Performing Department
Wildlife Management
Non Technical Summary
This project aims to advance a producer-identified research need surrounding the potential for barn owlsto help control rodent pests in winegrape vineyards.The project involves researchers from two universities and two winegrape growing regions within a single state (California) that are representative of other winegrape growing regions elsewhere in the West.Problem:This research proposal addresses a critical problem to a crop of enormous economic importance, and it focuses on pests that cause economic crop damage and are difficult to control with conventional practices. Moreover, new regulatory restrictions in the winegrape industry and the uniquely conspicuous relationship between land use and the wine consumer enhances the urgency of pursuing more environmentally friendly, economically viable, and socially acceptable pest control measures in this industry.The winegrape industry is of great significance to western states and the nation as a whole. Winegrapes comprise a high-value crop that is economically vital to western states and the US in general.In 2017, United States winegrape production was valued at $3.5 billion, and employs over 780,000 people in the U.S. California is America's #1 wine state, and as a single state it is the fourth largest producer in the world, with grapes ranking 2nd in California's agricultural commodities. Winegrapes are grown by over 5,900 growers in 49 of California's 58 counties, and the estimated annual retail value of California's wine production is $31.9 billion.This expansive industry has also strongly impacted natural habitats. In California, winegrapes are currently grown on 608,000 acres, and vineyard development is a major driver of habitat conversion of grasslands, savannah, and oak woodlands.In 2016, over 27 million pounds of active ingredients of pesticides were applied to California winegrape vineyards, prompting concern among consumers and environmental groups alike. These environmental impacts, coupled with an increase in public demand for sustainable agriculture, have led to strong interest in and demand for sustainable and organic winegrapes in California.For example, in 2018 there was a 13% increase in the number of certified sustainable wineries and an impressive 44% increase in the number of certified sustainablewinegrape vineyards in California. While strictly organic wine continues to be a relatively small niche of the industry (< 5% globally), its growth is rapid with a projected 12% growth to surpass $15 billion annually by 2025.This demand obviously has clear implications for the wine production industry, but also for tourism - wineries and vineyards are the second most popular tourist destination in California, contributing $7.2 billion in related expenditures annually.Managing pests is one of the premier challenges facing winegrape growers. For example, the Pest Management Strategy Plansfor California, Oregon, and Washington each identify rodents as key pests to winegrape vineyards.Asurvey of winegrape producersfound that over 50% used either toxicants, trapping, or both to control rodents, spending between $22 and $28 per acre annually on control efforts.Rodents in general, and gophers in particular, are notoriously problematic to control with chemicals and physical methodsdue to both the inefficiency of these methods or their documented and potential negative impacts to the environment. The use of rodenticides, especially anticoagulant rodenticides, is increasingly criticized because of impacts to non-target wildlife and pets, and there is a huge body of literature documenting their impacts to wild birds and mammals, from eagles and owls to foxes mountain lions, as well as to domestic dogs and cats. The signs are clear: in order to retain global leadership, the winegrape industry must find alternatives today that will reduce or replace reliance on toxic chemical rodenticides.Taken together, the profound economic importance of winegrapes to western states and beyond, the important problems posed by rodent pests, and the increasing public scrutiny and regulatory restrictions on toxicants all point to an urgent need to better understand alternative rodent pest control methods in vineyards. In the last 20 years, winegrape producers have increasingly experimented with artificial nest boxes to attract rodent-eating raptors, especially barn owls to winegrape vineyards.While this practice has been widespread for over 20 years, it is only recently being investigated rigorously and scientifically. This project aims to build upon recent work in California and other countries to (a) extend and complement some of the first experimental tests of whether the use of barn owl boxes can reduce rodent populations in agriculture, (b) develop a spatial model to help winegrape growers optimize the deployment of nest boxes for rodent removal, and (c) disseminate findings to key research and extension audiences.Approach & Benefits: The advances from this project have potential to yield considerable environmental and economic benefits. First, the results will clarify the impact of owl boxes on vole and other rodent foraging behavior in winegrape vineyards, complementing existing results on gophers and results from other countries and crops. These findings, collectively, help inform the use of barn owl nest boxes as rodent control tactic in IPM schemes for producers of winegrapes and other crops. Second, the project will quantify, for the first time, the cost of establishing and maintaining barn owl nest boxes relative to rodent trapping costs - providing useful clarity for farm managers' decision making. Third, the project will provide a spatial model to inform where to place nest boxes to enhance their likelihood of being occupied by breeding owls, which is a vital aspect of optimizing pest removal. Thus, this project will both improve existing pest management systems of nest boxes and advance our understanding of their implementation.While this project focuses on winegrapes in Western states, with proposed field work conducted in two regions in California, the project has much more widespread application and will benefit other crops and other areas. have a worldwide distribution, from savannas in Africa to rainforests in Australia, as well as agricultural landscapes across Europe, North America, Central America, Africa, and the Middle East. Mice, voles, and gophers are widespread throughout U.S. agriculture, and barn owls therefore have potential to provide farmers with economically valuable pest control services in many applications. Nest box programs have been utilized in oil palm plantationsand rice fields in Malaysia, in mixed agriculture in Israel, in sugar cane in Florida, in California vineyards and orchards, and alfalfa.Thus, this project shows promise to have widespread application, and could pave the way for adopting the tactic in other places and crops, or conducting parallel experiments, findings, and dissemination to clarify differences between crops.In addition, this projectwill promote the development of individual tools and tactics needed for pest management systems by supporting the discovery and development of an alternative pest management system. The use of barn owl nest boxes could be a replacement tactic, if new regulatory mandates and market forces render rodenticides infeasible or diminish their viability, or as a supplementary tactic to a conventional method, thereby increasing overall impact while protecting the longevity of efficacy of conventional tactics. Our approach includes field-scale experiments and will yield a spatial model that will serve as tool for making management decisions.
