Parakeets in the UK: Invasive Species or Cosmopolitan Migrant?

The sun sets over a late autumn sky. The fading daylight produces magnificent hues of pink and red against which the trees of the park shimmer with what, at a distance, could be mistaken for green summer leaves – except these trees shed their leaves some weeks ago. Approaching the park, a cacophony of shrill squawks grows until the trees are almost vibrating, and what at first seemed like leaves is revealed to be the plumage of dozens of bright green birds – ring-necked parakeets, a bird from the parrot family native to the Indian subcontinent and North Africa. But this isn’t Pakistan or Morocco, this is a small park in central London.

Over the past few decades, parakeets have become so prevalent in parts of London that they may be second only to pigeons as the most commonly sighted bird. Almost obnoxiously bright and producing a high-pitched squawk that pierces the air, parakeets are difficult to miss. Often traveling in large groups of up to a dozen, they have a boisterous presence that sets them apart from the more understated birds – magpies, blue tits, robins, blackbirds – that are native to the city. Yet equally, they bring a vibrance and splash of color to the grey metropolis that make it difficult to avoid a comparison with the cultural enrichment brought to the city through the many waves of human migration that have made London the place it is today.

Myths abound as to the origin story of London’s parakeet population. Some claim Jimi Hendrix released a breeding pair in the late 60s; others believe several escaped from the movie set for The African Queen. The more likely explanation involves the scare around “parrot-flu” in the 1950s that led many pet-owners to release their parakeets into the wild. Whatever their origin, parakeets have now spread far beyond the confines of London, and I have personally seen them in large numbers as far North as Leeds and Manchester. Their incredible success is, however, leading to some concern amongst conservationists, who worry about the impact they may be having on native birds. It’s reasonable to assume that such a rapid population increase is leading to competition between parakeets and native birds for vital resources and territory. Yet little concrete data has been generated on their ecological impacts in the U.K., in part because it is simply too early to know.

The orthodox view within conservation biology, represented by the sub-discipline known as “invasion biology,” tends to see non-native species as bad news, especially with the rapid population and range expansions that the ring-necked parakeet in England has seen. This presumption against non-natives is a deeply entrenched principle, stemming from an understanding that sees ecosystems as the result of the co-evolution of communities of species over long periods of time. The resulting adaptations and behaviors are uniquely suited for that specific community. On such a view, the introduction of a new species is bound to result in harm – new species are unlikely to have natural predators to keep their population in check, or may over-predate on native species who have not developed any strategies for defending themselves. Non-natives are also thought to be more likely to carry pathogens that native species have no immunity to.

We needn’t look far to find support for this view. Take the cane toad. Intentionally introduced to Australia in an effort to protect sugarcane crops from native cane beetles, their population exploded from 100 toads imported in 1932 to over 200 million estimated as of 2011. They produce a toxin that the native predators of Australia have not adapted to digest, and so predators that eat the cane toad often die as a result. Another example is the grey squirrel. Introduced to the U.K. from North America in the 19th century, they are larger and stronger than the native red squirrel. These significant competitive advantages promise an almost certain local extinction for reds in areas where greys are present. The greys are also carriers of, but immune to, the squirrel-pox virus that has had a disastrous impact on red squirrels.

Both the cane toad in Australia and the grey squirrel in the U.K. are famous examples of what conservationists call “invasive species” – species introduced to an area by humans and whose population sizes have increased uncontrollably to the point of negatively impacting native biodiversity. It is usually thought that non-native species, although not necessarily “invasive,” are much more likely than native species to exhibit the properties associated with invasiveness, such as aggressive spreading. As a result, conservationists often aim to control or even eradicate non-native species where possible. Early intervention is the surest way to prevent a new non-native from becoming established as an invasive. And that often means acting without a complete picture of the potential harms, as is the case with British parakeets.

