Meeting Abstract
Loons (Gaviiformes) are arguably one of the most successful groups of swimming birds. As specialist foot-propelled swimmers, loons are capable of diving up to 70 meters and remaining underwater for several minutes. They survive by capturing fish, a skill that requires a high level of maneuverability and speed. Despite the swimming prowess of loons, their locomotion has never been critically investigated. Our study used high-speed underwater cameras to film rehabilitating common loons (Gavia immer) at the Tufts Wildlife Clinic in order to analyze their swimming and turning strategies. Loons swim by synchronously paddling their feet laterally reaching 3 strokes per second. The swimming style of loons is unlike that of grebes or cormorants, instead incorporating aspects of both. The lateral foot movements of loons resemble grebes. However, loons accelerate through 30-60% of the paddling cycle similar to cormorants, whereas grebes maintain 24% regardless of speed. Swimming loons use head bobbing, previously documented in only 23 avian families. The eye of the loon is held still then accelerated 2-2.5 times faster than the body. This behaviour improves visual acuity by stabilizing the retina then increasing parallax to potentially improve depth perception. Our study is also the first to observe free maneuvers by diving birds. We find that loons alter relative timing and orientation of their feet to change direction. Turning loons consistently delay the propulsive stroke of the inside foot, which sometimes acts as a rudder to induce a sharper turn. Our findings are instrumental for understanding loon performance as well as the independent evolution of foot-propelled swimming in multiple avian taxa. Furthermore, loons could serve as inspiration for swimming robots, boats, or other engineered hydrodynamic structures.