Animal Health Component
80%
Research Effort Categories
Basic
20%
Applied
80%
Developmental
(N/A)
Goals / Objectives
This project has two core goals, with specific objectives and anticipated impacts as described below and in the logic model. The goals correspond to the Production Agriculture Focus Area of the IPM Roadmap, and are aimed to "Improve economic and social analyses of adopting and implementing IPM practices, including assessing the benefits of practice adoption". Specifically, this project will advance several goals identified by the Federal IPM Coordinating Committee under the Technical Development research need:• Develop low-risk suppression tactics, such as biological control.• Develop efficacious suppression strategies that are cost-effective to implement.• Develop a more-thorough understanding of beneficial impacts of pest management strategies.• Encourage and support the development of area-wide IPM projects to more effectively manage pests on regional or landscape scales.• Develop economic models for IPM that inform research on new pest management strategies, as well as decision tools for growers to implement management.Goal #1: Expand, complement, and fill remaining gaps in recent experimental evidence that barn owls reduce rodents in vineyards by assessing rodent activity in two winegrape growing regions of California representative of other winegrape growing regions in the West.Objective 1A: Complete controlled experiments by conducting chew block and remote camera surveys to assess temporal changes in rodent activity in replicated plots of vineyards with and without barn owl nest boxes in Napa and San Joaquin Counties in California.Objective 1B: Compare owl nest box costs with rodent removal costs based on published estimates and field-measured rodent trapping effort.Objective 1C: Establish baseline data for a future before-after-control-impact experiment on reduction of the rodent activity after adoption of nest boxes on the control vineyards used in this study.Goal #2: Develop a web-based tool with a spatial model of barn owl nest box occupancy in winegrape vineyards, to facilitate the adoption of this IPM tactic and inform producer decision-making to optimize its impact.Objective 2A: Conduct spatial modeling of nest box occupancy based on previously completed occupancy models and widely available land use/crop geospatial data.Objective 2B: Create web-based interface for producers to visualize, export, and/or print nest box occupancy probability maps.
Project Methods
Experimental design: This project will include two replicated treatments: plots in winegrape vineyards with no occupied barn owl nest boxes (none within 3 km) and plots near an occupied barn owl nest box (< 500 m). The selection of the 3 km and 500 m thresholds are empirically based on GPS telemetry location data (for barn owls hunting in vineyard-dominated ecosystems, 95% of locations were located within 3 km of their nest box, and 53% were within 500 m of the box).Thus, these two treatments provide meaningful comparisons of virtually no versus heavy barn owl hunting pressure, respectively.Our team currently monitors ~290 barn owl nest boxes located on 65 vineyards in Napa County, and we have identified collaborating landowners/managers for another 150 nest boxes in San Joaquin County. Vineyard fields will be selected that have similar row cropping, vine spacing, and other attributes that could affect rodent abundance. We aim to conduct this project in organic vineyards to avoid confounding effects of unmeasured impacts of rodenticide application on rodent abundance.Our experimental sample unit will be a rodent survey plot, spatially replicated on 16 plots with no barn owl boxes, and on 8 plots near occupied nest boxes.The rodent surveys will be temporally replicated in February (onset of owl occupancy but before heavy hunting pressure) and in June (peak hunting pressure, most occupied boxes with chicks 3-8 weeks old) in 2023 (Napa) and 2024 (San Joaquin County).Rodent surveys: Any assessment of the potential benefits of a biological pest control tactic for rodents must inherently rely on estimates of changes in rodent population size, behavior, or subsequent plant damage by rodents.General indices are frequently preferred given that they are practical to implement, are sensitive to changes in population size, allow for development of precision and variance estimates, and have few assumptions.This project will involve the use of chew blocks and remote cameras, and the "open hole" method. We willplacewax chew blocks at the base of vines at 5-6 m intervals following a 6 × 6 grid structure (n = 36 for each plot) and measuring the percent of mass (g) of the block removed after 48 hrs as an index of rodent activity. We can feasibly run 6 plots simultaneously (4 in vineyards without nest boxes, and 2 in vineyards close to nest boxes), so 4 runs will complete all 24 experimental plots.These grids will be run in February (low owl hunting pressure) and again in June (peak owl hunting pressure). Because rodent foraging on chew blocks cannot reliably be identified to species, we will deploy remote cameras on a subset of chew blocks