It’s March 31st, and as we trundle towards April, I realize how tardy I have been with general updates this year. Every season is a little different, and this one is throwing us some curves.
Nine Mile Hill shrouded in snow.
We saw our first copulation on our biggest lek, Cottontail Lek ten days ago (March 21st). This date is pretty normal. We’ve found one earlier (March 19th) in a couple of years, and later some other years. Usually once we see the first one, within a few days every lek is showing multiple copulations. Not this year! We got hit with a blast of really cold weather (lows around 10℉) as well as a few inches of snow. The females seemed rethink their interest in the males, and it was several days later before we saw the next mating on any of the leks. So while the breeding season opened at a fairly average time, I think the season as a whole is going to be on the late side. On balance, I’m not sure if this will be good or bad for our work this year. The longer we have big groups of real females on the lek, the harder it will be to give our robotic females a private audience. On the other hand, the males may stay interested in courtship a little bit longer so we may not have the problem of the males just giving up at the end of the season the way they sometimes do. We’ll have to see what happens!
Two male sage-grouse battle in the fresh snow on Chugwater Lek.
Other challenges we’ve had to contend with are the incredible shrinking leks. Our initial impression from the first couple of weeks of the season seems to be correct– male attendance is down considerably from last year in our area. This may be due to the drought the Lander area is experiencing, at least there’s not an obvious other candidate for the decline. Our sage-grouse manager contacts have mentioned that the rough demographic analysis from hunting data suggested low recruitment (not many yearling birds taken compared to the number of adults).
To give you a sense of the change in abundance since we started the project here: Monument Lek, our main focal lek since 2006 when it had over 100 males, has dropped to under 10 birds and males are not staying as reliably on their territories. Anna has still gotten some playback experiments done, but Monument is right on the edge of being useful or not as one of our experimental leks. We just showed the PBS Nature episode featuring our research (“What Females Want…”) as part of another outreach event down at the Lander Public Library. The footage was shot in 2007 when the male counts were an order of magnitude higher. The difference definitely makes us a little sad, and we are hoping this lek rebounds quickly as it has done in the past. Sue at the BLM told us that in the 80’s it was down to 4 birds, and later climbed back to over 100, so we hope this is another one of those cycles.
Shallow trenches prepared for laying microphone cables at Monument Lek. This lets us put microphones all over the lek, while keeping the cables underground. The speakers are for the playback experiment.
Otherwise we are in pretty good shape with most of our “normal” tasks. We have microphone arrays deployed on all three focal leks now, and have gotten several days of sound recording in. We’ve also gotten at least one round of counts at our non-focal leks, to help the local sage-grouse managers monitor the grouse population in the district. The only things we are missing are the new robots (Gail is working on taxidermy aspects now, so those should be ready soon), and the encounternet telemetry tags. I say “only”, although those are definitely two very important pieces for our research goals this year and in the next couple of years!
In my last post, I talked about the usefulness of our robotic grouse for studying complex social interactions on the lek. This week we tried another method for modifying a male’s social experience– audio playback.
Male Sage-Grouse listening to our rock speakers.
We have a long history of playing back sounds to the Sage-Grouse. For the first several years our basic behavior studies were running along side the ‘Noise Project’, an extensive research program into the effects of noise associated with energy development on the grouse. The centerpiece of the Noise Project was playing back the sounds of two common noise sources (drilling sounds and road noise) from the Pinedale Anticline/Upper Green River area. We used fake rock speakers, possibly the same kinds you might have seen in a SkyMall catalog, to play these sounds at leks, and compare how many birds showed up and their behavior between the noisy leks and control leks that had. I’ll talk more about the results from this project in a future post.
We also used the speakers in 2011, this time as part of the basic behavioral research program. We’ve been interested in the importance of “courtship skills” in the males, and part of that is how attuned males are to changes in their social environment. Does a male change his courtship behavior a lot when a female gets closer, or not very much? Our first experiment with the fembot showed this was related to the success a male has in courting females.
