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.

Deep archives: Penelope rolls out

Our first week of observations done, and we’ve already seen one copulation! Watching birds for hours on end at the Arboretum has actually proved to be quite enjoyable, due to the pleasant setting and perfect weather (apart from the fact that I’ve come down with a cold).

This post, however, will be about Penelope. Smuggled into Canada by Charlie, resurrected by Vanya, and given wheels with Charlie’s help again (see picture of driving practice here), Penelope is a stuffed peahen that I’m hoping to use for some behavioural experiments.

Eager to see what she could do, I whipped her out a couple of weeks ago when we were in the midst of catching and banding males (hoping that maybe she would entice some of our more difficult captures). Here’s a picture of her debut; it’s worth clicking on it and zooming in to see the peacock poking his head out from behind the pink chimney:

Penelope experiences some initial skepticism

(Photo credit: Rob Ewart)

Although the experience was hilarious, I found Penelope’s overall performance to be lacking. She inspired far more curiosity than lust on the part of the two males tested so far. Both stared intently and moved a little closer, but didn’t make a move. This could be due at least three things: (i) the unusual appearance of her wheels, (ii) her abnormal plumage colour (she was an injured bird from a farm that breeds birds with colour mutations, so she doesn’t quite look like a normal peahen), or (iii) her lack of grace/movement. We gave her another chance without the motorized base and got the same result, but there’s still no way to distinguish between (ii) and (iii) at this point.

I’m not giving up on Penelope yet. There were a lot of real, moving females around on that day, and the peacocks weren’t making any efforts towards them either . As the season progresses, the males should grow more restless (read: desperate), no doubt increasing her chance of success.

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

Deep archives: The opportunists

Soon, the city will be mine and Vigo’s… mainly Vigo’s.

Elephant seals trace letters on the beach

My friend Adriana recently confessed to me that, while she was enjoying this site, she’d been “skimming over the science stuff no offense”. I would like to assure her that yes, we have taken advantage of our days off here as well.

Early on, we had the good fortune of having a few visitors descend on Los Angeles from across North America: Charlie from Kingston, and Shiva and Paula driving all the way from Texas for President’s Day weekend. We saw the Getty museum and then went out for a ridiculously tasty dinner in Beverly Hills that, for the 5 of us, cost nearly what I make in a month as a grad student. At the table next to us, we noticed the Ghostbusters II actor quoted above – Jess I expect you to get this one without internet cheating!

Last week Rob and I traveled to San Francisco for a couple of days. We had been working at catching birds for 11 days straight, since I thought it would make the most sense to exhaust ourselves with catching and then take an extended break, allowing the birds time to settle down before starting observations. Rob has family in Palo Alto just a short drive away from San Francisco, so we were very lucky to have warm beds and delicious meals provided. We spent one day visiting the Monterey Aquarium (an amazing place) and one day getting a taste of San Francisco (quite literally – we visited Golden Gate Park and went for clam chowder at the waterfront before heading home). San Francisco is a beautiful city. We drove around some of the residential areas, and the houses have a lot of ingenious ways of dealing with the steep hills. I’m going to go there for another short visit on my way home to Canada in April – hopefully I’ll have more time to explore!

My favourite travel adventures seem to happen when you don’t have any expectations, and Rob and I found some of this kind of adventure on our way to San Francisco. We followed the winding route along the coastline on the way there, and happened upon a bunch of basking elephant seals on one of the beaches we passed (we only stopped because Rob was wondering what everyone else had pulled over for). Male elephant seals are 2-3 times the size of females. During the winter, they gather on the beach and fight violently over their harems. Unfortunately we were a few weeks too late to see the breeding activity: the harems were mostly rolling around, scratching themselves, yawning and tossing sand on their backs (as well as moulting and nursing a few pups, I guess). But they were still quite amazing creatures, and I was shocked at how close we were able to get (don’t worry – we kept to the path that had been marked out by an outfit called “Friends of the Elephant Seals”). The picture above is of some elephant seal wanderings, and here is one of a harem:

Elephant seal harems on the beach

Language Instincts: Grammar in nature

From November 18, 2006

Many linguists would claim that grammar is what sets human language apart from anything else in the animal world. Some would disagree – bird song, for example, can be quite complex and it is thought that there might be some rules involved in its underlying structure. The question is, at what level of complexity does this ‘grammar’ occur?

