USGS Brown Treesnake Research Overview:

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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_at_usgs.gov
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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
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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
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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
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Objectives of Brown treesnake (BTS) Research at
Mariana swiftlet Caves on Guam
Brown treesnakes may currently be limiting
Mariana swiftlet recovery and thus it is
necessary to reduce BTS numbers in areas of
conservation concern

1. Assess rate characteristics of BTS in caves
2. Assess residency (stable isotope diet analysis)
3. Assess current operational control of BTS at
   caves
4. Assess control tool deployment design
5. Assess if BTS mouse-baited traps are beneficial
   in caves

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Objectives of Brown treesnake (BTS) Research at
Mariana swiftlet Caves on Guam
Brown treesnakes may currently be limiting
Mariana swiftlet recovery and thus it is
necessary to reduce BTS numbers in areas of
conservation concern

1. Assess rate characteristics of BTS in caves
2. Assess residency (stable isotope diet analysis)
3. Assess current operational control of BTS at
   caves
4. Assess control tool deployment design
5. Assess if BTS mouse-baited traps are beneficial
   in caves

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After initial suppression of BTS in Mahlac the
peak in activity is in the 3rd quarter (July-Sept)
(80)
(4)
(1)
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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
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Relative to other populations of BTS on Guam the
size distribution at caves is skewed toward
larger, female snakes

ectothermic prey

ectothermic prey
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Objectives of Brown treesnake (BTS) Research at
Mariana swiftlet Caves on Guam
Brown treesnakes may currently be limiting
Mariana swiftlet recovery and thus it is
necessary to reduce BTS numbers in areas of
conservation concern

1. Assess rate characteristics of BTS in caves
2. Assess residency (stable isotope diet analysis)
3. Assess current operational control of BTS at
   caves
4. Assess control tool deployment design
5. Assess if BTS traps are beneficial in caves

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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
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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
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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
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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
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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
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1. 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.
2. 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

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Questions?
Co-authors Kevin Brindock, Robert Reed, Amy
Yackel Adams, MJ Mazurek, Will Pitt, Craig
Stricker
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