black rats

Despite the presence of invasive black rats (Rattus rattus), common mynas (Acridotheres tristis), and feral domestic cats (Felis catus), sooty terns (Onychoprion fuscatus) breed in large numbers on Ascension Island in the tropical South Atlantic Ocean. These introduced predators impact the terns by destroying eggs or interrupting incubation (mynas), eating eggs (mynas and rats), eating chicks (rats and cats), or eating adults (cats). Between 1990 and 2015, 26 censuses of sooty terns and five of mynas were completed and myna predation was monitored on 10 occasions.

Invasive alien species are one of the primary threats to native biodiversity on islands worldwide, and their expansion continues due to global trade and travel. Preventing the arrival and establishment of highly successful invasive species through rigorous biosecurity is known to be more economic than the removal of these species once they have established. However, many islands around the world lack biosecurity regulations or practical measures and establishing biosecurity will require social and financial investments.

Since 1999, the black rat (Rattus rattus) has been eradicated from 14 Italian islands, and eradication is ongoing on a further five islands. Most projects were funded by the European Union (EU) Life Programme. Over the years, eradication techniques have been improved and adapted to different situations, including aerial bait distribution on islands with large inaccessible areas, which otherwise would have relied on a manual bait distribution.

The Chagos Archipelago comprises some 58 islands covering 5,000 ha in the centre of the Indian Ocean. Black rats (Rattus rattus) were introduced about 230 years ago and have likely had a severe impact on the native terrestrial fauna, which is dominated by seabirds and land crabs. Most of the archipelago’s terrestrial land mass is vegetated with old coconut plantations, with over 75% of the native forest cleared for coconut from 26 of the largest islands.

Invasive black rats (Rattus rattus) were successfully eradicated during 2012 from Pinzon Island in the Galapagos archipelago using the rodenticide brodifacoum. Potential exposure to brodifacoum in Pinzon tortoises (Chelonoidis ephippium), Pinzon lava lizards (Microlophus duncanensis) and Galapagos hawks (Buteo galapagoensis) was mitigated by captive holding of subpopulations. This was successful for all species during and shortly after baiting, however mortality of Galapagos hawks occurred post-release, likely due to the persistence of residual brodifacoum in lava lizards.

The introduction of invasive rats, goats, and rhesus macaques to Desecheo National Wildlife Refuge, Puerto Rico led to the extirpation of regionally signifi cant seabird colonies and negatively impacted plant and endemic reptile species. In 2012, following the successful removal of goats and macaques from Desecheo, an attempt to remove black rats using aerially broadcast rodenticide and bait stations was unsuccessful.

Rat eradication techniques developed in New Zealand are a proven method for removing invasive rodents from islands worldwide. This technology moved rapidly from ground-based bait station operations to aerial application of rodenticides. Rat eradications on tropical islands using similar methods, have not always been as successful as those in temperate regions. As most previous eradications in the Caribbean have been on islands smaller than 50 ha, the eradication of black rats (Rattus rattus) from 207 ha Dog Island was a significant increase in size.

Rodent predation on eggs and chicks is one of the main threats to procellariiform species in the Mediterranean, where the black rat (Rattus rattus) and brown rat (R. norvegicus) have been present on many islands for centuries. The yelkouan shearwater (Puffinus yelkouan) is an endemic Mediterranean seabird species classified as vulnerable. Malta holds up to 10% of the global population; the largest colony, Rdum tal-Madonna (RM), protected as a Natura 2000 site, hosts around 500 breeding pairs. This colony has been monitored since its discovery in 1969.