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.

bait stations, Boiga irregularis, camera traps, conservation, eradication feasibility, incipient population, non-target species, trapping

The pace and scale of the introduction and spread of non-native reptiles continues to increase, as does recognition of the attendant ecological and economic harms they cause (Kraus 2009; Reed and Kraus 2010; Kraus 2015; Capinha et al. 2017). Snakes comprise a considerable proportion of these reptile invasions, many of which occur on islands where already-imperilled native species are at risk of extirpation or extinction by snake predation; examples include wolf snakes (Lycodon aulicus) on Mauritius and Réunion Island (Deso and Probst 2007), corn snakes (Pantherophis guttatus) and boa constrictors (Boa constrictor) on multiple Caribbean islands, California kingsnakes (Lampropeltis californiae) in the Canary Islands and multiple colubrids in the Balearic Islands (Tonge 1990; Perry et al. 2003; Bushar et al. 2015; Monzón-Argüello et al. 2015; Silva-Rocha et al. 2015). Invasive snake problems can be particularly intractable because of snakes’ cryptic nature and ability to withstand long periods without feeding (Durso et al. 2011; Siers et al. 2018a; Yackel Adams et al. 2018; Boback et al. 2020; Nafus et al. 2020). To date, there are no known examples of eradication of an invasive snake population at a scale larger than 1 ha (Campbell et al. 2012; DIISE 2023).

The most well-known and well-studied example of an island snake invasion is that of the brown treesnake (Boiga irregularis) on the island of Guam in the Western Pacific. Accidentally transported from the Admiralty Islands to Guam in shipments of military equipment following World War II (Rodda and Savidge 2007; Richmond et al. 2015), this slender, nocturnal, arboreal predator spread throughout the entire island by the mid-1980s (Savidge 1987) and achieved densities unprecedented for any natural non-aggregating snake population (Rodda et al. 1999a). The spread of brown treesnakes across Guam was followed by a wave of negative impacts to all native vertebrate taxa (Wiles 1987; Fritts and Rodda 1998) including collapses in nearly all native bird populations, resulting in the extirpation or extinction of 12 of 15 native forest birds and the functional extinction of the island’s entire forest avifauna (Savidge 1987; Wiles et al. 2003). This bird loss was followed by cascading effects on plants, invertebrates and ecological processes (Perry and Morton 1999; Rogers et al. 2012; Caves et al. 2013; Fricke et al. 2014; Freedman et al. 2018). Socioeconomic damages caused by the brown treesnake invasion of Guam include ‘home invasions’ and painful bites to humans including infants (Fritts 1988; Fritts et al. 1990, 1994), predation on domestic animals including the loss of small-scale poultry production (Fritts and McCoid 1991; Rodda and Savidge 2007), declines in tourism (Hall 1996; Shwiff et al. 2010) and costs of power outages caused by snakes short-circuiting transmission lines (Fritts 2002).

Methods and strategies for brown treesnake control are being developed, tested and implemented for the protection and restoration of Guam’s native flora and fauna (e.g. Aguon et al. (2002); Siers et al. (2017a, 2020a, b); Clark et al. (2018); Klug et al. (2021a, b); Pollock et al. (2021)). However, the first and highest priority for invasive brown treesnake control has been interdiction–the prevention of further spread of this harmful predator from Guam to other vulnerable locations throughout the Pacific (Hall 1996; Stanford and Rodda 2007; Perry and Vice 2009; Clark et al. 2018; Engeman et al. 2018). The Commonwealth of the Northern Mariana Islands (CNMI, especially Saipan, Rota and Tinian) and the Hawaiian Archipelago are at particularly high risk of invasion and severe ecological and economic consequences (Fritts 1988; Shwiff et al. 2010; BTSTWG 2015; Yackel Adams et al. 2021). Before the implementation of a full interdiction programme on Guam, live brown treesnakes were too-commonly found in cargo from Guam to Saipan, Hawaii and other destinations; since a USDA Wildlife Services operational control programme began in 1993, such encounters have dropped to nearly zero and Saipan continues to be considered snake-free (Hall 1996; Stanford and Rodda 2007; Yackel Adams et al. 2018, 2021).

