Effects of Bark Beetle Infestation on Chipmunks in Southeast Wyoming Andi Noakes

Native to Western North America One-year life cycle Later summer: adults leave dead pine trees & seek large, living, green trees (though tend to prefer old, unhealthy, or damaged) Attack by tunneling under bark, forming vertical egg gallery, and producing about 75 eggs Larvae hatch, tunnel away from gallery, spend winter under bark, feed until pupae transformation, early summer Leatherman et al. 1999, USDA 1990, USDA 2009 Mountain Pine Beetle (Dendroctonus ponderosae)

Killing Mechanisms Larvae mine phloem area, cut off tree’s nutrients Transmit blue stain fungi, which assist in killing the tree Coordinated mass attacks are common Species affected (most common) Ponderosa Pine Lodgepole Pine Limber Pine Leatherman et al. 1999, Parks Canada 2009, USDA 2009 Mountain Pine Beetle (Dendroctonus ponderosae)

Mountain Pine Beetle extent in Colorado and Southern Wyoming, 1996

Mountain Pine Beetle extent in Colorado and Southern Wyoming, 2009

Chipmunks as an Indicator Species Widespread Easy to monitor Inhabit a wide variety of habitats Disperse seeds and fungi Prey base for many predators Impact trophic cascade

Distribution of the least chipmunk Six subspecies occur in Wyoming Distribution

Eat a wide variety of foods including: nuts berries fruits grass fungi snails insects (Baker 1983; Bergstom 1999; Kurta 1995) Feed on the ground, in shrubs, and in trees. Store food in an underground caches for spring use (post-hibernation). Diet

Home range ha Require sufficient forest cover and sparse understory vegetation. Do not require a water source other than food due to a lower rate of water loss and greater tolerance for heat load. Can tolerate more arid sagebrush habitats than other chipmunk species. Heller and Gates 1971, Heller and Poulson 1972, Jones and Wang 1976, Chappell et al Habitat Requirements

Individuals become sexually mature at 10 months of age (Kurta, 1995). Most mating occurs when females first emerge from hibernation. Gestation lasts approximately 30 days (Hamilton and Whitaker, 1979). Litter size varies from 2 to 6 young. Reproduction

Study Objectives Evaluate habitat use and estimate density and abundance of chipmunk populations in two habitat types. Compare these data to previous years to assess changes and correlate chipmunk abundance with several habitat characteristics in pine forest and sagebrush steppe. Assess food availability in relation to extent of mountain pine beetle presence. Estimate diet composition of live-trapped chipmunks using stable isotope analysis on blood samples.

Study Areas

Vegetation: predominantly limber pine, ponderosa pine, lodgepole pine, quaking aspen, and common juniper. Example of Forest Grid

Vegetation: predominantly mountain big sagebrush with sparse limber pine. Example of Sagebrush Grid

Small tomahawk traps (Model 102). Baited with peanut butter, oatmeal, molasses, and apples. Trapping Methods

Traps arranged in 5 x 8 grids, 50 m apart. Left open during day (6:30AM- 5:00PM). Each grid trapped for 5 consecutive days. Trapping Procedures

Traps checked every evening. Recaptures PIT tags recorded and released. All other animals released immediately

Animal checked for presence of PIT tag No PIT tag Animal weighed Animal anesthetized with Isoflurane PIT tag inserted/blood Animal released Data Collection

Random trap site locations were surveyed Used Point-centered Quarter Method Measured distance to nearest tree and DBH Habitat Analysis

Recorded density of beetle kill Counted cones within 1 x 1 m plot Recorded understory as bare ground, grass, or shrub

Data Analysis Capture success: number of unique captures divided by number of open (available) traps. Calculated 95% confidence intervals. Naïve density: Number of unique captures divided by “effective trapping area” Effective trapping area: the area of the trapping grid with an added buffer based on average distance between two traps in consecutive captures. Formal population estimates: Closed population models as implemented in program “MARK”. Diet composition: Utilized SISUS to determine the most prominent food items in chipmunk diets

Capture Success

Naïve Density

Formal Population Estimates in 2010

Formal Population Estimates over Time

Formal Estimates Are Correlated With Naïve Densities

Precipitation Does Not Explain Abundance

Food Availability Differs Between Sagebrush and Forest Habitats

Diet Composition Differs Between Sagebrush And Forest Habitats Cones Flowers Fungi Chipmunks Invertebrates Berries Cones Invertebrates Berries Lichens SagebrushForest Chipmunks

Discussion Capture Success and Naïve Density Increased between early and late summer, but more so in forested habitats Recruitment of chipmunks likely occurred between trapping sessions, explaining the population increase

Discussion Abundance Was significantly higher in 2010 in forest and sagebrush grids 1 than recorded in similar efforts in previous years. Precipitation Changes in abundance could not be explained by precipitation. There is no relation between naïve densities and precipitation in 4 years of data in the forest and sagebrush grids that were trapped in all years.

Discussion Food availability Food availability may explain the population increase in the forest grid in 2010 as chipmunks appear to eat pine beetles and cones which were high in forest grids. Unclear what factors affect population trends in sagebrush (immigration?)

Discussion Diet Composition Cones make up a large proportion of chipmunk diets in both sagebrush and forest habitats In both habitats, berries and invertebrates are also important in chipmunk diet When pine trees die, a shift in diet composition is expected from cones to inverts, flowers, and lichen.

Because density estimates were consistently lower on the sagebrush grid and because cones were the main diet item, a reduction in forest extent from beetle kill will translate into reduction in chipmunk abundance on the landscape. Conclusion

Acknowledgements Merav Ben-David Liz Flaherty The Wildlife Management classes of 2006, 2008, 2009, 2010 The amazing field technicians of 2010 The Wyoming NASA Space Grant Consortium Wyoming EPSCoR

Questions?