A couple of recent studies have examined these claims about animal grammar with respect to communication in monkeys and birds. The interesting thing is that while the monkey researchers claim that their study animals cannot understand complex grammar, the bird researchers claim that their animals can.

First, some grammatical background: the kind of structure we are talking about here is called recursive grammar. This is the ability to insert phrases or clauses within other clauses. For example, we humans can say, “The bird sang from his perch”, or we can go further and say, “The bird, who had just caught a worm, sang from his perch”. We can go further still: “The bird, who had just caught a worm that was wriggling in the dirt, sang from his perch”. It is theoretically possible to keep on adding to a sentence like this forever, and come up with something that is infinitely long (but technically understandable).

In a recent paper in the journal Nature, researchers working with starlings claim to have demonstrated that, much like humans, birds can understand recursive grammar. Their methods involved creating a series of artificial songs following two different patterns: half of the songs had a novel element embedded into the middle of the song, while in the other half this element was added to the beginning or the end of the song. The results were that starlings could eventually learn to distinguish the two song-structure types.

While these results are definitely interesting, they don’t justify any sweeping conclusions about starling grammar (not yet, anyways). The ability to remember and distinguish different song patterns is surely different from the ability to use the patterns for the communication of specific information. The authors of the study have countered that even if the birds are simply using memory to distinguish the song-types, this behaviour is still “remarkable and previously thought beyond the realm of non-human abilities.”

Cotton-top tamarins

Interestingly, a similar study using cotton-top tamarins seems to demonstrate that recursive grammar is beyond the ability of these monkeys. This research involved teaching the monkeys an artificial grammar using recorded sounds, and testing whether or not certain deviations from the learned sound-order captured the monkeys’ attention. Apparently, the monkeys could recognize recordings that violated simple grammatical rules, but they did not respond to recordings that violated recursive grammar.

The monkey study was published in the journal Science, and in the same issue the psychologist David Premack provides several reasons why he thinks animals have not evolved language in the human sense. Premack believes that besides the lack of complex grammar, the lack of teaching, imitation, and voluntary control of sensory-motor systems is what sets animal communication apart from human language. But I’m not so sure that animals like primates and birds lack imitation and teaching. In any case, it would be interesting to know more about the patterns and structures underlying the whole spectrum of animal communication.

Here is a National Geographic article on the cotton-top tamarin study, and a Seed magazine article on starling grammar.

Language Instincts: Human impacts on animal communication

Bird song

From November 5, 2006

As a change of pace from previous posts, I’d like to look into some of the ways that the human-altered environment may be impacting avian communication. Recently, a number of articles have been published that examine the impacts of human activities on bird song.

Some background on bird song

Bird song is a surprisingly complex communication system that we are only just beginning to understand. In most species, male birds use song for two reasons: to defend territory, or to attract a mate. In either case, song is thought to be an honest signal of individual quality, much like sexually-selected plumage.

When defending territory, males will often sing short, simple songs, and face off in vocal battles with rival males. Because singing is costly in terms of energy and time, only a male in good condition can sing loudly and continuously. When attracting a mate, however, males change their tune and sing longer, more complex songs. The function of song in sexual advertisement is very similar to elaborate plumage ornaments in that it signals individual quality to potential mates. For example, in many bird species, females prefer to mate with males who sing more complex songs or have larger repertoires. Experimental work with zebra finches has shown that males subjected to stress during development sing less complex songs later in life than males whose development was trouble-free. Thus, song complexity may be a good signal of genetic quality that females can use when picking a partner.

Bird song and background noise

The acoustic environment in a city is much different than in a natural setting. The background noise in human-altered environments is louder and generally lower in frequency than it is in natural habitat. This presents a problem for animals trying to communicate.

In the last few years, a number of studies have been published showing that birds in cities alter their song characteristics in response to urban environments, for example by singing at a higher frequency to communicate efficiently over low-frequency background noise. This is probably not the result of natural selection favouring birds with innately different songs in urban populations. Instead, it is probably due to birds born in cities learning to sing at a higher frequency in order to communicate effectively in their acoustic environment.