Cocos Island (CHamoru name: Islan Dåno’) is a small atoll island situated approximately 2.5 km off the southern tip of the main island of Guam. Cocos Island was considered to comprise the majority of remaining snake-free habitat in Guam and is home to many vertebrates susceptible to brown treesnake predation, including some species that no longer persist on mainland Guam. Guam rails (Hypotaenidia owstoni: ko’ko’), once extinct in the wild due to brown treesnake predation, were introduced to Cocos Island where they have reproduced and thrived (Medina and Aguon 2000). The endangered Mariana skink (Emoia slevini) was extirpated from mainland Guam by brown treesnake predation, but a remnant population was recently rediscovered on Cocos Island (USFWS 2019). Other species, including regionally endemic lizards and birds, also persist on Cocos Island (Rodda and Fritts 1992).

While the high volume of commercial and military cargo and vessels originating from central and northern Guam has been scrupulously inspected for stowaway snakes, traffic between southern Guam and Cocos Island has received relatively little attention. A biosecurity plan was developed for the Island (USDA Wildlife Services 2009) to monitor for incursions of cats, rodents and snakes on Cocos Island, as well as control snakes in high traffic areas, i.e. vessels that visited Cocos Island daily for business. An awareness campaign targeted staff and visitors to Cocos Island to report sightings and conduct boat inspections. The implementation of personal craft inspections was voluntary with no regulatory enforcement.

In October 2020, a local fisherperson reported killing snakes on Cocos Island during a night-time visit to the atoll. Subsequent search efforts by the U.S. Geological Survey’s (USGS) Brown Treesnake Rapid Response Team (RRT; Stanford and Rodda 2007) confirmed a population of brown treesnakes on Cocos Island (Guam Department of Agriculture 2020; Barnhart et al. 2022). The RRT intermittently continued night-time searches through September 2021, with additional training exercises ongoing through September 2023 and had sighted 64 brown treesnakes (58 of which were captured and euthanised; U.S. Geological Survey 2023). As of September 2023, the volunteer group Friends of Islan Dåno had captured and removed 36 brown treesnakes (Martin Kastner, Friends of Islan Dåno, written communication, 2023) and USDA Wildlife Services had removed an additional 23 (Alyssa Taitano, USDA, written communication, 2023). Currently, these search and removal efforts continue intermittently while agencies plan for a more comprehensive response, potentially including an eradication effort (USDA Wildlife Services 2021a, b). Preliminary USGS data reflect an apparently reproductive population, with representatives of all size classes captured and much larger and heavier snakes than found in similar samples from Guam (Barnhart et al. 2022).

Several tools and techniques have been developed and continue to be improved for management of invasive brown treesnakes on Guam (Clark et al. 2018). The common human pharmaceutical acetaminophen (paracetamol) has been identified as an effective oral toxicant for brown treesnakes (Savarie et al. 2000; Siers et al. 2021) with a relatively low environmental risk profile (Johnston et al. 2002). A tablet containing 80 mg of acetaminophen has been registered with the U.S. Environmental Protection Agency as a vertebrate pesticide for brown treesnake control (Reg. No. 56228-34). Coupled with carrion baits (typically 4–6 g dead neonatal mice), acetaminophen baiting has been demonstrated to reduce brown treesnake abundance on a landscape scale (Savarie et al. 2001; Clark and Savarie 2012; Siers et al. 2020a, b), has become a mainstay of interdiction operations (Clark et al. 2012; Clark et al. 2018; Engeman et al. 2018) and is suggested to be capable of eradicating brown treesnakes on Guam within snake barriers, as part of an integrated pest management strategy (Nafus et al. 2022). Baiting can be more cost-effective than traditional trapping methods (Clark et al. 2012) and, as such, was thought to be a desirable eradication tool for managing the established brown treesnake population on Cocos Island.

