ICS wages war on feral cats, chickens and rats on Alphonse, soon to extend to other Islands

When people first started to settle on the Outer Islands, they also brought with them—albeit sometimes inadvertently—invasive species such as rats. They also brought cats for company and chickens as a food source. Today, these same species are causing a rampage on the biodiversity of our islands, creating an urgent need for eradication.

Because of human activities it is common nowadays to hear a rooster crowing at dawn on several Outer Islands of the Seychelles. While this is very traditional, for conservation however, domesticated animals gone wild and pests such as rats are not necessarily ideal in these circumstances as they can have devastating effect on the biodiversity of these islands.

Alphonse has been assessing and implementing measures to protect existing biodiversity on the island against such wild animals and pests since 2007, and today we take a look at proceedings there to eradicate existing threats through the lens of the Island Conservation Society (ICS) the "guardian of the custodian" on the island.

“Whilst we get large numbers of roosting seabirds, our breeding populations have always been small with low success rate,” states Conservation Officer, Jack Coupland. Conservationists believe that this could be a result of the high incidences of predators such as cats and rats on the island. Both cats and rats are incredibly adept predators as they are known to climb up trees to take down fledglings, grappling them off their perch before forcing them to the ground and consuming them. Similarly, chickens are also considered invasive since they compete for the same source of food as small reptiles, and share the same habitat as ground-breeding species and their foraging habit disrupts the ecosystem.

In 2024, it was estimated that the main island of Alphonse had a population of around 400 chickens and over 30 cats. To curtail this, ICS and its partners on the island have for the past seven months employed a full time staff to help with the eradication efforts of both feral cats and chickens. According to Coupland, so far, the team have exterminated 21 cats and over 200 chickens on Alphonse Island. ICS is also ramping up a combination of baiting, scent marking, and specific attracting calls to successfully eliminate the remaining cats and chickens in the most humane way possible.

Already regular trapping of rats around the island using passive baiting stations has proved successful on the existing colony of Wedge-tailed shearwater, a seabird species that dig burrows underground to lay eggs. Since the introduction of active pest control on Alphonse in 2017, the population of this species have been growing exponentially. This is great news, not just for the species, but for the island as a whole, as seabirds transfer huge amounts of nutrients from the sea to land – known as the marine subsidy – that then trickles down through the ecosystem benefiting a wide range of species, including the coral reefs and reef fish.  
Eradication of cats, chickens, and rats may seem heartless but there is a much larger mission at stake for Conservationists: preventing them from traveling to other islands in the Group; namely St Francois atoll, where coconut crabs and other ground-dwelling species are in abundance. The atoll is currently one of the rare places in Seychelles which is ‘predator-free’.

Total elimination of all three species however will take time and is already proven to be very costly for Alphonse Island which has a land area of 165 hectares made up of dense coconut trees and ferns. The ongoing efforts on Alphonse are estimated to cost ICS upwards of 20,000 USD monthly and over 50,000 USD annually. However, this is a small cost compared to the long-term cumulative damages inflicted by predatory species and ICS has plans to introduce similar vigorous eradication projects on other islands. Already, Desroches Island has benefitted through a SeyCCAT-funded project, where sophisticated rat traps have been installed to protect its Shearwater colony. The devices do not need to be checked every day, automatically share the number of kills they have completed via Bluetooth to the Conservation Officer’s phone.  Coupled with this, ICS and its partners through the Islands Development Company (IDC) are actively trapping rats, and an astounding 300 rats are killed per month. However, cats and chickens remain loose on the island and their total population is still uncertain. Similarly, on Ile Plate, there is ongoing trapping of rats, but the estimated over 200 chickens and at least 20 cats are not being targeted. A short bout of two months of active shooting and baiting by ICS resulted in reducing the population of both chickens and cats by half.

The same cannot be said for bigger islands such as Farquhar Atoll which covers an area of about 17,800 hectares. A massive project would be required to eradicate cats and chickens on the Atoll. Hence, ICS and its partners are only passively baiting for rats and cats, but lacks the resources and funds to aggressively eradicate them.

The same applies to Silhouette island, the largest terrestrial National Park of Seychelles – home to the rarest and smallest bats in the world, the endemic Seychelles Sheath-tailed bats (Coleura seychellensis or Sousouri bannann) – where gains have been slow and hard-won. Cats have been seen preying on these small bats that live in caves not far from the human population. Active trappings around the roost and around the island are targeting both rats and cats which their effect on the biodiversity cannot be underestimated. 
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Through careful management, key predators are slowly being removed on several islands. ICS’ efforts to control the population of cats, rats, and chickens and eventually eradicate them completely from Alphonse is proof that this process is an arduous one.                                                 

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