Weasels are vanishing - or are they just too sneaky to spot?

The forests and fields of North America hold secrets that even motion-sensitive cameras can’t always reveal. Among those secrets are weasels – small, swift, and almost invisible to modern wildlife monitoring.

These elusive predators have slipped through digital traps for decades, making scientists wonder whether their silence signals absence or simply stealth.

It’s not just curiosity that drives this concern. Weasels, as small mustelids, play vital roles in ecosystems. They control rodent populations and serve as prey for larger animals.

Understanding where they thrive or vanish can reveal larger patterns of ecological change. But until recently, researchers lacked a clear method to study their population numbers.

Challenge of monitoring weasels

Camera traps work well for large mammals. Deer, bears, and even coyotes often stroll past, triggering a flurry of images. But weasels are a different story.

Their bodies are small and they move fast. They often live in habitats with thick cover, making them almost invisible, even when present.

Roland Kays is a research professor at North Carolina State University and scientist at the N.C. Museum of Natural Sciences.

“We’re a little worried about the weasels,” said Kays. “We don’t see them very often, but it’s difficult to tell if they’re actually gone or if they’re just so sneaky that we can’t find them.”

“We decided that we needed to better understand the best method to detect them. There wasn’t a great consensus on that.”

The lack of consensus led Kays and a group of researchers to try something new. Instead of relying on luck, they decided to identify the best bait – and the best method – for attracting weasels to camera traps.

Designing a massive survey

Between January 2022 and April 2023, the scientists launched one of the largest camera-trap bait studies ever done for mustelids.

The team placed 486 cameras across 122 clusters in 14 U.S. states, focusing on areas where weasels were previously recorded or where habitat conditions seemed ideal.

Each site hosted a set of four trail cameras, positioned close enough to give weasels a full choice of lures while minimizing overlap between camera zones.

The researchers tested various bait types. These included red meat, raw chicken, cat food, and scent-based lures like anise oil, salmon oil, and a commercial product called Weasel Super All Call.

In 2023, they switched fully to meat baits after finding weak results from scent lures alone the year before.

The bait wasn’t just thrown on the ground. It was secured in cages to prevent theft by other animals. One new method, a cage-within-a-cage system, eventually proved highly successful in stopping bait robbers like raccoons and coyotes.

What the weasels preferred

“There is a huge variety of scent lures available, and trappers often make their own from all kinds of ingredients,” noted Kays. “As it turns out, however, just having a chunk of meat works the best.”

Red meat emerged as the top performer. It tripled the chance of weasel detection compared to scent lures alone.

Short-tailed weasels especially loved red meat, showing up twice as often at those bait stations than at sites with chicken or cat food. When salmon oil was added to the red meat, results improved even further – especially for short-tailed weasels.

In the southern U.S., long-tailed weasels appeared more frequently at chicken-baited sites. They also arrived faster. On average, it took just 14.5 days for a chicken-baited camera to record a long-tailed weasel, compared to nearly 40 days with red meat.

Cat food, by contrast, was the least effective. It took over 27 days to attract weasels – if it attracted them at all.

The least weasel may be in trouble

Of all the weasel species in North America, the least weasel remains the most mysterious. The study detected only four individuals in total – one in 2022 and three in 2023.

Their scarcity raises conservation alarms. Researchers have suggested that the least weasel may be the most endangered of the group, with one study estimating a 54% decline in this species’ habitat over the past century.

Even in targeted areas, where previous records or ideal habitats existed, least weasels barely registered. This highlights the need for specialized monitoring tools, such as enclosed camera traps like the Mostela, which have had some success in limited trials.

“Now that we have an understanding of the best ways to lure the weasels, we can be more confident in the findings of our surveys,” Kays said.

“When we have sites where we don’t detect them, we can be much more assured that they aren’t just in hiding, they’re really just not there at all.”

Activity patterns and behavioral clues

The study also revealed new insights into how different weasel species behave. Short-tailed weasels were active both day and night – an unusual pattern that differs from past observations in Europe and Canada.

In contrast, long-tailed weasels were mostly nocturnal or crepuscular, showing peak activity at dawn and dusk.

These activity patterns have practical implications. If researchers know when weasels are likely to appear, they can time camera placements and checks more effectively.

It also offers clues about predator-prey dynamics, as prey animals may adjust their own schedules to avoid these hunters.

Why bait matters

Getting the bait right was only half the battle. The researchers quickly learned that non-target species – especially raccoons and opossums – loved the bait too. Red meat and chicken were often stolen, reducing the time that bait remained in front of cameras.

In southern sites, bait theft was particularly high. This lowered detection rates. When cameras lost their bait early, they became less attractive to passing weasels.

In contrast, northern sites experienced less bait theft. That could explain why red meat worked so well in the north, where short-tailed weasels live.

The addition of salmon oil helped keep sites attractive even after the meat disappeared. Its strong scent lingered, possibly drawing in curious weasels until the bait was replenished. Cameras baited with salmon oil recorded detections in just 6.5 days, compared to 22 days without the oil.

Building a better monitoring system

This study provides a crucial step toward standardizing how we monitor small carnivores like weasels. With clear bait preferences identified, wildlife agencies can now deploy cost-effective, reliable surveys over large areas.

The best approach? Use red meat or chicken, depending on the region. Add salmon oil for stronger scent cues. Protect the bait using a cage-within-a-cage system. Place cameras in areas with prior weasel activity or suitable habitat. And check the traps monthly during winter, when meat lasts longer and bear activity is low.

Large-scale, standardized surveys like this can finally reveal what decades of anecdotal data couldn’t – the locations where weasels still thrive, and those where they don’t, and how their numbers change over time.

A new way to track weasels

Despite their size, weasels carry ecological weight. They matter. This study, which was published in Wildlife Society Bulletin, helps bring these predators out of the shadows.

The research team included experts from over 20 universities and wildlife agencies, and was led by corresponding author Scott M. Bergeson of Purdue University Fort Wayne. Funding came from the Federal Aid in Wildlife Restoration Act of 1937, a cornerstone of American conservation.

Thanks to their work, weasels are no longer invisible. We can now track their paths, confirm their presence, and protect what remains – one camera trap at a time.

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