Sage-grouse are a lekking species, in which many males cluster together to court females from small display territories. Each male performs an elaborate, stereotyped visual and acoustic display, and females are free to ‘shop around’ for mates. Males do not provide any resources or parental care, so we think a female chooses her mate for the genetic material he will pass on to her offspring. In spite of decades of research on sage-grouse, we still have much to learn about what makes certain males attractive. Evidence points to the acoustic signals being important; this forms the basis of much of the research program in Gail Patricelli’s lab. In 2006 we began a detailed study of sexual signaling near Lander, Wyoming.
Here’s a quick video of the spectacular display of the male sage-grouse. To see more, please visit my Youtube channel as well as the Patricelli Lab Youtube channel. You can also find links to additional photo galleries on my Photos page.
How do males adaptively vary their displays?
Models of sexual selection usually assume individuals have a single value for a given trait, and although animals typically vary their displays, this variation is often considered noise. We are attempting to understand how males might tactically alter their signalling behavior. We employ a combination of extensive field observations of mating success, video and audio recordings of courtship behavior, and experimental introductions of a realistic robotic female grouse that we can use to elicit changes in male display. First, we asked how males try to optimize both display rate and display amplitude (we believe females prefer both more and louder displays, but these two traits may negatively covary). We found that only non-preferred males faced this trade-off, while preferred males seemed to be able to increase both quantity and quality of displays. This study was recently published in Behavioral Ecology. Secondly, we will see how males use the unique directionality of their acoustic displays, and ask whether successful males are better able to aim their signals at the intended female receivers. The analysis for this is ongoing, and has led to additional undergraduate and post-graduate research projects measuring side biases in behavior in the sage-grouse (akin to left-handed/right-handed phenomena in humans). I presented preliminary results from these analyses at a recent meeting of the Animal Behavior Society.
Our current research is focusing on further understanding variation within and among males in their display effort. If females prefer males that “work hard”, why shouldn’t males always display at their maximum rate? We are using economic models of bargaining and negotiation to try to understand the interactions between males and females that might dictate how hard males should court and how long they should persist in courtship. Leks are great places to understand how market forces might affect courtship- the lek can be thought of as a large open-air bazaar where both males and females have some control of different stages in the courtship process, and both may have outside options that may influence their bargaining behavior. Our first prospectus on this framework was published in Current Zoology in 2011.
While examining sound spectrograms from our microphone array, we found evidence that males were in fact producing two simultaneous, non-harmonically related tones in the whistle. This points to a two-voiced system in which the syrinx– analogous to our larynx– has two sites of sound generation (although a phenomenon called biphonation could also account for the two tones). This was not known for grouse (in spite of decades of work by other researchers on sage-grouse vocal displays), or, in fact, from the galliform (a.k.a chicken-like) birds at all, and has initiated research on how sage-grouse and related birds make sounds. Our first paper describing this work was published in the Journal of Experimental Biology in 2009.
The mechanical sounds mentioned earlier have received relatively little attention from biologists. We have collaborators working on the mechanism of frequency modulation in these stridulations (more on this when it is ready for prime-time). Along side this mechanistic work, we are quantifying variation within and among males to determine whether there is any relationship between time or frequency components and male mating success, whether males might vary these depending on social context, and whether they could potentially be informative in individual identification. These analyses are led by our former undergraduate Becca Koch. We have a draft manuscript in prep, and Becca presented a preliminary analysis at the recent Animal Behavior Society meeting in Bloomington, Indiana.
How does the environment affect signaling?
While we expect much of the perceived differences in male displays are due to differences among the males themselves, we do know males fight for territories; another goal of our research is to compare territory quality- i.e. how well sound propagates across the substrate, and whether this relates to the mating success of males. We first mapped male territories and identified favored display sites. We then went in at night to broadcast sound from these sites (as well as less preferred sites within and outside of territories), and recorded how much sound made it to microphones placed in a ring around this omnidirectional speaker,and to microphones in the array. Analyses on these questions are ongoing.