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
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
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
The Mariana swiftlet currently occupies 3 caves on Guam
Population estimate = 1224 ± 164 birds
Mahlac: 1031 ± 201
Maemong: 97 ± 44
Fachi: 49 ± 35
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
Brown treesnakes may currently be limiting Mariana
swiftlet recovery and thus it is necessary to reduce BTS
numbers in areas of conservation concern
Objectives of Brown treesnake (BTS) Research at Mariana swiftlet Caves on Guam
1.
2.
3.
4.
5.
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
Brown treesnakes may currently be limiting Mariana
swiftlet recovery and thus it is necessary to reduce BTS
numbers in areas of conservation concern
Objectives of Brown treesnake (BTS) Research at Mariana swiftlet Caves on Guam
1.
2.
3.
4.
5.
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
After initial suppression of BTS in Mahlac the
peak in activity is in the 3rd quarter (July-Sept)
(80)
(4)
(1)
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
Relative to other populations of BTS on Guam the size
distribution at caves is skewed toward larger, female snakes
ectothermic prey
*
*
ectothermic prey
Brown treesnakes may currently be limiting Mariana
swiftlet recovery and thus it is necessary to reduce BTS
numbers in areas of conservation concern
Objectives of Brown treesnake (BTS) Research at Mariana swiftlet Caves on Guam
1.
2.
3.
4.
5.
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
Bird-Alone
Station
Mouse-Alone Trt
Paired Station
Bird-Alone Trt
Mouse-Alone
Station
Assessment of whether BTS traps are beneficial in caves or
are potentially attracting BTS and increasing predation risk
mouse-baited trap
Bird-Paired Trt
Mouse-Paired Trt
bird-baited trap
Bird-Alone
Station
Mouse-Alone Trt
Paired Station
Bird-Alone Trt
Mouse-Alone
Station
Does the presence of mouse-baited traps result in an increase
in catch-per-unit- effort (CPUE) of BTS in bird-baited traps?
Bird-Paired Trt
Mouse-Paired Trt
*mouse-baited
traps do NOT
increase risk of
BTS contacting
birds
Bird-Alone
Station
Mouse-Alone Trt
Paired Station
Bird-Alone Trt
Mouse-Alone
Station
Are mouse-baited traps effective at removing BTS when
paired with bird-baited traps?
Bird-Paired Trt
Mouse-Paired Trt
*mouse-baited
traps are effective
at removing BTS
in the presence of
birds
Bird-Alone
Station
Mouse-Alone Trt
Paired Station
Bird-Alone Trt
Mouse-Alone
Station
Are mouse-baited traps drawing in more BTS to the focal area
compared to bird-baited traps alone?
Bird-Paired Trt
Mouse-Paired Trt
*additional prey
odor does not
attract more
snakes to an area
Catch per unit effort (CPUE)
The BTS population is not as suppressed at
stations with only bird-baited traps compared
to stations with mouse-baited traps
Time (week)
bird-alone CPUE surpasses
all other treatments
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
Co-authors: Kevin Brindock, Robert Reed, Amy Yackel Adams, MJ Mazurek, Will Pitt, Craig Stricker
Additional Assistance:
Funding
Sources
DoD Navy
Stephen Mosher
Project Management
Lea’ Bonewell
Additional Partners
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
Questions?