But not everyone agrees with this hard-line approach. Recent arguments coming from both ecology and philosophy have questioned conservation’s traditional opposition to non-native species. The notion of co-evolved communities has fallen out of favor in ecology, replaced with a more chaotic picture in which ecological disturbance and species migration are the norm rather than the exception. If ecosystems aren’t close-knit communities of co-evolved species, there is less reason to presume that introduced species will inevitably harm or outcompete native ones. In reality, many non-native species have been hugely beneficial – the bumblebee, for example, has had great success as a pollinator of native plants in New Zealand, despite being non-native. Similarly, some native species can spread aggressively and harm other species. Bracken, a fern native to the U.K., is aggressively spreading and outcompeting other plant communities that tend to host higher levels of biodiversity. It seems that both native and non-native species can be harmful, beneficial, or a combination of the two.

The philosopher Mark Sagoff makes a comparison with human migration, stating that xenophobes often support their anti-migration arguments by providing individual examples of migrants who have committed violent crimes or cheated the system in some way. However, such individual examples clearly do not establish any general connection between the characteristic of being a migrant and the characteristic of being a criminal. Similarly, individual examples of non-native species that are also harmful aren’t enough to establish a general connection between non-nativeness and harmfulness. As Sagoff points out, if there were a general connection between non-native species and ecological dysfunction, then ecologists should be able to tell from biological/ecological data alone (rather than historical facts about a species’ origin) whether or not a species is native, simply by observing its functionality within a system. However, in practice, ecologists cannot distinguish natives from non-natives simply by examining organisms in a place.

An alternative approach may be to consider the impact of non-native species on biodiversity. A strong correlation between the introduction of non-native species and declines in biodiversity supports a strong stance against non-natives. However, the impact non-native species have on biodiversity is not straightforward. In a direct sense, non-native species can increase biodiversity at the local level, since the non-native is an additional species making the site one species richer. All else being equal, Britain is more biodiverse with parakeets than without them. However, at larger spatial scales, and particularly the global scale, species introductions can lead to ecological homogenization across systems – although individual systems become more diverse, they also become more similar to one another due to the replacement of endemic species with more globally prolific ones. As philosopher Christopher Lean (sarcastically) puts it in the Australian context: “Australia (and the world) has lost the desert bandicoot (Perameles eremiana) but gained the red fox, cat, black rat, and common pigeon; a triumph!” This tension indicates that the impact of non-natives on biodiversity is dependent on the scale at which we choose to measure it – a choice that depends on the types of diversity we perceive to be valuable. While we may value local diversity for its role in ecosystem functioning and productivity, global diversity carries other values, such as the heritage value of endemic species and the potential future uses that more unique species might turn out to have in terms of medicine or engineering.

This indicates that empirical scientific data in itself is often insufficient to settle the question of under what conditions a non-native species should be considered “invasive” and subjected to control measures. The answer is underdetermined by ecological and biological science alone, and ultimately requires the input of ethical, cultural, and aesthetic values to fill in the gaps. While there may be obvious prudential or instrumental concerns in cases where a non-native threatens an important resource or ecosystem service, in others, like that of the British parakeet, the correct response is ambiguous and depends on a host of competing value claims.

Decisions such as these shouldn’t be left purely to scientists, who are likely to share background assumptions and values that may not represent all those the decision impacts. Rather, control measures for Britain’s parakeet population should be subject to public consultation so that a diverse range of values can be brought to bear on the matter. A recent survey of nearly 4,000 British residents found some significant trends in social attitudes that could help to guide future control policies. Most notably, there was a significant rural/urban split, with 64.7% of rural respondents having a negative attitude towards the birds, compared with only 46.7% in urban areas. Additionally, although only 7.8% of respondents indicated a preference for parakeets in their local neighborhood, 83% agreed that they had pleasant aesthetics. These results point the way towards a control policy that focuses on containing British parakeets within urban centers where they are already established and perceived more positively, while utilizing control measures to prevent spillover into rural areas. Still, more research should be done on public perception of parakeets in Britain – biology alone can’t and shouldn’t decide their fate.