The new site for the blog will be: http://www.roslyndakin.com/blog
The new site for the blog will be: http://www.roslyndakin.com/blog
Were peacocks designed with this kind of audience in mind?
A while back I was searching for images of peacock feathers on Google, and I stumbled upon this article. It’s a piece by Stuart Burgess, an engineer who is head of the Department of Mechanical Engineering at Bristol University, and apparently also quite an opinionated creationist.
Burgess’ idea is that the peacock’s train feathers “contain an extremely high level of optimum design”, so much so that they provide evidence against Darwinian evolution. He thinks that the aesthetic features of the peacock are so complex, so contingent upon each other, that no step-by-step process of evolutionary change could have produced them. He’s right that these ornaments are highly complex, and that selection for this kind of extreme aesthetic feature presents a bit of a puzzle for evolutionary biology. To claim that the extraordinary complexity must be “irreducible”, however, is a big assumption.
The article provides a lot of amusing examples of twisted logic along the way. For example, one of the features that Burgess finds irreducibly beautiful is the fact that the peacock’s train forms a fan-like shape. This is because “the axis of every feather can be projected back to an approximately common geometrical center” – indeed, the body of the bird that grew them!
He also notes the wondrous spacing of the eyespot feathers: “Even though the display contains around 170 eye feathers, they are all visible and all spaced apart with a remarkable degree of uniformity. All the eyes are visible because the feathers are layered with the short feathers at the front and the longer feathers at the back. The eyes have an even spacing because each feather has the right length.” I suppose it’s equally fortunate that each of my arms has exactly the right length, or that my fingers are nicely ordered such that my thumbs are on the outside rather than in the middle. These kinds of patterns of development are ubiquitous in the animal kingdom, and not something special about peacocks. The problem is that Burgess assumes patterns require something extra special, like a bit of design work by an intelligent being, to produce.
For example, he goes on to talk about the fact that each eyespot is a digital pattern, since it is “formed by the combined effect of many small barbules”, which are the tiny branching structures that grow out of each feather barb (take a closer look here). He says,
Some patterns in nature are formed by natural growth mechanisms, as with the spiral shape of the nautilus shell. However, the eye pattern in the peacock tail requires the precise coordination of independent barbs and this cannot be achieved by a simple growth mechanism. Barbules on adjacent barbs coordinate perfectly with each other to produce the eye pattern.
Burgess claims that “the spacing of colours on each barb must be specified by instructions in the genetic code”. Because we can use a mathematical function to describe the shape of the eyespot, there must be something particularly complex in the peacock’s genome that produces that shape (math is really complex, right?). Indeed, “every detail in the peacock tail must be defined by genes in the genetic code of the peafowl”. And since there are so many fine details, we’re going to need a lot of genetic information.
Though he admits that “it is difficult to determine how many genes would be required to specify the aesthetic features of a peacock tail feather because it is not known how the tail feather grows”, he’s willing to hazard a guess, and it comes to… 20 genes. I think this meaningless number is supposed to shock us as being an impossibly large amount of information but it’s not even particularly high given that animals generally have well over 10,000 genes. It’s true that the eyespot is amazingly complex, and it would not be trivial for biologists to work out how it is produced at the cellular and molecular levels. Regardless, Burgess doesn’t seem to be aware of the fact that biological development can form patterns without having to specify every bit of information in the result somewhere in the genetic code.
Later on, Burgess lets natural selection in the back door. He tries to argue that even if science shows that peahens have hard-wired preferences for more “beautiful” males, we still can’t rule out design by a creator:
If there is a preference gene for aesthetic features, this does not prove that the sexual selection theory is true. The reason for this is that the Creator may have installed a preference gene as a means of ‘maintaining’ beautiful features. Beauty generally gives a disadvantage in terms of escaping from predators. If a peacock lost its colours due to a gene mutation, it would suddenly find itself more protected from predators. This is an example of where a loss of information could be a great advantage in terms of survival. Therefore, it is conceivable that the Creator would deliberately create preference genes for prominent aesthetic features such as colour.
Basically, because natural selection might act to reduce the peacock’s ornamentation, a good designer would put genes for aesthetic preferences in peahens as well – just in case.
I could go on – his explanation of how the colour is produced by the peacock’s feather barbules is just plain wrong (Figure 4) – but reality is actually more complex than he supposes (see figures here)! He also says, “the beauty of the peacock tail can be termed ‘added beauty’ because it appears to be surplus to that necessary to survive” – leading one to wonder exactly what level of beauty is necessary for survival.
A couple of months ago I came across another article by Burgess on peafowl. This one appeared to be a proper scientific paper in the journal Optics and Laser Technology. Published 5 years after the creationist article, this paper is entitled, “An analysis of optimal structural features in the peacock tail feather“.
