“We were expecting to find that the bigger, stronger guys — the high-quality males — would have the loudest bellows, because they can handle the costs of it,” said Megan Wyman, a graduate student in geography at UC Davis and the lead author of the study. “But instead, we found the opposite. My collaborator in San Diego wanted me to call the paper ‘Speak softly and carry a big stick.’”
The study is the first to examine how the amplitude, or loudness, of a mammal’s vocalizations correlate with reproductive success. It was published in the November issue of the journal Animal Behaviour.
Most studies of vocalized sexual signals among animals have focused on the pitch characteristics, timing and duration of calls. Amplitude has received much less attention, Wyman said, largely because loudness is especially difficult to measure in the field. By the time a grunt or a roar reaches a sound-level meter, its amplitude may have been affected by the animal’s distance from the meter, the direction the animal was facing when it called, wind conditions and a number of other factors.
Bison bellows are loud, low-frequency vocalizations performed by bulls during the rut. They are most commonly used when one male challenges another, typically when the two are within 45 to 90 feet of one another. Yet sometimes a bellow will attract bulls from further away, and this may be one reason that a herd’s dominant bulls keep their voices down, Wyman speculates.
“It could be that bulls provide information about their high quality through other signals — for example, the frequency or the duration of their bellows. So they don’t have to be louder, they just have to be heard,” she said. “If you bellow too loudly, it could bring in too many other bison to check you out.”
The bigger question raised by the study, Wyman said, is why lower-quality males don’t turn down the volume of their bellows to emulate their more successful rivals.
“That’s a lot harder to explain,” she said. “It could be that if you use a quieter volume, other bulls have to approach even closer to check you out, and any time you bring someone that close, there’s a higher risk of attack. And that’s the type of cost that these low-ranking bulls may not be able to bear.”
To learn how bison communicate with one another, Wyman and Michael S. Mooring of Point Loma Nazarene University, and a number of student interns spent two summers monitoring 325 wild bison in Fort Niobrara National Wildlife Refuge in the Sandhills region of north-central Nebraska. The animals were well habituated to the four-wheel drive vehicles the team used to shadow them, and each was easily identifiable by a unique brand it had been given as a calf.
Observing the herd for 14 hours each day during the two-month rut of July and August, the team was able to record each copulation and to detail the tangled web of connections between males and females as bulls lost and gained cows during their intense competitions. To assess where each bull ranked in the herd’s hierarchy of dominance, Wyman tallied outcomes of challenges between rivals, including threats that ended with an animal backing down in the face of combat, as well as full-blown, head-to-head fights. When calves were born the following spring, DNA samples were taken to determine parentage.
For measurements of amplitude, Wyman used a hand-held sound-level meter from the safety of her vehicle. With each reading, she also recorded specific behaviors of the bull, his female and any challenging rivals, as well as noting the factors that could affect the level of the reading such as the bull’s head orientation, its distance from the meter and wind conditions. After selecting for accuracy and quality, she narrowed some 2,000 readings taken from 67 bulls down to 408 readings from 44 bulls.
Her analysis showed that, on average, the least successful bulls — those with the lowest number of copulations and offspring — bellowed at least 50 percent louder than their more successful rivals, corresponding to decibel readings averaging from 109 per bull down to 103. This drop in volume correlated with a rise in the number of times a bull copulated from none to five, and the number of calves it sired from none to nine.
These data are just a portion of the information the researchers collected in the field with the overarching goal of understanding how bison communicate vocally. Yet the results clearly indicate that loudness as a factor of animal communication should receive more attention, Wyman said. “We’ve shown a way of using simple, affordable instruments in the field that can give a good measure of amplitude,” she explained. “I’m hoping that researchers will now start looking at amplitude as something that matters.”
Along with Wyman and Mooring, co-authors of the study are Professor Lynette Hart and Associate Researcher Brenda McCowan with the Department of Population Health and Reproduction in the School of Veterinary Medicine, and Associate Research Geneticist Cecilia Penedo in the Veterinary Genetics Laboratory, all at UC Davis. Funding for the study was provided by the National Science Foundation; the American Society for Mammalogists Grant-in-Aid; Animal Behavior Society Student Research Grant; and the Marjorie and Charles Elliott Fellowship Fund of University of California, Davis.About UC Davis
Liese Greensfelder | EurekAlert!
The balancing act: An enzyme that links endocytosis to membrane recycling
07.12.2016 | National Centre for Biological Sciences
Transforming plant cells from generalists to specialists
07.12.2016 | Duke University
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
07.12.2016 | Health and Medicine
07.12.2016 | Life Sciences
07.12.2016 | Health and Medicine