About

Duane Diefenbach, Ph.D., is a Professor of Wildlife Ecology and the leader of the Pennsylvania Cooperative Fish & Wildlife Research Unit at Pennsylvania State University. His academic interests include wildlife ecology, estimation of population parameters, and harvest management of game populations. He has a long-standing collaboration with the Pennsylvania Game Commission on research projects related to deer and deer hunters, focusing on topics such as survival and causes of mortality in fawns, effects of antler restriction regulations, dispersal behavior of female white-tailed deer, and the spatial distribution of hunters and deer harvest influenced by landscape features. Currently, he leads the Deer-Forest Study, a long-term investigation into the interactions between deer herbivory, vegetation, and soil conditions on forest ecosystems. Diefenbach is actively involved in research on wild turkey harvest, including the effects of hunting season changes and developing models for setting hunting regulations. He is also engaged in ecological and management studies of white-tailed deer and other wildlife species, contributing to the scientific understanding of population dynamics and conservation strategies.

Research topics

• Ecology
• Biology
• Demography
• Geography
• Genetics
• Medicine
• Evolutionary biology
• Zoology

Selected publications

• Accounting for non‐random samples with distance sampling to estimate population density

  Journal of Applied Ecology · 2025-02-12 · 2 citations

  articleOpen access1st authorCorresponding

  Abstract A critical assumption of standard distance sampling is that sampling lines are located such that animals are uniformly distributed as a function of distance from the line. Failure to meet this assumption can introduce bias in the estimator. Many studies have used landscape features, such as roads or rivers, as lines, which can violate assumptions of distance sampling in two ways. First, animals may be attracted or repelled by the landscape feature due to human activity (e.g. along roads) or habitat characteristics associated with the feature (e.g. rivers). Second, sampling along landscape features may not be representative of the larger area of interest. We used auxiliary data to generalize the distance sampling estimator and relax assumptions of a uniform distribution of animals relative to distance from the line (i.e. density gradient) and to allow the distribution of animals to differ by habitat type. The generalized estimator provides unbiased estimates of density within the area sampled but may not be representative of the study area. To address the problem of landscape features providing unrepresentative sampling, we used a resource selection model to estimate the proportion of the population that occurred within the surveyed area to obtain an estimate of abundance for the desired area of inference. We demonstrate our modified distance sampling estimator using white‐tailed deer ( Odocoileus virginianus ) in a 972‐km 2 study area. We conducted infrared surveys of deer from roads to collect distance‐to‐transect data. We used locations of radio‐collared deer to model the distribution of deer relative to the transects and to develop a resource selection model of deer based on distance to roads, habitat type, elevation and slope to account for roads being a non‐representative sample of the study area. Synthesis and applications . When using landscape features as survey lines, the density gradient and deer distribution can introduce either positive or negative bias, which makes it impossible to assess the bias introduced without auxiliary data. The estimator we developed can improve precision because we obtained a better fit to distance observations and accounts for non‐random placement of transects with minimal loss of precision.

  PublisherOA PDFDOI

• White-Tailed Deer Odocoileus virginianus (E. A. W. von Zimmerman, 1780)

  Fascinating life sciences · 2025-01-01

  book-chapter1st authorCorresponding
  PublisherDOI

• When the wild things are: Defining mammalian diel activity and plasticity

  Science Advances · 2025-02-26 · 23 citations

  articleOpen access

  Circadian rhythms are a mechanism by which species adapt to environmental variability and fundamental to understanding species behavior. However, we lack data and a standardized framework to accurately assess and compare temporal activity for species during rapid ecological change. Through a global network representing 38 countries, we leveraged 8.9 million mammalian observations to create a library of 14,587 standardized diel activity estimates for 445 species. We found that less than half the species' estimates were in agreement with diel classifications from the reference literature and that species commonly used more than one diel classification. Species diel activity was highly plastic when exposed to anthropogenic change. Furthermore, body size and distributional extent were strongly associated with whether a species is diurnal or nocturnal. Our findings provide essential knowledge of species behavior in an era of rapid global change and suggest the need for a new, quantitative framework that defines diel activity logically and consistently while capturing species plasticity.

  PublisherDOI

• Temporal Dynamics of Understory Assemblages and Implications for Northern Hardwood Seedling Recruitment

  SSRN Electronic Journal · 2025-01-01

  preprintOpen access
  PublisherDOI

• Atypical winter coat coloration of snowshoe hares near the southern extent of their range

  Ecosphere · 2025-03-01

  articleOpen accessSenior author

  Abstract Many species have a variety of adaptations to winter weather, but these adaptations could become maladaptive if winter snowfall and temperatures are more variable. Snowshoe hares ( Lepus americanus ) molt from a brown summer coat to a white winter coat, but reductions in snow cover could result in phenotypic mismatch, which in turn could reduce survival. Hare populations near the southern extent of their range might be especially sensitive to phenotypic mismatch because of variable winter weather, but variation in winter coat coloration could allow for these populations to persist in inconsistent snow cover conditions. Using capture data ( n = 59 individual hares) spanning 8 years, we document the prevalence of three atypical winter coat color phenotypes (brown bodies, brown‐ringed eyes, and brown ears) in a snowshoe hare population in Pennsylvania. The majority of hares in our study (84.7%) exhibited at least one of these atypical winter phenotypes, with a high probability of hares having brown‐ringed eyes or brown ears, and four hares remaining brown during the winter. The presence and high prevalence of non‐white winter phenotypes could be beneficial for hares in this population if winters are mild with low snow cover. If these phenotypes have a genetic basis, there may be evolutionary potential for hares to persist near the southern extent of their range, even in the face of changing winters.

