Most male birds try to attract mates with elegant gestures. Seabirds bob their heads and flutter their wings, while peacocks fan out their beautiful feathers. However, the white bellbird, endemic to the Amazon rainforest in Brazil, dispenses with the pleasantries and cut to the chase by shrieking in its prospective "date's" face at a deafening 125 decibels (Db)— the loudest bird call ever recorded. To put it in perspective, that is 40 Db higher than the safe hearing range for humans! Prior to this, the honor belonged to another Amazon-dweller — the aptly-named screaming piha — which has a peak recorded "song" volume of 116 Db.
Mario Cohn-Haft, one of the study’s authors, first became familiar with the loud birds through his expeditions in the mountains of the Brazilian Amazon. “We could hear them all over the place, they’re kind of the soundtrack of these forests,” says the ornithologist at Brazil's National Institute of Amazonian Research. “They give out these loud ringing sounds that sound like someone banging on metal, like a blacksmith.”
To find out how loud the bird actually was, he and Jeff Podos from the University of Massachusetts Amherst, trekked to the mountains of the Amazon rainforests in northern Brazil in December 2018 and then again in February 2019. What they discovered was fascinating.
The pigeon-sized white bellbirds begin their courtship with a slightly gentler shriek that averages about 116 Db. Upon attracting their potential mate's attention, they ramp up their effort with the deafening 125 Db "song." What was bizarre was that the male began by singing its first note with its back to the female and then turned suddenly. "It's really dramatic. You see this bird spinning around, and he's got his beak wide open," Podos said. "And he blasts the second note right in the place female would have been had she not been smart enough to back off."
The scientists, who published their findings in the journal Current Biology on October 21, 2019, are not sure why the females continue to stay relatively close even when the males are singing at full pitch. "Maybe they are trying to assess males up close, though at the risk of some damage to their hearing systems," Podos speculates. Since the unpleasant sound, which increases the male's risk of being detected, was not a survival technique, the researchers concluded that the females might have a preference for louder males. "She is effectively sticking her head in a speaker at a rock concert,” Cohn-Haft says.
The white bellbird's ability to screech loudly may be the result of its diet, which consists solely of fruits, some the size of golf balls, which the birds swallow in their entirety. Cohn-Haft and Podos believe the birds' tendency to open their beaks wide aid in amplifying their sound, resulting in the full-throated mating calls.
However, the scientists are puzzled about how the birds, both male and female, can withstand the loud songs without going deaf. Cohn-Haft and Podos hope to return to the region in early 2020 to see if they can detect the presence of any adaptations that may help prevent hearing damage. They also hope to witness a successful courtship to understand why loud males attract females.
Resources: earthsky.org, cbc.ca, CNN.com, sciencealert.com