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About the territory

The Bailiwick of Guernsey is part of the Channel Islands, and the last portion of the Duchy of Normandy remaining to the English Crown. In 1204 the rest of Normandy was lost to the French but the Channel Islands remained loyal to the English Crown. The islands are governed by their own parliaments; the States, in Guernsey & Alderney, and the Chief Pleas, in Sark.


Map of Guernsey

The Bailiwick of Guernsey consists of a group of islands situated in the English Channel, in the Gulf of St. Malo. The largest island is Guernsey with the capital, St Peter Port, at latitude 49°28′ North, longitude 2°32′ West; about 100km from England and 45km from France. There are seven inhabited islands and a number of uninhabited islets. The area of Guernsey is 63 km² with a population of 63,329. The other major islands are Alderney, 8 km² with a population of about 2400; Sark, 5 km² and a population of 600; Herm, only 2 km² and 60 inhabitants. The Bailiwick also has an intertidal zone of 1,240 hectares.


Guernsey has about 30 classes of vegetation, with grasslands being the dominant vegetation. The most threatened habitats are saltmarshes, dune slacks and open dune. As the islands are closer to France than the British Isles, Guernsey has a different set of species from most of the UK; the terrestrial species found are effectively a subset of those in North West France. Species lists can downloaded from this link: https://www.biologicalrecordscentre.gov.gg/

Guernsey Biological records Centre has recorded 4,449 species of plants and fungi, 5,757 species of insect, and 2,427 other invertebrate species. In December 2019, 354 avian species were recorded in the Bailiwick of Guernsey, however, only about 74 are breeding species. A working list of the birds of the Channel Islands is available to view at:  http://www.jerseybirds.co.uk/news/files/articles/working-list-of-ci-birds-to-dec-2019.pdf, Seabirds are the most important bird populations in the Bailiwick which boasts 1% of the World’s Northern Gannets.

There are 318 other vertebrates. This includes at least seven species of bat, however only three of these are common; the Common pipistrelle Pipistrellus pipistrellus (most common), then Natterer’s bat Myotis nattereri and the Grey long-eared bat Plecotus austriacus.

The Guernsey vole, Microtus arvalis sarnius, is endemic to Guernsey. The greater white-toothed shrew Crocidura russula is found in Guernsey, Herm & Alderney; it was recently introduced to Ireland but otherwise is not known in the British Isles. The lesser white-toothed shrew Crocidura suaveolens found on Sark is otherwise known only from Jersey & the Scillies. According to Edgar (2010) there are four indigenous species of amphibian and reptile, and one introduced species -the Western green lizard Lacerta bilineata.

Probably brown Long-eared bat Plecotus auritus (but not yet officially confirmed)

Policy and legislation

The Bailiwick of Guernsey has been included in the UK’s ratification of six multilateral environmental agreements (MEAs), these include the Convention on International Trade in Endangered Species (CITES), Convention on the Conservation of Migratory Species and Wild Animals (The Bonn Convention), and the Convention on Wetlands of International Importance especially as Waterfowl (Ramsar Convention). The Convention on Biological Diversity is extended to Jersey and recently to the Isle of Man but has yet to be extended to Guernsey. Limited local legislation is in place to protect wild birds and wildflowers, fifty sites in Guernsey have been recognized as Sites of Scientific Interest (SSSI’s) and Sites of Nature Conservation Interest (SNCIs), but they have little legal protection.

Invasive species & biosecurity

The Global Invasive Species Database (GISD) lists five alien invasive species: Sour fig Carpobrotus edulis, Parrot’s feather, Myriophyllum aquaticum, Japanese knotweed Polygonum cuspidatum , Japanese wire weed Sargassum muticum, and Leathery sea squirt, Styela clava. The carrier pigeon, Columba livia, is a native invasive species. Introduced mammals include rabbits Oryctolagus cuniculus, ferrets (Mustela furo),  hedgehogs Erinaceus europaea, signal crayfish (Pasifastacus leniusculus), house mouse Mus musculus, brown and black rats Rattus norvegius & R. rattus.

