MISSOULA – New research by University of Montana doctoral student Anthony Lapsansky provides insights into how four species of seabirds have developed the ability to cruise through both air and water.
Lapsansky’s study was published in the open-access journal eLife. It reveals that birds from the Alcidae family, which includes puffins, murres and their relatives, produce efficient propulsive wakes while flying and swimming. This means that the animals likely spend relatively low amounts of metabolic energy when creating the force they need to move in both air and water.
Lapsansky said the findings suggest that alcids have been optimized for movement in two very different environments through the course of their evolution.
“Birds that use their wings for ‘flight’ in air and water are expected to fly poorly in both environments compared to those that stick to either air or water only,” said Lapsansky, who is a Ph.D. candidate at UM’s Field Research Station at Fort Missoula. “In other words, these jacks-of-all-trades should be the masters of none. Interestingly, however, alcids seem to contradict this notion of a trade-off between aerial and aquatic flight performance, and we wanted to investigate this further.”
To gain a better understanding of the potential evolutionary trade-offs between the two types of flight, Lapsansky and his team tested whether alcids exhibit efficient Strouhal numbers when flying in water and air. Animals move in these environments by using oscillating appendages, and the Strouhal number describes the frequency at which an animal produces pulses of force with appendages to power its movement.
Only a narrow range of Strouhal numbers are efficient – if a bird flaps its wings too fast or too slow for a given amplitude and flight speed, then it wastes energy. But most birds have converged on this narrow range of Strouhal numbers, meaning that natural selection has tuned them to exhibit efficient flapping and swimming movements.
Additionally, Lapsansky and his team studied whether birds that fly in air and water use their muscles in the same way in both environments.
“Muscles typically consist of fibers that are tuned for specific activities, but this hardly seems possible when the same muscles are used for movement in two drastically different environments,” Lapsansky aid. “We hypothesized that alcids maintain efficient Strouhal numbers and consistent stroke velocities across air and water, which would allow them to mitigate the costs of being able to cruise through both environments.”
The team used videography to measure the wing movements of four species of alcids that differ substantially in body mass – from 450 grams to 1 kilogram – and represent distant branches of the alcid family tree. Their measurements showed that alcids cruise at Strouhal numbers between 0.10 and 0.40 in both air and water – similar to animals that stick to air or water only – but flap their wings approximately 50% slower in water.
Lapsansky said this suggests the birds either contract their muscles at inefficient velocities or maintain a two-geared muscle system, highlighting a clear cost to using their wings for movement in air and water.
“Our work provides detailed new insights into how evolution has shaped alcid flight in response to competing environmental demands in air and water,” said paper co-author Bret Tobalske, a professor and director of the Field Research Station, which is part of UM’s Division of Biological Sciences. “Further research is now needed to understand the necessary changes that take place in the flight muscles of these birds to allow them to transition between air and water and back again.”
Contact: Anthony “Tony” Lapsansky, UM doctoral student in ecology and evolution, 406-243-6631, firstname.lastname@example.org.