On her security camera, Strull saw the impact on Margot almost immediately. She says she used to receive texts from her neighbours complaining about Margot barking when she was left alone. Now, rather than pacing and barking, Margot peacefully naps, with Brahms or Beethoven on in the background, while her owner is gone. "There have been times where I haven't gotten home till 4am, and she's just asleep."

Other studies have come to similar conclusions. One from Queens University Belfast looked at the impact of three types of sound on kennel dogs and dogs in private homes: classical music, audiobooks and silence (the control group). After closely observing behaviour changes, the researchers concluded that classical music had a notable calming effect in "acutely stressful situations", such as a visit to the vet and a long car ride.

Not all styles of classical music are effective, though. Slow tempo (50-60 beats per minute or less), simple compositions with low or no percussive elements are best. That combination has been shown to reduce cortisol levels (the hormone that indicates a stress response) in dogs; however, the underlying reason for this effect is less well understood.

"The most sensible explanation is that there is something inherently relaxing about this genre of music, perhaps resulting in the release of chemicals that bring about a pleasurable state of mind," says Deborah Wells, co-author of the study and an animal behaviour researcher at Queen's University Belfast. 

Wells has studied the effects of classical music on a range of species, including those found at zoos, such as elephants and gorillas. "Zoo-housed elephants and gorillas showed welfare advantages, spending less of their time engaged in stereotypic behaviour, and/or aggression," Wells says. Other welfare advantages can include better eating and sleeping habits, stronger immune systems and improved fertility.

Listening to classical music appears to have helped Margot's anxiety (Credit: Madeleine Jett)

Animals and humans have innately different hearing capabilities. Dogs have about three times the hearing range of humans (frequencies up to 65,000 Hz), so they can hear higher pitches and sounds much further away than the average human ear can. 

Cats can detect even higher frequencies (up to 79,000 Hz), which is why a car horn down the street or even the crinkling of tin foil might send them running for the closet. Few studies have been conducted on the calming effects of music on cats; however, one study found a correlation. Researchers put headphones on 12 cats while they were under sedation for neutering and played three types of sounds in succession: Natalie Imbruglia's Torn, Barber's Adagio for Strings and AC/DC's Thunderstruck. The classical music choice resulted in the slowest breathing rate, the lowest heart rate, and the largest pupil dilation (all three indicators of a calming effect).

Classical music isn't the only genre that can soothe pets. Reggae and soft rock, with simple rhythms, slower tempos and no heavy percussion, have also been shown to relax dogs in shelters. Another study that observed 35 cats in a hospital found that instrumental music also lowered their respiratory rate, as long as it didn't have very high or low frequencies (think piano, flute and strings).    

Audiobooks might sound like they'd calm pets, especially with a soothing-voiced narrator, but the theory doesn't hold up in practice. A study Wells co-authored in 2022, which observed the reactions of 60 dogs to either classical music or audiobooks while their owners were briefly absent, found that audiobooks had little to no calming effect. Rather than sit or lie down as they did while listening to the music, most would just stare at the speaker emitting the audiobook recording.

Music with a slow tempo and not too much heavy percussion appears to be the most soothing to dogs (Credit: Madeleine Jett)

Even though numerous studies point to the calming power of classical music, that doesn't mean it will work on every dog, cat or elephant. The studies are mostly small in scale and short in duration, and mainly focus on shelter or hospital settings, which are notably stressful environments.

Another wrench in the research is the number of sub-categories within classical or instrumental music, and how that variation could significantly impact the music's effect.

When sound behaviourist and composer Janet Marlow observed this with her own pets, she began creating music to calm them, and eventually many others. "I began composing and testing music specifically tailored to the auditory biology of dogs, cats, horses and other species," she says.