  PublisherOA PDFDOI

• A framework for analyzing wild turkey summer sighting data

  Wildlife Society Bulletin · 2025-11-30 · 2 citations

  articleOpen access1st authorCorresponding

  Abstract Wildlife agencies collect data on productivity (e.g., proportion of hens with poults and number of poults per hen) of wild turkey ( Meleagris gallopavo ) to monitor population status and trends. However, sampling protocols to collect productivity data rely on opportunistic observations reported by wildlife agency personnel and the public and have changed over time and differed among agencies. A protocol to standardize data collection was adopted by most state wildlife agencies in 2019, but long‐term historical datasets exist that cannot be analyzed readily to make inferences about spatial and temporal patterns in wild turkey productivity. We developed statistical models to allow comparisons and model trends in productivity among and within states even though data collection protocols changed over time and differed among states. We found greater spatial variation in the proportion of hens with poults than the number of poults per brood, which may reflect how environmental factors influence wild turkey productivity. Our models can also provide inferences about productivity when data are limited or temporally discontinuous for some spatial units. Additionally, we found that temporal and spatial variation in data collection, even under the new protocol, can affect inferences about trends in productivity. The statistical models we developed address the uncontrolled nature of when and where data are collected and offer the ability to investigate long‐term patterns of productivity in relation to factors such as changing climate or habitat conditions.

  PublisherOA PDFDOI

• Multistage time-to-event models improve survival inference by partitioning mortality processes of tracked organisms

  Scientific Reports · 2024-06-25 · 2 citations

  articleOpen access

  Abstract Advances in tagging technologies are expanding opportunities to estimate survival of fish and wildlife populations. Yet, capture and handling effects could impact survival outcomes and bias inference about natural mortality processes. We developed a multistage time-to-event model that can partition the survival process into sequential phases that reflect the tagged animal experience, including handling and release mortality, post-release recovery mortality, and subsequently, natural mortality. We demonstrate performance of multistage survival models through simulation testing and through fish and bird telemetry case studies. Models are implemented in a Bayesian framework and can accommodate left, right, and interval censorship events. Our results indicate that accurate survival estimates can be achieved with reasonable sample sizes ( $$n\approx 100+)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mo>≈</mml:mo> <mml:mn>100</mml:mn> <mml:mo>+</mml:mo> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> and that multimodel inference can inform hypotheses about the configuration and length of survival stages needed to adequately describe mortality processes for tracked specimens. While we focus on survival estimation for tagged fish and wildlife populations, multistage time-to-event models could be used to understand other phenomena of interest such as migration, reproduction, or disease events across a range of taxa including plants and insects.

  PublisherOA PDFDOI

• Complex interactions of deer herbivory, soil chemistry, and competing vegetation explain oak–hickory forest tree regeneration in central Pennsylvania, USA

  Canadian Journal of Forest Research · 2024-10-11

  articleOpen access

  The root causes of forest tree regeneration failure are difficult to resolve, although numerous studies show ungulate herbivory, soil conditions, and competition from undesirable vegetation as likely contributors. To better understand the relative importance of each issue, we conducted a 7-year manipulative experiment to assess the interactive effects of white-tailed deer ( Odocoileus virginianus) herbivory, soil acidity, and competing vegetation on tree regeneration in oak–hickory forests of central Pennsylvania, USA. Outcomes depended on initial tree seedling abundance, and all three factors had significant interactions. At low initial seedling abundance, fencing resulted in the greatest increase, but all treatments had a positive effect on seedling growth and abundance. At higher initial seedling abundance, abundance failed to recover 7 years after herbicide treatment and soil pH was an important predictor. When soil pH was &gt;4.6 from lime application, seedling growth and abundance in unfenced controls with high initial abundance was comparable to the fenced-only treatment. Competing vegetation, assumed to be a symptom of excessive, long-term deer herbivory, does not seem to be the primary factor limiting tree regeneration in our study area. Ameliorating acid deposition warrants greater consideration as a management action because it could provide long-lasting benefits compared to short-term fence installations.

  PublisherDOI

• Neonatal antipredator tactics shape female movement patterns in large herbivores

  Nature Ecology & Evolution · 2024-12-04 · 2 citations

  articleOpen access
  PublisherOA PDFDOI

• Species and physiographic factors drive Indian cucumber root and Canada mayflower plant chemistry: Implications for white-tailed deer forage quality

  Journal of Environmental Management · 2022-11-16 · 2 citations

  article
  PublisherDOI

Frequent coauthors

• Christopher S. Rosenberry

  Pennsylvania Fish and Boat Commission

  80 shared

• Bret D. Wallingford

  Pennsylvania Game Commission

  61 shared

• Eric S. Long

  Seattle Pacific University

  21 shared

• Simon Chamaillé‐Jammes

  Université de Montpellier

  20 shared

• Robert J. Warren

  United Kingdom Atomic Energy Authority

  16 shared

• Marc E. McDill

  Pennsylvania State University

  16 shared

• Patrick J. Drohan

  16 shared

• Michael J. Conroy

  Epsom and St Helier University Hospitals NHS Trust

  15 shared

Labs

• Duane Diefenbach LabPI

Education

• Ph.D., Wildlife Ecology

  Penn State University

  1990

• M.S., Wildlife Biology

  University of Idaho

  1985

• B.S., Wildlife Biology

  University of Idaho

  1983