Since the early 1990s, live trapping with cage traps has been the primary method of brown treesnake removal and continues to be a foundational tool for research and management programmes (Engeman and Linnell 1998; Tyrrell et al. 2009; Clark et al. 2018; Engeman et al. 2018). Current trap designs are modifications of crayfish or minnow traps, composed of a cylindrical wire mesh trap body with a funnel at each end. Stock funnel openings are widened and covered with a wire mesh one-way flap to allow snakes access to the trap body, but blocking escape. A live mouse in a protective chamber is the lure that entices snakes into them. Although these brown treesnake traps are considered the most efficient snake traps in the world (Rodda et al. 1999b), care and provisioning of live mice is costly and infrared photography has indicated that many snakes that encounter traps fail to enter the trap (Yackel Adams et al. 2019). Moreover, as food resources become more abundant, live mouse traps may have decreasing efficacy, which is of potential importance in rapid response settings (Gragg et al. 2007; Stanford and Rodda 2007). Traps are also expensive and prone to damage by non-target species, particularly coconut crabs (Birgus latro) and Mariana monitors (Varanus tsukamotoi [nee indicus]). Due to these drawbacks, trapping is seen as an effective brown treesnake removal tool, but probably with greatest value when integrated with acetaminophen baiting (Nafus et al. 2022).

It is important to conduct pilot evaluations of the utility of potential control tools to establish their effectiveness prior to substantial investments in planning eradication projects (Genovesi 2001; Clout and Williams 2009). Identifying the limitations of control tools is critical for preliminary feasibility assessments and managing eradication costs. Prior to planning for an eradication attempt on Cocos Island, we sought to evaluate the practicality of acetaminophen baiting and live trapping in the context of the Island’s prey-rich environment which is similar to possible scenarios if brown treesnakes were to successfully arrive and establish a population in other areas vulnerable to invasion. Our general objectives for both methods were to evaluate: 1) brown treesnake removal rates with various tool implementation methods; 2) interference by non-target species with brown treesnake removal methods; and 3) potential harm to native species from brown treesnake removal methods.

The results of this study are clear: two of the primary tools for brown treesnake removal on Guam will not be effective for brown treesnake eradication on Cocos Island. Brown treesnake detection rates, based on visual CPUE, are apparently lower on Cocos Island (0.188 snakes/km) than most other detection efforts on Guam. Within a long-term 5-ha geographically enclosed population representative of disturbed limestone forest and secondary forest on Guam, Nafus et al. (2023) recorded 0.758 brown treesnakes per km of transect searched. In a 55-ha snake enclosure surrounding degraded limestone forest in northern Guam, Boback et al. (2020) documented a CPUE of 0.906 brown treesnakes per searcher hour, compared to 0.083 on Cocos Island. Following aerial baiting at this same site (Dorr et al. 2016; Siers et al. 2018), the CPUE dropped to 0.049 per hour, lower than the Cocos Island CPUE. With all of the caveats that come with using CPUE as an index of relative abundance (e.g. detectability differences amongst different habitat types), these data demonstrate that visual detection rates on Cocos Island are lower than unmanipulated habitat on Guam (24% compared to Nafus et al. (2023) per km and 9.2% compared to Boback et al. (2020) per hour before aerial suppression), but nearly twice as high as within an aerially-suppressed study plot (Boback et al. 2020). Nonetheless, despite 40% lower visual contact rates than on Cocos Island, the suppressed population on Guam continued to take non-toxic dead mouse baits at rates averaging approximately 20% (Siers et al. 2018b), while the Cocos Island bait take rate was 0%.

Live trapping with mouse lures prior to snake suppression on Guam yielded a capture rate of 0.3 snakes per 100 trap days (Nafus et al. 2018). These differences in snake detection rates by location indicate that greater bait or trap captures on Cocos Island would be expected given the level of effort we applied to each tool. Carrion bait take rates on Guam in areas without active brown treesnake control tend to range from approximately 30% to nearly 100% (Savarie et al. 2001; Clark and Savarie 2012; Siers et al. 2018b, 2019b, 2020a), while we failed to observe a single bait take within 2,427 bait monitoring days (upper 95% confidence interval of 0.151%). Trapping captures per 100 trap nights on Guam are commonly higher in areas where they are not being operationally suppressed, (4–9; Nafus et al. (2018)) and ranged as high as 25 to 60 in the 1990s (Rodda et al. 1999b). In areas on Guam in which brown treesnakes have been suppressed to 0.16 snake/ha (as estimated from forest interior visual survey CPUE), trapping CPUE was maintained at the rate of 0.3 captures per 100 trap nights (Nafus et al. 2018; Boback et al. 2020). When using live mouse lures on Cocos Island, we achieved only 0.0187 captures per 100 trap nights which is substantially lower than the anticipated levels based on Guam efforts (Guam CPUE 213 to 481 times higher than Cocos Island when compared to Nafus et al. (2018) results).

