In the first large-scale paired camera trap and autonomous recording survey for large African carnivores, researchers were able to identify individual leopards by their vocalisations with 93% accuracy.

It has been hailed as an important first step towards using bioacoustics in the conservation of leopards.

Leopards are listed as ‘vulnerable’ to extinction according to the IUCN Red List of Threatened Species mainly due to habitat loss and human-wildlife conflict.

But because leopards are solitary, nocturnal creatures that live across huge expanses of terrain, scientists struggle to gather reliable data that would help them reverse population declines.

There is little scientific research about the ‘sawing roar’ of a leopard — a repeated low-frequency pattern of strokes, often audible from at least a kilometre away, used primarily to attract mates and for territorial defence.

But studying leopards through the sounds they make — a technique known as bioacoustics and more typically used to monitor birds and marine species — would have the advantage of allowing researchers to monitor much larger areas.

It could lead to more complex studies such as population estimates, a key metric for helping policymakers and conservation practitioners understand how to manage landscapes and mitigate human-wildlife conflicts.

The research team conducted their study across a 450km2 expanse of the Nyerere National Park in Tanzania, where they attached 50 pairs of cameras to trees along roads and trails.

They placed microphones next to each camera so that they could identify the leopard from the camera and then extract the roaring bouts from the audio.

They then used a modelling system to analyse the temporal pattern of a leopard’s roar, and found individual identification was possible, with an overall accuracy of 93.1%.

The study shows that using multiple forms of technology to record complementary data can exploit a wider variety of species traits than single technology studies alone.

Lead author Jonathan Growcott, a PhD student at the University of Exeter, said: “Discovering that leopards have unique roars is an important but fundamentally quite basic finding that shows how little we know about leopards, and large carnivores in general.

“We hope it will allow leopards to become the focus of more acoustically complex science such as population density studies and open the door to more work on how large carnivores use vocalisations as a tool.

“Importantly, our success in using a combination of different types of technology could hopefully lead others to think about how to integrate different types of technology into their research, as the rich data this provides could really push science ahead and help us understand ecosystems and landscapes in a much more holistic way.”

The research was a collaborative effort between the University of Exeter, the Wildlife Conservation Unit at the University of Oxford, Lion Landscapes, Frankfurt Zoological Society, TAWIRI (Tanzania Wildlife Institute for Research) and TANAPA (Tanzania National Parks Authority), as well as computer scientists from Exeter and Oxford.

It was presented by Growcott at the British Ecological Society Annual meeting in Liverpool earlier this month, an event which brought together 1,500 ecologists.

Hazel Norman, CEO of the British Ecological Society said: “This study showing that individual leopards can be identified and monitored just through their roars is a brilliant example of how ecologists are applying novel ideas and technologies to uncover fascinating new insights into our natural world.

“Jonathan presented this research at our recent British Ecological Society Annual Meeting in Liverpool, which is a brilliant forum for ecologists to share their research and ideas with the ecological community and beyond.”

Changes in these spin states can be detected using optically detected magnetic resonance (ODMR), which measures fluorescence changes under microwave radiation. NDs with NV centers are biocompatible and can be designed to interact with specific biological molecules, making them valuable tools for biological sensing. However, NDs used for bioimaging generally exhibit lower spin quality compared to bulk diamonds, resulting in reduced sensitivity and accuracy in measurements.

In a recent breakthrough, scientists from Okayama University in Japan developed nanodiamond sensors bright enough for bioimaging, with spin properties comparable to those of bulk diamonds. The study, published in ACS Nano, on 16 December 2024, was led by Research Professor Masazumi Fujiwara from Okayama University, in collaboration with Sumitomo Electric Company and the National Institutes for Quantum Science and Technology.

“This is the first demonstration of quantum-grade NDs with exceptionally high-quality spins, a long-awaited breakthrough in the field. These NDs possess properties that have been highly sought after for quantum biosensing and other advanced applications,” says Prof. Fujiwara.

Current ND sensors for bioimaging face two main limitations: high concentrations of spin impurities, which disrupt NV spin states, and surface spin noise, which destabilizes the spin states more rapidly. To overcome these challenges, the researchers focused on producing high-quality diamonds with very few impurities. They grew single-crystal diamonds enriched with 99.99% ¹²C carbon atoms and then introduced a controlled amount of nitrogen (30-60 parts per million) to create an NV center with about 1 part per million. The diamonds were crushed into NDs and suspended in water.

