For mobile, landscape view is recommended.
The objective of the this project was to validate the use of aerial techniques to deploy acetaminophen–treated dead neonatal mice (DNM) baits to reduce brown treesnake (Boiga irregularis, BTS) populations in forested sites on Guam. In particular, this project developed an operational aerial control method for depopulating snakes on a landscape level that would reduce the risk of snakes in Department of Defense (DOD) cargo facilities before they enter into areas of military transport. Aerial delivery is a technique for depopulating BTS in large forest areas. Issues validated included the number of baits that landed above ground level, number of aerial deployments for reducing treated bait take by greater than 80%, duration of bait take reductions, compensatory increases in non-native rodent abundance, and impacts to non-target animals.
Thawed DNM were treated by inserting an 80 Milligram (mg) acetaminophen tablet into the body cavity through the mouth. The acetaminophen tablets were a specific formulation made by the United State Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center (USDA, APHIS, WS, NWRC), chemistry formulation labs in Fort Collins, Colorado. Radio transmitters also were implanted into the body cavity for tracking a subset of the treated DNM. Treated DNM baits were individually attached to 1.2 meter-long paper flag streamers with cardboard on each end of the paper streamers, hereafter defined as flag-baits. The paper streamer was folded accordion-style between the cardboard, forming a flat, compact flag-bait. The flag-baits were packaged into trays and frozen until deployed. Flag-baits were deployed by hand from a helicopter over a prescribed forested drop zone at 36 baits per hectares (ha), the Environmental Protection Agency (EPA) registered application rate (EPA Registration #56228-34 held by WS, NWRC). The double-ended cardboard streamers form an arc in the air and entangle the treated DNM in vegetation above ground level where they are consumed by Brown Treesnakes.
Radio-telemetered DNM (a subset of the total dropped) were tracked to determine the percent landing in the canopy, distance between baits, and fate of baits. Snake activity on the Habitat Management Unit (HMU) and Munitions Storage Area (MSA) aerial drop sites (55 ha each) and one 55 ha reference site (REF) was determined by untreated DNM taken from bait stations monitored twice monthly as an index of BTS numbers. Rodent numbers were monitored quarterly through capture of rats in live traps to evaluate possible compensatory increases in rodent abundance (as BTS abundance decreases, rodent abundance may increase). Costs were tracked and scaled up to a hypothetical 500 ha drop site to estimate costs of an operational scale control program. Lastly, projected cost savings of advancements in automated bait delivery devices were estimated and applied to a 500-ha drop site operational program.
A total of eight quantitative performance metrics and one qualitative performance metric for the demonstration plan were evaluated. Of the eight quantitative metrics, seven were met or exceeded, and one was marginally successful but complicated by extenuating factors. The qualitative performance metric was met.1
Performance Objective | Success Criteria | Criteria Met |
| Quantitative Performance Objectives | ||
| 1) Maximize landing of telemetered baits above ground level | > 80% of telemetered baits deployed above ground level across all drops. Minimum >70% of telemetered baits deployed above ground level per drop | Yes |
| 2) HMU test site: Reduce BTS abundance as measured by reduced telemetered treated DNM bait take by BTS | No more than four aerial deployments at 2 week intervals for reducing telemetered treated baits taken by BTS by >80% | Yes |
| 3) MSA test site: Reduce BTS abundance as measured by reduced telemetered treated DNM bait take by BTS | No more than five aerial deployments at 2 week intervals for reducing telemetered treated baits taken by BTS by >80% | No |
| 4) HMU test site: Reduce BTS abundance sufficiently to minimize interval between aerial maintenance deployments | At least 12 weeks between deployments for maintaining BTS bait take < 30% before next aerial drop | Yes |
| 5) MSA (no snake fence barrier aerial test site): Reduce BTS abundance sufficiently to minimize interval between aerial maintenance deployments | At least 4 weeks between deployments for maintaining BTS bait take < 30% before next aerial drop | Yes |
| 6) Minimize compensatory increases in non-native rodent abundance | < 20 % increase in rodent abundance | Yes |
| 7) Minimize non-target impacts (crabs, monitor lizards) | <10% bait take by non-target animals | Yes |
| 8) Maximize aircrew performance for delivering telemetered baits at regular intervals | Mean range of 17-23 m between telemetered baits | Yes |
| Qualitative Performance Objective | ||
| 1) Maximize aircrew work performance during aerial bait deployment | Aircrew able to perform duties effectively with minimal boredom/fatigue | Yes |
1See demonstration narrative in Final Report.
Flag-baits were deployed by hand from a helicopter at 36 baits per ha, the EPA registered application rate currently held by the WS, NWRC. Any changes to the application rate needed approval through the EPA which could take 2-3 years. The WS, NWRC technology transfer program can aid in this process to obtain approval for changes, potentially reducing the timeframe to approval.
Other non-regulatory implementation issues include cost of deployment of toxicant baits and monitoring associated with a large scale operational program. Wildlife Services and NWRC and public and private partners are currently working on technologies to help develop refinements to the technology that could result in significant cost savings such as automated technologies.
Scaling up operational programs may entail toxicant and bait procurement issues. Currently the NWRC is the only manufacturer of the acetaminophen tablets for use in aerial bait drops. NWRC could easily meet demand for tablets on the aerial bait drop but larger scale operations may require expansion of staff, facilities and equipment to meet demand. While equipment for hand baiting was readily available, equipment being developed for automated delivery of baits is not. All automated equipment is custom built and unique to this application and would likely need to be sole sourced to the supplier. This sole supplier situation is likely to remain the case in this niche market without substantial commercial growth potential. Currently automated delivery and equipment are in a research test phase of development by WS, NWRC.