One species used in our 2011 playback study: Pronghorn
Our experiment in 2011 was designed to look at another dimension of responsiveness- how attuned are males to the threat of potential predators? Here we chose alarm calls o f three different species that live with the sage-grouse: ravens, killdeer, and pronghorn antelope. We played these from the rock speakers and measured the strength of the grouses’ reaction, as well as how long it took them to resume their original behavior. Analysis is ongoing, so we don’t yet know how this sort of “ecological” responsiveness relates to their social responsiveness or their success on the lek.
Fast forward to 2013, and we’ve set up the speakers once again, this time to measure how males respond to other males. It would be great to have a robotic male, but as you can imagine, making a mechanical male that is realistic enough to give a convincing display would be a steep technical challenge (never mind making one sturdy enough to withstand an attacking male). Instead, we are playing back the sounds of male struts from the rock speakers to see how males respond to a simulated male at the edge of the lek. Anna has been putting together recordings with different call rates, so we can see if they are attuned to differences in the signals that males may be sending out. We’ve only just begun, but this will hopefully allow us to collect some interesting data on how males respond to other males while Gail puts together the new fleet of robots.
We also played a control vocalization– Horned Lark.
In other news, we observed the first copulation of the season yesterday! The breeding season has officially begun. Our earliest observation ever was on March 19th (in two different years), so we are on the early end of things.
Yesterday we got to take off our researcher hats and put on our outreach hats (we also traded our field clothes for some clean pants). Gail and I brought “Snooki”, the latest version of our robotic female grouse, down to Lander to participate in Teen Tech Week at the public library. Word had spread among the library staff; they were quite excited to get to meet the robot in person. Some of the kids were apprehensive, but most jumped right in to give the test drive. I had loaded some videos of the fembot and the grouse on my iPad so they could see how she looked in action.
With the exception of the wheels, the robot makes a pretty convincing sage-grouse. This version has the mechanics tucked inside a fiberglass shell that was poured over a grouse-specific taxidermy mold. Gail artfully arranged real grouse skins over this to complete the disguise. “Snooki” can turn in place using the wheels, the body can pivot down, the neck bend up and down, and the head can swivel back and forth. You can see a video of the fembot in action at the bottom of this post.
Fembot (left) and "undressed" fembot, right.
One of the common questions we get at this sort of event is “Is the robot just for fun? What do you do with it?” Let me take a moment to answer that.
Our robotic sage-grouse
In my recent post, I talked about how we use leks as a way to study sexual selection and mate choice. Most studies of lekking animals have looked at male traits that don’t vary much over the course of the breeding season. For example, in peafowl, biologists can look at which males have the longest tails or most tail eye-spots, and see if that might relate to patterns of mate choice. You could picture this as each male holding up a sign with his “score”, and females look around until they find the male with the highest score.
Anyone who’s watched animal courtship knows that males and females aren’t always politely assessing each other from a distance. Real courtship often involves complex decisions and interactions: deciding whom to approach, how quickly, reading signals or cues and responding accordingly. For a male to succeed in the mating game, the skills required to navigate the complex world of courtship can be as important as the physical traits he carries. Some of you may even have personal experience with this situation– meeting someone who is very attractive but who comes on a little too strong, for example.
Unfortunately we don’t know much about the importance of these “social skills” in non-humans because they can be hard to measure, especially in the wild. This is where the robot comes in. With a robotic female, we can control one side of the conversation. The fembot gives us two important tools for comparing males on the lek.
Male courting fembot.
First, it presents all males with a standardized stimulus. In live courtships, females may approach the top guys much more closely and provide signals of interest, while other males are consistently given the cold shoulder. The robot lets us measure all the males on an even playing field.
Second, it allows us to experimentally control the conditions of courtship. In a previous experiment, we could look at how male sage-grouse responded to a very basic aspect of female behavior– how close or far away she is from a male. With the more advanced version of the robot that we debuted last year, we could send either “coy” or “interested” signals to the males. I’ll describe the plan for this year’s experiments when we get a little closer to conducting them.
The older version of the robot ran on train tracks. Here we are moving her closer to two admirers.
The robot also serves an important function as a target of courtship- one of the skills we are interested in is the male’s ability to aim his best signal at the female, and in a past iteration, the robot could record what a female would hear, rather than what a biologist can record from some arbitrary position on the lek.
There are several ways that biologists can manipulate an animal’s social environment (video playbacks in the lab, audio playbacks of bird song, etc), but the robot gives us a unique way to interact with animals in wild.
