Tag / eyespots

by Roslyn

Furious about eyespots

I think I flubbed an interview this week. My supervisor Bob and I just published a paper that is getting some press, because it addresses a recent controversy about the peacock’s train1. Eager for the interview with Nature News, I wasn’t exactly prepared with good lines for the reporter to go on – and I wonder if that’s why he had to pump up our story as a “furious debate”2.

In truth, most of the “debate” played out in a flurry of news articles back in 2008. That was when Mariko Takahashi and her colleagues in Tokyo and Kanagawa published the fruits of their exhaustive 7-year study of the peafowl at the Izu Cactus Park in Shizuoka, Japan3. I’ve never met Takahashi, although I did meet her supervisor and one other player in this story at a conference back then, and all were quite friendly. But the title of Takahashi’s 2008 paper, “Peahens do not prefer peacocks with more elaborate trains” was a direct jab at an earlier one, “Peahens prefer peacocks with more elaborate trains”, by Marion Petrie in the UK4. Takahashi and her coauthors had the difficult task of proving a negative – and they did it pretty convincingly, with the aid of a much more extensive data set than anyone had gathered before with this species. The upshot? For a peacock in Japan, having a bigger train ornament doesn’t necessarily win you any favours with the ladies.

Bigger in terms of the number of eyespots visible in the ornament during courtship, that is; males have about 150 on average, each on the end of a single feather. The results of the Japanese study were in direct contradiction to Marion Petrie’s earlier work as well as some recent studies of peafowl in France suggesting that eyespot number is often correlated with male mating success4,5. What’s more, in the 1990s Petrie had confirmed the causal effect of eyespots by showing that you could alter a male’s fate just by removing about 20 of them6.

Peacock in flight

Taken at the Los Angeles Arboretum in 2009. Photo by Roslyn Dakin.

The Japanese team proposed a rather bold new hypothesis. Perhaps the cumbersome, ridiculous train ornament is obsolete – a relic of sexual selection past, no longer used by females in quite the same way as it was when it first evolved3.

This was taken up with gusto by the news media. Check out the headlines: “Peacock feathers: That’s so last year”, “Have peacock tails lost their sexual allure?”, “Peacock feathers fail to impress the ladies”. Amusingly, this last article was also published with the title, “Female peacocks not impressed by male feathers” by Discovery News7-10. Males could probably be forgiven for striking out with those elusive female peacocks, since they don’t actually exist.

Headlines aside, Takahashi’s interpretation is somewhat of a concern. Here’s why: creationists picked up on this story too11.

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by Roslyn

Deep archives: Irreducible beauty

Peacocks and audience at the Toronto Zoo

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!

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by Roslyn

Deep archives: Lek perspective

Scene from a lek at the Bronx Zoo

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 birds 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:

Juvenile male lesser bird of paradise

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by Roslyn

Deep archives: Numbers, gathered

With our first two weeks of observations behind us, I thought I’d write about what we’ve gathered so far.

Fifteen copulations, all involving unstickered males: 6 for male 30, 5 for male 42, 3 for male 31, and 1 for male 38 (this last one is most triumphant since 38 is a male with stickers on the backs of his eyespots!). The remaining 16 males haven’t achieved anything yet, but that sort of skew (with the majority of males missing out on mating entirely) is normal for peafowl.

Two males display to a feeding peahen

Two males display to an uninterested female, while she feeds on some seeds provided by park visitors. Feeding the peafowl is not allowed.

Twelve attempts to touch the birds: okay, we haven’t really been counting (and if we had, this would probably outnumber the copulations). On a daily basis we scold people who try to touch and stroke the feathers of displaying peacocks. The offending demographic is about half children, half grown women; I feel a little bad about scolding the children, but grownups should know better.

Three soundbites: the most ridiculous one from a lady looking at a peacock with his train unfurled, overheard by Rob: “Now look at that and tell me there isn’t a creator!” Irreducibly beautiful indeed. The most astute comments have come from children: a couple of them exclaimed in surprise that the peacock feathers looked just like eyes, and today one boy asked, referring to the peacock’s crest feathers, “Why does he have a mohawk?”

One attempt by a juvenile male to mate with another juvenile male, and one attempt by an adult male to mate with a human female (not me). I think the former was a case of the juvenile males being eager to practice on anything, but I’m not sure about the latter.

And sadly, no Easter treats: yesterday was the “Great Easter Egg Hunt” at the Arboretum, and even though we thought we’d have an advantage over all the children since we’d be arriving when the treats were still being hidden, we failed to turn up anything. We also had to cut the morning short since all the commotion was impinging on lek activities.

As for Penelope, she’s staying in for now. Since there are real females about, I think a better use of our time is to get a handle on their preferences; I’ll bring Penelope out for round two in about a week or so.

by Roslyn

Deep archives: Eyeful or eyesore?

Experimental peacock

One of the main reasons for coming to California this year is that I’m doing an experiment to understand how peahens choose their mates. Specifically, I’m testing whether the colour of the males’ eyespot feathers is important.

My methods? Hundreds of coloured stickers, cut from sheets of sail tape.

The good news is the sail tape seems to work – most of the stickers stay on the feathers, and, since they’re so light, they don’t seem to have any effect on how easy it is for the males to display their tails.

I have a couple of treatment groups: control males with no stickers, males with black stickers (like the rather unlucky one pictured above; compare him to the male pictured here), and males with white stickers…

Experimental peacock

Everyone at the Arboretum wants to know what we’ve been finding. I have to shrug when they ask me – it will take many hours of observation over the next few weeks before I can say whether the black/white treatments have any effect on the females (we haven’t seen a single copulation yet). One thing I didn’t anticipate is the extent to which the white dots manage to captivate human observers. The black dots, on the other hand, don’t even get noticed by people. My guess is that the peahens won’t be so oblivious.

ps. The new header photograph of mechanical birds was taken by Charlie at the MIT museum. And, for those concerned about the possible effect of the weight of the stickers [Martin], we’ve applied stickers to the backs of the feathers of a bunch of birds as well…

Experimental control

by Roslyn

Deep archives: I get my hands dirty

One thing I’ve felt a little bad about here is the amount of shit, literally, that my field assistant Rob has had to deal with. He’s the one who has to hold each peacock still in his lap for about an hour while I carefully measure and apply stickers to all of their tail feathers, and he takes a hit whenever the peacocks do what any reasonable animal would do when restrained by a giant predator. And these hits happen frequently.

I realize that this kind of mess is all just part of field biology (and I tried to give Rob some advance warning to this effect). However, it’s one thing to talk about it and another thing entirely to be on the receiving end. I hope Rob was happy today when we came across a little mystery in the park that had me get my hands a little dirty as well – the mangled remains of a peacock tail, the first direct evidence of peacock predation that I’ve ever seen

The specimen had a few eyespot feathers and the longest train feathers intact, along with some of the golden-coloured lower back feathers and (brace yourself) the last few fleshy vertebrae. I dutifully checked through the train to make sure that it was not one of our banded males (we sample the longest 5 train feathers from all of them, so if this was a banded male I would have found evidence of this), and then I took all of the eyespot feathers I could find. This afternoon, I returned to the scene after realizing that I could measure the length of the tail as well. A quick check of the tape measure (101 cm) confirmed that this was definitely not one of our banded birds (all had tails well over 115 cm).

Some peacock forensics

Biology nerds might also be interested to know that the most of the eyespot feathers were missing from the tail (only the very longest and very shortest feathers were there). My guess is that the others were lost in the struggle, evidence that this bird may have indeed been caught by the tail.