In it, Burgess rehashes many of the same arguments about the extraordinary complexity of the eyespots. He even reuses the figures from the creationist magazine article. Gone are the references to the intelligent creator and irreducible beauty, however. Instead, he infers that because peacock feathers are simultaneously optimized “in the three areas of structures, optics and aesthetics” they provide “a key lesson for engineers and physicists”. That is, “different disciplines should work together to explore common features that can allow simultaneous optimal design in widely different areas.”
A thinly-veiled attempt to publish an intelligent design rant as science. It brings up a few questions, though. Was the journal, which is apparently peer-reviewed and publishes only original work, aware of Burgess’ other article? And is it possible to plagiarize yourself? (that is, by re-using your own figures without citing where they were originally published)
Having finished my field work this year, I thought I’d keep up with this blog by writing about interesting things that other people have seen animals do.
To start: this BBC science news report on the discovery of a “sex pest” seal that attempted to mate with a penguin, brought to my attention by Rob Ewart (the original paper can be found here but you will need a subscription to the journal to read the whole thing).
Apart from the entertainment factor – the abstract to the scientific paper concludes, “we report a case of interspecific sexual harassment bridging the rank of vertebrate class” – there are a few interesting issues here. The first being, why on earth would the seal do this? The authors provide a few possible answers. Apparently these fur seals sometimes eat king penguins, so perhaps by some strange mis-wiring, predatory arousal translated into sexual arousal in this case. Alternatively, the seal may have been too young to find a real mate, desperation leading it astray. Or, intriguingly, the young seal could have been play mating, a form of practice for the real thing later on.
The second issue: why on earth would a scientific journal publish something like this? Is it really that unusual for hormonally-charged animals to make the occasional mistake? This year alone I witnessed a peacock give chase to a human female (with the characteristic “hoot” of excitement that accompanies all mating attempts), and I’ve seen several peacocks attempt the same with guinea fowl and squirrels. All of these events happened with males that were displaying intently but that hadn’t had any peahen visitors in quite some time. Is this paper really such a novel finding, or are the authors just as desperate as the seal?
On reflection, it’s probably important to document these unusual behaviours somewhere, since it would be an interesting outcome if they turned out not to be mistakes after all. Young peacocks, for example, will frequently display their undeveloped train feathers to each other (pictured above). This male-male display may seem futile, but I wouldn’t be surprised if the kind of dancing skill required later in life demands some practice. Similarly, in Costa Rica I remember hearing juvenile long-tailed manakins displaying long after the real mating season had ended, no doubt honing their skills for next year. There’s even some evidence that the reason male manakins pair up for their co-ordinated display dances, even though only the dominant member of the pair will get to mate, is for the practice.
The full citation for the seal paper:
And two on long-tailed manakin displays:
Males display in the “Wild Asia” exhibit at the Bronx Zoo, which can only be seen by riding the zoo monorail. The structure behind the three peacocks is the monorail track.
I’ve had some success on this trip after all. The weather was perfect for my model experiments yesterday (sunny, warm, not too much wind), and although I wasn’t able to fit in quite as many trials as I was hoping for, the ones that I was able to accomplish worked perfectly. Of 16 successful trials (i.e. ones where the male danced for the model), 6 ended in a copulation attempt. In California, 3 of 22 trials ended in such an attempt. This apparent geographical difference in Penelope’s popularity is a bit of a mystery (it could be because a number of my California trials were at the end of the breeding season, when males were somewhat less motivated and harder to trick). Nevertheless, it’s safe to say that overall she was a hit.
One reason I didn’t get as many trials as I could have was that the Bronx peacocks were the most skittish ones I’ve encountered so far. When I stepped into the nyala enclosure at 7 am yesterday, I had about 2 hours to collect as much data as I could (as many as 20 five-minute trials, I figured). But it took a long time for the males to get used to me being in there. I spent the first hour waiting quietly (and nervously) for one of them to make a move, while they did the same – watching me carefully and no doubt waiting for me to leave. This stand-off shouldn’t be too surprising, though, since the Bronx Zoo birds have enough space to live their entire lives away from people.
This morning, I moved across the Bronx River to work in “Wild Asia”, and the birds there were even more difficult. Happily, though, I was able to get a video of a male reacting positively to Penelope, which will be excellent for illustrating exactly how she worked.
I also made a trip to the “World of Birds” exhibit. They have some pretty amazing animals there – here is a picture of another lek-breeding bird, the lesser bird of paradise:
Unfortunately, the juvenile male in the picture is not as spectacular looking as the adult (who was nowhere to be seen), but he was moving his wings around in a pretty cool practice display. The next picture is of a palawan peacock pheasant, a close relative of peafowl:
The male peacock pheasant also has iridescent eyespots which it displays for the female during courtship, but in this species the eyespots really are on the tail feathers (unlike the peacock, where the eyespots are on the upper-tail coverts).