The resulting NDs had a mean size of 277 nanometers and contained 0.6-1.3 parts per million of negatively charged NV centers. They displayed strong fluorescence, achieving a photon count rate of 1500 kHz, making them suitable for bioimaging applications. These NDs also showed enhanced spin properties compared to commercially available larger NDs. They required 10-20 times less microwave power to achieve a 3% ODMR contrast, had reduced peak splitting, and demonstrated significantly longer spin relaxation times (T₁ = 0.68 ms, T₂ = 3.2 µs), which were 6 to 11 times longer than those of type-Ib NDs. These improvements indicate that the NDs possess stable quantum states, which can be accurately detected and measured with low microwave radiation, minimizing the risk of microwave-induced toxicity in cells.

To evaluate their potential for biological sensing, the researchers introduced NDs into HeLa cells and measured the spin properties using ODMR experiments. The NDs were bright enough for clear visibility and produced narrow, reliable spectra despite some impact from Brownian motion (random ND movement within cells). Furthermore, the NDs were capable of detecting small temperature changes. At temperatures around 300 K and 308 K, the NDs exhibited distinct oscillation frequencies, demonstrating a temperature sensitivity of 0.28 K/√Hz, superior to bare type-Ib NDs.

With these advanced sensing capabilities, the sensor has potential for diverse applications, from biological sensing of cells for early disease detection to monitoring battery health and enhancing thermal management and performance for energy-efficient electronic devices. “These advancements have the potential to transform healthcare, technology, and environmental management, improving quality of life and providing sustainable solutions for future challenges,” says Prof. Fujiwara.

The national survey found that discarded frozen items make up about 6% of wasted household food in the United States. Based on frozen food’s relatively small contribution to food waste and other findings in the study, researchers say urging consumers to stock their freezers might be one way to prevent premature disposal of food.

Results showed that though overall food waste remained high, there was a bright spot: Freezing food was associated with less food landing in the trash.

“We found that households with home freezing behaviors are more likely to have less food waste than other households,” said Lei Xu, first author of the paper and a postdoctoral scholar specializing in agricultural and food economics at The Ohio State University.

“Food waste is not just an economic loss — it also causes environmental damage because more than 90% of wasted food goes to the landfill, and this can produce greenhouse gas emissions,” Xu said. “The findings suggest that in the future, if we can encourage households to have home freezing behaviors, this small change in food storage habits can have a large environmental impact.”

Xu completed the study with graduate student Ran Li and senior author Brian Roe, professor in the Department of Agricultural, Environmental and Development Economics at Ohio State. The research was published recently in the British Food Journal.

Roe has been studying household food waste for years, but this is the first study to tease out where frozen food fits into the food waste picture. Recent estimates have suggested about 30% of food in the United States is wasted, but other research led by Roe suggests consumer food waste is trending upward.

“The fact that food waste is still increasing may suggest to policymakers that campaigns could be useful to educate households about balancing purchasing behavior and making the most of the food they buy,” Xu said.

The current study data comes from frozen food-related questions added to the summer 2022 wave of the U.S. National Household Food Waste Tracking Survey in which 1,067 households participated. Respondents were asked to estimate the percentage of all discarded food in the previous seven days that had been frozen and whether it was bought frozen or was unfrozen and placed in the freezer later. They also reported the typical frequency of buying frozen foods.

The responses indicated that 85% of U.S. households buy frozen foods and among those, 55% of participants reported they purchased frozen food to reduce waste. Frozen food purchasers were more likely to shop infrequently — two to three times per month — and were more likely to be living in households with annual income of under $50,000. The most common categories of discarded frozen foods were meat (20% of total frozen food waste), vegetables (22%) and potatoes and grains (15% each).

“Based on what we’re seeing among households, we still have space to increase awareness to save food by using freezing behavior,” Xu said.

Data showed a link between frequent home freezing and significantly less total food waste. Respondents most likely to freeze fresh items or extra food were aged 45 years and older and living in households of three or more people — a possible sign, the authors said, that consumers with a home freezing routine may be more experienced at managing meals for a group and motivated to avoid food waste.

What the team considered somewhat surprising — and enlightening — was the finding that about 30% more of wasted frozen food was discarded from the refrigerator than from the freezer.

“Thinking about why that happens, it might mean they don’t understand food storage techniques and don’t understand how long they should keep certain foods and where they should put it,” Xu said. “This suggests more explicit food storage instructions on food labels could educate consumers about how to correctly store foods to reduce waste.”

Trends in the data suggest that consumer education about the freezer’s role in saving food could make a difference economically and environmentally, Xu said, and also help address the societal problem of food insecurity experienced by 10% of U.S. households.

“Half of consumers buy frozen food to reduce waste. What about the other half?” she said. “We want to increase social awareness of how to save food, and explain how people use frozen food and home freezing techniques to save food. And freezing is one of the most accessible techniques because essentially all households have a refrigerator and freezer.”

This work was supported by the USDA National Institute of Food and Agriculture, the National Science Foundation and a gift from the Frozen Food Foundation that facilitated collection of a larger survey sample size.