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science, health and technology

The "background" performers in male courtship rites

Lance-tailed manikins and their song and dance routines
by Eric Jackson

On March 7 the regulars at the Smithsonian's Tuesday afternoon science lecture series got to hear about some ornithology. Dr. Emily H. DuVal, who has worked at the Smithsonian Tropical Research Institute before and later at the University of California at Berkeley's Museum of Vertebrate Zoology and is now associated with Germany's Max Planck Institute for Ornithology, spoke about "the adaptive significance of cooperative male courtship in the lance-tailed manikin."

No, it wasn't about hippie orgies among birds.

It seems, however, that the males of these tropical forest birds frequently perform song and dance duets to attract females, and if one of the latter shows interest, the beta male departs and the alpha male does or does not succeed in mating.

DuVal noted that despite the common depiction of nature as a brutal competition in which the strongest survive and the others don't, actually there is both cooperation and conflict all throughout the natural world. For humans raised in individualistic societies competition may be easily enough understood, but "the evolution of cooperation is more complicated."

Sure, it's easy enough to understand birds sharing parental duties around the nest (which many species in fact do not do), or cooperation in foraging or defense of a habitat. But why, she asked, would a beta male cooperate to help an alpha male attract a mate?

She posed three hypotheses: first, that the beta males might get direct benefits by themselves being able to mate as the result of their performances; second, that cooperation with beta males might indirectly help the beta males propagate their lineage by ensuring that close relatives mate; and third, that the beta males are just waiting their turn to take the lead role and by playing their part will later become alpha males who mate.

DuVal tested these possibilities by observations, experiments and DNA sampling over five years on Isla Boca Brava in Chiriqui province.

The genetic tests indicated that beta males occasionally produce offspring, but very rarely. They also showed that alpha and beta males are not closely related, which explodes the second hypothesis.

But she noted that from one season to the next, the lineup of birds performing in a spot is subject to change, and that quite often the beta males "inherit" the alpha role when the dominant partner is removed from the scene. This was shown both in field observations and by experiments in which alpha males were removed.

But then, it seems, most betas who have advanced to alpha status eventually revert back to the beta role in subsequent seasons, especially in the experimental studies.

Thus there is more study to be done, but it appears that beta male lance-tailed manikins play the beta role with a reasonable hope that their time will come to step in and play the lead role. If that's true then there would be a direct biological benefit, albeit a delayed one, for playing second fiddle.

Also in this section:
Presentations by science and technology writer TA Heppenheimer
STRI Science Symposium
The biology of male bird duets
Economic inequalities in a part of Amazonia without much of a market
Is there a "best system" of health insurance?