My favourite part of the “World of Birds” was not a real bird, however. It was a hallway lined with 6-foot tall photographs of birds eating and being eaten. The hallway led you into a room with more of these grisly photographs, arranged around a 6-foot tall black poster with the following caption:
Refreshingly frank in a venue full of children. I must have looked pretty strange taking pictures of it, though.
I’m back at the Bronx Zoo now, with the model peahen, attempting some more behavioural experiments. My first day was both good and bad. I had no trouble finding my accommodations on the zoo grounds last night – I’m staying in the “Bat Cave”, so named because of the bats.
(Not really – the apartment is called the Bat Cave because it’s on the ground floor of the building pictured below, which also houses the families of three zoo staff members that live permanently on site…)
If the fact that several staff members live on site doesn’t give you a sense of how well-equipped this zoo is, perhaps the contents of my apartment will. I have my own kitchen, washer and dryer for laundry, animal-themed blankets on the bed, and if bored I can read anything from The Iliad to Seabiscuit:
Books in the Bat Cave: no one can complain about the selection.
The zoo even has it’s own NYPD patrol.
In the future, all police will drive golf carts.
I managed to head out this morning at 6 am, beating the peafowl by at least an hour (since, for birds, they tend to roost until fairly late in the morning). It didn’t take long to find the main lek; males were roosting conspicuously in most of the surrounding trees. It was a spectacular one – at least 10 males displaying in view of one another, with another 5-6 quite close by. At first glance, this would seem ideal. I had an excellent view of a large number of birds. However, all of the display territories were nested within mammal enclosures that I couldn’t access. The birds were just out of my reach, and I needed males in accessible areas so that I could set Penelope up nearby.
I spent the rest of the day on foot, continuing to explore the peafowl haunts with Penelope in tow (I walked at least 15 km today all told – this zoo is huge!). People were startled, fascinated and amused by Penelope, and many of them tried to talk to me about her. Normally this would have been slightly annoying, but today it helped me stay positive despite the other frustrations. By afternoon, I had managed to get a few good peacock videos and permission to work in one of the mammal enclosures for tomorrow. I’ll be in and out with Penelope before the nyala (an African antelope) are released into the enclosure for the day, and again at the end of the day after they’re put inside for the night.
Although I’m very happy to be back in Canada (having decided that Los Angeles is a terrible place to live, mostly because of all the driving), I have to admit that the people of California were quite friendly. I found the peafowl to be equally amenable. Since mating activity was finished during my last week in Los Angeles I decided to take some photographs of them (and other birds at the Arboretum, including the hummingbird in the border above). Here are a few of my favourites…
A peacock on the lawn: the male below manages to guard his territory while simultaneously resting in the shade. These birds can be surprisingly camouflaged at times.
Other times, this is not the case:
A peahen on a nest: one of the first females to lay chose to do so in the sink of the men’s bathroom. This one appears to be more fortunate, but I wasn’t around long enough to see any peachicks.
A female with Penelope: the model drew a lot of negative attention from the ladies. This picture was taken when I had Penelope stashed away in some bushes; after a lengthy inspection, the real female (on the left) started pecking at her aggressively.
I’ve been meaning to photograph peafowl in flight for at least a year, now, and I sat under a roosting tree for nearly two hours to get these last pictures. First, a peahen:
And, my favourite from the same morning: peacocks do it too!
I am very excited to report that Penelope has finally lived up to her name!
Here she is right before being courted by male no. 30:
(Photo credit: Rob Ewart)
The secret to her success? You have to present her to males that are already (preemptively) inspired to display their tails. When you present her to a male that is resting on his territory, he just watches her curiously out of the corner of his eye while making himself look busy feeding and/or preening. But sometimes males will have their tails up when there aren’t any real females in the immediate area (either because they expect females to arrive very soon, or because some females have just left the area, or possibly because these males simply have the energy for it and nothing else is more pressing at the moment). Penelope’s best strategy is to target these males: when you initially approach them, they are slowly turning in circles as they keep a look out for their next female target. When you put Penelope in front of them, they enter into a pattern of dancing that is quite clearly directed towards the stuffed bird.
During one of the trials with male no. 30 (shortly after the picture above was taken), the peacock backed up alongside the model, shivered his train at her for an infinitesimal amount of time, and mounted her almost immediately for a mating attempt. Although initially shocked (and delighted) we soon remembered that we had to intervene, and certainly won’t let it happen again.
Update: Penelope was mounted two more times in California (bringing her total to three different males). I am with her now at the Bronx Zoo in New York City for some further experiments, and am determined to start writing here regularly again!