Our failure to attract brown treesnakes to baits and traps is most likely due to the extraordinary abundance of preferred live prey on Cocos Island, particularly large geckos, birds and their eggs, compared to the relatively prey-depauperate nature of Guam’s forests resulting from prolonged brown treesnake predation (Fritts and Rodda 1998; Wiles et al. 2003; Siers 2015). Cocos Island is populated by abundant lizards, many of which have been extirpated from parts or all of Guam by brown treesnake predation, such as federally and locally endangered Mariana skinks, locally endangered littoral skinks (Emoia atrocostata), fragile Micronesian geckos (Perochirus ateles) and Pacific snake-eyed skinks (Cryptoblepharus poecilopleurus), as well as mutilating geckos (Gehyra mutilata), oceanic geckos (G. oceanica) and green anoles (Anolis carolinensis). Small brown treesnakes, in particular, appear to be specialists on small lizards, which are an almost exclusive prey item in stomach contents (Savidge 1988; Siers 2015). They also exhibit strong preference during laboratory feeding trials (Lardner et al. 2009) and present a venom composition that is more effective for ectotherms as juveniles (Mackessy et al. 2006). Our green anole sighting rates were relatively high (15.5/km), but close to estimates from the snake-free island of Saipan (14.9/km; Lardner et al. (2019a)), while observations of this species in brown treesnake stomach contents from mainland Guam are extremely low in forest habitats, from where they have been essentially extirpated by brown treesnake predation (Rodda and Fritts 1992; Siers 2015). Relatively large oceanic geckos, which are roughly equivalent in mass to a small mouse, may additionally offer a rewarding prey item that reduces the efficacy of bait- and lure-based control tools on Cocos Island. We commonly observed oceanic geckos on Cocos Island (11.3/km), while they are no longer documented in brown treesnake stomach contents on mainland Guam (Siers 2015), having been essentially extirpated by brown treesnake predation (Rodda and Fritts 1992). Nafus et al. (2023) recorded no observations of green anoles or oceanic geckos and their total lizard sighting rates were 6.0/km (4 species) compared to 37.8/km (10 species) on Cocos Island, indicating substantially greater lizard prey availability. Unchecked brown treesnake predation and population growth could put all small lizard species at risk of almost certain local extinction on Cocos Island (Rodda and Fritts 1992; Rodda et al. 1997; Fritts and Rodda 1998; USFWS 2019).

Of all the ecological damage that have occurred since their introduction to Guam, the pervasive impacts of brown treesnake predation on birds have been the most profound (Savidge 1987; Wiles et al. 2003; Pollock et al. 2019; Klug et al. 2021b). Our Cocos Island bird sighting rate of 32.8/km and 11.3/hour is high, given the well-documented collapse and functional extinction of the forest bird avifauna on mainland Guam (Savidge 1987; Wiles et al. 2003). Any experienced brown treesnake searcher can attest that bird sightings in forest habitats on mainland Guam are quite rare, earning Guam its reputation for “silent forests” and the cascading ecological effects of bird loss (Savidge 1987; Rodda et al. 1997; Rogers 2011, 2020). Nafus et al. (2023) documented only four bird sightings of indeterminate species in 816.2 km of transect searching in the northern Guam 5-ha enclosure (0.005 birds/km). It is unclear how severely brown treesnake predation on Cocos Island has affected the abundance of bird and lizard prey species, but prey resources clearly remain much more abundant on Cocos Island.

Brown treesnakes on Guam that forage in areas of increased prey availability, including birds, such as urban areas and swiftlet caves, tend to be in better body condition (Siers 2015; Siers et al. 2017b; Yackel Adams et al. 2019; Klug et al. 2021b), a characteristic that is evident in the extremely heavy snakes that have been found during visual surveys on Cocos Island. The mean weight of snakes reported in other contemporary studies on Guam (Siers et al. 2017b) suggests that the average weight of snakes removed from Cocos Island during the period of this study is much greater. There is also emerging evidence that brown treesnakes conditioned to feeding on live birds exhibit less attraction to rodent-based baits and lures (Nafus et al. 2021). During brown treesnake removal from Cocos Island, encounters with seabirds, Guam rails and Micronesian starlings (Aplonis opaca) were not uncommon (U.S. Geological Survey 2023), supporting the impression that avian prey currently remain abundant on Cocos Island relative to Guam. For these reasons, it is apparent that, although brown treesnakes on Guam will readily consume carrion, live lures are far more effective than any dead animal baits or other inanimate lures (Shivik et al. 2000; Savarie and Clark 2006; Kimball et al. 2016) and that the availability of abundant preferred prey (birds) on Cocos Island diminishes the attraction to carrion baits.

