Here’s another fascinating piece of natural history from the Cornell Lab of Ornithology. In this series of short observations staff producer and biologist Marc Dantzker breaks down the mating behavior and social interaction of the Greater Sage-Grouse (Centrocercus urophasianus) in five sections.
Lekking or lek mating is a breeding behavior where males come together in a place and perform competitive displays to impress visiting females. While males do their “hello check me out” dances, females asses their qualities and choose their partners for copulation. What are the characters that make a male “handsome” to the females in this breeding aggregation?
“It’s my turf…”
Most of the lek mating activity is male to male aggression. Males claim small patches of lek areas and defend their territories. Physical fighting is a costly and risky behavior because of potential deadly injuries. For this reason most male to male aggression are ritualized indirect aggression to minimize direct contact. However things can quickly flare up and escalate into a full blown fight. Outcome of these fights determine the boundaries of the territories as well as decision making of females.
The Male Display
“Males display, females choose” may appear to be a general rule in nature but sex roles can change depending on who does the highest investment in reproduction. In seahorses and pipefishes males become pregnant and take care of babies and therefore females compete for males.
Back to the question: What are the characters females are looking for? Females want to see “honest signals” that demonstrates genetic quality of males which will increase the survival chances of the offspring. Males therefore have exaggerated armaments and ornaments that spark supernormal stimuli in female brains. The plumage and display choreography of elite male Sage Grouses is selected by females over many generations.
Females are the ultimate judges. How consistent is a male? Was that a one time cool display or can he do it again (and again)? Birds are excellent group of animals to study supernormal stimuli but it also affects other animals. Take the mane of a male lion for example. Female lions love dark manes which is extremely burdensome for males in the intense heat of the African savanna. This time it is not the aggressive physical qualities but the defiance of the male against the environmental background is the stimulus. All these factors get tallied up by female judges and thus some males become more successful in reproducing compared to the others. Biologists call this phenomenon as reproductive dominance.
Elite males are therefore reproductively dominant individuals that females prefer. Elite males carry qualities that will contribute to the survival of offspring. In 1930 an influential biologist R.A. Fisher (1890 – 1962) encapsulated the concept as the Sexy Son Hypothesis. In the 1980s a variation of the theme was proposed as the Good Genes Hypothesis by evolutionary biologists W.D. Hamilton (1936 – 2000) and Marlene Zuk. You can learn more about male ornaments in birds in Cornell Lab of Ornithology.
Birds are excellent study systems for understanding evolution. If you are into more bird related studies you can check out the Junco Project or other Cornell Lab of Ornitology productions such as An Illustrated Introduction to Speciation and An Illustrated Introduction to Natural & Sexual Selection.