Graduation Date
Fall 2025
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources, option Wildlife
Committee Chair Name
Frank Fogarty
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Matthew Johnson
Second Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Third Committee Member Name
Hunter Harrill
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Fourth Committee Member Name
Jake Verschuyl
Fourth Committee Member Affiliation
Community Member or Outside Professional
Keywords
Bird communities, Structural retention, Snags, Cavity nesting birds, Forest management, Hierarchical models, Pacific Northwest
Subject Categories
Wildlife
Abstract
Managed forest lands in Oregon and Washington produce wood products and host diverse bird communities, though standing dead snags are often limited. State forest practices rules governing forest harvest dictate retention of a minimum number of trees when forests are clearcut harvested. However, little research has explored how the slope position and aggregation of retention, and the supplemental inclusion of mechanically created snags, affects use of these forest units by wildlife, especially highly mobile taxa such as birds. I used an avian point count sampling approach, within a replicate-block experiment dictating unit-level slope position, aggregation, and snag retention treatments, to inform Bayesian hierarchical models exploring how these retention characteristics influence the bird communities in managed forests.
Community-wide species richness occupancy models at two scales showed that including upslope retention or created snags resulted in higher model-predicted species richness, while split-patch units without created snags had the lowest predicted species richness. In 31 single-species models, all species that responded significantly to different aggregations were more abundant with a single aggregate retention patch, often regardless of that patch’s slope position. Many species – including some early seral, cavity nesting, and canopy-associated species – were more abundant in circles with created snags. A cavity nesting guild abundance model further showed this positive response to mechanical snag creation.
I show that aggregating retention into fewer, larger patches benefits bird species richness and abundance of mature forest-associated species. Additionally, I show that including mechanically created snags in structural retention patches increases abundance of cavity nesting birds.
Recommended Citation
Healey, Aidan M., "Effects of experimental structural retention position and aggregation on avian communities in managed forests of the Pacific Northwest, U.S." (2025). Cal Poly Humboldt theses and projects. 2507.
https://digitalcommons.humboldt.edu/etd/2507