Small Mammal Studies
Without food, there is no survival for northern spotted owls. Key owl prey species are studied by the Lesmeister Lab to track habitat availability and the interrelationship between small mammals and the predators that consume them. A multitude of forest dwelling species are woven into the trophic webs we study – these connections are what drive the forest ecosystem, and our research seeks to understand their complexity.
Research at HJ Andrews Experimental Forest
Since 2011, small mammals have been studied by the Lesmeister Lab at HJ Andrews Experimental Forest in Oregon’s Mackenzie River Valley. Through primarily mark-recapture studies, a multitude of publications have arisen on abundance, spatiotemporal associations, and vital rates of small mammal species inhabiting this woodland area.
What started as Matt Weldy’s master's thesis continues to be a key source of data on small mammal populations in undisturbed old-growth forests, and has driven analysis on how changes to prey availability can affect the spatiotemporal dynamics of predator populations, including northern spotted owls.
What started as Matt Weldy’s master's thesis continues to be a key source of data on small mammal populations in undisturbed old-growth forests, and has driven analysis on how changes to prey availability can affect the spatiotemporal dynamics of predator populations, including northern spotted owls.
ORIGINAL RESEARCHMatt Weldy's original research focused on four co-occurring species: Humbolt’s flying squirrel, Townsend’s chipmunk, western red-backed vole, and deer mice.
Utilizing six years of small mammal live-trapping data collected between 2011 and 2016 at HJ Andrews, Matt analyzed the ways in which distribution is dependent on resources. Abundance of these late successional forest dwelling species depends on berry producing shrub cover, canopy openness, elevation, and minimum winter temperatures. These associations vary between each species, but serve as important factors for considering where and when potential owl prey might be found – and thereby, eaten. Matt's research was published in the Journal or Wildlife Management in 2019. |
FURTHER DISCOVERYSmall mammal live-trapping continues on HJ Andrews with crews heading into the field each fall. In a 2021 article, Matt Weldy, Damon Lesmesiter, and Clinton Epps (Oregon State) explore the effects of emigration on estimates of age and sex specific survival rates for Humbolt's flying squirrel and Towsend's chipmunk. Analyzing nine years of live-trap data, they show the importance of considering and accounting for emigration in small mammal survival estimates.
In 2020, an article published in the Journal of Mammalogy utilized the original data set collected on HJ Andrews to analyze vital rates (survival and recruitment) of Townsend's chipmunk and Humbolt's flying squirrel. The findings of this analysis suggest a difference in life history strategies for these co-occurring species: flying squirrel populations depend on stable survival rates for overall growth, where as recruitment is prioritized by chipmunks.
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Learn more about the research occurring at HJ Andrews
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Red Tree Vole Ecology
Red tree voles are deeply dependent on old growth forests, preferring conifer dominant habitat with trees over eighty years old and in a variety of sizes. Endemic to western Oregon and Northern California, this rare arboreal rodent nests fifty feet or higher in the air and subsists off a diet of Douglas fir needles. The Lesmeister Lab explores this old growth dependency, seeking to understand the utility of younger forest stands for population connectivity, and striving to assist land managers in conserving this threatened vole species.
Forest structure has been identified as a deciding factor for red tree vole occupancy – the older, more multi-layered, and complex the forest is, the more likely red tree voles are living there. Due to timber harvest, the availability of this complex habitat is extremely limited. Instead, young and old forests form a patchwork on the landscape. Mark Linnel seeks to understand the effects of this on red tree voles. His research illustrates the potential utility of young forest stands in providing connectivity for disparate vole populations.
Multi-layer, complex forests provide more suitable red tree vole habitat than young, homogeneous forest stands
Weighing in at two ounces and less than eight inches in length, red tree voles are a low-vagile species meaning their capacity for movement and dispersal is limited. In order to protect genetic flow within the greater tree vole population, forest connectivity at a larger, landscape-level scale needs to be considered.
The Lesmeister Lab researches red tree voles high up in the canopy of Douglas fir trees, accessed by climbing rope and ascender. Research methods to collect data on this elusive mammal include camera trapping and deployment of artificial nest substrates.
Camera traps installed at artificial nest sites recorded predator prey interactions in the canopy. Species from Steller's jay to flying squirrel were found attempting to predate upon red tree voles. The data collected in this study was synthesized in a 2020 article, and the results provide an interesting look at the efficiency of some predators. Weasels came out on top in predation rate where as northern spotted owls, who have historically relied about red tree voles as prey, were recorded as a much less efficient predator. More research is needed to fully understand the effects of predation on this threatened tree vole species.
Western Spotted Skunk & Trophic Dynamics
Old growth forests are host to a wide array of interconnected species both above and below ground. Marie Tosa investigates the interactions between carnivores and their small mammal prey, looking specifically at diet and energy flow. This food web focused approach seeks to expand understanding of the structure and function of old growth forest ecosystems in the Pacific Northwest.
RESEARCH OBJECTIVESMarie’s field-work concluded in August 2019. She is currently in the data processing stage of analysis. Research objectives for the project were to:
1. Use radio-telemetry to help determine causes of death in small carnivores and estimate survival rates 2. Use radio-telemetry to locate and describe rest and den site locations of western spotted skunks 3. Develop a better understanding of the seasonality of the diet of carnivores in the Oregon Cascades using new genetic technology 4. Test micro-GPS technology in old growth forests Marie and her team collected 876 scat samples, thousands of camera trap images, spatial data through radio telemetry, along with other invaluable data. Methodology even included scat detection conservation canines. The research journey was documented by Marie in her blog, Skunk Tales. |
PRELIMINARY RESULTSExtracting DNA from scat samples had yielded preliminary results on the diet of various carnivore species in Western Oregon. Utilizing DNA metabarcoding, Marie and her team have found the following:
– Mountain lions focus their predation efforts on mule deer, while bobcats and grey fox consume small mammals – Spotted skunk and black bear diets include large amounts of vegetation and invertebrates – With the exception of mountain lions, there is a high degree of dietary overlap between each carnivore species studied Marie created diet trees comparing bobcat and mountain lion consumption. Mountain lions are much more specialized in their diet, where as bobcats are a generalist consumer eating a wide variety of species.   |
PHOTOS FROM THE FIELD
The study of trophic dynamics looks at energy flow through an ecosystem, using data about vegetation, herbivorous species, predators, fungal decomposition, and the ways in which all of these components interact. The HJ Andrews Experimental Forest has been utilized for over seventy years as a National Science Foundation Long Term Ecological Research site. Data on forests, streams, and watersheds has been compiled since 1950. Marie seeks to connect this existing information with emerging data on small mammal and small carnivore species. The goal is to gain a deeper understanding of the dynamic processes occurring in this ecosystem, and how these small mammal communities are effected by disturbances such as logging or climate change.
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