Darwin’s other finches

The Galapagos finches are an icon of evolution. But you don’t have to go all the way to the Galapagos to see finches which have evolved different beaks and different body shapes in order to specialise for different kinds of food and different lifestyles.

These are all species of finch that Darwin might conceivably have seen in his garden in Kent, or perhaps when he dropped off his family at the church on Sunday and went for a country walk while they were in the service. Some would have been common; others are long shots. I’ve arranged them in approximate order of beak size in the classic Galapagos fashion.

The reason the Galapagos finches make such a good teaching example is that even to a casual observer they look closely related. Indeed, from personal experience I can say that they offer a tricky identification problem: when you have several species which are only distinguished by size and shape of beak, and those features are highly variable within the species anyway… it can be frustrating.

It’s very easy to use them to tell a straightforward story of a few original finches — maybe just a single pair — being blown across to the islands from South America, and then, as the population grew and split between different islands, diverging to fit into slightly different lifestyles. It is the evolutionary process reduced to the simplest possible case.

The evolutionary history of the species pictured here is no doubt rather more complicated; rather than being isolated on an oceanic archipelago, they are part of a family that ranges around the whole northern hemisphere and into Africa. And they look rather more distinct than the Galapagos species.

Even so, apart from a general similarity of body shape and behaviour, there are some suggestions in the plumage that these birds are related. The fact that so many species of finch have one or two pale wingbars is probably not a coincidence. And, after all, that’s what we mean when we say that species are part of the same family: they are all descended from some single ancestral species of finch. Perhaps that original finch had wingbars. Notice as well that they nearly all have slightly forked tails.

And although the story of these finches is so much more complicated and wide-ranging than the Galapagos species, it is essentially the same thing. Those first few finches may not have been isolated on an oceanic island, but it is still a story of a few ancestral birds, somewhere, who bred and spread into different areas, formed different populations, and adapted to subtly different ecological niches. There are still plenty of similarities; they are basically seed eaters, they tend to have complex songs, they are largely arboreal. But they vary from goldfinches who eat thistle seeds to hawfinches with a beak strong enough to crack open a cherry stone.

Darwin actually mentions finches in The Origin of Species. Since 1859, we have become more used to the idea that taxonomical groups (like ‘finches’) equate to shared bloodlines. But the things we know intellectually may still be hard to internalise. So it’s not surprising that, before he had told the world his idea, Darwin found people were uncomfortable with it:

when I first kept pigeons and watched the several kinds, knowing well how true they bred, I felt fully as much difficulty in believing that they could have descended from a common parent, as any naturalist could in coming to a similar conclusion in regard to the many species of finches, or other large groups of birds, in nature. One circumstance has struck me much; namely, that all the breeders of the various domestic animals and the cultivators of plants, with whom I have ever conversed, or whose treatises I have read, are firmly convinced that the several breeds to which each has attended, are descended from so many aboriginally distinct species. Ask, as I have asked, a celebrated raiser of Hereford cattle, whether his cattle might not have descended from long-horns, and he will laugh you to scorn. I have never met a pigeon, or poultry, or duck, or rabbit fancier, who was not fully convinced that each main breed was descended from a distinct species. Van Mons, in his treatise on pears and apples, shows how utterly he disbelieves that the several sorts, for instance a Ribston-pippin or Codlin-apple, could ever have proceeded from the seeds of the same tree. Innumerable other examples could be given. The explanation, I think, is simple: from long-continued study they are strongly impressed with the differences between the several races; and though they well know that each race varies slightly, for they win their prizes by selecting such slight differences, yet they ignore all general arguments, and refuse to sum up in their minds slight differences accumulated during many successive generations. May not those naturalists who, knowing far less of the laws of inheritance than does the breeder, and knowing no more than he does of the intermediate links in the long lines of descent, yet admit that many of our domestic races have descended from the same parents—may they not learn a lesson of caution, when they deride the idea of species in a state of nature being lineal descendants of other species?

The Galapagos finches, incidentally, are not actually ‘true’ finches. That is, they are not members of the Fringillidae, the family that includes all the species pictured here. They were previously thought to be in the Emberizidae, another large family of seed-eating birds including the buntings, American sparrows, juncos and towhees. But apparently (and I’m only getting my information here from Wikipedia) the latest thinking is that they are tanagers.