These findings demonstrate that higher prey availability negatively affects brown treesnake detection and capture rates. On Guam, temporary experimental suppression of rodent prey abundance was demonstrated to increase trap capture rates (Gragg et al. 2007) and increasing movement distances of brown treesnakes (Christy et al. 2017). Free-ranging brown treesnakes that have recently taken large meals have been experimentally demonstrated to significantly reduce movement for 5 to 7 days, with an associated reduction in the ability to visually detect or trap snakes during this time (Siers et al. 2018a). Foraging for carrion may also be a futile strategy for brown treesnakes on Cocos Island where coconut crabs and Mariana monitors rapidly remove all carrion from the ground (Figs 7–9). Moreover, prior studies have indicated that brown treesnake attraction to carrion and especially mouse carrion, may decrease as snakes increase in size (Shivik and Clark 1999; Nafus et al. 2021), while large snakes may be the most important demographic to remove from the perspective of both avian conservation and eradication potential (Savidge 1988; Yackel Adams et al. 2019; Nafus et al. 2022).

Both baiting and trapping appear to be relatively safe for Cocos Island wildlife. In only two instances did a native bird (a Pacific reef heron and a Guam rail) take a bait (both DNM) from the ground. Although acetaminophen may also be toxic to birds, they are not known to have the same genetic basis for sensitivity to acetaminophen toxicosis as snakes (van den Hurk and Kerkkamp 2019) and crows in cage trials picked around acetaminophen tablets rather than ingesting them, with no signs of toxicosis (Avery et al. 2004). Clearly, crabs and Mariana monitors quickly cleanse the forest floor of any carrion baits containing acetaminophen. Crabs tend to eat around acetaminophen tablets when consuming carrion baits and show no signs of toxicosis (Johnston et al. 2002). On the other hand, Mariana monitors were the most problematic scavengers of baits on the ground and in bait stations and other monitor species are susceptible to acetaminophen toxicosis (Mauldin and Savarie 2010). Although recent evidence indicates that Mariana monitors are native to the Mariana Islands (Weijola et al. 2020), Mariana monitors on Cocos Island are being actively depredated by GDAWR for the protection of endangered Guam rails and their nests. It is likely that several small Mariana monitors succumbed to acetaminophen toxicosis and would continue to do so if acetaminophen were used as part of a brown treesnake eradication programme on Cocos Island. Small Mariana monitors were also frequently caught live in traps; these could be released unharmed, but GDAWR requested that trapped Mariana monitors be removed and euthanised rather than released, in furtherance of their Guam rail protection efforts. Some small coconut crabs and hermit crabs expired in brown treesnake traps, likely due to dehydration, although the numbers would not be expected to have population-level impacts. Factors such as these need to be considered when assessing the potential environmental impacts of baiting or trapping for invasive snakes, although ineffectiveness in our case could make these issues moot.

The practical information on baiting and trapping is of little avail when brown treesnake removal by these techniques is almost completely ineffectual in the context of abundant alternative prey availability. Initial eradication discussions for Cocos Island included a notional plan of a 20 × 20-m grid of bait stations and a 40 × 40-m grid of traps. At this density, we might have arrayed as many as 825 bait stations and 206 traps with live mouse lures across the entire 33 ha of the Island for the duration of an eradication attempt that is expected to last at least 5 to 10 years (based on ad hoc population estimates and demographic projections; USDA Wildlife Services (2021a)). The pilot studies we report here have forestalled what might have been very costly investments in baiting and trapping with little or no payoff. Financial estimates for the costs of an island-wide baiting and/or trapping effort are beyond the scope of this article, complicated and inflated by considerations, such as boat travel, transect establishment etc., although these issues also affect visual search and removal efforts.

