Evidence that eradicating black rats ( Rattus rattus ) has boosted the

Evidence that eradicating black rats Evidence that eradicating black rats

((Rattus rattusRattus rattus) has boosted the ) has boosted the

recovery of rare reptiles and recovery of rare reptiles and

seabirds on Antiguan islands.seabirds on Antiguan islands.

Jenny C. Daltry Jenny C. Daltry

Fauna & Flora InternationalFauna & Flora International

Karron J. JamesKarron J. James, , Andrea OttoAndrea Otto, and , and

Toby N. RossToby N. Ross

Environmental Awareness GroupEnvironmental Awareness Group

Antiguan Racer Conservation Project, AntiguaAntiguan Racer Conservation Project, Antigua

Study area: Study area: The Offshore Islands of AntiguaThe Offshore Islands of Antigua




• More than 30 islands

• Range from <0.1 to 184 hectares.



• More than 30 islands

• Range from <0.1 to 184 hectares.

• Mix of private and state-owned

• Nearly all colonised by Black Rats (Rattus rattus)

Black or Ship Rat (Black or Ship Rat (Rattus rattusRattus rattus))OmnivorousOmnivorousNative to India/Central AsiaNative to India/Central Asia


Antiguan Racer (Antiguan Racer (Alsophis antiguaeAlsophis antiguae))Critically EndangeredCritically EndangeredEndemic to AntiguaEndemic to Antigua


Antiguan Racer (Antiguan Racer (Alsophis antiguaeAlsophis antiguae))Critically EndangeredCritically EndangeredEndemic to AntiguaEndemic to Antigua


• Vanished from mainland Antigua after Asian mongooses were introduced (1890s).

• By 1980s, the snakes were only on Great Bird Island (8.4 hectares)

Great Bird Is.

Mark-recapture study in 1995 found 50 ± 7 individuals.Mark-recapture study in 1995 found 50 ± 7 individuals.More than 50% of the snakes had injuries consistent More than 50% of the snakes had injuries consistent with rat bites.with rat bites.


Great Bird Island

Rat eradication programme began in 1995.Rat eradication programme began in 1995.Forestry staff and NGO volunteers eradicated rats from Forestry staff and NGO volunteers eradicated rats from Great Bird Island and neighbouring islands.Great Bird Island and neighbouring islands.


Methods:

• Cut grid (10x10m or 20x20m) across each island (4-6 weeks).

• Placed brodifacoum briquettes (KleratTM) on grid intersections (3 weeks).

Rat eradication programme began in 1995.Rat eradication programme began in 1995.Forestry staff and NGO volunteers eradicated rats from Forestry staff and NGO volunteers eradicated rats from Great Bird Island and neighbouring islands.Great Bird Island and neighbouring islands.


Methods:

• Cut grid (10x10m or 20x20m) across each island (4-6 weeks).

• Placed brodifacoum briquettes (KleratTM) on grid intersections (3 weeks).

• 100% effective on every island.

Black Rats were eradicated from 12 islands between Black Rats were eradicated from 12 islands between 1995 and 2006.1995 and 2006.(Two islands were re-invaded by rats).(Two islands were re-invaded by rats).


x

x

Permanent bait stations in use since 2001. Permanent bait stations in use since 2001. Designed to detect and kill invading rats.Designed to detect and kill invading rats.


Methods:

• Use commercial bait stations for rats.

• Stations raised off ground to exclude crabs.

• Contain KleratTM

0.005% brodifacoum

• 80 stations, checked every 5-6 weeks.

Antiguan Racer population more than doubled within Antiguan Racer population more than doubled within two years of eradicating rats from Great Bird Island.two years of eradicating rats from Great Bird Island.


Methods:

• Standard mark-recapture study every 1-2 years.

• Snakes marked using PIT tags.

• Use Begon’s (1979) Weighted Mean estimator.

Antiguan Racers have been re-introduced from Great Antiguan Racers have been re-introduced from Great Bird Island to 3 islands (after eradicating rats).Bird Island to 3 islands (after eradicating rats).

