Engineering and ecological approaches reduce Pacific tree frog intrusion into leafy green agriculture

A widely recognized challenge in wildlife-agriculture conflict lies at the interface of leafy greens production and frogs. Leafy greens in the Salinas Valley requires irrigation which provides attractive habitat to local frog species. Specifically, the Pacific tree frog has become a major concern in production environments with frogs dispersing out to leafy green fields, increasing the potential that frogs will be harvested with produce. Several gaps in knowledge have made it difficult for growers to control frogs. Our project will address several gaps, including fence design, deterrent tests, noninvasive interruption of breeding cycles, and onsite frog risk assessments to gain a more complete understanding of Pacific tree frog biology and production risk. Growers have individually attempted to mitigate frog intrusion but unfortunately, results have not been as successful as desired. Therefore, a critical need exists to develop novel methods to improve frog exclusion from leafy green environments. Traditional drift fences have not been effective but few, if any modifications to the traditional form and materials have been tested. As part of our study, engineers will develop new fence designs that incorporate uniquely textured materials, angles, traps and deterrents, all of which are expected to reduce the climbing ability of the Pacific tree frog. We will use live frogs in controlled environments to test whether they are adversely affected by a given material or design. Optimal test designs will later be implemented in production environments to assess their efficacy in real-world situations. Mating and the annual proliferation of new frogs is a central feature of the conflict between frogs and growers. Frogs use acoustic signals to attract mates and ultimately produce young. We will determine the effectiveness of acoustic playback to detract frogs from ag-adjacent water. Specifically, we will record male mating calls and play them back from a selected location expecting a portion of females to investigate the false calls, thereby keeping their offspring away from sensitive production environments. In order to fully assess the effectiveness of a mitigation strategy, we must understand the local frog populations. We will complete targeted frog surveys at selected sites within leafy green production farms. We will assess frog abundance, density, vegetative cover, size and type of water bodies, as well as peaks in breeding and dispersal. The results of the surveys will guide the development of risk assessments for growers to use on their own fields. We will synthesize the data from all aspects of the project in order to develop a comprehensive and integrated approach to improving frog management. The impact of our study will be immediate in that growers will have access to new information and techniques that can be implemented on their own fields. With sound scientific data backing up the recommendations, growers can invest in management infrastructure that reduces their risk of frog intrusion.