I've threatened to do this diary for a while, since another diary which was anything but "educational" on evolution was published in late fall.
About a year ago I had a glorious moment when I had the chance to see thirteen prepared specimens of the Galapagos finches at the American Museum of Natural History, here in NYC. It was one of those precious moments in life where you see the culmination of years' worth of work appear in front of your eyes fully-formed. (I can imagine many feeling the same way this week ;) )
Join be after the break, for more on little tiny weenie birds.
In his famous series of voyages on the HMS Beagle, Darwin served as the ship's naturalist. He spent nearly five years on his mission (sounds like Star Trek!) and the discoveries made there were of obviously astounding importance in the fields of biology. It is difficult to fully appreciate just how radical and revolutionary a departure his ideas were, even if the germs (or if you wish to be a wag, the "genes") had been in place for a few generations. There was no concept of genetics, no idea of molecular science or biochemistry. He didn't have the scientific tools we have today, just the willingness to be guided by the data, not the dogma.
Darwin wasn't much of an ornithologist, and he needed significant help from John Gould upon his return to England to properly identify each species' structures and diet. Many of his initial misunderstandings actually slowed his work down. First, a glossary.
Blackbird- has different meaning in England than the US. We call icterids blackbirds; their blackbird is a close relative to the American Robin. This is a bird (thrush family) that lives and nests in trees, but gets most of its insect/worm food from the ground. Usually a hefty bird compared to other songbirds. They have beaks that are more like thick tweezers or pliers, designed to pull and yank, not crush. Most are dull colored, blend in with the ground or soil. Notable exceptions are the bluebirds, who blend in with angels.
Finch- think big beaks intended to crack small seeds. Relatively slow birds for their size, but then again seeds don't tend to fly away. Loads of really lovely tropical finches, and in the US we have the glorious goldfinch. (Close cousins to some buntings.) Mostly social birds, another example are the weaver finches, also known as house sparrows or English sparrows.
Grosbeak- think really big beaks. Generally bigger than finches, live longer and don't tend to congregate in large flocks during breeding season. The most famous is the cardinal (formerly known as the cardinal grosbeak, and if you use that expression it either dates you as being older than dirt, or having lots of old books which give you the old names of birds.) Some of these birds are seriously beautiful, if slightly chunky; evening and rose breasted grosbeaks come to mind. Famous for being exceptional parents and having pretty voices.
Tanager- fructivores for the most part, but they'll also eat seeds. More omnivorous and colorful than the other birds, the males of these two families will burn holes in your retina- especially scarlet and western. Their beaks are not specialist's as the grosbeak, they are more a bird of all trades. Some say, they are closely related to other very blindingly colorful birds, known as warblers.
Warblers- two separate clans (that aren't really very closely related) the Old World warblers are smallish dainty birds who make their living almost exclusively on insects. That description matches the New World warblers, AKA "North American wood-warblers" (the object affection of most springtime birdwatchers) but the old-world birds are more like our kinglets. They aren't nearly as nervous as the NAWW, and they have more of a social structure, not quite like chickadees but close. Very fine pointed and chiseled beaks, designed for catching insects. Related a bit to flycatchers.
Woodpeckers- iconic birds, mostly insectivores but many eat ants (I know ants are insects, but there's a reason why we group them differently when it comes to birds. Ants for the most part live in large colonies, and unless you catch them out of their hills they requires significantly different strategies and beaks to catch them. This factors greatly into our discussion of the Galapagos finches, and one of the truly most amazing birds in the entire world- but more about that later.) We call them songbirds, but that's because some people think "squak" is a song. For the most part they do their singing with their beaks, tapping out their tunes on hardwoods or bark, or the occasional piece of aluminum siding or gutter. Very intelligent birds, up their with the crows and ravens (corvids) and not far away from dogs and cats, which aren't birds and don't have beaks even though some cats "headbutt".
Vampires- much beloved in modern literature, these winged animals (when not wearing capes and saying "Good Evening" make their living by sucking blood. They generally have two very pointed teeth, or in the case of another really amazing species of bird two very pointed beaks. Unlike fictional vampires that live in the Olympic peninsula, these birds do not turn their victims into the undead, they just snack on them, along with fruits, nuts and seeds. Another granola bird, except with a taste for blood.
