Constructed hibernacula support biodiversity at a coastal restoration project

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Alistair L. Dobson and Seth Frazer, Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, Lisa Stratton and Ryan Clark, Cheadle Center for Biodiversity and Ecological Restoration, Santa Barbara, CA

Background/Question/Methods
Ecological restoration seeks to provide quality habitat and maximize native biodiversity in small reserve areas. In restoration projects that begin on largely degraded and/or barren landscapes, constructing habitat-providing features such as hibernacula, structures for small organisms to seek refuge, can aid in the site’s colonization, particularly by small vertebrate species. In 2018, at the start of the North Campus Open Space ecological restoration project in Goleta, California, 63 hibernacula were constructed across a 90-acre landscape, scraped bare for its transformation from a golf course into coastal slough and associated habitats. These simple hibernacula consist primarily of concrete slabs (salvaged from the golf course) piled into meter-deep holes, providing many variably spaced crevices. Although these hibernacula were constructed with the intent to provide habitat for small vertebrate colonizers, a systematic assessment of their species richness and use patterns had yet to be made. Thus, in February and March of 2021, we endeavored to quantify biodiversity at the hibernacula using three survey methods: visual surveys, camera trapping, and footprint tracking tunnels. During this pilot study period, we examined 35 hibernacula for five nights each to record different species’ visitation patterns.
Results/Conclusions
Visual surveys and footprint tracking tunnels were not as informative as camera trapping efforts, which revealed at least 23 vertebrate species (8 mammal/12 bird/3 reptile) visiting the hibernacula. All 35 sites were occupied with an average of 5.28 ±1.62 species visiting each site during the 5-night camera trapping period. Ground squirrels, fence lizards, rabbits, mice, and Burrowing Owls were the most common visitors and likely occupants of these structures. Less common visitors included song and shore bird species, and meso-carnivores, two of which were new sightings at the restoration site (spotted skunk and grey fox). Occupants moved in and out of crevices and tunnels in a hibernaculum, while visitors moved over or around the structure, often investigating its entrances. Ground squirrels were the most frequently observed species and may play an ecologically important role by creating tunnels underneath the hibernacula, thereby engineering habitat for other vertebrates. Close monitoring of this process following the construction of a hibernaculum would be valuable for understanding its importance. Overall, we conclude that constructed hibernacula are a simple and low-cost method for supporting small vertebrate biodiversity and colonization at an early stage of restoration. Further implementation and monitoring of constructed habitat features is needed to determine their value, effectiveness, and contribution towards supporting biodiversity on restoration sites.