to boxes by martens will be even longer in areas that are not currently marten-occupied, such as the

Goose Creek and Mill Creek sites. However, martens that do (potentially) re-occupy the

Goose Creek and Mill Creek sites may actually be more likely to visit and use boxes than at the Pecwan Creek site, due to the comparative paucity of suitable natural structures at those sites. Regardless, strong inferences about the effectiveness of marten boxes as a conservation measure for the Humboldt marten are premature. Longer-term monitoring of marten boxes in the form of remote cameras and occupancy surveys will hopefully elucidate their effectiveness further.

In September 2010, the U.S. Fish and Wildlife Service (USFWS) was petitioned to list the Humboldt marten as endangered or threatened under the federal Endangered

Species Act (ESA), and in July 2014, the USFWS initiated a 12-month status review for the petition. On April 7th, 2015, the USFWS deemed that federal listing for the

Humboldt marten is currently not warranted (Office of the Federal Register 2015).

Despite the USFWS decision, it is undeniable that the Humboldt marten is in need of a comprehensive conservation strategy to promote its recovery and persistence; protecting existing natural resting structures should be one of the highest priorities of this strategy.

Forest management practices that retain snags and defective large live trees, leave large woody debris such as logs in situ, and create slash piles with smaller woody debris (rather than burning or chipping it) should be encouraged wherever martens occur. Large cavity- bearing live trees and snags are particularly important structures, as they take the longest to develop. Artificial structures will not perfectly replicate the conditions of these natural structures, and a natural structure should never be harvested under the rationale that it can simply be replaced with an artificial structure.

However, the majority of suitable late-seral and old-growth forests in the historical range of the Humboldt marten have already been harvested. The future of the

Humboldt marten may be as dependent on developing suitable conditions in young, harvested forests, as on protecting remaining late-seral and old-growth habitats.

Artificial structures in the form of marten boxes may increase availability of resting and denning locations in harvested forests, thereby improving habitat suitability for martens.

Despite the limited timeframe, the results of this study indicate that martens and other animal species will visit and enter marten boxes. Marten boxes may not only supplement naturally-occurring resting structures in young, harvested forests that are already marten- occupied, but may also facilitate marten population expansion from marten-occupied areas to adjacent unoccupied areas, improve connectivity between patches of marten- occupied habitat, and ultimately accelerate suitability of harvested forests as habitat for martens and other cavity-dependent forest wildlife.

LITERATURE CITED

Andruskiw, M., J.M. Fryxell, I.D. Thompson, and J.A. Baker. 2008. Habitat-mediated

variation in predation risk by the American marten. Ecology 89: 2273-2280.

Baker, J.M. 1992. Habitat use and spatial organization of pine marten on southern

Vancouver Island, British Columbia. Thesis, Simon Fraser University, Burnaby,

British Columbia, Canada.

Bate, L.J., E.O. Garton, and M.J. Wisdom. 1999. Estimating snag and large tree

densities and distributions on a landscape for wildlife management. USDA Forest

Service GTR-PNW-425, Pacific Northwest Research Station, Portland, Oregon,

USA.

Birks, J.D., J.E. Messenger, and E.C. Halliwell. 2005. Diversity of den sites used by

pine martens (Martes martes): A response to the scarcity of arboreal cavities?

Mammal Review 35: 313-320.

Bissonette, J.A., D.J. Harrison, C.D. Hargis, and T.G. Chapin. 1997. The influence of

spatial scale and scale-sensitive properties on habitat selection by American

marten. Pages 368-385 in J.A. Bissonette, editor. Wildlife and landscape

ecology. Springer-Verlag, New York, New York, USA.

Brady, M.J., T.S. Risch, and F.S. Dobson. 2007. Availability of nest sites does not limit

population size of flying squirrels. Canadian Journal of Zoology 78: 1144-1149.

Bull, E.L. and A.D. Partridge. 1986. Methods of killing trees for use by cavity nesters.

Wildlife Society Bulletin 14: 142-146.

Bull, E.L. and T.W. Heater. 2000. Resting and denning sites of American martens in

northeastern Oregon. Northwest Science 74: 179-185.

Buskirk, S.W. and R.A. Powell. 1994. Habitat ecology of fishers and American martens.

Pages 283-296 in S.W. Buskirk, A.S. Harestad, M.G. Raphael, and R.A. Powell,

editors. Martens, sables, and fishers: biology and conservation. Cornell

University Press, Ithaca, New York, USA.

Buskirk, S.W. and L.F. Ruggiero. 1994. The American marten. Pages 7-37 in L.F.

Ruggiero, K.B. Aubry, S.W. Buskirk, L.J. Lyon, and W.J. Zielinski, editors.

