Gopher Tortoise, Tortoise, 1832

Whitfield, Steven M., Valle, Daniel, Figueroa, Adrian, Chin, Brianna, Bravo-Gallegos, Hugo & Leone, Frank, 2022, Burrow Characteristics and Habitat Associations of Gopher Tortoises in Urban Pine Rockland Reserves (Miami, Florida, USA), Ichthyology & Herpetology 110 (1), pp. 22-32 : 29-30

Gopher Tortoise ecology and conservation in extreme south

Florida.

— Our study is one of very few empirical studies of tortoises at the extreme southern limit of their geographic range (but see Enge et al., 2004; Whitfield et al., 2018; Figueroa et al., 2021). Kushlan and Mazotti (1984) studied a coastal population of tortoises at Cape Sable (Everglades National Park, Monroe County, Florida), an isolated formation of coastal dunes on the extreme southwest of Florida’s mainland. This is likely the most climatically similar site to the localities we describe, although the geology and ecology of the Cape Sable population is quite different with regard to vegetation and soils, and with responses to intense tropical storms and hurricanes. Still, Waddle et al. (2006) documented dramatic declines in this population between the 1980s and 2000 and suggested that storm surge from repeated hurricanes had destabilized the sand dunes used by Gopher Tortoises there. While both Zoo Miami and Deering were heavily impacted by hurricanes (including Hurricane Andrew and Hurricane Irma), the geology of these sites is apparently not as susceptible to storm impacts as is Cape Sable, as the limestone matrix interspersed with sand may prevent destabilization of sand formations.

While we were able to identify a considerable number of burrows at each site, few of the burrows we observed were occupied. Only seven burrows at Zoo Miami were occupied and only nine at Deering were occupied. Past researchers have attempted to estimate the number of tortoises based on the number of burrows, but use of such ‘‘correction factors’’ often leads to inaccurate assessments of population size ( Burke, 1989; Breininger et al., 1991; McCoy and Mushinsky, 1992). Still, these two sites appear to represent small and isolated, but reproductive populations. More formal efforts to estimate population size will be critical to understanding management scenarios for the tortoises.

The continued presence of Gopher Tortoises in pine rocklands is particularly surprising given the isolation of these preserves within a dense urban matrix. These tortoises face direct impacts from habitat loss, risk of injury or mortality by automobile collision, and direct displacement by people. In fact, despite extensive ongoing conversion of natural areas to low-density urban habitats, the state wildlife agency has (to our knowledge) never required surveys or issued removal permits for Gopher Tortoises within the entirety of Miami-Dade County.

The rocky soils of the pine rocklands have been considered low quality tortoise habitat by both past biologists ( Auffenberg and Franz, 1982) and by state wildlife agencies (FWC, 2012), yet we are unaware of any empirical evidence for this claim. As we show, the rocky substrate appears to limit burrow depth; yet it is unclear that deep burrows are necessary in a subtropical climate or that such shallow burrows directly lead to a fitness disadvantage. In contrast, the frost-free climate of south Florida allows nearly year-round tortoise activity ( Moore et al., 2009) and may shorten time to maturity ( Mushinsky et al., 1994) or enable higher reproductive rates ( Ashton et al., 2007) than in the more northern portions of the range.

It may appear surprising that a state-threatened species that constructs rather conspicuous burrows could go nearly unreported in an urban area for two decades ( Enge et al., 2004; Krysko et al., 2010). However, such data deficiencies are common for fauna within the pine rocklands of south Florida. The Florida Bonneted Bat ( Eumops floridanus ), a south Florida endemic found in pine rocklands that is now listed under the ESA, was only formally described as a species in 2004 ( Timm and Genoways, 2004). The rockland endemic Rim Rock Crowned Snake ( Tantilla oolitica ) has been documented by biologists fewer than 40 times ( Hines, 2011; USFWS, 2015). The pine rockland endemic Miami Tiger Beetle ( Cicindelidia floridana ) was undetected from 1934 until its rediscovery in 2007 ( Brzoska et al., 2011) and is also now protected under the ESA ( USFWS, 2016). Two butterfly species and more than ten pine rockland plant species have been added to the ESA since 2010 ( Salvato, 2003; Possley et al., 2016; Trotta et al., 2018). A large and distinctive pine rockland trapdoor spider, Ummidia richmond , was only formally described in 2021, and is apparently also a south Florida endemic that occurs primarily in pine rocklands ( Godwin and Bond, 2021). A data gap concerning Gopher Tortoises within natural areas embedded in urban Miami is not exceptional; rather, this is typical of a more expansive data deficiency regarding terrestrial fauna in extreme south Florida —and pine rocklands in particular. In this environment, discoveries and rediscoveries of threatened species are surprisingly commonplace.

The tortoise populations we examine in this study were anticipated to be extirpated by the beginning of this century ( Auffenberg and Franz, 1982) and have been mostly overlooked by both tortoise biologists and management agencies ( Schwartz and Karl, 2005; Smith et al., 2006; FWC, 2012). This is surprising because Gopher Tortoise populations on the western extent of the geographic range have long been protected by the ESA in response to loss of habitat, and because the extent of habitat loss in the southern portion of the range has been far more rapid and extreme. The status of southern populations of Gopher Tortoises should be reexamined, as the severe and ongoing decline in this portion of the species range will likely require increased management attention to avoid extirpation.