A summary from an SAA (Society for American Archaeology) paper presented earlier this year titled, “Individuals from Isotopes: Can Stable Isotopes Distinguish the Remains of Different Cooper’s Hawks (Accipiter cooperii)?” by Jonathan Dombrosky, Miranda LaZar, Corrie Hyland, and Seth D. Newsome.
In archaeology, animal bones aren’t just fragments of the past—they are part of the larger story of how humans lived, what they ate, and how they related to the natural world. But determining how many individual animals are represented in an archaeological site isn’t always straightforward. Traditional methods like the Minimum Number of Individuals (MNI) help estimate that count, but they have their limits—especially when bones are fragmentary or look very similar.
A recent study led by Jonathan Dombrosky and associates explores whether stable isotope analysis—a technique that measures the dietary chemical signatures left behind in bones and tissues—might offer another way to identify individual animals. The research centers on Cooper’s hawks, birds of prey that are part of the ecosystem in the U.S. Southwest and occasionally appear in archaeological faunal assemblages.
What the Researchers Did
The team studied 20 modern Cooper’s hawks collected in Albuquerque, New Mexico, analyzing three isotopes—carbon (δ¹³C), nitrogen (δ¹⁵N), and hydrogen (δ²H)—from both bones and soft tissues like muscle and liver. These isotopes provide insights into diet, habitat, and seasonal movement. The goal was to see whether differences in these chemical signatures could be used to reliably tell one hawk from another.
They approached the analysis in three ways:
1. Basic Data Analysis: They found that isotope values became more consistent within each individual when focusing on bones that grow in similar ways (such as wing and leg bones referred to as long bones). This consistency made it easier to distinguish between individuals.
2. Overlap Analysis: Almost all the hawks had similar isotope values but overlap decreased when only long bones were used. Such bones provide the clearest chemical differences because they likely represent an average of an individual’s diet over its life, while other bones represent diet closer to when the bird perished.
3. Predictive Modeling: Using machine learning techniques, the authors tested over 900 different model iterations. The most accurate models came from those that just used long bones and all three isotopes at once. These models correctly predicted individual identity about 75–78% of the time.
Why It Matters
Understanding how many animals were present at a site is important for interpreting how people lived in the past. In many Indigenous cultures, animals are regarded as relatives and teachers, not simply resources. Each individual animal holds value—not only biologically, but spiritually and culturally.
Stable isotope analysis, when used thoughtfully, has the potential to support a more nuanced and respectful understanding of such relationships. It can help researchers trace patterns of hunting, food sharing, and even ceremonial use of animals—without erasing the individuality of the animals themselves.
A Step Forward, with Care
While the study shows some promise, it highlights many challenges. Isotope values can vary widely even within a single animal, and different tissues grow and change at different rates. The method is not perfect—but it opens the door to further research that centers both scientific rigor and cultural awareness.
By continuing to refine these approaches, and by partnering with descendant communities who bring deep knowledge of the landscapes and animals involved, archaeologists can better honor the full context in which these remains exist.
Did You Know? Cooper’s hawks are agile hunters that weave through forests at high speed to catch smaller birds. In life, they are part of vibrant ecosystems. In death, their remains can help tell stories that connect ecology, culture, and care for the past.