American marten, fisher, lynx, and wolverine in the western United States.

USDA Forest Service GTR-RM-254, Rocky Mountain Forest and Range

Experiment Station, Fort Collins, Colorado, USA.

Carey, A.B. 2002. Response of northern flying squirrels to supplementary dens.

Wildlife Society Bulletin 30: 547-556.

Carey, A.B. and J.D. Gill. 1983. Direct habitat improvements – some recent advances.

USDA Forest Service GTR-RM-099, Forestry Sciences Laboratory, Olympia,

Washington, USA.

Carvalho, F., R. Carvalho, A. Mira, and P. Beja. 2014. Use of tree hollows by a

Mediterranean forest carnivore. Forest Ecology and Management 315: 54-62.

Cline, S.P., A.B. Berg, and H.M. Wight. 1980. Snag characteristics and dynamics in

Douglas-fir forests, western Oregon. Journal of Wildlife Management 44: 773-

786.

Cockle, K.L., K. Martin, and T. Wesolowski. 2011. Woodpeckers, decay, and the future

of cavity-nesting vertebrate communities worldwide. Frontiers in Ecology and

the Environment 9: 377-382.

Czeszczewik, D., W. Walankiewicz, and M. Stanska. 2008. Small mammals in nests of

cavity-nesting birds: Why should ornithologists study rodents? Canadian Journal

of Zoology 86: 286-293.

Dawson, N.G. and J.A. Cook. 2012. Behind the genes: diversification of North

American martens (Martes americana and M. caurina). Pages 23-38 in K.B.

Aubry, W.J. Zielinski, M.G. Raphael, G. Proulx, and S.W. Buskirk, editors.

Biology and conservation of martens, sables, and fishers: a new synthesis.

Cornell University Press, Ithaca, New York, USA.

Doty, J.B. and R.C. Dowler. 2006. Denning ecology in sympatric populations of skunks

(Spilogale gracilis and Mephitis mephitis) in west-central Texas. Journal of

Mammalogy 87: 131-138.

Edworthy, A.B. and K. Martin. 2013. Persistence of tree cavities used by cavity-nesting

vertebrates declines in harvested forests. The Journal of Wildlife Management

77: 770-776.

Everest, F.H. and G.H. Reeves. 2007. Riparian and aquatic habitats of the Pacific

Northwest and southeast Alaska: ecology, management history, and potential

management strategies. USDA Forest Service GTR-PNW-692, Pacific Northwest

Research Station, Portland, Oregon, USA.

Fokidis, H.B. and T.S. Risch. 2005. The use of nest boxes to sample arboreal

vertebrates. Southeastern Naturalist 4: 447-458.

Fox, L., III. 1996. Current status and distribution of the coast redwood. Pages 18-20 in

J. LeBlanc, editor. Proceedings of the conference on coast redwood forest

ecology and management. Humboldt State University, Arcata, California, USA.

Franklin, J.F., T.A. Spies, R. Van Pelt, A.B. Carey, D.A. Thornburgh, D. Rae Berg, D.B.

Lindenmayer, M.E. Harmon, W.S. Keeton, D.C. Shaw, K. Bible, and J. Chen.

2002. Disturbances and structural development of natural forest ecosystems with

silvicultural implications, using Douglas-fir forests as an example. Forest

Ecology and Management 155: 399-423.

Gehrt, S.D., D.L. Spencer, and L.B. Fox. 1990. Raccoon denning behavior in eastern

Kansas as determined from radio-telemetry. Transactions of the Kansas Academy

of Sciences 93: 71-78.

Glen, A.S. and C.R. Dickman. 2006. Home range, denning behaviour and microhabitat

use of the carnivorous marsupial Dasyurus maculatus in eastern Australia.

Journal of Zoology 268: 347-354.

Gibbons, P., C. McElhinny, and D.B. Lindenmayer. 2010. What strategies are effective

for perpetuating structures provided by old trees in harvested forests? A case

study on trees with hollows in south-eastern Australia. Forest Ecology and

Management 260: 975-982.

Goldingay, R.L., M.J. Grimson, G.C. Smith. 2007. Do feathertail gliders show a

preference for nest box design? Wildlife Research 34: 484-490.

Grinnell, J., J.S. Dixon, and J.M. Linsdale. 1937. Fur-bearing mammals of California.

University of California Press, Berkeley, California, USA.

Hakes, W.A. 1983. Nest boxes as a coppery-tailed trogon management tool. Pages 147-

150 in J.W. Davis, G.A. Goodwin, and R.A. Ockenfels, editors. Snag habitat

management: proceedings of the symposium. USDA Forest Service GTR-RM-

99, Rocky Mountain Forest and Range Experiment Station, Fort Collins,

Colorado, USA.

