Wildlife and Ecosystem Conservation:
Post-Rat Eradication and Monitoring on Pinzón
Post-Rat Eradication and Monitoring on Pinzón
Charles Darwin Foundation; Galapagos National Park Directorate; Island Conservation
Funded in 2012; ongoing
Rat bait is dropped on Rabida Island in 2011. (Photo © GNPD)
The black rat (Rattus rattus), which was accidentally introduced to the archipelago by pirates and/or whalers in the 17th or 18th centuries, and the brown rat (Rattus norvegicus), are currently among the most serious threats to Galapagos biodiversity. Introduced rats, both black and brown, wreak havoc among the wildlife of Galapagos by preying on eggs and hatchlings of bird and reptile species, to such an extent that one species of Galapagos tortoise has had no natural recruitment for nearly a century, and some unique bird species have become critically endangered. Their control and possible eradication in specific sites is a major priority for conservation in the islands.
Recent successes in rodent eradications on a number of small- and medium-sized islands (e.g., Rábida, 499 ha was the largest) in the Galapagos Islands have provided conservation managers sufficient knowledge and expertise to carry out the planned rat eradication on Pinzón (1815 ha) in 2012, with little risk to native fauna and flora. This represents the largest island within the archipelago from which rats will be completely removed.
Pinzón is home to giant tortoises (approximately 100 of the original old natives and an estimated 400 repatriated tortoises ranging in age from 5-40 years old), snakes, lava lizards, hawks, passerine birds including several species of Darwin’s finches, and endemic invertebrates and vegetation. Recent toxicological studies on reptiles and experience in maintaining hawks in captivity during the period of risk (method used during eradication on Rábida and other small islets) have filled those knowledge gaps and helped quantify and mitigate potential risk to non-target species.
Phase one of the project — assessing the potential risk to non-target species, calibrating the application rate of toxic baits and logistical planning — has been completed. Phase two, the shortest and most expensive part of the work, is the application of approximately 40 tons of bait by means of helicopter. The final phase of the project will be long-term monitoring of ecosystem recovery.
Timeline: Rats in Galapagos
- 17th Century: First introductions of black rats and mice to Galapagos at Santiago Island, by privateers.
- 18th Century: Introductions continue as whalers and privateers continue to use Galapagos as a base in the South Pacific.
- 1835: First specimen of introduced rat collected by Charles Darwin from Santiago island.
- 1891: Black rats collected on Floreana and San Cristobal following human colonization. Black rats collected on Pinzón, probably introduced by whalers in previous century.
- 1929: Last collections of endemic rice rats on Santa Cruz Island.
- 1942: Black rats established on Baltra and from there to Santa Cruz. Continuing introductions on smaller and uninhabited islands.
- 1965: Tortoise rearing program initiated for Pinzón tortoises because of no recruitment in the 20th century due to depredation by rats.
- Early 1980’s: Brown rat introduced to Santa Cruz and San Cristobal; unsuccessful control attempts on Venecia and Mosquera islets.
- 1981: Galapagos petrel population on Floreana decrease of 33% due to predation by rats.
- 1983: First successful control of black rats at Cerro Pajas, Floreana (Galapagos petrel breeding colony). Black rats found on Pitt Islet.
- 1984: Endemic rice rats on Santa Cruz driven to extinction by black rats.
- 1988: Unsuccessful rat eradication attempt on Pinzón.
- 1989: Black rats eradicated on Pitt Islet. 1990: Black rats increasing on Pinzón after unsuccessful eradication.
- 1994: Brown rat found on Rábida and suspected on Isabela.
- 1996: Storm petrel reproduction on San Cristobal severely impacted by rats.
- 1997: small population of endemic rice rats discovered on Santiago (had been considered extinct since collected in 1906).
- 1998: Black rats successfully eradicated from the Mariela islets.
- 2000: Rat eradication begun on 4 of the Bainbridge islets.
- 2002: Rat eradication on 2 of the Bainbridge islands confirmed successful. Unsuccessful eradication attempt on Lobos Island.
- 2007: Hawksglen Foundation support investigation of remaining endemic rice rats on Santiago and the population on Santa Fe. Galapagos Conservation Trust, Galapagos Conservancy and Lindblad/National Geographic Fund supported Plan Pinzón, prepared with input from international experts. Rats eradicated from North Seymour and Mosquera thanks to support from Ken and Diane Saladin.
- 2008: Galapagos Conservancy and Lindblad/National Geographic Fund commit support for Project Pinzón. Boston Environmental agrees to fund rat eradication trials.
- 2009: Lindblad/National Geographic Fund, Frankfurt Zoological Society and Keidanren Nature Conservation Fund confirm support for rat eradication. North Seymour still rat free. Mangrove finch reproductive success considerably improved by rat control in nesting area on western Isabela.
- 2010: Summary of black rat colonization in Galapagos: At least 35 islands and islets and currently present on over 90% of land area. CDF and partners compiled list of non-target species on islands where eradications are being planned. New bait trialed on North Plazas.
- 2011: First toxicity trials on reptiles (non-target animals) carried out. Non-target risk assessment produced and approved by authorities. Rat eradication carried out on Rábida and islets around Santiago. after temporary resettlement of all hawks found on Rábida, Bartolomé, Bainbridge 3, and Sombrero Chino to aviaries on Santiago.
- 2012: Black rats successfully eradiated from Pinzón Island.
- 2014: First group of tortoise hatchlings encountered on Pinzón Island in over 100 years, following the rat eradication.