in each grid (8 cameras per grid of 36 chew blocks).We will establish open-hole grids using up to 2 gopher holes per grid cell (max 72 per plot), and record the number of holes excavated and their proportion re-plugged by active gopher activity 48 hrs laterand repeated in February and June as described above.The chew blocks and cameras will be deployed in the morning, whereas the "open hole" method can be employed later in the day, enabling these two survey techniques to be pursued simultaneously in the field.The experiments will be run in Napa County in spring/summer of 2023, and in San Joaquin County in spring/summer of 2024. A general linear mixed effect model (with plot as random effect) will be used to evaluate the hypothesis that rodent activity (continuous variable for % chew block consumed, and binary proportion of hole plugged, logistic response) varies among treatments and time periods.Cost analysis: We will build a simple cost model for barn owl boxesand compare its outputs to estimated costs of conventional rodent control tactics.An emerging cottage industry of entities selling and installing barn owl nest boxes provides estimates for costs to deploy and maintain barn owl nest boxes in vineyards.We will combine these values with several other parameters obtained from farmer interviews and previous research to arrive at a simple model for the cost of barn owl nest boxes per year (both actual costs each year and box investment and replacement costs amortized over all years).Combining this formula with estimates of rodent removal from the landscapewill allow us to provide ranges of costs for pest removal services as functions of nest box density and owl box occupancy rate, expressed in costs per acre.We will compare these costs to estimated costs for other forms of rodent control based on three sources: published estimates, interviews with producers in our study, and empirical measurements of person-hours from Baldwin, unpubl and from our own deployment of research methods, coupled with estimated costs for traps and labor (minimum wage).Web-based tool:Using ~290 currently monitored (in Napa) and 150 newly identified nest boxes (in San Joaquin), we will continue to monitor nest box occupancy.TEvidence suggests that barn owl nest box occupancy is best predicted by three "box variables" [1) Whether the box is made or wood (preferred) or plastic, 2) entrance hole orientation (North or East preferred), and 3) height (preferred at least 10 feet off the ground)], and by the composition of the habitats within 2.2 km of the nest, with barn owls favoring boxes with larger proportions of uncultivated habitats nearby.These results, which can be formalized in a composite resource selection probability functionwill provide a relatively simple formula for calculating probability of nest box occupancy in a geospatial grid cell. Thus, a GIS map of the probability of nest box occupancy can be calculated for the winegrape vineyard acres in California by using the freely available CropScape geospatial datasource. Johnson will complete this analysis, and the resulting GIS output (providing rasterized projection of probability of nest box occupancy) will be made available on a Cal Poly Humboldt-maintained webpage.Assessment:Program assessment will follow two pathways: internal team assessment and continuous improvement, and measurable assessment to quantify impacts of Objectives #1 and #2. Internal assessment will occur as periodic meetings with stakeholders, including graduate students, participating producer collaborators, and project directors.We will also quantitatively measure impacts of outcomes, once per reporting cycle. Impact 1A - Increased availability of information by which producers can evaluate whether and how to adopt the use of barn owl nest boxes as biological pest control - will be measured as the number of dissemination presentations, number of extension materials and websites incorporating this studies' findings, and views and downloads on associated social network sites.Impact 1B - Increased development of graduate and undergraduate students - will be measured by the completion of two Master's theses and the number of student-hours spent engaged in this project. Our goal will be for at least half of all students involved to be Hispanic and/or low-income. Impact 1C - Significant contribution to scientific literature on the use of barn owl nest boxes as potential to reduce pests in agriculture - will be measured by the publication of manuscript(s) summarizing findings, and by the citation frequency of those paper(s).Impact 2A - Increased availability of information by which producers can optimize placement of nest boxes to enhance barn own occupancy - will be measured as number of dissemination presentations, number of extension materials and websites incorporating this studies' findings, and views and downloads and followers on the web-based portal and associated social network sites.Impact 2B - Contribution to scientific literature on the occupancy patterns of barn owl nest boxes - will be measured by the publication of a manuscript summarizing findings, and by the citation frequency of that paper.