• Rabbit Island (1999)

• Green Island (2002)

• York Island (2008)

All three colonies are breeding well.


Rabbit

Green Is.

York Is.

Great Bird Is.

10 x incease in snake population since rat eradication 10 x incease in snake population since rat eradication programme began.programme began.


Seabirds and pigeon colonies have been monitored by Seabirds and pigeon colonies have been monitored by the authors and local volunteers.the authors and local volunteers.


Massive increase in seabird and pigeon colonies after Massive increase in seabird and pigeon colonies after eradicating rats.eradicating rats.

Breeding pairs of birds on Great Bird Island and the Galley Islands


Massive increase in seabird and pigeon colonies after Massive increase in seabird and pigeon colonies after eradicating rats.eradicating rats.

Breeding pairs of birds on Rabbit, Redhead and Lobster Islands


• Antigua’s offshore islands were designated an Important Bird Area in 2009.

• The seabird colonies are becoming a tourist attraction.

Could these increases be due to factors other than Could these increases be due to factors other than removing rats?removing rats?


A rapid survey was conducted in 2010 to compare A rapid survey was conducted in 2010 to compare islands with and without rats.islands with and without rats.

Seabird survey conducted in June 2010:

• 6 islands with rats present.

• 9 islands cleared of rats by OICP

• 9 very small islets never known to have rats.

Standardized methods used for every species.


No breeding seabirds were found on the rat-infested No breeding seabirds were found on the rat-infested islands. islands.

RATS PRESENTRATS REMOVEDNEVER HAD RATS?

Breeding pairs of seabirds on offshore islands, June 2010


1995

1995

1995

1998

1998

1998 19

98

2001

2006

• Other bird species

• Marine turtles

• Lizards

• Land snails

Anecdotal evidence that other species are more Anecdotal evidence that other species are more abundant on rat-free islands.abundant on rat-free islands.More research needed.More research needed.


• Direct predation of eggs, young, even adults.

• Depletion of prey/ food sources.

• Gross changes to habitats.

How do rats affect animal populations? How do rats affect animal populations?


Great Bird Island

1995 – Just before rats were eradicated

BirdsBirds

Great Bird Island

2005 – After 10 years without rats.


Some Lessons Learned: Some Lessons Learned:

1. Black rats do have seriously harmful impacts on 1. Black rats do have seriously harmful impacts on Antiguan biodiversity. Antiguan biodiversity.

2. Rats can be controlled, even in public areas, and t2. Rats can be controlled, even in public areas, and the he recovery of native species can be very rapid.recovery of native species can be very rapid.

3. Ideally, monitoring of flora and fauna should begin 3. Ideally, monitoring of flora and fauna should begin before rats are eradicated.before rats are eradicated.


4. Restoring islands also has a powerful social impact: 4. Restoring islands also has a powerful social impact: This project has motivated many people from diverse This project has motivated many people from diverse backgrounds to become conservationists.backgrounds to become conservationists.

Acknowledgements


Project PartnersProject Partners

Forestry Unit, Ministry of AgricultureForestry Unit, Ministry of Agriculture

Environmental Awareness Group (EAG)Environmental Awareness Group (EAG)

Fauna & Flora International (FFI)Fauna & Flora International (FFI)

Island Resources FoundationIsland Resources Foundation

Durrell Wildlife Conservation TrustDurrell Wildlife Conservation Trust

Black Hills State UniversityBlack Hills State University

Co-sponsorsCo-sponsors

Disney Worldwide Conservation FundDisney Worldwide Conservation Fund

Mohammen bin Zayed Conservation FundMohammen bin Zayed Conservation Fund

Syngenta (donate KleratSyngenta (donate KleratTMTM))

USFWS – Critically Endangered Animals Conservation FundUSFWS – Critically Endangered Animals Conservation Fund

USFWS – Neotropical Migratory Birds Conservation ActUSFWS – Neotropical Migratory Birds Conservation Act

Documents

Evidence that eradicating black rats ( Rattus rattus ) has boosted the