A third of the vascular plants in the Bailiwick are non-native, many of these are of no concern. Some invasive species are native. The Wild Plants Protection Ordinance (1950) prohibits the sale of wild plants without the permission of the Environment Department. The Noxious Weeds (Guernsey) Law (1952) as amended by The Noxious Weeds Ordinance (2001) makes it illegal for landowners to allow certain species of plants to flower and set seed. Currently these are: Ragwort Senecio jacobaea, Hemlock Water Dropwort Oenanthe crocata, and the thistles Cirsium vulgare and Cirsium arvense.

Problems with invasive non-native species

Rats are a particular concern as they spread disease and are a threat to breeding birds.

Sour fig is very invasive in coastal and dune grassland and scrub. It causes smothering, reduced regeneration of native flora and changes to soil pH and nutrient regimes. Parrot’s feather chokes small ponds and wetland areas, it is overwhelming all but the most robust plants (Soft Rush Juncus effusus , Great Water Dock Rumex hydrolapathum and Sallow Salix cinerea) in the St Sampson’s Marais in Guernsey. Japanese knotweed forms dense stands that shade and crowd out all other vegetation, displacing native flora and fauna, and the overwintering canes and leaves are slow to decompose. It does not yet seem to be as much of a problem in the Bailiwick of Guernsey as it is in the UK. Japanese wire weed forms dense monospecific stands which reduce light, decrease flow, increase sedimentation and reduce ambient nutrient concentrations available for native kelp species. It has also become a major nuisance in recreational waters. Leathery sea squirt easily establishes wherever it is introduced. It can reach extreme densities and out-compete native organisms for food in the water column. It also predates on the larvae of native species causing population declines. It is a nuisance to mussel and oyster farmers.

New Zealand Pigmy Weed, Crassula helmsii is a non-native invasive species not listed on the GISD database but the Guernsey Biological Records Centre states that it is an even worse problem than Parrot’s feather, particularly in Mannez Quarry in Alderney and La Société Guernesiaise’s nature reserve at Rue des Bergers in La Grande Mare in Guernsey.

Priority invasive non-native species and actions

Asian hornets were first recorded in Guernsey in 2017. The following year, 8 secondary nests were destroyed. In 2019 the States of Guernsey implemented the Asian Hornet Strategy and employed specialist staff to raise awareness, locate and destroy all Asian hornets found on the island (including Herm and Sark).

Extensive attempts have been made by the Guernsey Conservation Volunteers manually removing Sour fig, but large amounts are in inaccessible locations on the cliffs. The Alderney Wildlife Trust also runs Sour fig removal events throughout the year.

Following the discovery of a number of discrete populations of Himalayan balsam in 2020 and 2021 there is now an active campaign encouraging the general public to report sightings of this invasive plant so that it can be eradicated where it occurs. It is not thought to be widely established along the many island douits (streams) or on wetland nature reserves.


The Department of Agriculture, Countryside and Land Management Services are building on the success of the Asian hornet strategy and are currently developing an Invasive Non-Native Species (INNS) Action Plan to be implemented in 2022/23. This plan covers three key areas, biosecurity, early detection and rapid response and management of established INNS. A portal will be developed within the Guernsey Biological Records Centre website to inform the public about newly prioritised invasive threats (identified by horizon scanning) and facilitate the reporting of these invasive species.


Rural Tree Planting Scheme (1992 – 2006): In response to Dutch elm disease 180,000 trees were planted on over 800 sites across Guernsey, Herm & Sark.

The Asian Hornet Team verify all reported sightings of Asian hornets across the Bailiwick of Guernsey and coordinate the control programmes across the other islands which includes Alderney, Herm, Jethou and Sark. Further information is available at https://www.gov.gg/asianhornet and a dedicated Facebook page at Asian Hornet Team – Guernsey https://www.facebook.com/asianhornetguernsey/

Useful information


Guernsey Biological Records Centre Manager   gsybiorecords@gmail.com

Asian Hornet Strategy – asianhornet@gov.gg

La Société Guernesiaise - Secretary@societe.org.gg

Guernsey Trees for Life - https://www.trees.gg/


Edgar, P. (2010). The Amphibians and reptiles of the UK Overseas Territories, Crown Dependencies and Sovereign Base Areas: Species Inventory and Overview of Conservation and Research Priorities (external link). Bournemouth, UK: Amphibian and Reptile Conservation.