Barn owls exert top-down effects on the abundance and behavior of rodent pests

Author

Katherine C. LarsonFollow

Graduation Date

Winter 2024

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Wildlife

Committee Chair Name

Matthew D. Johnson

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Roger A. Baldwin

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Daniel Barton

Third Committee Member Affiliation

HSU Faculty or Staff

Keywords

agriculture; American barn owl; chew blocks; giving-up density; integrated pest management; optimal foraging theory; predator-prey dynamics; rodent, top-down; winegrape vineyard

Subject Categories

Wildlife

Abstract

Predators can exert top-down effects on their prey by direct consumption, by imposing risk of predation, or a combination of both. However, empirical evidence for these effects is mixed and inconsistent. Barn owls in agriculture present a system with attributes that should, according to theory, lead to strong top-down effects, but research is limited and the distinction between effects on prey abundance and behavior remains unresolved. Understanding the top-down effect of predators on pests is a cornerstone of integrated pest management and important where barn owls may contribute to the control of rodents on farms. Vegetation can mediate the top-down effects of predators on their prey, but this has received little attention for barn owls and rodent pests, limiting the information farmers can use to manage their fields to harness the effect of barn owls. To help fill these gaps, we surveyed above-ground foraging rodents and monitored barn owl nest boxes at six winegrape vineyards in Napa Valley, California USA from February to July in 2023. We deployed chew block grids to determine the direct effect of barn owls on rodent abundance and used giving-up density (GUD) trays and camera traps to determine the effect of barn owls on rodent perceived predation risk and activity, respectively. We found that, over the range of hunting pressures observed (from nearly no owls to about 3 occupied boxes with 6 adults and 8 chicks within a 1-km radius), barn owls reduced rodent (predominately deer mouse, Peromyscus spp.) abundance by 38-52% and increased perceived predation risk by 16- 38%. Results also suggest that vegetation cover favors the acoustically attuned barn owls over the visually oriented rodent pests. These results contribute to growing evidence that barn owls can be used as biological control in agricultural systems and that vegetation can be managed to optimize their impact. We advise that growers maintain the vine canopy of leaves, pruned twigs on the ground, and vegetation cover in a cover crop row grown between vine rows to elevate perceived predation risk in mice. We also recommend that, to the extent feasible, farmers time mowing to reduce mouse activity when crops are particularly vulnerable.

Citation Style

JWM

Recommended Citation

Larson, Katherine C., "Barn owls exert top-down effects on the abundance and behavior of rodent pests" (2024). Cal Poly Humboldt theses and projects. 813.
https://digitalcommons.humboldt.edu/etd/813