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: 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.

Deep archives: Lek in flux

The peacocks here are fickle.

Just when we think the good stuff is about to begin, we’ll have a day where all they want to do is sleep and eat. And it doesn’t seem to be based on the weather (at least not in any simple way), since the activity level has waxed and waned over the past week despite consistently warm clear days.

The one thing we’re sure of is this: we arrived here just on the cusp of the breeding season (more or less perfect timing, although possibly a little too early). We didn’t see any males display their trains our first day, but as time wore on we saw a few opportunistic male dances (despite a lack of female interest). About a week in, we started to hear a lot more calling by males in the morning, and we saw a few more displays and a little male-male aggression. It seemed as though males were starting to establish their territories. Each morning, we’d notice them spreading a little further away from the ideal habitat around the park entrance and cafe.

One morning this week we saw five males positioned strategically around the outskirts of a the big lawn to the north of the cafe, stationary but neither feeding nor resting (which certainly suggests territorial behaviour to me). The next day, a handful of new males had spread into the staff parking lot where we process captured birds. When we brought our first catch of the day back into the shady corner of the lot for processing, one of these new males started following us. A beggar, we initially thought, until he actually started trying to attack the bird Rob had in hand. Apparently the sight of male plumage is enough to provoke an attack even if it’s suspended above the ground under the arm of a giant! We’ve solved this problem by moving our sampling station and by having me chase away the odd interrupting bird (which sometimes ends in both of us running in circles).

Most recently, we are starting to see a few males in regular territories but we still can’t tell what is going on with the bulk of them. Our strategy is to put all of our efforts into catching until the middle of next week. Then, we’ll head to San Francisco for a couple of days off and hope that things will settle down by the time we get back!

Deep archives: Advanced moves

A follow-up to my previous post:

The other day, we were back at the Arboretum in the afternoon to catch birds during the second active time for peafowl (the birds like to get things done in the early morning and late afternoon, with an extended siesta between noon and 4pm). Within minutes of arriving, we’d caught our first male, but didn’t finish processing him until about 5 pm. Sunset was approaching and I didn’t think we’d have enough daylight to nab another. I headed to the bathroom to wash the peablood off of my hands and Rob went to check on our most recent capture, with the understanding that we’d meet back at the car in a few minutes and head home.

On my way back from the bathroom, Rob emerged from behind some shrubbery clutching yet another peacock, this one caught singlehandedly!

As we raced to process this bird before sunset, Rob rather excitedly explained how he’d accomplished his feat. First, he grabbed the bird’s legs from behind as we normally do. Then, he spent a few moments calling out for me, and when he realized I wasn’t coming he sat and puzzled over what he had to do next: singlehandedly get the bird into the reverse position where he would be able to use his body to secure its wings without letting it go.

While I’m still not too clear on the details, I can tell you this much: it involved kicking off his sandals and using his feet.

Deep archives: How to wrangle a peacock

1. Lure them with food, fish nets at hand. Realize that peacocks, although desperately hungry and willing to come perilously close to human feeders, are not willing to present their backsides to you. Also realize that peacocks know what nets are, and are capable of learning which people are associated with food, and which are associated with nets. Begin to despair that peacocks are much better adapted than previously thought.

2. Decide that fish nets are far too inefficient. Dream up a design for a netted trap that lies flat on the ground (food placed in the middle) with handles at either end for peacock wranglers to hold. Trap has netted sides and a netted top that can be drawn closed by lines also held by the two wranglers. Once a bird is lured into the middle of the trap, wranglers can raise the net and pull it closed over the bird. Spend several days seeking out parts and building this trap using PVC piping and garden trellis netting in the junkyard behind the Arboretum green houses, only to find that peafowl are suspicious of the PVC piping and unwilling to step over it to get at the food in the centre. With a great deal of patience, manage to coax one male into the centre of the trap, but just barely miss catching him when the net is drawn closed too slowly.

3. Design two other traps: one snare for snagging the bastards’ feet with a line (complete with a pulley system to ensure extreme speed of snaring) and one remote-controlled caribiner (similarly intended to hook and grab the legs). Decide that the caribiner might present a high risk of leg injury. Discover that although the birds are wary of the snare, it can be more easily camouflaged and thus has potential.

4. After two near-captures with the snare one morning, spot a male displaying to the females who were drawn to the area by our snare bait (peanuts). Have one wrangler sneak up behind this extremely focused male in the throes of his display and grab his legs firmly from behind (note that person must overcome fear of projectile excrement first). Have the second wrangler swoop in to secure the wings.

So far we’ve managed to catch 14 adult males here using technique no. 4… and much to my relief, we are starting to see the banded males regularly in certain areas around the park. If anyone has any more suggestions for how we might go about catching these birds I’d love to hear them!

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: Do animals lie?

