Rose-ringed parakeets – thoughts about invasive species.

I first saw them maybe thirty years ago. I was on the Thames path at Kew when I heard a loud squabble in the big trees on one of the islands in the river.

It was a strange sound, an unfamiliar mob-handed squawking and screeching, as if a terrible avian row had broken out. The trees were in spring leaf so I couldn’t see them immediately.

And then my eye was in and they were everywhere: brilliant green birds, scores of them, their colour, their cross-bow silhouettes, their bolting flight. I had been a birdwatcher when I was a kid and I knew these weren’t British birds, certainly not as I had known them.

Parakeets I was told, rose-ringed parakeets, escapees from cages. I didn’t think much about it. I assumed – this was thirty years ago and climate anxiety was not as intense – that the next cold winter would kill them off. Decades later I moved to Tooting in South London, close to the Common, and they were everywhere. They would descend – mob-handed again – into neighbours’ gardens, chattering and squabbling, plundering whatever trees were in fruit.

Tooting Common Pond

They bought colour, noise, energy and a kind of buoyancy – there was optimism in their resilience, their conviviality, their raucous spirits. But they also bought with them some uncomfortable questions.

The language of 19th century nationalism and scientific racism.

I could not shake the sense that they were not native, not ‘of these parts’, but I was also aware that when it came to birds, I had no clear idea what that meant, or even whether I should worry about it.

Partly the unease was linked to the way they were talked about in irritable letters to newspapers, and how close it was to the language of political xenophobia, how easily people reached for the words that disfigured debates about human migration. There was talk of invaders and aliens, illegal immigrants, of how their vigour and opportunism threatened the livelihoods of our plucky native species.

It was the language of nineteenth century nationalism and scientific racism but transposed to the gardens, scrubs and commons of south London. When it came to human migration, there was little doubt that this talk was politically explosive – that awful Brexit squabbling the latest, saddest mutation – but when it came to birds, to flora and fauna, did it matter? `

Slaughter on Guam.

For environmentalists, invasive species have what English ecologist Charles Elton calls ‘explosive’ potential. Displaced from the checks and balances of their ordinary environments, in the right conditions their numbers can grow exponentially.

SARS-CoV-2

Consider the virus SARS-CoV-2. Chances are its numbers were reasonably stable in its host population – possibly bats – but by making a leap to a different (human) species, it triggered replication on a planetary scale.

For a gloomy account of the havoc caused by introduced species we can head to the island of Guam and the years following the accidental introduction of the brown tree snake in the late forties. Guam is the largest and southernmost of the Mariana Islands in the western Pacific.

Forty-five kilometres long, about halfway between Japan and New Guinea, it has long been a major forward US air base. Before Boiga irregularis slithered out of a piece of military hardware and escaped into the brush, Guam had no shortage of birds – 18 native and seven introduced species in numbers described by naturalists as ‘plentiful’. The only native snake – the Brahminy blind snake – was equipped with the aggression and predatory potential of an earthworm, which it also resembles in size.

Cetti Bay Guam

Today Guam is an avian desert. Ten of its twelve native species of forest birds have gone, with the last two described as ‘functionally extinct’ – they no longer play a significant role in the island’s ecosystem and are unlikely to be viable.

What makes an ecosystem healthy?

Zebra mussels, water hyacinths, Nile perch, Himalayan balsam, Colorado beetles, brown tree snakes: alien or invasive species – what we might call species that appear to us to be in the wrong place – can create havoc, devastating local populations and threatening human welfare. If we set to one side human interests, at the risk of excessive simplification, the problem is about balance, stability and complexity.

The good of an ecosystem – the thing worth preserving from alien species – is something like balanced complexity.

Himalayan balsam

From this perspective, the stability of ecosystems is the result of millennia-long struggles. Over time, all the biological and non-biological parts of a healthy ecosystem tend towards a steady state – something like homeostasis – often with a high level of biodiversity.