Harper, M.J., M.A. McCarthy, and R. van der Ree. 2005. The use of nest boxes in urban

natural vegetation remnants by vertebrate fauna. Wildlife Research 32: 509-516.

Hearn, B.J. 2007. Factors affecting habitat selection and population characteristics of

American marten (Martes americana atrata) in Newfoundland. Dissertation,

University of Maine, Orono, Maine, USA.

James, D.A., A. Bachan, and R. Kannan. 2011. Installation of artificial nest cavities for

the endangered Great Hornbill: a pilot study in southern India. The Raffles

Bulletin of Zoology 24: 73-76.

Jimerson, T.M., E.A. McGee, D.W. Jones, R.J. Svilich, E. Hotalen, G. DeNitto, T.

Laurent, J.D. Tenpas, M.E. Smith, K. Hefner-McClelland, and J. Mattison. 1996.

A field guide to the tanoak and Douglas-fir plant associations in northwestern

California. USDA Forest Service R5-ECOL-TP-009, Pacific Southwest Region,

San Francisco, California, USA.

Juskaitis, R. 1999. Mammals occupying nest boxes for birds in Lithuania. Acta

Zoologica Lituanica 9: 19-23.

Kilgo, J.C. and M.A. Vukovich. 2014. Can snag creation benefit a primary cavity nester:

response to an experimental pulse in snag abundance. Biological Conservation

171: 21-28.

Knutson, K. L. and V. L. Naef. 1997. Management recommendations for Washington’s

priority habitats: riparian. Washington Department of Fish and Wildlife,

Olympia, Washington, USA.

Laliberte, A.S. and W.J. Ripple. 2004. Range contractions of North American

carnivores and ungulates. BioScience 54: 123-138.

Lambrechts, M.M., K.L. Wiebe, P. Sunde, T. Solonen, F. Sergio, A. Roulin, A. Moller,

B. Lopez, J. Fargallo, K.M. Exo, G. Dell’Omo, D. Constantini, M. Charter, M.W.

Butler, G.R. Bortolotti, R. Arlettaz, and E. Korpimaki. 2012. Nest box design for

the study of diurnal raptors and owls is still an overlooked point in ecological,

evolutionary, and conservation studies: a review. Journal of Ornithology 153:

23-34.

Lindenmayer, D.B., C.I. MacGregor, and R.B. Cunningham. 2003. The use of nest

boxes by arboreal marsupials in the forests of the central highlands of Victoria.

Wildlife Research 30: 259-264.

Lindenmayer, D.B., and J. Fischer. 2006. Habitat fragmentation and landscape change:

an ecological and conservation synthesis. Island Press, Washington, District of

Columbia, USA.

Lindenmayer, D.B., A. Welsh, C.F. Donnelly, M. Crane, D. Michael, C. Macgregor, L.

McBurney, R. Montague-Drake, and P. Gibbons. 2009. Are nest boxes a viable

alternative source of cavities for hollow-dependent animals? Long-term

monitoring of nest box occupancy, pest use and attrition. Biological Conservation

142: 33-42.

Lindenmayer, D.B., W. Blanchard, L. McBurney, D. Blair, S. Banks, G.E. Likens, J.F.

Franklin, W.F. Laurance, J.A.R. Stein, and P. Gibbons. 2012. Interacting factors

driving a major loss of large trees with cavities in a forest ecosystem. PLOS ONE

7: 1-16.

Long, R.A., P. Mackay, W.J. Zielinski, and J.C. Ray. 2008. Noninvasive survey

methods for carnivores. Island Press, Washington, District of Columbia, USA.

MacKenzie, D.I., J.D. Nichols, G.B. Lachman, S. Droege, J.A. Royle, and C.A.

Langtimm. 2002. Estimating site occupancy rates when detection probabilities

are less than one. Ecology 83: 2248-2255.

Madikiza, Z.J.K., S. Bertolino, R.M. Baxter, and E.D. Linh San. 2010. Nest box use by

woodland dormice (Graphiurus murinus): the influence of life cycle and nest box

placement. European Journal of Wildlife Research 56: 735-743.

Martin, K. and J.M. Eadie. 1999. Nest webs: a community-wide approach to the

management and conservation of cavity-nesting forest birds. Forest Ecology and

Management 115: 243-257.

Martin, K., K.E.H. Aitken, and K.L. Wiebe. 2004. Nest sites and nest webs for cavity-

nesting communities in interior British Columbia, Canada: nest characteristics

and niche partitioning. The Condor 106: 5-19.