Although we are based out of the University of California Davis, our field studies of Sage-Grouse take us to west-central Wyoming. This is one of the best places to find this species, with lots of good habitat for the grouse and other sagebrush specialists.
View from our camp, 2011
It’s also a stunningly beautiful place to get to work. Our camp looks out on the eastern face of the Wind River Range, a spine of the Continental Divide near Lander, Wyoming. Although we are less than an hour from town, we feel like we are in the middle of nowhere. We can see distant lights from Riverton, and a bit of city glow from Lander, but otherwise we have this patch of heaven almost to ourselves.
Driving through Nevada
The first challenge we face is simply getting all of our gear out to the site. This takes careful packing followed by a long drive through the lonely spaces of Nevada and Utah.
Work trailer arrives.
Once we’ve landed in Lander, the next step is to get the camp set up. Besides our RV, we have to rent a work trailer, as well as propane service. Thankfully we have electricity; there’s a line that runs the well pump for the cattle water tanks in the summer that we can use in the spring (the cows don’t come up until May when we are done with our research- we’ve been fortunate to coordinate with the local grazing leaseholders on this).
Propane tank arrives- nice to have heat, hot water, and cooking capability without having to run into town to fill canisters all the time.
Home sweet home.
Looking for tracks or poop on the lek.
Our first field technicians arrived on March 3rd, and the following day we were out at dawn looking for grouse on the leks. It’s still very early in the season- at least 2 weeks before the earliest sage-grouse mating we’ve ever recorded during our years out here. This means some leks will still be empty while others will have a few males starting to set up territories. Our first visit is to the most accessible lek called Chugwater Lek (in our area each display ground has a unique name). We didn’t see any birds, and a search of the lek surface showed no fresh sign. Our first birds didn’t show up here until March 7.
Scanning Cottontail Lek to count grouse.
Cottontail Lek is our largest lek, and on our first visits there we did find males starting to set up territories. This was the first chance for the crew to see the courtship display, and they were suitably impressed (just wait until they get to experience it from a blind down on the lek instead of a distant look-out point!) We were also treated to a large herd of pronghorn moving past in the early morning light. This was also a new animal for some on the crew. They are taking to the western wildlife quickly, although some are still getting used to the idea of a landscape without any trees!
Pronghorn Antelope near Cottontail Lek
Over the next couple of weeks we will be gearing up for our data collection, which will involve setting up a grid of stakes on the lek to help with territory mapping, installing microphone cables on the leks, starting to get photographs of the males to distinguish them, and hopefully capturing and banding some as well.
I’m kicking off my blog for the 2013 research season with a brief description of what makes sage-grouse such a great bird to study for someone interested in animal behavior and evolutionary biology.
Male sage-grouse courts a female.
One of North America’s most spectacular birds is also a species that not many people have seen. I’m referring to sage-grouse: I study the more widely distributed greater sage-grouse (Centrocercus urophasianus); I have yet to personally see the less common Gunnison’s sage-grouse (Centrocercus minimus), but that is definitely on my wish list. Given the spectacular plumage of a male sage-grouse in display, why are these birds so hard to see? A quick look at a female sage-grouse tells you the girls are built for crypsis- well adapted to blending in with their environment. For most of the year male sage-grouse also play the hiding game, so unless scared into flight they may pass unnoticed. Yet for a couple of months in winter and spring, males come into their traditional display grounds (called leks, from a Swedish word for “child’s play”) and put on one of the greatest shows on earth. These leks are often in fairly remote areas, and males typically attend them only in the early morning hours. Both of these reasons help explain why getting a look at this spectacle can be a bit of a challenge.
These unusual breeding clusters have captivated not only birders but evolutionary biologists as well. In about 90% of birds, both parents provide some care for the nestlings. In those cases, females are often choosing their mates at least partly on the material benefits they get from this partnership, whether it be the quality of the male’s territory or his ability to provision the female during incubation or the chicks once they’ve hatched. [Note- in many birds males and females mate outside of this pair bond, but that is a tale for another day]. Lekking species are therefore unusual among birds in that males don’t form a bond with their mate nor provide any child care. Scientists are still trying to unravel some of the puzzles that leks represent. Why do males cluster together to display, rather than searching around for females, following females around, or spacing themselves farther apart and defending larger territories like most other birds do? If males aren’t helping raise the kids, why are females so picky? What benefits do females get from choosing one male instead of another? And given that females often pick only a few among the many males on a lek, why do the “loser” males bother to stick around?