Liar

From November 11, 2006

In my last few posts you may have noticed a theme: signals that are used to advertise sex in the animal world are generally thought to be honest ones. In fact, animal communication in general is pretty truthful. There may be different reasons for this: some signals may be impossible to fake (for instance, toad calls may contain honest information about the caller’s size simply because bigger bodies produce lower-frequency sounds). But even when a signal could be faked, the evolution of dishonest signaling is very unlikely. There is a simple reason for this: in the long run it would not benefit receivers to respond to a signal that could be cheated.

This is something that we might find surprising given the amount of deception that goes on in human interactions. Is deception really so rare in animal communication systems? Are there any animals liars?

We have some examples of deceptive communication between different species: for example, ground-nesting birds will fake an injury to draw a predator away from their nest, and some birds in mixed-species flocks will give false alarm calls to increase their own foraging success. Within species, however, the examples of deception are few. We know deceptive communication occurs within a number of primate species. Interestingly, some recent work using ravens has shown that, much like many primates, birds may also be capable of intentionally deceiving conspecifics.

This result came as a bit of an accident during an experimental study on social learning and scrounging in foraging ravens. The researchers provided their ravens with a series of covered plastic boxes that served as food caches (some containing pieces of cheese; some empty). The boxes were arranged in clusters and ravens were videotaped during their foraging explorations. Right from the start, the researchers noticed an interesting pattern between a pair of male ravens: rather than search for his own food, a dominant male relied on a subordinate male’s explorations, following the subordinate male around and eating the food that he discovered.

It eventually became apparent to the researchers that the subordinate raven wasn’t the only one being exploited in this situation. He had developed a strategy to trick his competitor. Whenever the subordinate male found a cluster of boxes containing food, he would quickly move on to a different cluster and start opening boxes there. The dominant male would soon follow, leaving the subordinate free to return to the other boxes and enjoy his snacks at leisure.

The parallels here to primate behaviour are interesting: chimpanzees have been known to walk away from a food site in order to induce other group members to do the same, and then return later to enjoy the food in privacy. Does the ability to communicate deceptively say something special about the cognitive evolution of a species?

You can read the raven study here.

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: 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!

Language Instincts: “Run, run as fast as you can, you can’t catch me…”

Motmot

From October 5, 2006

What does the racquet-shaped tail of a turquoise-browed motmot (the bird seen at right) have in common with the tail of a deer and the rhyming gingerbread man of fairy tale fame?

They are all important signals in the communication with predators.

The turquoise-browed motmot has a strange looking tail. The two central tail feathers are elongated and designed with weaker barbs towards the ends of the feathers. These barbs wear away to give the feathers an unmistakable tennis-racket shape. When faced with a predator, the motmot will repeatedly wag its tail from side to side in an exaggerated, pendulum-like way (see video of a related motmot species performing the wag display here). Bold move, you might think – and you would be right. The wag display will often draw the one’s eye to a motmot that might not have been seen otherwise, and no doubt it has the same attention-grabbing effect on predators. So why do it?

A researcher from Cornell University, Troy G. Murphy, recently looked into this problem, studying motmot colonies that nest in abandoned quarries and wells in Mexico. He developed several hypotheses to explain the tail wagging behaviour, and then performed careful observations of the context of over 100 wag displays to discriminate between the explanations.

His hypotheses were as follows: (i) The motmot wags its tail as a warning alarm signal to other motmots, alerting them to the presence of the predator. This means that the signal would be beneficial to nearby individuals (such as kin or mates) even though it might be dangerous for the signaler to draw attention to himself. (ii) The motmot wags its tail as a self-preservation alarm signal. The signal should still be directed to other motmots, but instead of being dangerous for the signaler it might benefit him by encouraging other nearby motmots to move closer together or even mob (attack) the predator. (iii) The motmot wags its tail as a pursuit-deterrent signal directed at the predator itself. Much like the gingerbread man, the tail wag would say, “Run, run as fast as you can, you can’t catch me…” This kind of predator-prey communication would actually benefit both adversaries: the prey gets to stay where he is while the predator avoids wasting energy on what would probably be futile chase.

Murphy found that when presented with a predator, the turquoise-browed motmot will perform the wag display even if it is alone and not within sight of other motmots. He also found that motmots are just as likely to tail-wag when they are alone as when they are near their mate, or near any other motmots. These observations allow us to reject (i) since the display is obviously not intended for motmot receivers. Murphy was also able to reject (ii) since the birds do not move closer together or mob when a predator approaches.

From this evidence we can conclude that the tail wagging must be a signal to the predator, communicating that the motmot has spotted the threat and is ready to escape. Interestingly, the tail of many ungulates has a similar pursuit-deterrence function. For example, some white-tailed deer will signal to chasing predators by flagging their conspicuous tails. Pursuit-deterrence signals have also been observed in lizards (arm-waving to deter predators) and fish (swimming right up and inspecting predators directly to deter them). Too bad for the gingerbread man – if he had stayed in one place and relied on his signaling he might not have been eaten after all.