Maser, C., R.G. Anderson, K. Cromack Jr., J.T. Williams, and R.E. Martin. 1979. Dead

and down woody material. Pages 78-95 in J.W. Thomas, editor. Wildlife habitats

in harvested forests: the Blue Mountains of Oregon and Washington. USDA

Forest Service Agricultural Handbook No. 553.

McComb, W.C. and R.E. Noble. 1981. Nest-box and natural-cavity use in three mid-

South forest habitats. The Journal of Wildlife Management 45: 93-101.

Messenger, J.E., J.D.S. Birks, and T. Braithwaite. 2006. An artificial natal den box for

pine martens (Martes martes). Pages 89-98 in M. Santos-Reis, J.D.S. Birks, E.C.

O’Doherty, and G. Proulx, editors. Martes in carnivore communities. Alpha

Wildlife Publications, Sherwood Park, Alberta, Canada.

Mirza, Z.B. 2011. Understanding the ecological linkages of ecosystems to conserve

wildlife. The Journal of Animal and Plant Sciences 21: 415-420.

Myers, C.H. 2010. Diurnal rest site selection by ringtails (Bassariscus astutus) in

northwestern California. Thesis, Humboldt State University, Arcata, California,

USA.

Office of the Federal Register. 2015. Endangered and threatened wildlife and plants; 12-

month finding on a petition to list Humboldt marten as an endangered or

threatened species. Federal Register 80: 18742-18772.

Payer, D.C. and D.J. Harrison. 2003. Influence of forest structure on habitat use by

American marten in an industrial forest. Forest Ecology and Management 179:

145-156.

Patterson, J.E.H. and S.J. Patterson. 2010. Multiple annual litters in Glaucomys sabrinus

(Northern flying squirrel). Northeastern Naturalist 17: 167-169.

Poole, K.G., A.D. Porter, A. de Vries, C. Maundrell, S.D. Grindal, and C.C. St. Clair.

2004. Suitability of a young deciduous-dominated forest for American marten

and the effects of forest removal. Canadian Journal of Zoology 82: 423-435.

Porter, A.D., C.C. St. Clair, and A. de Vries. 2005. Fine scale selection by marten

during winter in a young deciduous forest. Canadian Journal of Forestry

Research 35: 901-909.

Powell, R.A., S.W. Buskirk, and W.J. Zielinski. 2003. Fisher and marten. Pages 635-

649 in G.A. Feldhamer, B.C. Thompson, and J.A. Chapman, editors. Wild

mammals of North America: biology, management, and conservation. The Johns

Hopkins University Press, Baltimore, Maryland, USA.

Prange, S. and T.J. Prange. 2009. Bassariycon gabbii (Carnivora: Procyonidae).

Mammalian Species 826: 1-7.

Purcell, K.L., J. Verner, and L.W. Oring. 1997. A comparison of the breeding ecology

of birds nesting in boxes and tree cavities. The Auk 114: 646-656.

Ransome, D.B. and T.P. Sullivan. 2004. Effects of food and den-site supplementation

on populations of Glaucomys sabrinus and Tamiasciurus douglasii. Journal of

Mammalogy 85: 206-215.

Raphael, M.G. and L.C. Jones. 1997. Characteristics of resting and denning sites of

American martens in central Oregon and western Washington. Pages 146-165 in

G. Proulx, H.N. Bryant, and P.M. Woodward, editors. Martes: taxonomy,

ecology, techniques, and management. Provincial Museum of Alberta,

Edmington, Alberta, Canada.

Remm, J. and A. Lohmus. 2011. Tree cavities in forests – the broad distribution pattern

of a keystone structure for biodiversity. Forest Ecology and Management 262:

579-585.

Ruggiero, L.F., E. Pearson, and S.E. Henry. 1998. Characteristics of American marten

den sites in Wyoming. The Journal of Wildlife Management 62: 663-673.

Santos-Reis, M., M.J. Santos, S. Lourenco, J.T. Marques, I. Pereira, and B. Pinto. 2005.

Relationships between stone martens, genets, and cork oak woodlands in

Portugal. Pages 147-172 in D.J. Harrison, A.K. Fuller, and G. Proulx, editors.

Martens and fishers in (Martes) in human-altered environments. Springer US,

New York, New York, USA.

Shuttleworth, C.M. 1999. The use of nest boxes by the red squirrel Sciurus vulgaris in

coniferous habitat. Mammal Review 29: 63-68.

Slauson, K.M. and W.J. Zielinski. 2004. Conservation status of American martens and

fishers in the Klamath-Siskiyou bioregion. Pages 60-70 in K. Merganther, J.

