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Patrick D Barnhart

Publications and source records attributed to Patrick D Barnhart.

4 recordsLinked to original sources
USGS2024

Limitations of invasive snake control tools in the context of a new invasion on an island with abundant prey

In October 2020, a new population of invasive brown treesnakes ( Boiga irregularis ) was discovered on the 33-ha Cocos Island, 2.5 km off the south coast of Guam. Cocos Island is a unique conservation resource, providing refuge for many lizards and birds, including endangered species, which were extirpated from mainland Guam by invasive predators including brown treesnakes. We sought to evaluate the usefulness of toxic baiting with acetaminophen-treated carrion baits and cage trapping, common tools for the control of brown treesnakes on mainland Guam, as potential eradication tools on Cocos Island. We evaluated multiple bait types and bait presentations: on the ground, suspended in the canopy emulating aerial bait applications and in four plastic-tube bait station configurations intended to exclude non-target species. We monitored all baits with time-lapse cameras. Despite improved exclusion of non-targets by bait station design, most baits were quickly removed by non-target species, particularly coconut crabs ( Birgus latro ) and Mariana monitors ( Varanus tsukamotoi ). Monitoring of 1,250 baits available for 2,427 bait nights resulted in no observations of brown treesnakes taking any bait. Subsequently, we tested two trap types commonly used on Guam and compared trapping success with live versus dead mouse lures. In 10,553 trap nights using live and dead mouse lures, we only captured one brown treesnake, in a trap with a live mouse lure. These baiting and trapping rates are so low as to be ineffectual for all practical purposes. Concurrent visual searching and hand capture of brown treesnakes during initial rapid response efforts demonstrates that these low baiting and trapping success rates are not a result of low snake density. We make a case for our assumption that the ineffectiveness of these tools on Cocos Island is due to the context of extremely high abundance of preferred live prey, primarily large geckos and birds. Our results have profound conservation ramifications, because any future island invasions by brown treesnakes are likely to occur within similarly prey-rich environments where these baiting and trapping methods might be similarly ineffective.

NeoBiota↗
USGS2021

Can we prove that an undetected species is absent? Evaluating whether brown treesnakes are established on the island of Saipan using surveillance and expert opinion

Detection of invasive species and decisions centered around early detection and rapid response (EDRR) are notorious challenges for decision makers. Detection probability is low for cryptic species, resources are limited, and ecological harm (especially for island ecosystems) can result from failure to remove invasive species due to inadequate or delayed surveillance efforts. Due to the proximity to the U.S. territory of Guam and inter-island traffic, the Commonwealth of the Northern Mariana Islands (CNMI) is at high risk of colonization by the invasive and cryptic brown treesnake ( Boiga irregularis ; BTS). There have been numerous reports of snakes and 7 confirmed specimens secured at ports of entry on the island of Saipan in the CNMI over the last four decades, raising the possibility that a population might be established. Establishment of BTS on Saipan is a major concern, as evidenced by the ecological and economic disruption that occurred on Guam. We evaluated the possibility of a small localized population on Saipan using evidence from surveillance efforts in 1999, 2007, 2009, 2016, and 2018, and from results of expert assessment of the credibility of non-confirmed reports of snakes for the period 1982–2013. For active surveillance efforts, we use a Poisson-based model to estimate the 95% probability of at least one snake being detected at a stated density given the level of sampling effort and detection probability. Based on this collective evidence we conclude there is a low probability that Saipan currently has an incipient population of BTS. However, with the continued presence of BTS on Guam, continuing commercial and military transportation in the region, and relief shipments responding to increased storm intensity, Saipan remains highly vulnerable to accidental introductions. Effective surveillance remains a crucial element for detection of any species, but this may be particularly true for a cryptic snake that is difficult to control once established.

Management of Biological Invasions↗
USGS2020

Landscape dominance of introduced herpetofauna on an oceanic island

Habitat loss and fragmentation can negatively impact native wildlife and facilitate establishment of introduced species. On islands, introduced species are a primary cause of extinction and can alter community membership through predation or competition for resources. Consequently, elucidating the distribution of introduced and native species can improve understanding of the potential synergistic effects of land use and introduced species on native island species. The island of Saipan in the Commonwealth of the Northern Mariana Islands has a long history of herpetofaunal introductions. However, the distribution of native and introduced herpetofauna on Saipan is poorly understood, and the effects of land use and introduced species on the native herpetofauna are largely unknown. In 2018, we randomly selected sites on Saipan from established island-wide transects and used multiple detection methods, repeated surveys, and single-season occupancy models to account for imperfect detection and construct species distribution models. We investigated the role of biotic and abiotic factors in explaining occupancy and detection of Saipan’s native and introduced herpetofauna. We recorded 2568 observations representing 1 amphibian and 11 reptile species. Introduced species were encountered 3.8 times more frequently and were 33% more broadly distributed than native species. Occupancy for the native forest dwelling species Emoia caeruleocauda and Perochirus ateles was positively associated with elevation and enhanced vegetation index, suggesting that human habitat modification at lower elevations may be reducing their suitable habitat.We found evidence of a range contraction for the imperiled P. ateles and suggest potential avenues for implementing targeted conservation of native herpetofauna.

Global Ecology and Conservation↗