Geology topics

B.D. Sparklin

Publications and source records attributed to B.D. Sparklin.

4 recordsLinked to original sources

USGS2010

Estimate of herpetofauna depredation by a population of wild pigs

Herpetofauna populations are decreasing worldwide, and the range of wild pigs (Sus scrofa) is expanding. Depredation of threatened reptile and amphibian populations by wild pigs could be substantial. By understanding depredation characteristics and rates, more resources can be directed toward controlling populations of wild pigs coincident with threatened or endangered herpetofauna populations. From April 2005 to March 2006 we used firearms to collect wild pigs (n = 68) and examined stomach content for reptiles and amphibians. We found 64 individual reptiles and amphibians, composed of 5 different species, that were consumed by wild pigs during an estimated 254 hours of foraging. Primarily arboreal species (e.g., Anolis carolinensis) became more vulnerable to depredation when temperatures were low and they sought thermal shelter. Other species (e.g., Scaphiopus holbrookii) that exhibit mass terrestrial migrations during the breeding season also faced increased vulnerability to depredation by wild pigs. Results suggest that wild pigs are opportunistic consumers that can exploit and potentially have a negative impact on species with particular life-history characteristics. ?? 2009 American Society of Mammalogists.

Journal of Mammalogy↗

USGS2009

Effect of experimental manipulation on survival and recruitment of feral pigs

Lethal removal is commonly used to reduce the density of invasive-species populations, presuming it reduces population growth rate; the actual effect of lethal removal on the vital rates contributing to population growth, however, is rarely tested. We implemented a manipulative experiment of feral pig (Sus scrofa) populations at Fort Benning, Georgia, USA, to assess the demographic effects of harvest intensity. Using markrecapture data, we estimated annual survival, recruitment, and population growth rates of populations in a moderately harvested area and a heavily harvested area for 200406. Population growth rates did not differ between the populations. The top-ranked model for survival included a harvest intensity effect; model-averaged survival was lower for the heavily harvested population than for the moderately harvested population. Increased immigration and reproduction likely compensated for the increased mortality in the heavily harvested population. We conclude that compensatory responses in feral pig recruitment can limit the success of lethal control efforts. ?? 2009 CSIRO.

Wildlife Research↗

USGS2008

Change-in-ratio density estimator for feral pigs is less biased than closed mark-recapture estimates

Closed-population capture-mark-recapture (CMR) methods can produce biased density estimates for species with low or heterogeneous detection probabilities. In an attempt to address such biases, we developed a density-estimation method based on the change in ratio (CIR) of survival between two populations where survival, calculated using an open-population CMR model, is known to differ. We used our method to estimate density for a feral pig (Sus scrofa) population on Fort Benning, Georgia, USA. To assess its validity, we compared it to an estimate of the minimum density of pigs known to be alive and two estimates based on closed-population CMR models. Comparison of the density estimates revealed that the CIR estimator produced a density estimate with low precision that was reasonable with respect to minimum known density. By contrast, density point estimates using the closed-population CMR models were less than the minimum known density, consistent with biases created by low and heterogeneous capture probabilities for species like feral pigs that may occur in low density or are difficult to capture. Our CIR density estimator may be useful for tracking broad-scale, long-term changes in species, such as large cats, for which closed CMR models are unlikely to work. ?? CSIRO 2008.

Wildlife Research↗

USGS2008

Ground-based rodent control in a remote Hawaiian rainforest on Maui

Effective control of introduced mammalian predators is essential to the recovery of native bird species in Hawai'i. Between August 1996 and December 2004, introduced rodents were controlled within three home ranges of the Po'ouli Melamprosops phaeosoma, a critically endangered Hawaiian honeycreeper. Rats were controlled using a combination of ground-based rodenticide (0.005% diphacinone) application and snap traps. Beginning in August 2001, we monitored the effectiveness of these rodent control efforts. Relative abundances of Black Rats Rattus rattus and Polynesian Rats R. exulans were measured in each of five snap-trapping grids seven times over a 35-month period. Rat populations decreased inside of the rodent control areas, but control effectiveness differed between rat species. During the first year of monitoring, target control levels for R. rattus were consistently achieved in only one of the rodent control areas. Control techniques were refined in areas failing to meet targets. Subsequently, we achieved target control levels for R. rattus more consistently in all three rodent control areas. However, relative abundances of R. exulans did not differ between rodent control and reference areas, indicating that our rodent control techniques were insufficient to reduce population levels of this species. These findings signify a need for further improvement of rodent control methods in Hawai'i, especially for Polynesian Rats, and demonstrate the critical importance of periodic monitoring of the response of rodent populations to management. In the future, managers may need to design rodent control operations targeting R. rattus and R. exulans independently to achieve best results.

Pacific Conservation Biology↗