Williams, and E. Jules, editors. Proceedings of the 2nd Conference on Klamath-

Siskiyou Ecology. Cave Junction, Oregon, USA.

Slauson, K.M. and W.J. Zielinski. 2007. The relationship between the understory shrub

component of coastal forests and the conservation of forest carnivores. Pages

241-244 in R.B. Standiford, G.A. Giusti, Y. Valachovic, W.J. Zielinski, M.J.

Furniss, editors. Proceedings of the redwood region forest science symposium:

what does the future hold? USDA Forest Service GTR-PSW-194, Pacific

Southwest Research Station, Albany, CA, USA.

Slauson, K.M., W.J. Zielinski, and J.P. Hayes. 2007. Habitat selection by American

martens in coastal California. The Journal of Wildlife Management 71: 458-468.

Slauson, K.M. and W.J. Zielinski. 2009. Characteristics of summer and fall diurnal

resting habitat used by American martens in coastal northwestern California.

Northwest Science 83: 35-45.

Slauson, K.M., J.A. Baldwin, W.J. Zielinski, and T.A. Kirk. 2009. Status and estimated

size of the only remnant population of the Humboldt subspecies of the American

marten (Martes americana humboldtensis) in coastal northwestern California.

USDA Forest Service, Pacific Southwest Research Station, Redwood Sciences

Lab, Arcata, California, USA.

Slauson, K.M., W.J. Zielinski, and T.A. Kirk. 2010. Effects of forest restoration on

mesocarnivores in the northern redwood region of northwestern California.

USDA Forest Service, Pacific Southwest Research Station, Redwood Sciences

Lab, Arcata, California, USA.

Slauson, K., M. Delheimer, W. Zielinski, and M. Szykman Gunther. 2014. The effects

of restoring cavity structures for mammals on young post-logging forests of the

redwood region. USDA Forest Service, Pacific Southwest Research Station,

Redwood Sciences Lab, Arcata, California, USA.

Slauson, K.M. et al. In prep. A conservation assessment and strategy for the Humboldt

marten (Martes caurina humboldtensis) in California and Oregon. Unpublished

report produced by the Humboldt Marten Conservation Group.

Stevenson, S.K., M.J. Jull, and B.J. Rogers. 2006. Abundance and attributes of wildlife

trees and coarse woody debris at three silvicultural systems study areas in the

Interior Cedar-Hemlock Zone, British Columbia. Forest Ecology and

Management 233: 176-191.

Stone, K.D., G.A. Heidt, W.H. Baltosser, and P.T. Caster. 1996. Factors affecting nest

box use by southern flying squirrels (Glaucomys volans) and gray squirrels

(Sciurus carolinensis). American Midland Naturalist 135: 9-13.

Taylor, S.L. and M.G. Raphael. 1988. Identification of mammal tracks from sooted

track stations in the Pacific Northwest. California Department of Fish and Game

74: 4-15.

Tews, J., U. Brose, V. Grimm, K. Tielborger, M.C. Wichmann, M. Schwager, and F.

Jeltsch. 2004. Animal species diversity driven by habitat heterogeneity/diversity:

the importance of keystone structures. Journal of Biogeography 31: 79-92.

Thornburgh, D.A., R.F. Noss, D.P. Angelides, C.M. Olson, F. Euphrat, and H.J. Welsh.

2000. Managing redwoods. Pages 229-261 in R.F. Noss, editor. The redwood

forest: history, ecology, and conservation of the Coast Redwoods. Island Press,

Washington, District of Columbia, USA.

Tiedt, A.R. 2011. Den site selection of ringtails (Bassariscus astutus) in west central

Texas. Thesis, Angelo State University, San Angelo, Texas, USA.

Twining, H. and A. Hensley. 1947. The status of pine martens in California. California

Fish and Game 33: 133-137.

United States Department of Agriculture, Forest Service. 1992. Final Environmental

Impact Statement (FEIS) on management for the northern spotted owl in the

national forests. States of Washington, Oregon, and California. USDA Forest

Service, Portland, Oregon, USA.

United States Department of Agriculture, Forest Service. 2007. Ecological subregions:

sections and subsections for the coterminous United States. USDA Forest

Service/ECOMAP Team, Washington, District of Columbia, USA.

Warakai, D., D.S. Okena, P. Igag, M. Opiang, and A.L. Mack. 2013. Tree cavity-using

wildlife and the potential of artificial nest boxes for wildlife management in New

Guinea. Tropical Conservation Science 6: 711-733.

Zielinski, W.J. and T.E. Kucera. 1995. Introduction to detection and survey methods.

