"A thirsty crow wanted water from a pitcher, so he filled it with pebbles to raise the water level to drink," summarizes a famous Aesop Fable. While this tale is thousands of years old, animal behaviorists still use this challenge to study corvids (which include crows, ravens, jays, and magpies) and their use of tools. In a recent Nature Communications study, researchers from a collaboration of universities across Washington, Florida, and Utah used radioactive tracers within the brains of several American crows to see which parts of their brains were active when they used stones to obtain food from the bottom of a water-filled tube.

Their results indicate that the motor learning and tactile control centers were activated in the brains of the more proficient crows, while the sensory and higher-order processing centers lit up in the brains of less proficient crows. These results suggest that competence with tools is linked to certain memories and muscle control, which the researchers claimed is similar to a ski jumper visualizing the course before jumping.

The researchers also found that out of their avian test subjects, female crows were especially proficient at tool usage, succeeding in the challenge quickly. “[A] follow-up question is whether female crows actually have more need for creative thinking relative to male crows,” elaborates Loma Pendergraft, the study’s first author and a graduate student at the University of Washington, who wants to understand if the caregiving and less dominant role of female crows gives them a higher capacity for tool use.

While only two species of crow (the New Caledonian crow and the Hawaiian crow) inherently use twigs and sticks as foraging tools, this study also suggests that other crow species, like the American crow, have the neural flexibility to learn to use tools.

A less invasive look at bird brains

Due to their unique behaviors, complex social structures, and reported intelligence, crows have fascinated animal behavioralists for decades. Scientists can study crows' brains in real time by using 18F-fluorodeoxyglucose (FDG), a radioactive tracer, which the researchers injected into the crows' brains. They then use positron emission tomography (PET) scans to see which brain areas are activated during different tasks.

“FDG-PET is a method we use to remotely examine activity throughout the entire brain without needing to do any surgeries or implants,” explained Pendergraft. “It's like [a functional] MRI.” The FDG-PET method is non-invasive, as the crows aren’t required to sit still, which minimizes the stress the crows feel during the experiment.  In the Nature Communications study, Pendergraft and his team ensured the crows were anesthetized before scanning them.

FDG is also used in various medical imaging techniques, such as diagnosing Alzheimer’s disease or screening for cancerous tissue. “Basically, the body treats it as glucose, a substance needed for cells to stay alive,” Pendergraft added. “If a body part is working harder than normal, it's going to need extra glucose to power the additional activity. This means we can measure relative FDG concentrations within the brain as a proxy for relative brain activity.”