Mammal Inventory at Oregon Islands National Wildlife Refuge, Crook
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Mammal Inventory Report Crook Point, Oregon, 2009. Siskiyou Research Group Introduction and Study Area The Crook Point Unit of Oregon Islands National Wildlife Refuge is a 134-acre undeveloped coastal headland located approximately 12 miles south of Gold Beach, Oregon. Notwithstanding post-European settlement activities of livestock grazing and timber harvesting, Crook Point provides exceptional examples of coastal headland habitats, which have largely disappeared from Oregon as a result of development and conversion (Kagan 2002). Currently, Crook Point provides habitat for rare plant species such as Poa unilateralis, Lasthenia ornduffii, and Artemisia pycnocephala (Kagan 2002, Chan 2001, Bilderback 2008). Moreover, the associated offshore islands and rocks provide important nesting habitat for seabirds, haul-out and breeding areas for marine mammals, and suitable cliff habitat for nesting peregrine falcons (Ledig 2009). Saddle Rock, the largest island associated with Crook Point, provides nesting habitat for a large population of Leach’s storm petrels (PRBO 2004). There is evidence the Saddle Rock population is being decimated by mammalian predators (reference). In 2000 U.S. Fish and Wildlife Service (USFWS) acquired this coastal headland making it the second mainland unit in the Oregon Islands National Wildlife Refuge system. Presently USFWS is focusing on site restoration, resource protection, and biological inventory, monitoring, and research. This mammal survey is part of an effort to document the biological diversity of Crook Point. Prior to this survey no systematic mammal inventory work has been conducted at Crook Point. Objectives The primary objective of this survey was to compile a mammalian species list for Crook Point using multiple detection methods of trapping, motion-triggered trail cameras, direct observation, and animal sign (prints, scat, excavations). Secondary objectives sought to compare mammalian diversity and abundance between the largest vegetation types, and to collect tissue samples for genetic analysis to determine if genetic differences exist between Microtus populations on Saddle Rock and mainland Crook Point. Products A database (Microsoft Access®) containing polygon information, captured species information, and spreadsheets of data tabulations will be provided in conjunction with this report. Other products generated by this survey included a small number of study skins and skulls from collected mammals, microtine tissue samples, and an electronic file of digital photographs of animals taken by the trail cameras. Mark P. Miller of the USGS Forest and Rangeland Ecosystem Science Center in Corvallis, Oregon conducted genetic analyses of microtine tissue samples. Preliminary results from this work are available and a final report is expected in May 2010. Methods Vegetation associations identified, described, and mapped by Kagan (2002) were used to stratify the study area into sampled polygons for measuring mammalian diversity (Figure 1). In addition to the 18 vegetation types described by Kagan (2002), I added 3 plots identified as Saddle Rock, Beach (wrack line), and Road for a total of 21 vegetation units (Table 1). Of the 21 vegetation units, 8 were not sampled due to accessibility (e.g. steep 1 Mammal Inventory Report Crook Point, Oregon, 2009. Siskiyou Research Group bluffs, cliffs, or impenetrable vegetation) or because of small size. I assumed that mammals utilizing these areas would be represented through survey efforts occurring in adjacent vegetation plots. Figure 1. Infrared aerial photograph of Crook Point showing refuge property boundaries, vegetation units, and approximate locations of selected transects and trap centers. 2 Mammal Inventory Report Crook Point, Oregon, 2009. Siskiyou Research Group I reviewed animal-habitat associations and species range maps (Verts and Carraway, 1998) to determine mammal species most likely to occur at Crook Point (Table 2) and the best sampling methods for detecting these species (Quayle 1998, Gomez, 2008). I conducted trapping fieldwork in two sessions, May 20, - May 25, 2009 and June 19, - June 25, 2009 when mammal activity is high (Verts and Carraway, 1998) and there is a low probability of rainfall - and consequently a lower probability of weather related trap mortalities. Trail camera survey work began in November 2009 and concluded in February 2010. I operated the trail cameras in winter when naturally occurring food sources are presumably less abundant and carnivores might be more attracted to the meat- baited stations. With exception, the basic trapping configuration used in each sampled vegetation unit consisted of a transect line of 10 Sherman live traps (3”X3”X9”), 