Graduation Date
Spring 2025
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources, option Wildlife
Committee Chair Name
Matthew Johnson
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Micaela Szykman Gunther
Second Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Third Committee Member Name
Daniel Barton
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Keywords
Habitat quality, Barn owls, Napa valley, Nestlings, Physiology, Land use, Agriculture, Integrated pest management, Heterophil-lymphocyte ratio, Feather corticosterone, Growth bars, Sustainability, Habitat ecology
Subject Categories
Wildlife
Abstract
The global environmental impacts of increasing agricultural demand a transition to sustainable farming practices, including the use of integrated pest management to decrease reliance on harmful pesticides. Vineyard managers in Napa Valley, California, have implemented this strategy by establishing nest boxes that attract barn owls (Tyto furcata) which, in turn, provide an ecosystem service by removing rodent pests. Studies in this system have found uncultivated landcover to be positively associated with distributional and demographic measures of habitat quality for barn owls, but individual measures have not been thoroughly explored. I examined three physiological conditions of barn owl nestlings (heterophil-lymphocyte [H:L] ratio and growth bars, as well as early, late, and total feather corticosterone [fCort]) to see if these indicators of chronic stress correlated with the composition and configuration of the landcover surrounding their nest boxes at the local and landscape scales, while also accounting for characteristics of the brood and nest box. Based on H:L ratios, nestlings in boxes with less oak savanna and more urban landcover at the landscape scale exhibited significantly higher levels of chronic stress, and stress was high for early- and late-hatching broods. Nestling age was significantly and positively associated with growth bar width, though the methodology for quantifying growth bars was affected by feather development and may have minimized the effect of landcover. Findings from early and late feather corticosterone were inconsistent, while total feather corticosterone lacked any significant associations with landcover, nest box, or brood characteristics. By exploring three different physiological conditions, I provide additional evidence for barn owl habitat quality in Napa Valley, reveal how measures of chronic stress vary in their suitability during nestling development, and offer further suggestions for prospective investigators who aim to measure physiological conditions.
Citation Style
JWM
Recommended Citation
Cortez, Christian, "Physiological conditions of barn owl (Tyto furcata) nestlings as indicators of habitat quality within the wine-growing region of Napa Valley" (2025). Cal Poly Humboldt theses and projects. 2295.
https://digitalcommons.humboldt.edu/etd/2295