PE Klug, KM Brindock, RN Reed, AA Yackel Adams, MJ Mazurek, WC Pitt, CA Stricker

1. Protection of Caves Important to the Endangered Mariana Swiftlet through Effective Deployment of Control Tools Based on Brown Treesnake Behavior PE Klug, KM Brindock, RN Reed, AA Yackel Adams, MJ Mazurek, WC Pitt, CA Stricker National Military Fish and Wildlife Association March 2014 E-mail: pklug@usgs.gov

2. Prior to the introduction of the invasive brown treesnake (BTS) the island of Guam had a sustainable avian community Native forest species still breeding on Guam Native species still on Guam Native species extinct or extirpated from Guam Non-endemic bird species extirpated from Guam

3. The Mariana swiftlet is the last sustainable breeding population of native forest bird on Guam Native forest species still breeding on Guam Native species still on Guam Native species extinct or extirpated from Guam Non-endemic bird species extirpated from Guam

4. The Mariana swiftlet currently occupies 3 caves on Guam Population estimate = 1224 ± 164 birdsMahlac: 1031 ± 201 Maemong: 97 ± 44 Fachi: 49 ± 35

5. Ring of BTS traps and toxic-bait tubes around caves and visual surveys within caves are current control measures • Perimeter trapping with mouse-baited traps Mahlac = 40, Maemong= 29, Fachi= 25 traps • Bait tubes added to perimeter trap line Mahlac = 36, Maemong= 29, Fachi = 25 • In-cave visual surveys 12 per quarter in each cave (48 surveys/year) 60 min searches with night vision goggles * Mahlac: 5 bait tubes inside and 2 traps at cave mouth

6. Brown treesnakes may currently be limiting Mariana swiftletrecovery and thus it is necessary to reduce BTS numbersin areas of conservation concern Objectives of Brown treesnake (BTS) Research at Mariana swiftlet Caves on Guam • Assess rate & characteristics of BTS in caves • Assess residency (stable isotope diet analysis) • Assess current operational control of BTS at caves • Assess control tool deployment design • Assess if BTS mouse-baited traps are beneficial in caves Photo by Jack Jeffrey

7. Brown treesnakes may currently be limiting Mariana swiftletrecovery and thus it is necessary to reduce BTS numbersin areas of conservation concern Objectives of Brown treesnake (BTS) Research at Mariana swiftlet Caves on Guam • Assess rate & characteristics of BTS in caves • Assess residency (stable isotope diet analysis) • Assess current operational control of BTS at caves • Assess control tool deployment design • Assess if BTS mouse-baited traps are beneficial in caves Photo by Jack Jeffrey

8. After initial suppression of BTS in Mahlac the peak in activity is in the 3rd quarter (July-Sept) (80) (4) (1)

9. Of the 14 brown treesnakes that had stomach contents, 8 contained swiftlet carcasses Visual Interior Cave Search Male BTS (n = 15) Female BTS (n = 48) ** Initial 21 BTS caught in Mahlac not included prey bulge swiftlet remains swiftlet remains

10. Relative to other populations of BTS on Guam the size distribution at caves is skewed toward larger, female snakes * ectothermic prey * ectothermic prey

11. Brown treesnakes may currently be limiting Mariana swiftletrecovery and thus it is necessary to reduce BTS numbersin areas of conservation concern Objectives of Brown treesnake (BTS) Research at Mariana swiftlet Caves on Guam • Assess rate & characteristics of BTS in caves • Assess residency (stable isotope diet analysis) • Assess current operational control of BTS at caves • Assess control tool deployment design • Assess if BTS traps are beneficial in caves Photo by Jack Jeffrey

12. Assessment of whether BTS traps are beneficial in caves or are potentially attracting BTS and increasing predation risk Bird-Alone Station Bird-Alone Trt mouse-baited trap Mouse-Alone Station Mouse-Alone Trt Bird-Paired Trt Paired Station Mouse-Paired Trt bird-baited trap

13. Does the presence of mouse-baited traps result in an increase in catch-per-unit- effort (CPUE) of BTS in bird-baited traps? Bird-Alone Station Bird-Alone Trt Mouse-Alone Station Mouse-Alone Trt Bird-Paired Trt *mouse-baited traps do NOT increase risk of BTS contacting birds Paired Station Mouse-Paired Trt

14. Are mouse-baited traps effective at removing BTS when paired with bird-baited traps? Bird-Alone Station Bird-Alone Trt Mouse-Alone Station Mouse-Alone Trt Bird-Paired Trt *mouse-baited traps are effective at removing BTS in the presence of birds Paired Station Mouse-Paired Trt

15. Are mouse-baited traps drawing in more BTS to the focal area compared to bird-baited traps alone? Bird-Alone Station Bird-Alone Trt Mouse-Alone Station Mouse-Alone Trt Bird-Paired Trt *additional prey odor does not attract more snakes to an area Paired Station Mouse-Paired Trt

16. The BTS population is not as suppressed at stations with only bird-baited traps compared to stations with mouse-baited traps Catch per unit effort (CPUE) Time (week) bird-alone CPUE surpasses all other treatments

17. Multiple factors may have contributed to the decline of Mariana Swiftlets, but it appears BTS may be limiting recovery with larger, female snakes found in caves. • Deploying mouse-baited traps in focal areas may not increase predation risk on prey of concern and may alleviate risk by suppressing the BTS population

18. Co-authors: Kevin Brindock, Robert Reed, Amy Yackel Adams, MJ Mazurek, Will Pitt, Craig Stricker Questions? Additional Assistance: DoD Navy Stephen Mosher Project Management Lea’ Bonewell Colorado State University Björn Lardner Shane Siers Julie Savidge Guam-Based Biologists Thomas Hinkle Matthew Cook Meredith Campbell Elden Holldorf McKayla Spencer Kevin Donmoyer Justine Kaseman Marijoy Viernes Charlotte Robinson Patrick Barnhart Funding Sources Additional Partners