Black Wheatears (Oenanthe leucura) nest in caves and on ledges on cliff faces in Spain and Morocco. As is the case for most bird species - and in contrast to mammals, which are typically polygamous - it requires two adults to successfully rear a clutch of chicks and so Black Wheatears are superficially monogamous, although a great deal of fooling around occurs behind the scenes.
The theory of evolution by natural selection is blissfully simple but it has many subtle consequences, which are still being worked out. One of these consequences results from the fact that the cost of sex is very different for males and females. Whereas males can, by and large, "fuck and forget", females are stuck with the baby until it is capable of defending itself. The standard evolutionary outcome of this conflict between the sexes is that females spend a lot of time choosing among potential suitors whereas males will, literally, shag a red spot on a stick (in the case of Herring Gulls). Sometimes, however, females have the last laugh. For reasons that are often lost in evolutionary history, choosy females prefer to mate with males that have a particularly extravagant variant of an arbitrary trait. The classic example is the peacock's tail, which is presumed to have evolved as a result of "runaway" selection. Runaway selection is one form of an evolutionary arms race. In the case of peacocks, males with larger and more elaborate tails left more offspring, which inherited the big tail genes and so on...until the tails became so big that their bearers couldn't fly any longer and were eaten before they could screw. So today there is an uneasy detente between male and female peacocks, with the most successful males having tails that are just big enough to lure a female but not so big as to be an insupportable handicap.
In the case of Black Wheatears, sexual selection has imposed a delicious cost on males. Although the females lay their eggs on bare rock and do not require a nest of any kind they do need a criterion by which to distinguish among the willing and wanton males. The criterion that natural selection latched onto is stone-carrying. Male Black Wheatears spend their summers carrying stones from the bottom of the cliff upon which their beloved wishes to nest to the top. A male Black Wheatear weighs about 35 grams and several times a day he carries to the nest stones that weigh about a tenth of that. This is the equivalent of a human male carrying small television sets up a mountain incessantly, every day for a month, using only his teeth. Would you do that for your girlfriend? A typical male Black Wheatear transports 3.5 kilograms, or 100 times his own weight, from the bottom of the hill to the top in a season. If he is lucky his partner will then consent to sex and, if he is even luckier, will not subsequently cuckold him. Think on this story, the next time you worry about your mortgage.
I learned about Black Wheatears this past weekend while driving though Monfrague National Park in Extremadura, Spain, with my old friend Rob. We had stopped at a famous viewpoint, from which you can look across the valley at a vast limestone outcrop, with massive strata wrenched into vertically aligned slabs by incomprehensible geological forces in the distant past. We didn't see Black Wheatears but there were Griffon and Egyptian vultures, Black Storks, four species of Hirundines and a pair of Blue Rock Thrushes to make up for it. Birding in the company of a genuine expert and enthusiast is a lot more fun than doing it on your own and I felt momentarily the tug of another obsession.
Rob did all the driving on this trip and so I was free to admire the passing scenery. While we drove, we talked. Conversations with Rob take some getting used to, because they are punctuated with irrelevant bird names. A typical conversation last weekend went something like this.
Tom: "D'you remember..."
Rob: "Woodchat Shrike"
Tom: "...when I stabbed your in the leg with a scalpel..."
Rob: "Booted Eagle. Yes. How could I...Golden Oriole...forget."
Tom: "I still laugh about that..."
Rob: "Hoopoe"
Tom: "...to this day."
Rob: "Ortolan Warbler."
Tom: "Oh, Elizabeth David says they are delicious."
Rob: "Rock Bunting."
After 25 years of traveling with Rob I am pretty much inured to his ornithological take on Tourette's Syndrome but I'm glad that there were no recording devices running last weekend.
From Madrid we drove west to the Sierra de Gredos, penetrating as far into the mountains as the road would permit. From the head of the road there is a broad path leading uphill that everyone follows. Leave the path and cut cross-country and you are suddenly, magically alone. Across the valley I spied a colony of Veratrum album, the plant that interests me more than any other, and while Rob waited on a rock, I struggled across the valley to the colony to take photographs. Higher up we found seed capsules from an unidentified daffodil and spent half an hour on hands and knees collecting them. It was a blisteringly hot day and higher still we swam in a stream that a month earlier would have been snowmelt and stood under a waterfall that pounded our shoulders like a Hungarian masseuse. That evening we sat on a stone slab in the garden of our hotel sharing a bottle of red wine and looked over the Rio Tormes to El Barco de Avila, Rob with his binoculars, me doing most of the sharing.
The following morning we headed south west through the Valle del Jerte through orchards of cherry trees laden with fruit and stopped in Jerte to buy a couple of kilos for a few Euros. The cherries were enormous, the size of small tomatoes, perfectly ripe and by far the finest I have ever eaten. We had lunch at a touristy restaurant on the the Plaza Major in Trujillo, a town built with conquistador gold. A vast statue of Pizarro, conqueror of the Incas, mounted on a warhorse dominates the square. Looking at the statue, it is not so hard to understand how this Extremaduran peasant and his band of scurvied followers struck such fear into Inca hearts that they gave him their nation and their very existence.
To reach Trujillo we had driven through the dehesa of Extremadura, an ancient managed landscape of scattered Cork Oaks and Holm Oaks, dissected by rivers and streams. It is one of the most biodiverse ecosystems in Europe and owes its continued existence to three economically important components: Cork Oaks, pigs that eat the acorns and turn them into the world's finest ham and fighting bulls. With bull fighting on the wane and plastic corks and screwtops rapidly replacing the genuine article, the fate of the dehesa currently hangs in the balance. Only the (high) price of pata negra makes it worthwhile for landowners to continue managing the land in the traditional way. It was therefore with a sense of moral obligation, in no way influenced by gluttony, that we ordered and consumed a large plate of ham for lunch, along with various other tapas and a flask of cold red wine.
It was a fine way to spend a weekend. My flight home (Easyjet, obviously) was delayed by two hours and I finally crawled into bed at 2.15am on Monday morning. My descent into drug-induced oblivion was disturbed only by the knowledge that I'd have to be up at eight to take the kids to Legoland, more of which in another post.
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