Pages 1-15 in W.J. Zielinski and T.E. Kucera, editors. American marten, fisher,

lynx, and wolverine: survey methods for their detection. USDA Forest Service

GTR-PSW-157, Pacific Southwest Research Station, Albany, California, USA.

Zielinski, W.J., K.M. Slauson, C.R. Carroll, C.J. Kent, and D.G. Kudrna. 2001. Status of

American martens in coastal forests of the Pacific states. Journal of Mammalogy

82: 478-490.

Zielinski, W.J., R.L. Truex, G.A. Schmidt, F.V. Schlexer, K.M. Schmidt, and R.H.

Barrett. 2004. Resting habitat selection by fishers in California. Journal of

Wildlife Management 68: 475-492.

APPENDICES

The marten box design was adapted from a “den” box design (Messenger et al.

2006) developed by the Vincent Wildlife Trust (VWT) for European pine martens in

Scotland. Boxes had a rectangular shape (similar height and width dimensions, smaller depth dimensions), a sloping roof to shed water, a circular entrance on each side of the lower portion of the rear box component, and a central interior chamber with an access shaft or “chimney” on either side of the chamber. The interior chamber size is based on natural den sizes of female European pine martens (Messenger et al. 2006).

I retained wood length dimensions, wood width dimensions, and overall box size from the VWT design. Exterior box dimensions are approximately 60 cm height by 55 cm width by 25 cm depth; interior box dimensions are approximately 55 cm height by 50 cm width by 20 cm depth; interior chamber dimensions are approximately 55 cm height by 25 cm width by 20 cm depth. I increased wood thickness from the VWT design to 3-5 cm. Fully-constructed boxes weighed approximately 30-35 kg.

I made a number of structural modifications to the VWT design to increase structural strength, extend box durability, improve water resistance, and increase protection (for martens and other species) from predators. First, I constructed the majority of the marten boxes (n=45) out of salvaged old-growth redwood, and a smaller

57 number of boxes (n=10) out of western red cedar. Redwood and cedar are ideal materials for marten box construction, as they are native to northwestern California, and are naturally resistant to moisture and rot. I chose these materials over the marine-grade plywood used in the VWT design to increase structural integrity of boxes, particularly due to concerns of box damage by black bears. Furthermore, I joined the corners on all exterior box pieces, used a strong construction adhesive (Liquid Nails®, Strongsville,

OH) on all wood joints, and fastened all wood joints with 10-15 cm long TimberLok® wood screws (Fastenmaster Inc., Agawam, MA).

Additionally, I decreased the size of the marten box entrances to allow unrestricted movements by martens and smaller animals, while attempting to exclude fishers and other larger-bodied animals. Entrances were ~6.5 cm diameter, slightly larger than mean skull sizes of male martens (Powell et al. 2003), and similar to trap “cubby” entrances used by other marten researchers (K. Slauson, pers. comm.) in live-trapping applications.

I mounted each marten box on the largest diameter live tree available in a given stand, and placed them at 4-5 m height. I raised boxes using a fairly simple hauling system consisting of a pulley, rope, and an auto-locking belay device designed for rock climbing purposes. To anchor the hauling system, I attached the pulley to a 15 cm eyebolt drilled into the mounting tree above the box placement. To lift and mount the box, I used a 5 m long articulated ladder (Model M1A-8-16B, Werner Co., Greenville,

PA). In contrast to traditional extension ladders, articulated ladders can be used in multiple configurations and break down into ~1.5 m long sections for ease of carrying.

I mounted marten boxes on trees using a cleat system of 5 cm width by 40 cm length wooden cleats, with two cleats attached to each box and two corresponding cleats attached to each mounting tree. I screwed upper and lower tree cleats to the mounting tree, placed the box cleats on top of the tree cleats, and through-bolted each set of cleats.

This should prevent damage (e.g., girdling) by boxes to trees as the trees age and grow.

Cleat attachment to the mounting tree was with 25 cm-long Timberlok® screws.

Timberlok® screws have two major advantages over traditional lag screws, in that they are self-drilling (i.e., they do not require a drilled pilot hole), and they are difficult to shear (e.g., traditional lag screws have a tendency to break when over-torqued). I used an

18V cordless impact driver drill (Model LXDT04CW-R, Makita USA, Mirada, CA), rather than a traditional cordless drill. Impact driver drills simultaneously use bit rotation and concussive action to drive screws, provide two to three times the torque of traditional cordless drills, and are necessary to efficiently drive long screws into live trees.