A good or healthy ecosystem is likely to be stable, complex and with the maximum available environmental niches occupied. Such an ecosystem is better able to withstand the shocks native to a dynamic planet. To get a sense of what is at stake, it is worth considering the polluted waters of the Black Sea in the early nineties.

Of sea walnuts and the end of times.

Mnemiopsis leidyi – the sea walnut – is a self-fertilising comb jelly from New England. Small, transparent and stingless, it reaches maturity in a fortnight, at which point it can release up to 8000 eggs a day. Its diet is principally copepods – micro crustaceans – small fish, along with fish eggs and larvae. Released into the nutrient-rich black sea, almost certainly via the ballast water of a merchant ship, and without predators, its numbers exploded.

Sea walnut

One 1990 estimate put its biomass at 900 million tonnes, 95% of the total animal biomass of the Black Sea.

Out snorkelling, the Ukrainian biologist Yu Zaitsev counted 500 in a single cubic metre of sea. Unsurprisingly, fish stocks collapsed, along with the commercial fisheries that depended upon them.

If a healthy ecosystem reaches toward complexity, to an evolved equipoise, then this vision of the Black Sea is its mutant negative. The complex web of marine life torn to pieces.

Splicing the Book of Revelation – a plague of jellyfish – with contemporary environmental forebodings, the idea of a sea dead but for the drifting gelatinous monotony of a trillion jellyfish surely captures our apocalyptic terrors, our dread of an exhausted biosphere.

Myths of the fall?

This brings us to a vital contemporary debate. To risk over-simplification again, on the one hand are those who see the job of environmental action as the protection of as much pristine wilderness as remains; that and wherever possible the return of damaged ecosystems as close to their original state as possible. The Amazon rainforest, the Okavango Delta, the Russian Taiga, the Canadian Boreal forest – this is wilderness said to have an uninterrupted link to pre-human times, notwithstanding the long occupancy by indigenous peoples too often and too easily erased.

Canadian lake and forest

Their source of value lies in their distance from human interference: pristine; untouched; natural; inviolate.

These are places where we can still feel nature’s deep independence, where we can steal some perspective on purely human preoccupations. If nature has intrinsic value, apart and aside from human uses, this is where we go to intuit it, even though for most of us it is more an idea than somewhere known or visited. This view has lapsarian echoes. Nature is cast as Eden, and humanity – human technical knowledge in particular – is the despoiler.

The new wild?

These ideas are at work in me and I have a great deal of sympathy with them: the spoliation, the plunder, the world devastated for trinkets destined for landfill. It is sickening. Think of what we have lost. But at the same time a different narrative is emerging, one in which myths of the fall don’t participate so much. According to this view, there has never been an Eden. Life had not evolved to a state of (pre-human) maximal complexity, stability and balance.

Nature has no telos, no final point of achievement. It is opportunistic, wily, always on the shift. Species come and go. Ecosystems rise and fall. Nothing is fixed, finished or final.

Increasing data also suggest that our impact on the world – our Anthropocene – is older and deeper than we have thought, that we have been entangled with nature, making our mark, long, long before the chimneys of the English Black Country started chuffing out their smoke.

From this perspective our primary environmental goal should not be preservation and return. This would render once living ecosystems museum pieces – hardly natural in any obvious sense of the word – and commit us to the ceaseless, and ultimately futile task of resuscitating ghost ecosystems. Instead, proponents of what Fred Pearce calls ‘the new wild’ argue that we should acknowledge how intimately human activity is woven into the biosphere.

Even small facts here can be painful: an unopened tin of Spam on the slopes of the Sirena Deep; the translucent stomach cavities of deep-sea amphipods a-glitter with microplastics. We have slashed and burnt relentlessly. But we need also to champion the extraordinary power of nature to adapt and rejuvenate. Yes we must learn to live differently. But we should also celebrate nature’s vigour and opportunism, seek hope not in a frozen past but in those parakeets bantering around my hometown. Rather than premonitions of environmental catastrophe these noisy arrivistes might just be a mark of nature’s irrepressible vigour.

Julian Sheather

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