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All animals live in or seek a set of climate conditions they find tolerable. This “climate envelope” partially determines where animals are found, but the continued existence of many species now rests on the outcome of human-driven climate change.

Rising temperatures are the available climate niches of many species into areas which were previously too cool. While their ranges shift poleward or to higher elevations, their habitat downslope or closer to the equator shrinks, as it becomes too hot to live in.

Flying and marine animals are relatively free to follow these shifting niches. Birds and butterflies are two examples. New species arrive regularly in the UK with the warming climate and are generally by enthusiasts and scientists alike, given that they are a natural effort by a species to make the best of a difficult situation.

However, many grounded species, including reptiles and mammals, cannot disperse through habitats split apart by roads and other human-made obstacles, or cross natural barriers like the Channel. This limits their ability to find suitable conditions and makes them vulnerable to extinction.

Nowhere to go?

Here is the dilemma for conservationists like us.

We normally focus on preserving species within their modern ranges, and have traditionally viewed species that end up outside theirs as a problem. But retaining the status quo is increasingly untenable in the face of unchecked climate change.

Should we consider conserving species that have moved, or been moved, outside of the native ranges that existed before industrial society and its greenhouse effect? Should we even consider deliberately moving species to conserve them? Introduced species that have established just outside of their native ranges, in slightly cooler climates, offer a glimpse of the likely consequences.

Our in north Wales focused on one such migrant. Aesculapian snakes (Zamenis longissimus) are nonvenomous reptiles that mostly eat rodents and are native to central and southern Europe, reaching almost to the Channel coast in northern France.

Two accidental introductions, one in Colwyn Bay, north Wales, and another along the Regent’s Canal in London, have allowed this species to thrive in Britain. It is not actually novel to our shores, but it disappeared during a previous ice age and has probably been absent for about 300,000 years.

While the introduced UK populations appear to be thriving, of this snake in the southern parts of its range have discovered a rapid decline, potentially due in part to climate change.

A good neighbour

Given their status as a non-native species, we were keen to find out how Aesculapian snakes are surviving in chilly north Wales, further north than anywhere they currently occur naturally. To do this, we implanted 21 snakes with radio transmitters and spent two summers tracking them around the countryside.

Our results surprised us. The snakes had a trump card which seemed to help them weather the cool climate. They were frequently entering buildings – relatively warm refuges – while they were digesting food or preparing to shed their skin. They also used garden compost bins for shelter and to incubate their eggs.

Even more surprisingly, most residents did not mind the snakes. In fact, many had no idea they had snakes as neighbours because they kept such a low profile, typically hiding in attic corners. The snakes appear to coexist with normal suburban wildlife, and there are no indications that their presence is affecting native species.

Should successfully established, innocuous immigrants be proscribed and potentially eradicated, as is ? Or should they be valued and conserved in the face of current and impending climate change?

Protecting and conserving the maximum possible diversity of species and ecosystems is the heart of the conservation agenda. However, the rapid pace of change forced upon our planet requires us to rethink what is practical and desirable to achieve.

Conservation within the silos of national boundaries is an increasingly outdated way of trying to maintain the diversity underlying global ecosystems. Instead, conservationists may need to accept that the rapidly changing environment necessitate shifts in the ranges of species. And perhaps, even assist those species incapable of moving on their own.

Unlicensed “guerrilla” releases are obviously unacceptable due to risks (for example, the potential to introduce devastating diseases such as the amphibian-killing ) and other . Even legitimate reintroductions , due to there being too few individual specimens, pollution or predation from invasive species.

Aesculapian snakes will be considered by the government for addition to the , which would be grounds for eradication. It would be tragic if species such as this became extinct in parts of their natural range, while thriving introduced populations just to the north of their pre-industrial distribution are treated as undesirable aliens that must be removed.

Instead, we argue that this innocuous species should be the figurehead for new thinking in conservation biology, that incorporates the reality of impending further climate change and dispenses with the narrow constraints of national boundaries and adherence to pre-industrial distributions.

, Postdoctoral Research Fellow in Herpetology, and , Professor of Zoology,

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