Meanwhile, DNA testing has shown another notable island family, the Hawaiian honeycreepers, are in fact finches that have evolved to become nectar eating, with long, narrow curved beaks like sunbirds. And the euphonias, a group of blue and yellow birds that were previously thought to be tanagers, have been moved into the finches as well.

These changes are part of a revolution in taxonomy that has been enabled by DNA testing technology. How Darwin would have loved it.

» The finches pictured are, from top to bottom: siskin, redpoll, goldfinch, chaffinch, brambling, linnet, greenfinch, bullfinch, crossbill and hawfinch.

All the pictures except the goldfinch and the linnet are © Sergey Yeliseev and used under a Creative Commons by-nc-nd licence. The goldfinch is © Isidro Vila Verde and used under a by-nc licence. The linnet is © Ian-S and used under a by-nc-nd licence.

The Beak of the Finch by Jonathan Weiner

This book was recommended to me when I was in the Galapagos; I finally got round to reading it and I’m really glad I did. It’s an account of Peter and Rosemary Grant’s long-term study to measure the effects of natural selection on finches in the Galapagos. When this book was published in 1994, the study had been going for twenty years, but it’s still ongoing.

The choice of Galapagos finches isn’t just because of their iconic status in history of evolution; they’re an isolated population, they’re particularly variable, and a few very similar competing species live together in a very simple environment — only a few species of food plant, and almost no other small birds.

Over that period, they and their students have collected a staggering amount of data; detailed measurements of every finch on the island of Daphne Major, and records of who breeds with who, where their territories are, what songs they sing, what they eat, which territories are most productive, how the food supply varies from year to year and so on. That data has enabled them to show not just that tiny variations (in this case, particularly beak size) can have a measurable effect on the survival and breeding prospects of a bird, but that a change to the environment — a very wet year or a drought — can select for different physical characteristics to the extent of having a measurable impact on the average measurements of the population.

In effect, they have showed that you can observe evolution in action and that in the right circumstances it can happen extremely fast.

I really thought this was an excellent book. The detailed account of a single large research study sets it apart from all the other popular accounts of evolution I’ve read. There’s easily enough material to sustain a whole book and Weiner does an excellent job of communicating all the details with enough human interest to keep the book getting bogged down.

(my) bird of the year, 2006

While I’m rounding up 2006.

2006 was a pretty good birding year for me, mainly because of my trip to Andalusia at Easter and Galapagos/Ecuador in the autumn. But I did get one lifer in Britain this year, which for a rather occasional, fair weather birder like me was very exciting. That was Horned Grebe (what used to be called Slavonian Grebe), which I saw in the sea off Hampshire when I was visiting my sister last month. But a winter-plumage grebe some way out to sea isn’t going to be my bird of the year, nice though it was (and the grebes are a great family of birds).

The new birds I saw in Spain were particularly exciting because I’ve been using European bird guides for 20 years now, and the birds in the guide which are not found in the UK have a particular glamour for me. However gorgeous the bird, if you’ve never heard of it before you see it, it’s not as exciting as something you’ve wanted to see for decades.

The three best birds on that trip were probably Collared Pratincole, Azure-winged Magpie, and Royal Tern. For once, I can illustrate a bird with a picture of my own. This is a Collared Pratincole:

It’s one of those appealing animals that has rather obviously evolved away from the standard model of its ancestors into a different niche. As I said about this photo on Flickr, “Runs like a plover, flies like a tern.” Pratincoles are waders, like plovers and sandpipers, but at some point in their evolutionary history they took to catching insects on the wing. Perched they look like rather stretched plovers; in flight their long, pointed wings and agile flight make them look like terns or swallows.

Azure-winged Magpie is just a beautiful bird. Like most crows, they have a bit of personality, but it’s those incredible blue wings and tail that make them special. And Royal Tern is a rarity; a basically new world species that also breeds on the Atlantic coast of Africa (Mauritania, I think, but don’t quote me on it) and occasionally turns up on the south coast of Spain, where I saw it. So that was cool.

The Galapagos was full of good stuff, of course. The total list wasn’t that huge (53), but there were some classy birds on it.

Some species worthy of note:

Everyone’s favourite Galapagos bird, the Blue-footed Booby. It has blue feet! And a silly name! Flightless Cormorant – for me, the name says it all. Woodpecker Finch – the least finch-like of the ‘Darwin finches’, and so the most striking example of adaptive radiation. Swallow-tailed Gull- the world’s only nocturnal gull. And frigatebirds, which I’ve seen a few times before but are just one of my favourite families of birds.

