Invaseive Species Week - Non-native Birds
Non-native species may have been introduced by humans either on purpose such as pheasants for shooting or by accident such as exotic cage birds escaping. Some non-native species can upset the ecological balance in an area and threaten native wildlife but not all non-native species are harmful. It is hard to determine which species will become a problem, as the examples below will demonstrate, but when a non-native species does establish itself and thrive to the detriment of the native ecosystem this species is known as an invasive species.
The Ring-Necked Parakeet is the UK’s only naturalised parrot with an estimated 8600 pairs now found in parks and gardens. The stronghold of the population is Greater London, the south-east and south-west of England but they are colonising areas further afield and have been recorded as far north as the Scottish borders and west into Wales. Popular pets since Victorian times, inevitably some birds escaped and survived in the wild. However, it wasn’t until 1969 that breeding was confirmed in Kent. The species has gone from strength to strength and can survive our less than tropical winters. The ring-necked parakeet favours holes in trees as nesting sites and can out compete native species such as woodpeckers, nuthatches and starlings for these sites. Like all birds living in the wild in the UK they are protected by law but can be culled under licence where they represent a serious threat to the conservation of a native species, are damaging crops or present a risk to air safety near airports.
When thinking about invasive bird species it is hard to look past the Canada Goose, originally a native of North America. Although a few true migrants of this species do turn up on the west coast of Scotland, the majority of the 200,000 UK birds are descended from birds introduced to stately homes by Victorian. They form large, noisy flocks and are often regarded as a nuisance in parks where they congregate and their droppings can pollute ornamental ponds and lakes.
The Little Owl, was introduced into Britain in the 19th century and found across much of England, although less common in Scotland and Wales. Often seen during daylight hours when they like to perch in trees or on telegraph poles, they have a characteristic way of bobbing their heads up and down when alarmed. Although a non-native species, the Little Owl has had no noticeable affect on native wildlife and would not be classed as invasive. The species has seen a decline in recent years, although the reasons for this are not fully understood. Current estimates for this species suggest that the population is around 5000 individuals, with a 24% decline between 1995 and 2008.
Although the “coo coo cuk” call of the Collared Dove appears to be a quintessential sound of a British village in spring, the species had not been recorded in Britain before the mid-1950s. When the first Collared Dove turned up on the North Norfolk coast in 1955 it was quite an event and many birders travelled to see it. When a pair breed in Norfolk the following year, the nest site was kept secret and guarded against egg collectors. By 1957 it was reported to be breeding in Lincolnshire and Kent and individuals were seen in Scotland that same year. By 1970 there was an estimated 25,000 breeding pairs in the UK. The species is native to Asia, and prior to the 1930s Turkey and the Balkans were the furthest west the species had spread. During the next 20 years the species expanded its range rapidly and colonised most of Europe and has now spread as far north as the Arctic circle in Norway, west to the Canary Islands and south to Morocco. The reasons for the sudden expansion have not been fully explained but theories suggest it may have been a genetic mutation combined with changes in farming and agriculture that enabled the species to spread and colonise so quickly. The Collared Dove is a non-native species that colonised the UK by natural means and is now regarded as part of the British fauna.
We are more careful today than in Victorian times when it comes to releasing species into the wild but the influence of humans on the environment in the form of agricultural intensification and climate change may mean we see more species colonise the UK over the coming decades.