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Birds-of-paradise have it all

You can’t have it all, is a phrase many of us have probably heard throughout our lives, but new research on birds-of-paradise suggests that maybe you can…at least if you are a bird-of-paradise. Russell Ligon, a postdoctoral researcher at the Cornell Lab of Ornithology and his coauthors Christopher Diaz, Janelle Morano, Jolyon Troscianko, Martin Stevens, Annalyse Moskeland, Timothy Laman, and Edwin Scholes III suggests that male birds-of-paradise not only have the looks, but they also have the pipes and the moves.

Western Parotia

Western Parotia Parotia sefilata

  • Papua, Papua Barat, Indonesia

Traditionally, we tend to think in terms of trade-offs, so while you might get that shiny new car, that new house is out of reach. In the words of Alfred Russell Wallace, “our finest singing birds were plainly colored…while the gorgeously ornamented birds of the tropics have no song (Wallace 1889).” Certainly, examples exist today where Wallace’s statement rings true. Just think about the drab House Wren that sings a complex bubby song fit for an orchestra. But Ligon’s new research casts doubt on the idea proposed by Darwin and Wallace of one-for-one tradeoffs related to sexual selection.

Females, Ligon says aren’t just evaluating what males look like, they are evaluating how well the male sings, dances, and looks, all in one. This means that natural selection is acting not only on color but on vocal complexity and behavioral displays at the same time, what the authors term the “courtship phenotype.”

Western Parotia

Western Parotia Parotia sefilata

  • Papua, Papua Barat, Indonesia

Think about it this way, Ligon says “when you want to go to a restaurant you rely on all sorts of things when evaluating your choices. How is the service? Is the food good? Is it reasonably priced?” Ligon and colleagues suggest that birds-of-paradise are no different. Females evaluate plumage coloration and complexity, behavioral displays, and vocal repertoire all in one.

If females evaluate males based on suites of characteristics, males should have more than just good looks. Indeed, they found evidence that male birds-of-paradise do have it all.  As the number of colors on a male increased so did the number of different types of sounds the bird made. In other words, males were not trading plumage color for vocal repertoire, they had both. Elaborate dancers also had a large catalog of different sounds—think Dancing with the Stars meets American Idol.

(A) Species that have high color diversity also have high acoustic diversity (B) Species with diverse dance moves also have greater diversity in song. Birds-of-paradise illustrations by Szabolcs Kókay

Interestingly, Ligon and colleagues also found that where a bird spends most of its time makes a difference. Birds-of-paradise that displayed on the ground had more dance moves than those that displayed in the canopy. And that makes sense because on the dark forest floor males might need to shake it a little bit more to grab the attention of a female. Above the canopy where there is less interference from trees and shrubs, males sang more complex notes, as they are more likely to be heard.

Graphic shows which types of displays are most common at varying heights in the rainforest. Birds-of-paradise illustrations by Szabolcs Kókay; background illustration and graphic design by Jillian Ditner. Graphic courtesy of the Cornell Lab of Ornithology.

This still begs the question of how did male birds-of-paradise get so outlandish in the first place? In the absence of mammalian competitors in New Guinea, these fruit-eating birds didn’t have to worry about fighting over fruit with monkeys and squirrels and females could spend more time choosing a mate. More time spent evaluating mates pushes males to stand-out from others, whether through voice, feathers, or dance. But Ligon and colleagues suggest for the first time, that it is the combination of physical and behavioral traits that enable elaborate plumages and behaviors to evolve in the first place. Because females choose males based on more than one characteristic, Ligon says that is what allowed for fancier and fancier males.

Why one might ask, do we see such elaborate plumage and behavioral displays in birds-of-paradise, but not other species? Think of it this way Ligon says “if you are a five-star restaurant you have more flexibility to tinker with the menu and try new things. And because you already have a good customer base, you’re not going to lose out if you try something new.” Because female birds-of-paradise judge male quality based on a combination of characteristics, males, the authors suggest, may be able to evolve new features while still maintaining their overall attractiveness to females. The next step, according to Ligon, is to put this tantalizing idea to the test with additional data.

While humans may not get to have it all like male birds-of-paradise, museums including the Macaulay Library do. Ligon and his colleagues took advantage of the unique collection of videos and sounds archived at the Macaulay Library. They drew upon thousands of hours of archived videos, examining 961 video clips and 176 audio clips as well as 393 museum specimens from the American Museum of Natural History in New York City. As Scholes puts it “collections like those at the Macaulay Library hold answers to questions those collecting the data never even thought possible.”


Video caption: A male Western Parotia performs a courtship dance for females who are looking on from above. The codes on the left are the categories researchers used to measure body-position moving (BP1), changing direction while moving (BP2), Shape-shifting (SS1), bowing (O3), ornamental head plumage accentuation (OPMH), ornamental flank plumage accentuation (OPMF), ornamental head plumage by moving the head (OPAH), and ornamental flank plumage accentuation by moving the torso (OPAC1)

References
Ligon, R. A., C. D. Diaz, J. L. Morano, J. Troscianko, M. Stevens, A. Moskeland, T. G. Laman, and E. Scholes III. 2018. Evolution of correlated complexity in the radically different courtship signals of birds-of-paradise. PLoS Biol 16(11): e2006962 https://doi.org/10.1371/journal.pbio.2006962

Wallace, A. R., 1889. Colours and ornaments characteristic of sex. Darwinism: an exposition of the theory of natural selection with some of its applications.