It was also just a pleasure to be at sea for a week and be able to watch real marine species, the kind that only come to land to breed: shearwaters, petrels and storm petrels. I’ve seen other shearwater species a few times before, and they’re great things. They ride the air currents just above the waves, whipping along stiff-winged with one wing-tip practically touching the water surface and occasionally swivelling from one side to the other. But to see storm petrels was one of various lifetime ambitions fulfilled on that trip (I have a lot of wildlife-related lifetime ambitions, so I’m not going to run out anytime soon), and they weren’t a disappointment. Whereas shearwaters seem perfectly suited to the rigours of the open ocean — all wing, seeming to travel effortlessly with just the tiniest movements — storm petrels are delicate little fluttery birds. The Japanese call them umi-tsubame: sea swallows. Their cutest habit is ‘walking’ on the water – flying just above the sea with their feet pattering on the surface whille they look for food. I could happily watch them for hours.

And so to Ecuador. Birding in the tropics is just extraordinary: the sheer number of species makes it quite unlike birding up here in the north. And so many of them are colourful (parrots, toucans, hummingbirds, trogons, quetzals, tanagers) or just excitingly different (woodcreepers, spinetails, antbirds, antpittas, tapaculos). The birds that stand out in memory include Chestnut-crowned Antpitta, Yellow-rumped Cacique, Long-billed Woodcreeper, Grass-green Tanager, Streaked Tuftedcheek, Plate-billed Mountain-Toucan, and perhaps the cutest bird in the whole world, the Booted Racket-tail.

But for my bird of year, we’re going back to the Galapagos and the Waved Albatross:

To see albatross was another lifetime ambition. They are the epitome of wildness; breeding on remote rocky islands in the southern oceans and spending most of their time out at sea. And they’re big; Waved isn’t the biggest species, but it still has a 7′ 7″ wingspan. When one of those flies low overhead, as they did when we were on the island where they breed, it’s a special moment. It was great to see them on land and get a really good view of them, and particularly to see them ‘dancing’: the pair mirrors each other movements and go through a whole repertoire of posing, beak-rattling, throwing their heads back, leaning one way and the other. But for me it was especially satisfying that I saw my first one at sea. We were out on deck looking for whales and the albatross went past quite unexpectedly — it was the opposite end of the archipelago from where they breed — and as soon as I was sure I screamed ‘Albatross! Albatross!’; largely, it has to be said, to the bemusement of all the non-birders around me. That moment, when you suddenly see a bird you really want, is such a rush. I’m sure it taps into millions of years of our ancestors’ hunting instincts. But I’m not picking Waved Albatross as my bird of the year just because it gave me an adrenaline hit. It was a special bird.

In the Galapagos

I´ve got a couple of hours in Puerto Ayora (on Santa Cruz, in the Galapagos), so I thought I´d post a quick note.

I can recommend the Galapagos. For a start, the landscape is more varied and more beautiful than I expected; somehow in my head it was all rocks, but from island to island the colour of the rocks and soil changes, the vegetation varies – I mean it´s mainly pretty arid, and so it´s lots of cactus and thornbushes, but one island will be an expanse of rippled black lava with a few small cacti, and another will be densely covered with bushes. This afternoon we´re going to the highlands for the first time, where it´s actually quite green.

We´ve seen most of the Galapagos specialties now – the two iguanas, the flightless cormorants, the finches (5 of the 13 species so far). Wild giant tortoises this afternoon. I´ve snorkelled with sea-lions and penguins and turtles, I was particularly thrilled wih the penguins.

Actually though, apart from the special Galapagos stuff, it´s been nice just being at sea. I hadn´t really thought about it before I came, but it´s great just being able to watch shearwaters and storm-petrels from the boat. And we´ve had dolphins riding the bow-wave of the boat. But almost my most exciting marine sighting was watching manta rays jump clear of the water and tumble back with a big splash.

The famous tameness of the animals is quite interesting; I expected it of the endemic species that have evolved in an environment without predators, but species like Great Blue Heron, which are wary of people in the rest of the Americas, have been letting us get within about 10 feet. We watched one grab a newly hatched turtle from below the sand.

So it´s all good.