It has been suggested that local changes in bird song may lead to the divergence of communication systems between different populations. Because many female birds choose mates based on song characteristics, this divergence could lead to reproductive isolation between urban birds and surrounding populations. Cities therefore provide a unique opportunity for researches studying bird song in a number of different ways. Understanding how communication is altered in these environments may help us understand the evolution of signal diversity. At the same time, this work could help us understand the best ways to manage urban animal populations.

Language Instincts: The evolution of sexual signals

From October 28, 2006

This Thursday Al Uy from Syracuse University came to talk to the Ecology, Evolution and Behaviour group at Queen’s. Al spoke about his research on the ecology and evolution of visual signaling in birds.

Plumage colour in birds is known to be involved in conspecific communication, including the signaling of quality to potential mates. In many species, females can gain information about the condition or health of a certain male just by assessing the colour of his feathers. Sexual selection for honest signaling is often implicated in the evolution of brightly coloured plumage, much like the evolution of the peacock’s tail described in my last post.

Al Uy is interested in understanding how sexual selection might contribute to the speciation process, since changes in sexual signals can lead to reproductive isolation between two populations. He pointed out that this idea originated with Darwin, who noticed that often the only difference between closely related species is a sexually dimorphic trait such as male plumage colour. To understand why this might be, Al studies the plumage colour of small birds called the bearded manakins with an interesting mating system: the males gather at display sites called leks, where they clear an area of the forest floor and dance to attract females. There are several subspecies of bearded manakins, all with striking differences in male colouration (whereas the females are all plain and look alike). Here are two of the manakin subspecies Al works on (golden-collared and white-bearded males):

Golden-collared manakinWhite bearded manakin

The signal function of manakin beards

Al began his talk by discussing his investigation of the signal function of colour in the golden-collared manakin, which formed the groundwork for his research in signal diversification. Al and his students have found that the yellow colour of the male ‘beard’ plumage functions as a signal of male quality that females assess during male dancing displays, since males with brighter yellow beards tend to be larger, have higher display rates, and obtain more matings than their dull-bearded counterparts.

Al also tested whether the brightness of the male plumage translated into conspicuousness from the point of view of the female manakins. He used a model that took account of avian perception, ambient light during male display, the reflectance of male plumage and the reflectance of the visual background during display (the dancing court). Consistent with the predictions of sexual selection theory, male conspicuousness as calculated by this model was related to male mating success. In other words, more conspicuous males obtained more matings. Unexpectedly, Al found that the darkness of the visual background was actually more important in explaining the variation in mating success than plumage reflectance, suggesting an important role of the visual habitat in shaping conspicuousness and the evolution of lekking. Al thinks that the lek mating system might have arisen from males becoming more competitive for the specific areas of the forest providing the best visual background for display. In the near future Al plans to test this idea by comparing the reflectance properties of the lek habitat with other areas in the forest.

Why are there so many beard colours?

The next part of Al’s talk focused on his main research interest: understanding what factors might promote the diversification of sexual signals like manakin beard colour. The basic hypothesis he is testing is that changes in the visual habitat can drive the diversification of visual signals. In order for plumage colour to be conspicuous (and therefore most effective as a signal) it needs to match the available light, contrast the background, and be tuned to the receptivity of the target individuals (females). Changes in any of these factors could have promoted the evolution of the four different male colour types found in the bearded manakins.

Al plans to test this hypothesis in several ways. First, he will examine whether or not the evolution of retinal physiology might be driving the diversification of male colour. He plans test this idea by comparing the abundance of retinal cones between the different manakin subspecies. If females from different subspecies have retinas that are optimally sensitive to the beard colours of their mates, then changes in female perception might be driving changes in male beard colour.

Al is also testing his ideas about colour diversification by studying a hybrid zone of golden-collared and white-bearded manakin populations. This is an area of Costa Rica where a river divides populations of the two manakin subspecies, although the yellow plumage trait (found in golden-collared manakins) extends slightly into the white-beaded population. One hypothesis Al is currently testing is whether this trait introgression has occurred because yellow plumage is intrinsically more attractive to the manakin females, although at this point he can only speculate as to why this might be. Al is testing this possibility by examining mate choice in the area where both yellow and white males are competing for the same mates.

