Scientists have created a massive database called FracFeed that tracks how often predators have empty stomachs versus full ones. By collecting information from nearly 5,000 diet studies across 1,507 different animal species—from birds and fish to insects and mammals—researchers now have a better way to understand whether predators are finding enough food in their environments. This information helps scientists learn about the balance between predators and their prey, and how environmental changes might affect entire ecosystems. The database includes data collected over 135 years from animals all around the world, making it one of the most comprehensive collections of predator feeding information ever assembled.

The Quick Take

  • What they studied: How often predators have empty stomachs versus full stomachs, and what this tells us about whether predators are finding enough food in nature
  • Who participated: Nearly 4.3 million individual animals from 1,507 different species studied across 4,920 separate diet surveys. The animals included birds, fish, mammals, insects, snakes, and many other creatures from oceans, rivers, and land around the world
  • Key finding: Scientists created a database showing that the proportion of predators with empty stomachs varies greatly depending on the species, location, and time period—suggesting that food availability and predator feeding success differ widely across ecosystems
  • What it means for you: This database helps scientists better understand how healthy predator populations are and whether ecosystems have enough prey to support their predators. It could help predict how ecosystems might change when food becomes scarce or abundant

The Research Details

Researchers didn’t conduct new experiments themselves. Instead, they gathered information from thousands of published scientific studies where other scientists had examined what predators were eating. They looked for a specific piece of information that’s often overlooked: how many predators had empty stomachs versus full ones. This information came from three types of studies: some scientists cut open predators to look at their stomach contents (lethal method), others used a tube to gently remove food from stomachs without harming the animal (lavage method), and others simply watched predators in nature to see if they were actively feeding (direct observation). The researchers organized all this information into one searchable database, including details about where and when each study happened, what species was studied, and how big the predators were.

The number of empty stomachs is actually a really useful clue that scientists had been ignoring. When many predators have empty stomachs, it might mean food is hard to find. When most predators have full stomachs, it might mean food is plentiful. By collecting this information from thousands of studies, scientists can now see patterns across different species and ecosystems that would be impossible to spot from individual studies alone. This helps us understand the invisible connections between predators and their food sources.

This is a data compilation project rather than a traditional research study, so it doesn’t have the same type of quality measures as experiments. The strength of this work comes from the enormous amount of data collected (over 135 years, multiple continents, many species) and the careful organization of that data. The main limitation is that the quality depends on how carefully the original researchers reported their findings. The database is transparent about its methods and sources, which is a good sign. The researchers are also asking for more contributions to fill gaps, especially from parts of the world that are underrepresented in the current database.

What the Results Show

The FracFeed database now contains information from 4,920 different diet surveys covering 1,507 animal species and more than 4.3 million individual animals. The data spans from 1887 to 2023—over 135 years of scientific observations. The animals studied include an incredibly diverse range of predators: cnidarians (like jellyfish), birds, fish, mammals, reptiles, insects, and many others. These predators were studied in three different types of environments: oceans, freshwater rivers and lakes, and land. The database shows that the proportion of predators with empty stomachs varies dramatically depending on which species you’re looking at, where they live, and when they were studied. This variation suggests that food availability and predator feeding success are very different across different ecosystems and time periods.

The database includes important additional information beyond just empty versus full stomachs. For each study, researchers recorded the exact location where the survey happened, the time period it covered, the body size of the predators studied, and how many different types of prey were found. This extra information makes the database much more useful because scientists can now ask questions like: ‘Do bigger predators have more empty stomachs than smaller ones?’ or ‘Do predators in certain regions have more success finding food than others?’ The researchers also standardized all the species names using a system called the Open Tree of Life, which makes it easier to compare data across different studies that might have used different naming conventions.

Scientists have been studying what predators eat for over a century, but they’ve typically focused on describing what was in the stomachs that weren’t empty. The proportion of empty stomachs has been largely ignored or not reported in most studies. This new database changes that by bringing attention to this overlooked information. Previous research has suggested that empty stomach proportions could be a useful indicator of how well-fed predators are and how much food is available, but no one had ever compiled this information across so many species and ecosystems. This database makes it possible to test those ideas on a much larger scale than ever before.

The database is only as good as the original studies it’s based on. If researchers didn’t report the number of empty stomachs in their original work, that information can’t be included. Some parts of the world—particularly North and Central Asia and North and Central Africa—are underrepresented in the database, which means we know less about predator feeding patterns in those regions. Different researchers used different methods to collect their data (cutting open animals, using tubes, or watching them), and these methods might give slightly different results. The database also depends on researchers being willing to share their data and contribute to it. Finally, the proportion of empty stomachs is just one piece of information about predator health and food availability—it doesn’t tell the whole story by itself.

The Bottom Line

Scientists should use this database to better understand how predator populations are doing and whether ecosystems have enough food to support them. Conservation managers could use this information to monitor whether their efforts to protect prey species are working. Researchers studying climate change and ecosystem health should consider using empty stomach proportions as one indicator of ecosystem stress. However, this information should be combined with other data sources rather than used alone to make important decisions. (Confidence: Moderate—this is a new tool that needs to be tested and validated)

Scientists studying ecology, conservation, and animal behavior should care about this database. Environmental managers and conservation organizations can use it to monitor ecosystem health. People interested in understanding how nature works and how different species depend on each other will find this information valuable. However, this is primarily a tool for professionals and serious students rather than the general public. If you’re a casual nature enthusiast, you might find it interesting but probably won’t use it directly.

This database doesn’t promise quick results or changes. It’s a long-term tool for understanding patterns in nature. Scientists will need months or years to analyze the data and publish new findings. Any changes based on this information—like new conservation strategies—would take even longer to show real-world effects. Think of it as building a better map of nature so we can make smarter decisions in the future.

Want to Apply This Research?

  • If you’re a wildlife watcher or citizen scientist, you could track the feeding status of predators you observe (fed vs. not fed) along with the date, location, and species. Over time, this personal data could contribute to understanding local patterns and potentially be added to databases like FracFeed
  • Start paying attention to whether predators you encounter appear to be actively hunting or feeding versus resting. Keep a simple log with photos, dates, and locations. This observation habit helps you become a more engaged naturalist and contributes to citizen science efforts
  • Maintain a long-term observation journal of predator activity in your local area. Track seasonal patterns in feeding behavior, compare year-to-year changes, and share observations with local naturalist groups or citizen science platforms. This creates a personal contribution to understanding ecosystem health

This research describes a database tool for scientific research and does not provide medical or health advice. The FracFeed database is designed for use by scientists and researchers studying ecology and animal behavior. If you have questions about how this research might apply to specific conservation or environmental management decisions, consult with qualified ecologists or environmental professionals. This database is a compilation of existing research and should be used alongside other data sources for important decision-making.