Instead, available funding is being programmed for visual searching and manual removal of snakes, the only tactic that has thus far been effective on Cocos Island. Although night-time visual searching can be logistically challenging, disruptive to work schedules and tedious, it is also the tool that is considered to be the least biased with respect to snake sizes, putting all brown treesnake size classes at risk of detection (Rodda et al. 2007; Christy et al. 2010; Yackel Adams et al. 2018; Lardner et al. 2019b). To date, there have been no documented successful invasive snake eradications beyond a temporary 1-ha experimental exclusion plot (Campbell et al. 2012); however, with judicious and sustained application of the right techniques, the small, isolated island of Cocos Island could potentially be the location of the first successful island-wide eradication.

Further work would be beneficial to validate whether live bird lures would be more effective than mice and carrion on Cocos Island. Field and laboratory experiments have demonstrated that traps with a live bird as the lure show increased capture rates of large, well-conditioned snakes, as well as longer trap investigation times overall compared to those with mouse lures (Yackel Adams et al. 2019; Klug et al. 2021a; Nafus et al. 2021). Additionally, a pattern of feeding success on birds may reduce a brown treesnake’s interest in rodents and this may be particularly true on an island where rodents were eradicated in 2009. Verification of the disinterest of Cocos Island snakes to all potential attractant-based lures would be an important next step.

In the event of future invasions, prospects for complete removal of brown treesnakes from larger, prey-rich islands with difficult-to-access terrain would be challenging, particularly when our results indicate that application of the newly developed landscape-scale aerial baiting technology would be ineffective (Siers et al. 2020b). Work to differentiate between the context dependency of control tool attraction, based on total prey availability or species compositions of prey, can also be informative in amending current interdiction programmes or developing emergency response protocols if an incipient population of brown treesnakes is located on another island.

Our results indicate that standard invasive brown treesnake control tools, acetaminophen baiting and trapping with mouse lures, are seemingly not effective enough to warrant significant investment of limited project resources where preferred alternative prey are abundant. These results have profound ramifications for the potential of rapid removal and eradication of incipient brown treesnake populations on any other islands at risk of invasion, such as the Hawaiian Islands, the Northern Mariana Islands and throughout Micronesia and the rest of the Pacific where snake-free islands are rich in diversity and density of potential prey (e.g. Lardner et al. (2019a), Table 1). This work underscores the benefits of a continued emphasis on interdiction – prevention of accidental translocation through strong pre- and post-border inspections and reduction of potential stowaways in high-risk areas on Guam – over reliance on early detection and rapid response to resolve any new brown treesnake invasions that might occur. These results are also important for consideration of prevention, early detection, rapid response, suppression and/or eradication of other invasive snakes on islands or elsewhere. Similar issues are likely to be faced during any invasive snake removal programme, particularly where abundant alternative prey is available.

We’d like to thank all additional participants in the field work associated with these studies, including Jordan Barcinas, Ahmi Cacapit, Juan-Carlos Mungaray, Ella Norris and Alyssa Taitano. Zach Quiogue, Elizabeth Frasch, Amn Nacpil, Brianna Montgomery, Martin Felisan, Shiho Koike, Thomas Fies, Scott Goetz, Levi Gray, Thomas Hinkle, Charlene Hopkins, Peter Xiong, Marijoy Viernes, Dusty Jordan and Karen Watson contributed to the USGS RRT efforts to remove BTS from Cocos Island mentioned in this report. Olympia Terral and Martin Kastner coordinated the volunteer brown treesnake capture efforts. The contracted support from the University of Guam was facilitated by Adrian Ares, Daniel Lindstrom, Aubrey Moore and Cathleen Moore-Linn. We also wish to thank all participants in Cocos Island eradication planning, permitting and environmental compliance consultation including Michelle Bogardus, Dawn Bruns, Jacqueline Flores, Jeffrey Flores, Thomas Hall, Steve Hanser, Martin Kastner, MaryJo Mazurek, Benton Pang, Jeff Quitigua, Haldre Rogers, Jason Suckow, Olympia Terral and Lorena Wada. This research and the USGS rapid response was made possible by funding from the U.S. Department of the Interior Office of Insular Affairs coordinated by Hailey McCoy. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.