Given that most of the boxes used in this study were in the field for at least 12 months, we can learn from how they performed for this duration. There was no box attrition and negligible box damage from storms, falling branches, or animal activity, which indicates that the box construction is structurally sound. The paired cleats, along with 25 cm-long wood screws, appear to be a very strong attachment system. This is evidenced by numerous occasions of black bears photographed on top of boxes or pulling/hanging on boxes, with no negative impact to the integrity of box attachment.

Additionally, the re-sizing of box entrances appeared to completely exclude fishers from entering boxes.

However, I would suggest a number of further modifications to the marten box design for future applications. The trade-off for using redwood and cedar materials

(rather than plywood) was a significant increase in box weight, which made it difficult to transport boxes long distances and also made it difficult to mount boxes safely. If using thick-dimension wood (redwood or cedar), I would suggest incorporating only one entrance and entrance shaft to the box, which would significantly decrease box weight by decreasing box size, and would also make boxes more transportable and easier to mount.

Additionally, I would move the entrance to the camera-facing side of the box, which should maximize detectability by cameras of animals entering boxes.

To further improve effectiveness of future monitoring efforts, I recommend hinging the lid of the marten box, rather than bolting the lid on. While bolting the lid on provided a secure attachment, it made lid removal extremely difficult. Hinging the lid would allow researchers to periodically inspect box interiors for animal use, rot or water damage, or clean box interiors if necessary. Another possibility to improve monitoring would be to drill a small hole in the box for inserting an endoscopic camera. This would allow box inspection without removing the lid, although the hole would have to be well- sealed when not in use. Finally, box entrances could be modified to include a hair snare, which would provide a passive method for collecting genetic information from animal species using boxes.

60 Appendix B: Marten box design schematic (Messenger et al. 2006), box structural components, box deployment, and examples of animal visitation at boxes in the Pecwan Creek study site in northwestern California. 61 Appendix C: Complete results from track plate surveys to assess carnivore species occupancy at the Goose Creek and Mill Creek study sites in northwestern California, July to September 2013. Includes number of track plate boxes surveyed at each study site and across study sites (n) and number of track plate boxes surveyed that a given species was detected at each study site and across study sites (detected). Goose Creek Mill Creek Total Treatment Control Treatment Control n Detected n Detected n Detected n Detected n Detected Carnivore Fisher 20 3 20 1 20 9 20 11 80 24 Gray fox 20 0 20 0 20 2 20 4 80 6 Humboldt marten 20 0 20 0 20 0 20 0 80 0 Mustela sp. 20 3 20 1 20 0 20 0 80 4 Ringtail 20 1 20 0 20 0 20 0 80 1 Western spotted skunk 20 0 20 1 20 9 20 6 80 16 Small Mammal Douglas squirrel 20 1 20 0 20 0 20 1 80 2 Dusky-footed woodrat 20 3 20 4 20 3 20 7 80 17 Northern flying squirrel 20 0 20 2 20 0 20 0 80 2 Peromyscus sp. 20 2 20 2 20 1 20 3 80 8 Tamias sp. 20 1 20 2 20 1 20 0 80 4

62 Appendix D: Complete marten box monitoring results, including visitation and use at by 10 mammal species at the Goose Creek, Mill Creek, and Pecwan Creek study sites in northwestern California, June to October 2014. Includes total number of marten boxes (n); total number of boxes visited by a given species (visited); total number of visits at marten boxes for a given species (total); and whether or not a given species was documented to enter a marten box (use). Goose Creek Mill Creek Pecwan Creek Total n Visited Total Use n Visited Total Use n Visited Total Use n Visited Total Use Carnivore Fisher 16 4 5 N 19 12 41 N 8 11 34 N 43 27 80 N Humboldt marten 16 0 0 Y 19 1 1 N 8 14 67 N/A 43 15 67 Y Raccoon 16 0 0 N/A 19 2 5 N 8 0 0 N/A 43 2 5 N Ringtail 16 1 1 N 19 1 5 N 8 1 1 N 43 3 7 N Western spotted skunk 16 0 0 N 19 0 0 N/A 8 1 1 N/A 43 1 1 N Small Mammal Douglas squirrel 16 8 54 Y 19 16 151 N 8 14 207 N 43 38 412 Y Dusky-footed woodrat 16 0 0 N/A 19 2 12 Y 8 0 0 N/A 43 2 12 Y Northern flying squirrel 16 5 14 N 19 12 59 Y 8 11 84 N 43 28 157 Y Tamias sp. 16 0 0 N 19 6 9 N 8 5 30 N/A 43 11 39 N Western gray squirrel 16 2 4 N 19 3 5 N 8 2 12 N 43 7 21 N

