USAF, USFWS, and Island Conservation Attempt to Eradicate Rodents at Wake Atoll 18-Sep-18 As of:

Wake Atoll

Goals and Approach Goal: Approach: Remove 100% of the rodent population (Rattus exulans & Rattus tanezumi) from all three islands (Peale, Wilkes and Wake) Approach: Award project to USFWS via intergovernmental fund transfer Utilize biological window for operation; maximize exposure to targets and minimize exposure to non target species Apply two applications of Brodifacoum 25w (85,000 lbs) to all three islands via bait stations, hand and aerial broadcast Implement USAF biosecurity plan and monitor

Baiting Methods Hand Broadcast, bait bags, aerial broadcast with a bait bucket , and bait stations

A total of 37,423.13 kg of Brodifacoum was used Bait Rates Orange areas indicate areas where bait stations had to be used, everything else was bait by the helicopter 1821 acres A A total of 37,423.13 kg of Brodifacoum was used

Baiting Exclusion Zones Target App Rates: App 1: 18 kg/ha App 2: 9 kg/ha Large Exclusion Zones Areas in orange show areas that had to be treated differently from standard aerial methods 60 ha excluded 1,344 Bait Stations in 266 buildings 607 Abandoned Structures

Environmental Challenges 737 ha of ground to treat Thick vegetation that was difficult to navigate Large pemphis intertidal zones 12 Miles of shoreline 700 ha approximately surrounded by a lot of water

Environmental Challenges Natural Food Competition Non – Target Consumption Natural food availability

Commensal Challenges Food Sources from the Chow Hall and Dorms Food Availability from the Disposal Facility Commensal component

Structural Challenges Underground Utilities Large Historic and Complex Infrastructure There were known and unknown underground infrastructure Large and complicated infrastructure required special treatment, many abandoned buildings, and underground structures, not mapped

Installation Challenges Years of Old Debris Operating on and near an Active AF Runway There were many acres of old rusted debris that made sowing in with hand bait very difficult and dangerous A FOD walk had to be done on both runways after each aerial application (very time consuming) AF regulations about hot re-fueling on the tarmac

Logistical Challenges Getting a private helicopter and all the supplies needed to such a remote military installation

Mechanical Challenges Unknown bait rate applications from faulty equipment

Rat Sightings Post Application 1 June Rat – was considered a mummified rat and was not source of concern 25 June 2012 – A rat was run over near the golf course A Rapid Response Team was deployed twice after June and spot treated all 6 areas

Post Aerial Application of Brodifacoum Determinations 3 rats recovered post application were confirmed to be Rattus exulans and of the same DNA makeup as the pre-application species To date no Rattus tanizumis have been discovered on any of the 3 islands To date neither R. tanizumi or R. exulans have been found on Peale R. exulans have aggressively re-populated the atoll Some bait was recovered within the shoreline 10% of fish tissue sampled tested positive for brodifacoum residual Non-target take was considerably less than anticipated (only 6 birds)

Most Likely Causes for Unsuccessful Outcome

Rats Could Not… All rats could not eat a lethal dose of bait (or a lethal dose via secondary consumption of other bait consumers) possible reasons: There were gaps in coverage There was insufficient bait for all rats because it was eaten by non-target species before rats were able to consume a lethal dose Rats had a higher tolerance than expected to the toxicant

Rats Would Not… All rats would not eat a lethal dose For some rats there was a bait aversion acquired from previous control efforts For some rats there was a natural or learned aversion of bait stations There was an inter-species competition that excluded some R. exulans either physically or behaviorally from accessing bait, particularly from bait stations Some rats chose not to eat bait, or enough of it because of palatability of the bait and or availability of natural commensal food sources, and/or because of seasonal behavioral changes (e.g. breeding females confined to nests or smaller home ranges)

Bird populations post effort

Wake Island Rat Eradication Questions?