(This is a 3-hour time lapse video of the lek. The males appear as small black-and-white specks at the bottom of the frame)
Lekking animals also tend to be high on the charisma scale. Besides the spectacular sage-grouse and their cousins the prairie chickens and sharp-tailed grouse, other lek-breeders include some of the most beautiful and acrobatic birds out there, including birds of paradise, neotropical manakins, peacocks, cock-of-the-rock, some hummingbirds, and ruffs. When we see a species in which males are larger or more colorful than females, we presume these differences are related to an evolutionary process called sexual selection, where one sex- often the males- competes either directly for access to females or indirectly by producing the best advertisement among the other males. This certainly seems plausible for sage-grouse; not only are adult males almost twice the weight of females, but they have a range of specialized feathers, brightened skin patches, and other unique structures.
Male sage-grouse showing his inflated vocal sacs.
The distinctive air-filled vocal sacs are actually part of the digestive system; once inflated with air, powerful muscles just under the skin help move and shape the them during display. In spite of decades of research and routine collection by hunters, we are still finding surprising structures in these birds. Just recently we discovered that male sage-grouse have an almost songbird-like syrinx (sound-producing organ analagous to the human larynx) capable of producing two tones at once. All of this adds up to the bizarre appearance of the male that has presumably evolved through sexual selection- the males with the more elaborate versions of these unique features get to mate with more females and pass on more copies of their genes to the next generation.
These differences between males and females extend to courtship behaviors as well; males and only males have a characteristic “strut” display. A male’s strut serves to attract females to the lek from across the landscape, to woo females once they are on the lek, and most likely to help claim their small patch in the midst of all the other males. Each display lasts about two seconds and involves coordinated movements of the wings and body.
For sage-grouse, courtship is not just a visual spectacle. Males produce a variety of sounds during the strut display. The first two notes actually are not vocalizations at all, but instead made by rubbing stiff, pointed breast feathers against the inside of the wings. This is somewhat analogous to how crickets chirp. Making sounds with feathers may sound unusual, but it has evolved repeatedly in birds. Some common species in the Bay Area that do this include Mourning Doves (the ‘wee-wee-wee-wee’ made during take off) and Anna’s Hummingbirds (the loud chirp made at the nadir of the male’s dive display).
Spectrogram of a sage-grouse display. The two feather-produced 'swish' notes occur at about 2.6 and 3.6 seconds. The first low frequency 'coo' note is at 4 seconds, and is followed by the pop-whistle-pop at about 4.3 seconds. You can hear this in the video above.
The remaining notes are true vocalizations made by the syrinx, although unlike most birds they are made with the beak closed. These sounds start with a series of three low frequency ‘coo’ notes, and conclude with an up-down-up ‘whistle’ note sandwiched between two staccato ‘pops’. You can see these in the spectrogram- this is a visual representation of sound and you can read it much like reading music, with time progressing towards the right, pitch becoming higher towards the top of the figure, and the darkness representing something like loudness. Females may care about some very subtle differences in these sounds when they are looking for a high quality mate. Researchers have compared sound recordings of successful and unsuccessful males and found differences in the relative timing of the two ‘pop’ notes, and maybe the loudness of the whistle. What is amazing is that the differences between ‘Mr. Right’ and ‘Mr. Wrong’ are on the order of less than a tenth of a second. Females may have quite the ear when it comes to picking their mate!
That’s a quick introduction to sage-grouse in the spring. I feel extremely lucky to have heard and seen this show for the past several years as part of my research at the University of California, Davis. Along with Professor Gail Particelli, graduate student Anna Perry, and our intrepid field crew, we will be conducting research into several aspects of sage-grouse behavior and ecology from our field site just east of the Wind River Range in Wyoming. Over the next couple of months I’ll be discussing what it takes to set up a camp like this, how we use new technologies (including robotic birds!) to study courtship in this species, and review some of the conservation studies out of our lab. I hope you’ll join me for our 2013 field season!
