Reindeer vocalization can offer cues to potential mates, study suggests

The sounds produced by male reindeer probably tell potential mates a lot about the caller: their age, size and weight. These are all important considerations for a female during the rut, according to a new Concordia-led study.

While this is true of different mammals, reindeer vocalization has been understudied compared to other species.

Writing in the journal Bioacoustics, the authors report that acoustic features from the vocalizations made during the rutting season likely convey reliable information about male reindeers’ attractiveness or quality to potential mates.

These vocalizations are intended for both females and males, they note. The grunts of a rutting male indicate both their potential attractiveness to a mate and their maturity and strength to male rivals.

“In this context, we wanted to see if the receiver could differentiate males just by their call,” says Robert Weladji, a professor in the Department of Biology and the paper’s corresponding author.

“The aim was to investigate the vocalizations and see what acoustic features are there and assess whether those features are associated with males’ qualities such as age and weight.”

What’s the frequency, Rudolph?

The researchers recorded vocalizations from a semi-domesticated reindeer herd in northern Finland during the rutting season in early autumn 2019. They took recordings from 10 different males of reproductive age, between 2.5 and 5.5 years, with 75 high-quality grunts selected for analysis. They then analyzed the grunts using specialized software.

They looked at two parameters: the fundamental frequency and the formant frequencies.

The fundamental frequency is the lowest frequency produced by the vocal cords in the larynx. It determines the pitch of the sound.

Formant frequencies are resonant frequencies produced by the shape and size of an animal’s vocal tract as sound travels through it. These formants help convey information about an individual animal’s identity, physical attributes or emotional state.

While the fundamental frequency does not consistently provide reliable information on an animal’s attributes, formant frequencies appear to be cues to age and body size. Lower frequencies and lower formant spacing are associated with older and larger animals.

The researchers found that reindeer have a particularly difficult style of vocalization to analyze. They were not able to extract the fundamental frequency either digitally or manually. However, they did have better success with formant frequencies.

Reindeer vocal anatomy also complicated matters. The researchers note that reindeer possess an air sac in their vocal tract, but its purpose remains largely unknown.

“We were hoping that our study would help us understand the role of the air sac or help us hypothesize how it influences vocalization, but we were unable to achieve this,” says lead author Laura Puch, MSc 22. “However, we can speculate on its role based on results of studies from other species.”

Weladji hopes to eventually use their findings further by studying the female response to the signals in male vocalizations through a process called playback experiment.

“If acoustic parameters of male vocalizations are conveying specific information, can we manipulate that?” he asks. “Can we mimic them using artificial intelligence or other tools to see if a female responds? If they do, then we can be certain that the acoustic features that we’ve identified are the tools males are using to tell females that they are the most fit or most attractive.”

Øystein Holand of the Norwegian University of Life Sciences and Jouko Kumpula of the Natural Resources Institute of Finland (Luke) contributed to this study.