2 Tomahawk live traps (model 201), and an array of 4 pitfall traps. Typically, a trap center was identified in each vegetation unit where a pitfall array was constructed. Pitfall traps were assembled from stacking and duct-taping two 64-ounce tin cans together. The bottom was removed from the top can to create a 16-inch deep metal tube that was placed into a hole created by a posthole digger. The lip of the top can was placed flush with the ground. In most sampled vegetation units a pitfall array consisted of 4 pitfall traps arranged in a 2- dimensional tetrahedron (Figure 1). The outer pitfalls were placed approximately 3 meters from the central pitfall and between the central pitfall trap and the outer pitfalls an artificial drift fence of 3.5-inch high plastic garden border material was staked in place. The purpose of this drift fence was to direct small animals toward a pitfall. Nesting material of grass was placed in each pitfall for cover and thermal protection for caught animals. Also, mealworms were placed in pitfalls to reduce shrew mortality from starvation. Two Tomahawk traps were placed within 10 meters of this pitfall array. In forested polygons one Tomahawk trap was placed on the ground and one Tomahawk trap was attached to the bole of a tree (with aluminum nails) approximately 1.5 meters from the ground. In non-forested polygons both Tomahawk traps were placed on the ground. Transect lines consisted of 10 Sherman traps placed at 15-meter intervals. Transect lines were established near trap center and individual Sherman traps were subjectively placed on or near the transect line to take advantage of natural drift fences such as downed trees, rocks, and topography, which also offered cover from sun, wind, and moisture. Cedar shingles were placed on top of both Sherman and Tomahawk traps to provide additional protection from weather. To compare mammalian diversity and abundance between the 4 largest vegetation units (Sitka Spruce/Salal Forest (2), Sitka Spruce/Red Alder/Thimbleberry Riparian (6), South Coast Headland Prairie (8), and Open South Coast Headland Erosion Forblands and Dunes (10)), 3 basic trapping configurations were established in each vegetation unit (polygon) for a total of 48 traps/polygon (30 Shermans/12 pitfalls/6 Tomahawks). The typical pitfall configuration was changed from the 2-dimensional tetrahedron shape to a linear shape in polygon 6 to better conform to the linear nature of the inner riparian 3 Mammal Inventory Report Crook Point, Oregon, 2009. Siskiyou Research Group habitat. Trapping was conducted for 5 trap-nights (Wilson 1996, Quayle 1998, Gomez 2008). Figure 2. Basic Trapping Configuration, Crook Point, Oregon Pitfalls built from 2 stacked tin cans. Drift fence 2 Tomahawks placed within Pitfalls 10 m of trap separated by center 3m and 120o Transect line: 10 Sherman traps spaced every 15m. One basic trapping configuration was placed in each of the smaller vegetation polygons (Disturbed Area (1), Old Pasture (4), Sitka Spruce Regenerating Forest (5), Headland Riparian Shrublands (14), and Red Alder/Salmonberry Riparian Forest (19)) for a total of 16 traps/polygon (10 shermans/4 pitfalls/2 Tomahawks). For the remaining 3 sampled polygons (Saddle Rock (20), Road (23), and Beach (22)), a modified trapping configuration was used. On Saddle Rock one transect line of 20 Sherman live traps was established. Tomahawk traps and pitfall traps were not used on Saddle Rock in order to minimize disturbance to nesting Leach’s storm petrels. The Beach wrack line (polygon 22) consisted of one transect of 15 Sherman live traps, 2 Tomahawk traps, and a linear array of 4 pitfall traps. The Road plot (polygon 23) was identified as unique even through it traverses several vegetation units already described. Ten Tomahawk traps were deployed along this linear plot. Additionally, two large (coyote-sized) live traps were deployed for 5 days along the Beach transect (polygon 22) and the Headland Riparian Shrubland transect (polygon 14). These traps were camouflaged in vegetation (polygon 14) and driftwood (polygon 22). 4 Mammal Inventory Report Crook Point, Oregon, 2009. Siskiyou Research Group All Sherman and Tomahawk traps were baited with a mixture of rolled oats, peanut butter, and molasses, except for 4 of the Tomahawk traps located along the Road plot (polygon 23), which were baited with alfalfa pellets to target Sylvilagus. The extra large Tomahawk traps were baited with canned dog food/dry cat food/peanut butter bait mixture. Traps were checked daily. Specimens were collected for difficult-to-identify insectivores and microtines and study skins and skulls were prepared to validate field identifications. Project-related animal mortalities provided some specimens. Collection of insectivores, microtines, and geomyids were identified to species using