I've gone to all that trouble to give you a little idea of the diversity of many families of birds. I barely scratched the surface, but the reason I had to go into this detail is because there is (at least) one species of each of the 13 Darwinian finches that has both physical and behavioral characteristics to match each of the families listed!
Bear in mind that these finches are estimated to have derived from one progenitor species of bird, and relatively recently! The best-guess estimates are two to three million years (give or take another million) which contradicts the scientific findings of the Young Earth creationists who believe it took only 200 - 1200 years.
What is most astonishing for a birder, is the way these creatures that have such varied body styles and behaviors could speciate in such a brief time span whereas it is estimated passerines such as yellow warblers, scarlet tanagers and Baltimore orioles (all three species young look very much alike, except for size and beaks) took about 30 million years.
Their island habitats permitted very rapid changes in behavior and structure to amplify, and to allow complete different species to radiate at a pace much faster than "terrestrial" birds. Living on an island chain without any mammals or similar birds as competition, small changes permitted these birds to breed very rapidly whenever a beneficial mutation gave them even the slightest advantage. The normal patterns predicted by "punctuated equilibrium" became magnified on these islands, and one has to wonder how many even more idiosyncratic and unexpected species and attributes are now extinct?
For the purpose of brevity, I'll group closely related "genotypes" together.
That gives us seven distinct types of bird:
- Ground finches, such as the small, medium, and large ground finches.
- Vampire finch.
- Cactus finches.
- Tree finches, again small, medium, and large.
- Woodpecker finch. (Not really a woodpecker)
- Warbler finch.
- Cocos Island finch (this bird may be remotely related, as opposed to very closely. Some suggest a different lineage altogether.)
Notice the astonishing variety of birds that we find here. You would expect to find such diversity in a medium sized nation, not just a small island chain. But this does not represent all of the birds on the islands, this just represents the adaptive radiated evolutionary products of just one species which first arrived on the islands some 1-5 million years ago.
Let me quote Darwin himself on this; "...one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends."
This is the secret of these finches- they were literally "dropped from out of the heavens" onto these islands, and found themselves on an abundant landscape with little competition at all.
Mammals have been known to cross large bodies of water by accident by hitching a ride on floating debris, but it is most rare. Birds have the obvious advantage in their ability to travel great distances by flying, but for the most part migrating birds generally take the path their parents flew. You do get frequent "accidentals" during migration season, as birds sometimes get screwed up compasses but they don't fly north instead of flying south, they most often error by a 90 degree angle, flying east instead. This happens more frequently than flying west for the winter. But migrants have an advantage because as they fly they have feedback; they can see the ground below and they stop off for refueling every few hundred miles. Some songbirds will fly very long distances over water, but with few exceptions it is limited to a few hundred miles, rarely over 500.
One theory is they were blown in by storms. It is possible.
All animals mutate. This is actually very common, and is essential for survival as they adapt to the species that prey upon them, the microbiotic flora and fauna which infect them, and changing conditions. What is most often misunderstood about evolution is the concept of direction.
It has none.
Species mutate strictly at random, and those changes most often neither help or hinder their survival; most changes are minimal. Those that are not benign or beneficial, almost always die out before the bird can breed, hence it ends immediately. But any changes which assist even in the slightest gives a breeding advantage to that particular animal. Once again this is often misinterpreted as "survival of the fittest." In this case, each major change (speciation) did not supplant the previous species, but allowed it to subtly shift focus into a niche that was previously unexploited. In an environment such as this, with almost no competition from mammals or few bird species, underutilized resources permitted the rapid and through expansion of those who could suddenly take advantage of them.
This is the most critical point of evolution. Any animal that can use the available resources in ways that couldn't be done by other existing species could then use this advantage to rapidly populate and break free from the originator population. As time goes by, the change gets amplified through the same process, and secondary characteristics heighten the changes. Birds have "cultures"; behaviors and songs which males and females use to attract mates. While various finch species do on occasion hybridize with other species of finches, because they don't sing the same songs and have the same mating rituals this is relatively rare. Culture and niche tend to enrich the differences from species to species. In many species of bird (I can use as the best example that I know the Empidonax complex- any birders in the audience will be able to back me up that these birds are often impossible to differentiate unless you're hearing them sing, or can accurately describe the type of tree they are in) song of behavior is the easiest ways to tell them apart.