As the last of the golden wych elm leaves settled on the woodland floor in the Blyth valley, the dank grey chill of late November sent me scuttling for an early winter reprieve in Tenerife. Such a fascinating island for the naturalist and so easily reached from Britain. All the sunseekers off to the bars and beaches of Los Cristianos and Playa de las Americas keep the travel costs down for those of us who are seeking the wilder side of the island. Sometimes in the airport departure lounge there are other travellers in boots and walking gear and we exchange little smiles and nods, oddities like mackerel caught up in a shoal of herring.
There can surely be few places in the world that pack as much variety into such a small space as Tenerife manages to. The largest of the Canary Islands, it is a bit smaller than the island of Lewis and Harris in the Hebrides (perhaps not a hugely helpful comparison as I am certain that many more Brits, and indeed many more Scots, will have been to Tenerife than have ever been to the Outer Hebrides, so let’s say it’s about the same size as County Durham) and it is staggeringly mountainous with the volcanic cone of Mount Teide soaring to almost 4000m at its heart, and a great ridge of mountains with stupendous cliffs dividing the island into two halves with completely different climates.
The moist trade winds hit the north-west side of the mountains brewing up clouds that keep them green and verdant, while the south-east side bakes in the rain-shadow. You can walk over the crest of the ridge from shadowy, evergreen, subtropical cloud forest
to dry stony semi-desert with Euphorbias and other weird and wonderful succulents in a matter of minutes;
while just a few km away, via woodland of tree-heather and (largely overgrown) farmland,
are fragrant pine forests;
and a few more take you onto the stark lava fields of Teide itself studded with brooms and the giant 2m tall flower-spikes of Tajinaste Echium wildpreti (related to Vipers Bugloss).
Truly Tenerife is a pocket continent.
At their closest the Canaries are only 100km from the coast of Morocco, and like North Africa itself they belong, biogeographically, firmly to the Palaearctic rather than the Ethiopean realm. The remarkable thing is just how many endemic species and subspecies they support given this proximity to the continental landmass. But then that is one of the fascinations of islands. The mix of species they end up with seems so random, and the extent to which the ones that do colonise then diverge in their characteristics from their congeners on the mainland seems utterly unpredictable. Take the birds. The avifauna of the Canaries is, basically, a rather limited subset of widespread Eurasian species. But why is it, given how many Palaearctic migrants turn up there en route between Europe and Africa, that so few have established resident populations? And why is the Blue Tit the only tit that has made it there, and why is it so gloriously, deeply blue in comparison with its anaemic European cousins?
The Red-Billed Chough Pyrrhocorax pyrrhocorax has made it across from the Atlas Mountains of Morocco but is to be found only on the island of La Palma (essentially a smaller version of Tenerife) where it swaggers about in true chough style in large flocks.
Tenerife is clearly visible from La Palma, 85km away, but there are no living choughs there now, although sub-fossil bones found in caves tell us that there used to be. Choughs are more than capable of sea-crossings – witness their recolonisation of Cornwall from Wales in 2002 (just in time to pre-empt a reintroduction project!) and have also been shown to move between Brittany and Britain.
The distances involved are much the same as those between the different Canary Islands so what is stopping them?
I spent quite a bit of time last week looking for Blue Chaffinches. Unlike its Blue Tits, which are a single species found wherever there are trees and bushes, Tenerife’s chaffinches have split into two – a normal (albeit darker than ours) generalist chaffinch Fringilla coelebs canariensis,
and the dusky blue-grey Blue Chaffinch Fringilla teydea that has evolved a rather chunkier bill. This is found only in the pine forests and is said to feed primarily on the seeds of the endemic Canary Pine Pinus canariensis. I have no doubt they do, although the ones I managed to watch were hunting for the seeds of Codeso Adenocarpus foliolosus (a leguminous shrub endemic to the Canaries) on the forest floor or fly-catching in the canopy. Anyway it has found a niche for itself that has led to its divergence from the other chaffinches of the island. But I wonder how secure that niche is? Greenfinches Carduelis chloris have colonised Tenerife within the last fifty years and I saw one in the pine forest looking quite at home. And what of those pine cone specialists par excellence, the crossbills Loxia sp? They seem to be capable of evolving rapidly to tackle different conifer species and new situations (the Scottish Crossbill Loxia scotica has developed as a separate species within the last ten thousand years), are notoriously irruptive and live just across the water from the Canaries in the Atlas Mountains. How long can it be before they make it over?
So much to ponder!