The other question Al would like to answer is: what stops yellow males from sweeping further into the white population? It seems unlikely that the river is a physical barrier isolating these populations since birds are certainly capable of crossing it. Instead, Al is looking into the possibility that a change in the visual habitat on either side of the river is maintaining the separation between these two populations. In other words, white birds in succeed in their habitat (despite some introgression of yellow males) because white is the most conspicuous and best colour for displaying in that habitat.

Although Al’s talk was a bit long, it was enjoyed by the audience at Queen’s for telling a complete story without being overly technical, and some went so far as to claim it was the “best talk ever” (Dev Aiama). You can read more about Al Uy’s research here.

Language Instincts: Sex and honesty, or the mating scene for peacocks

Choosing between two males

From October 28, 2006

It doesn’t take an expert to realize that the extravagant song, dance and plumage of male birds (see videos in my last post) are intended as some sort of communication to potential mates. However, the insight that sexual ornaments are signals was a critical one that provided a mechanism for sexual selection and vindicated one of Darwin’s most important ideas. Darwin, of course, was the first to point out that extravagant male traits persist despite their probable costs because females prefer them. The example Darwin often referred to is the enormous and flashy tail of the male peacock (you can see for yourself at this online collection of all of Darwin’s writings).

It wasn’t until the 1970s when Amotz Zahavi suggested his handicap principle that we really began to understand why females prefer certain males. Zahavi’s idea was that extravagant sexual ornaments should be thought of as signals, and these signals are not selected in spite of their costliness but because of their costliness. A costly signal is an honest one; only the highest quality males can express it to its fullest extent. Females should be selected to prefer traits that are costly for males to produce because preference for an honest signal should yield the most benefits. Preference for a dishonest signal (one that a low-quality male could fake) should be weeded out by natural selection.

Darwinians had to wait a long time for honest signaling theory, and they had to wait even longer for someone to test these ideas with respect to the peacock. In the late 1980s and early Marion Petrie began to study what peahens actually look for in a mate. Following the love lives of peafowl in a London zoo, Petrie found a correlation between the number of eye-spots on a male tail and the number of peahens willing to mate with him.

Petrie’s next step was to test this correlation experimentally by decreasing the number of eye-spots on the tails of some males (by simply cutting them off). The question was whether the number of eye-spots directly influences mating success. Her results? Males who had eyespots removed were significantly worse off in terms of their number of mates compared with their mating success in the previous year.

Petrie also looked at the quality of peacock offspring, and found that the larger the eye-spots of a peacock dad, the better his offspring survive, suggesting that males with more extravagant tails are high quality individuals. This means that peahens gain a genetic benefit for their offspring by mating with well-plumed males. So the tail of the peacock would appear to be an honest signal of male quality rather than an arbitrary preference after all.

One other intriguing result of the work done by Petrie and her colleagues is that peacocks tend to display close to their kin. This suggests that kin selection has shaped males to aid their kin in attracting more females, and may provide a reason why poor-quality males who don’t get any mates bother to display at all. Interestingly, experimental work has shown that peacocks are able to recognize their brothers even when they do not hatch from the same nest. My question is: is it possible that birds might use some sort of visual cues that involve plumage for kin recognition?

Language Instincts: Advertising sex

From October 24, 2006

…bird sex, that is.

Male birds will do some pretty bizarre things in the name of sex. Here are some examples of displays put on by males in order to advertise their quality to potential mates (all the clips are from David Attenborough’s “Life of Birds” series for the BBC).

The superb lyrebird of Australia builds a small mound in the forest and sings a complex tune combining his own songs with songs (and noises) that he picks up from his environment:

Superb Lyrebird

The birds of paradise of Papua New Guinea are a strange bunch. Here are some clips of the extraordinary visual displays performed by these males:

Birds of Paradise

Wilson’s bird of paradise also has a very strange pattern of ornamental plumage (this video is also hilarious because of Attenborough’s sneaky hiding places):

Wilson’s Bird of Paradise

More to come on the topic of sexual signaling soon!