A white-necked jacobin hummingbird. Credit: Kristiina Hurme, UW Department of Biology

What motivates humans to don garments? One motive is that altering attire permits individuals to customize their appearance in hopes of attracting or evading attention. Fresh studies spearheaded by the University of Washington indicate that hummingbirds may implement a comparable strategy.

It has been recognized for a considerable time that some — though certainly not all — female white-necked jacobin hummingbirds adopt the vividly colored feathers characteristic of males. In a research article published February 19 in Animal Behaviour, a collective of investigators from UW and Carnegie Mellon University have unveiled the rationale: They are emulating males. This deception leads to diminished hostility from other hummingbirds and enhanced access to food sources.

“This investigation employs a mental framework we’ve been articulating for a while in our publications and provides it with a mathematical basis,” stated Jay Falk, an evolutionary biologist who directed this research during his postdoctoral tenure within the UW biology department. “It can be straightforward to perceive natural selection as a mechanism that is perpetually selecting one singular ideal. However, this framework enriches our comprehension of how variation, particularly variation within genders, can signify a stable eventuality.”

Utilizing the concepts of game theory and integrating previously amassed behavioral data, the researchers formulated a model of hummingbird conduct to deepen their insight into how certain birds opt for their colors. The results indicated that “hybrid signals” — a balance that can take place when communicators in a specific context may be untruthful — likely exist in the wild.

“In these hummingbirds, females aim to replicate males,” asserted Kevin Zollman, a co-author of the research and director of Carnegie Mellon’s Institute for Complex Social Dynamics. “If all of them opted to do so, they would likely find themselves disbelieved. Thus, they establish an equilibrium where some of them ‘deceive,’ and they are occasionally ‘trusted.’”

Such mimicry helps clarify how female polymorphism — wherein females of a species can exhibit diverse forms — endures among white-necked jacobins and additional hummingbird varieties.

“This model proficiently elucidates this enigmatic female polymorphism in one species, while also providing a framework to investigate testable predictions regarding differences in plumage, or the absence of such, between genders across hummingbirds,” remarked Alejandro Rico-Guevara, a UW assistant professor of biology and co-author of the investigation. “We can apply this to comprehend signals beyond plumage coloration, such as varied behaviors or body features, like elongated tails or acoustic signals, which would entail different expenses for the communicators and diverse model results.”

Carl Bergstrom, a UW biology professor, also contributed as a co-author. This study was financed by the National Science Foundation Postdoctoral Research Fellowship in Biology Grant given to Falk, along with the Walt Halperin Endowed Professorship and the Washington Research Foundation as Distinguished Investigator awarded to Rico-Guevara.

This piece is a modification of a press release from Carnegie Mellon University.