PE Klug, KM Brindock, RN Reed, AA Yackel Adams, MJ Mazurek, WC Pitt, CA StrickerNational Military Fish and Wildlife Association

March 2014 E-mail: pklug@usgs.gov

Protection of Caves Important to the Endangered Mariana Swiftlet through Effective Deployment of Control Tools

Based on Brown Treesnake Behavior

Prior to the introduction of the invasive brown treesnake (BTS) the island of Guam had a sustainable avian community

Native species still on Guam

Native species extinct or extirpated from Guam

Non-endemic bird species extirpated from Guam

Native forest species still breeding on

Guam

The Mariana swiftlet is the last sustainable breeding population of native forest bird on Guam

Native species still on Guam

Native species extinct or extirpated from Guam

Non-endemic bird species extirpated from Guam

Native forest species still breeding on

Guam

The Mariana swiftlet currently occupies 3 caves on Guam

Population estimate = 1224 ± 164 birdsMahlac: 1031 ± 201Maemong: 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 trapsMahlac = 40, Maemong = 29, Fachi = 25 traps

• Bait tubes added to perimeter trap lineMahlac = 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

Objectives of Brown treesnake (BTS) Research at Mariana swiftlet Caves on Guam1. Assess rate & characteristics of BTS in caves2. Assess residency (stable isotope diet analysis)3. Assess current operational control of BTS at caves4. Assess control tool deployment design5. 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 Guam1. Assess rate & characteristics of BTS in caves2. Assess residency (stable isotope diet analysis)3. Assess current operational control of BTS at caves4. Assess control tool deployment design5. 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

After initial suppression of BTS in Mahlac the peak in activity is in the 3rd quarter (July-Sept)

(80)

(1)

(4)

Male BTS (n = 15)

** Initial 21 BTS caught in Mahlac not included

Female BTS (n = 48)

Visual Interior Cave Search

Of the 14 brown treesnakes that had stomach contents, 8 contained swiftlet carcasses

swiftlet remains

prey bulgeswiftlet remains

Relative to other populations of BTS on Guam the size distribution at caves is skewed toward larger, female

snakes

ectothermic prey

ectothermic prey

*

*

Objectives of Brown treesnake (BTS) Research at Mariana swiftlet Caves on Guam1. Assess rate & characteristics of BTS in caves2. Assess residency (stable isotope diet analysis)3. Assess current operational control of BTS at caves4. Assess control tool deployment design5. Assess if BTS 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

Assessment of whether BTS traps are beneficial in caves or are potentially attracting BTS and increasing predation risk

Bird-Alone Trt

Mouse-Alone Trt

Mouse-Paired Trt

Bird-Paired Trt

mouse-baited trap

bird-baited trap

Paire

d St

ation

Mou

se-A

lone

St

ation

Bird

-Alo

ne

Stati

on

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 Trt

Mouse-Alone Trt

Mouse-Paired Trt

Bird-Paired Trt

Paire

d St

ation

Mou

se-A

lone

St

ation

Bird

-Alo

ne

Stati

on

*mouse-baited traps do NOT

increase risk of BTS contacting

birds

Are mouse-baited traps effective at removing BTS when paired with bird-baited traps?

Bird-Alone Trt

Mouse-Alone Trt

Mouse-Paired Trt

Bird-Paired Trt

Paire

d St

ation

Mou

se-A

lone

St

ation

Bird

-Alo

ne

Stati

on

*mouse-baited traps are

effective at removing BTS in the presence of

birds

Are mouse-baited traps drawing in more BTS to the focal area compared to bird-baited traps alone?

Bird-Alone Trt

Mouse-Alone Trt

Mouse-Paired Trt

Bird-Paired Trt

Paire

d St

ation

Mou

se-A

lone

St

ation

Bird

-Alo

ne

Stati

on

*additional prey odor does not attract more

snakes to an area

bird-alone CPUE surpasses all other treatments

The BTS population is not as suppressed at stations with only bird-baited traps compared

to stations with mouse-baited traps

Time (week)

Catc

h pe

r uni

t effo

rt (C

PUE)

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

Questions?

Funding Sources

Additional Partners

Additional Assistance:

DoD NavyStephen Mosher

Project ManagementLea’ Bonewell

Colorado State UniversityBjörn Lardner

Shane SiersJulie Savidge

Guam-Based BiologistsThomas HinkleMatthew Cook

Meredith CampbellElden Holldorf

McKayla SpencerKevin DonmoyerJustine KasemanMarijoy Viernes

Charlotte RobinsonPatrick Barnhart

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