Sight is the most important sense for a raptor in pursuit of prey. Vision guides movement, and the birds use sight cues to time their attacks. As physicist and co-author Suzanne Amador Kane of Haverford University explains, goshawks predominately use two pursuit strategies. In the first, the goshawk sets an intercept course with their prey’s path. Because of the oblique angle of the raptor’s path, the prey has a hard time detecting the goshawk as it closes in. The downside of this strategy is that the hawk gets one brief shot at the prey, and it is easy to miss. If that happens, the goshawk will switch strategies and start chasing the prey. In this mode, the prey stays static in the raptor’s visual field.
But these two modes of pursuit don’t completely describe the goshawk’s hunting strategy, and Kane says there is about 25 percent of each pursuit that she and her colleagues are working to classify. “We don’t yet have a unified theory of raptor pursuit strategy,” she said.
Similar research has already overturned some assumptions about the way raptors hunt. In 2013, Kane and a colleague did video analysis on falcons, and showed that the birds did not arc around their prey as previously thought, but used an combination of intercept and chase strategies similar to the goshawk. This hypothesis, which Kane says had been well-regarded, came from a combination of on-the-ground observations and clues from raptors’ eye anatomy. The research was good, says Kane, but suffered from the limited technology. Head-mounted cameras now let scientists see what the birds see.
In the video below, Kane explains in greater detail how she and her colleagues analyzed the footage, and what it means for the way goshawks hunt.