Effects of predator exclusion on nest and hatchling survival in the gopher tortoise

Abstract

Gopher tortoise (Gopherus polyphemus) populations are declining throughout the Southeast, and high levels of predation on nests and juveniles have been suggested as a potential contributor to this decline. Therefore, we documented gopher tortoise nest success and hatchling survival relative to mammalian predator control. We used 4, large (approx. 40-ha) fenced, predator exclosures to exclude mid-sized mammalian predators: bobcat (Lynx rufus), raccoon (Procyon lotor), Virginia opossum (Didelphis virginianus), fox (Urocyon cinereoargenteus and Vulpes vulpes), coyote (Canis latrans), nine-banded armadillo (Dasypus novemcinctus), and skunk (Mephitis mephitis); 4 unfenced plots served as controls. We monitored nests for survival through hatching and used radio-telemetry to examine hatchling survival. We radio-tracked 40 hatchlings for up to 329 days, but we were only able to track 8 individuals from a single nest at an unfenced plot because of high nest predation. Mean nest survival was greater at exclosures than at unfenced controls (F 1, 2 ¼ 45.80, P ¼ 0.0001). Hatchling survival differed (x 2 ¼ 5.839, P ¼ 0.016) between unfenced plots (37.5%) and exclosures (74.4%), suggesting that mammals also were significant predators of hatchlings. The number of juvenile (<13 cm in diameter) and subadult tortoise burrows (13-21.9 cm) increased over a 6-year period in exclosures, providing further support for an effect of excluding mammalian predators on nest and juvenile tortoise survival. ß 2012 The Wildlife Society.

Investigation of cues used by predators to detect Snapping Turtle (Chelydraserpentina) nests

“…Nest caging is a commonly used and often an effective nest protection method (e.g., Breckenridge 1960;Ratnaswamy et al 1997;Kornaraki et al 2006;Kurz et al 2011;Perez-Heydrich et al 2012;Riley and Litzgus 2013;Smith et al 2013). Cages may be placed directly over the nest or buried in the substrate around the nest chamber.…”

Effects of Culling on Mesopredator Population Dynamics

“…Increased raccoon densities have been linked to cascading effects on local biological communities through increased predation on a diverse array of taxa [6], [2], [25], [26] and increased transmission of infectious diseases [9], [27]. Moreover, as raccoons are the primary reservoirs of rabies in North America, their increasing numbers represent acute threats to human and livestock health [8], [11].…”

An Evaluation of the Nine-banded Armadillo as Predators of Gopher Tortoise and Northern Bobwhite Quail Nests in Florida

“…Engeman et al (2005) found that 49% of marine turtle nests at two locations in Florida were depredated by armadillos. Armadillos were responsible for 16% of quail nest failures at Tall Timbers Research Station in north Florida and Pebble Hill Plantation in southwest Georgia (Staller et al, 2005) and one gopher tortoise nest failure at Joseph W. Jones Ecological Research Center in southwest Georgia (Smith et al, 2011). Contrary to these findings, however, armadillos at our study sites (JBWMA and NFREC) were the primary visitor of only 4% (n 5 3/78) of artificial quail nests and did not appear to consume any eggs during these visits.…”

“…Nine-banded armadillos are considered to be general omnivores (Redford, 1985), feeding predominantly on beetles, earthworms, millipedes, and fly larvae (Fitch et al, 1952;Sikes et al, 1990). They also feed opportunistically on small vertebrates (see review in McDonough and Loughry, 2008) and eggs of a variety of ground nesting species of conservation concern including sea turtles (Engeman et al, 2003(Engeman et al, , 2005, gopher tortoises (Gopherus polyphemus, Douglas and Winegarner, 1977;Smith et al, 2011), and northern bobwhite quail (Colinus virginianus, Staller et al, 2005). Gopher tortoises are considered threatened by the IUCN (IUCN, 2010), the state of Florida (Gruver and Murphy, 2011) and the state of Georgia (Jensen, 2009).…”