63 Appendix E: Complete results of habitat transects for standing resting structures at the Goose Creek, Mill Creek, and Pecwan Creek study sites in northwestern California, July to October 2014. Includes mean diameter at breast height (DBH) and DBH range of hardwood and conifer live trees and snags, and number of structural element types (branch platform, broken top, cavity) within each standing structure type. Type (n) Mean DBH (cm) DBH Range (cm) Branch Platform Broken Top Cavity Live Tree (n) Goose Creek (25) Hardwood (9) 81 71-87 0 (-) 0 (-) 9 (100%) Conifer (16) 134 65-189 4 (25%) 8 (50%) 4 (25%) Mill Creek (21) Hardwood (0) (-) (-) (-) (-) (-) Conifer (21) 153 88-305 7 (33%) 12 (57%) 2 (10%) Pecwan Creek (36) Hardwood (15) 83 66-102 0 (-) 1 (7%) 14 (93%) Conifer (21) 117 81-171 10 (47%) 6 (29%) 5 (24%) Snag (n) Goose Creek (17) Hardwood (0) (-) (-) (-) (-) (-) Conifer (17) 146 96-198 (-) 11 (65%) 6 (35%) Mill Creek (9) Hardwood (0) (-) (-) (-) (-) (-) Conifer (9) 138 104-192 (-) 2 (22%) 7 (78%) Pecwan Creek (25) Hardwood (3) 95 79-123 (-) 0 (-) 3 (100%) Conifer (22) 123 93-199 (-) 9 (41%) 13 (59%)

64 Appendix F: Review of previous literature documenting nest box use by mammals. Carnivore species are in bold lettering. Source Focal Species Location Brady et al. (2007) Southern flying squirrel South Carolina (USA) Carey (2002) Northern flying squirrel Washington (USA) Czeszczewik et al. (2008) Fat dormouse (Glis glis), forest dormouse (Dryomys nitedula), Poland Fokidis and Risch (2005) Southern flying squirrel South Carolina (USA) Goldingay et al. (2007) Feathertail glider (Acrobates pygmaeus), squirrel glider (Petaurus norfolcensis) Australia Hakes (1983) Ringtail, western gray squirrel Arizona (USA) Harper et al. (2005) Brushtail possum (Trichosurus vulpecula), ringtail possum (Pseudocheirus peregrinus) Australia James et al. (2011) Common palm civet (Paradoxurus hermaphroditus) India Juskaitis (1999) European pine marten, fat dormouse, red squirrel (Sciurus vulgaris) Lithuania Lindenmayer et al. (2003) Brushtail possum, Leadbeater's possum, ringtail possum Australia Lindenmayer et al. (2009) Leadbeater's possum Australia Madikiza et al. (2010) Woodland dormice (Graphiurus murinus) South Africa McComb and Noble (1981) Eastern gray squirrel, fox squirrel, southern flying squirrel Louisiana, Mississippi (USA) Messenger et al. (2006) European pine marten Scotland Patterson and Patterson (2010) Northern flying squirrel Ontario (Canada) Ransome and Sullivan (2004) Douglas squirrel, northern flying squirrel British Columbia (Canada) Shuttleworth (1999) Red squirrel England Slauson et al. (2014) Douglas squirrel, dusky-footed woodrat, northern flying squirrel, Pacific marten California (USA) Stone et al. (1996) Eastern gray squirrel, southern flying squirrel Arkansas (USA) Tiedt (2011) Ringtail Texas (USA) Warakai et al. (2013) Sugar glider (Petaurus breviceps) New Guinea

65 Appendix G: Review of previous literature concerning carnivore species documented to use tree cavities for resting or denning purposes. Source Species Location Buskirk and Ruggiero (1994) American marten North America (Canada, USA) Carvalho et al. (2014) Common genet (Genetta genetta) Europe (Portugal) Doty and Dowler (2006) Striped skunk (Mephitis mephitis) North America (USA) Doty and Dowler (2006) Western spotted skunk North America (USA) Gehrt et al. (1990) Raccoon North America (USA) Glen and Dickman (2006) Spotted-tailed quoll (Dasyurus maculatus) Australia Martin et al. (2004) Short-tailed weasel (Mustela erminea) North America (Canada, USA) Messenger et al. (2006) European pine marten Europe (UK) Mirza (2011) Common palm civet Asia (Pakistan) Mirza (2011) Yellow-throated marten (M. flavigula) Asia (Pakistan) Myers (2010) Ringtail North America (USA) Prange and Prange (2009) Olingo (Bassaricyon gabbii) South America (Peru) Santos-Reis et al. (2005) Beech marten (M. foina) Europe (Portugal) Slauson and Zielinski (2009) Pacific marten North America (USA) Zielinski et al. (2004) Fisher North America (USA)