Buzz
This image captures a group of three wolves howling. The spectrogram—a graphical depiction of sound frequencies over time—displays each wolf's unique vocal signature. Thick lines represent the fundamental frequency and harmonics of their howls.
Daniela Passilongo, an Italian biologist, believes that analyzing visual representations of wolf howls, rather than relying solely on auditory data, could improve conservation strategies. Her recent study in Frontiers in Zoology demonstrates that using spectrograms to count wolf voices is more effective than traditional census methods.
Accurately counting wolves is a challenging endeavor. After significant population declines in the 20th century, wolves are now recovering in regions like the United States, Mexico, and Western Europe, reclaiming over two-thirds of their historical habitats. To prevent their decline, scientists must monitor and manage wolf populations meticulously, starting with identifying pack locations and sizes.
Tracking wolves is no simple task, as they roam vast territories and are naturally cautious around humans. Traditional methods like genetic sampling, GPS collars, and camera traps are costly and labor-intensive. However, wolves have a unique way of announcing their presence—through their howls—making auditory tracking a viable alternative.
Wolves communicate through howling, and packs become particularly vocal when they detect other wolves nearby. This behavior helps them mark their territory, protect resources, and avoid clashes with rival packs. Wildlife biologists often use howling surveys to locate and monitor wolf packs. By playing recorded howls or mimicking the sounds themselves, researchers can prompt a pack to respond. Analyzing the chorus of replies allows them to determine the pack's location and estimate its size based on the number of distinct voices.
While howling surveys are cost-effective and practical, they aren't always accurate. Passilongo notes that typically, only a few wolves initiate the howling, with the rest joining in simultaneously, making it hard to distinguish individual voices. Factors like pitch variations and echoes can further distort perceptions, leading to overestimations. For instance, during the Civil War, Ulysses S. Grant mistook the howls of two wolves for a pack of nearly 20.
Scientists have discovered that each wolf has a unique vocal signature visible on spectrograms. Passilongo and her team explored whether visualizing these howls could provide more accurate pack size estimates than auditory methods alone.
The team created spectrograms of howl choruses with known sizes, using recordings from zoo wolves or human volunteers mimicking howls. Researchers, unaware of the actual chorus sizes, accurately identified the number of wolves (or humans) in 92% of cases by analyzing the spectrogram lines. When two researchers examined the same spectrogram of a 37-wolf chorus, their size estimates consistently matched, unlike their auditory assessments, which often varied significantly.
The team highlights that identifying individual wolf howls through their spectrogram signatures offers greater accuracy than traditional howling surveys and overcomes many of their limitations. This method is simpler, more cost-effective, and only necessitates basic recording equipment and accessible sound analysis software. For biologists tasked with monitoring wolf populations and ensuring their protection, this approach is invaluable, helping them maintain thriving packs and preserve their iconic howls.
