Active Season Microhabitat and Vegetation Selection by Giant Gartersnakes Associated with a Restored Marsh in California

Abstract

Studies of habitat selection can reveal important patterns to guide habitat restoration and management for species of conservation concern. Giant gartersnakes Thamnophis gigas are endemic to the Central Valley of California, where >90% of their historical wetland habitat has been converted to agricultural and other uses. Information about the selection of habitats by individual giant gartersnakes would guide habitat restoration by indicating which habitat features and vegetation types are likely to be selected by these rare snakes. We examined activity patterns and selection of microhabitats and vegetation types by adult female giant gartersnakes with radiotelemetry at a site composed of rice agriculture and restored wetlands using a paired case-control study design. Adult female giant gartersnakes were 14.7 (95% credible interval [CRI] = 9.4–23.7) times more likely to be active (foraging, mating, or moving) when located in aquatic habitats than when located in terrestrial habitats. Microhabitats associated with cover—particularly emergent vegetation, terrestrial vegetation, and litter—were positively selected by giant gartersnakes. Individual giant gartersnakes varied greatly in their selection of rice and rock habitats, but varied little in their selection of open water. Tules Schoenoplectus acutus were the most strongly selected vegetation type, and duckweed Lemna spp., water-primrose Ludwigia spp., forbs, and grasses also were positively selected at the levels of availability observed at our study site. Management practices that promote the interface of water with emergent aquatic and herbaceous terrestrial vegetation will likely benefit giant gartersnakes. Given their strong selection of tules, restoration of native tule marshes will likely provide the greatest benefit to these threatened aquatic snakes.

Integrating growth and capture–mark–recapture models reveals size‐dependent survival in an elusive species

“…Radiotelemetry studies show that giant gartersnakes select areas with higher cover of emergent vegetation, and occupancy studies show that snakes primarily occur in or near areas that were historically tule marsh (Halstead et al 2014(Halstead et al , 2016. Radiotelemetry studies show that giant gartersnakes select areas with higher cover of emergent vegetation, and occupancy studies show that snakes primarily occur in or near areas that were historically tule marsh (Halstead et al 2014(Halstead et al , 2016.…”

“…In addition to the relationship between survival and snake size, we also found survival of giant gartersnakes was positively related to the cover of emergent and floating vegetation. Radiotelemetry studies show that giant gartersnakes select areas with higher cover of emergent vegetation, and occupancy studies show that snakes primarily occur in or near areas that were historically tule marsh (Halstead et al 2014(Halstead et al , 2016. Thus, it is intuitive that snakes survive at a higher rate in habitats that have more emergent vegetation cover, which better replicate the tule marshes these snakes inhabited before widespread land use change.…”

Influence of seasonality and gestation on habitat selection by northern Mexican gartersnakes (Thamnophis eques megalops)

“…Selection of dense cover has been documented for several species of gartersnakes [ 6 , 14 , 55 ], watersnakes [ 53 ], vipers [ 1 ], and pythons [ 75 ]. Low-height cover might be especially important at the hatchery because it supports high numbers of predators, including raptors, herons, and bullfrogs [ 40 ].…”

“…Selection of habitat features is not static because animals can alter selection based on daily or seasonal variation [ 11 , 12 ]. In snake species, behaviors such as hibernating, breeding, and foraging can strongly influence habitat selection [ 1 , 13 , 14 ]. Habitat modification and loss can restrict the ability of animal species to move about the landscape to preferentially select required resources [ 15 , 16 ].…”

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“…Fish and Wildlife Service (USFWS), CDFW, or both must also include long-term management and not just preservation of habitats (Bunn et al 2013). Although typically not accessible to the general public, these lands offer research opportunities similar to public conservation lands, and conservation banks such as Gilsizer Slough Giant Garter Snake Conservation Complex and Natomas Basin Conservancy reserves have provided long-term access to research and monitoring (e.g., Halstead et al 2012Halstead et al , 2015Halstead et al , 2016Rose et al 2018cRose et al , 2018bRose et al , 2019.…”