Even though a blue whale is much heavier than a tuna, the mammal consumes less energy per unit of weight than the fish when they travel the same distance. For years, these sort of comparisons have dominated our understanding of the energy efficiency of animal movement, which is important for designing vehicles inspired by nature.
But Neelesh Patankar, professor of mechanical engineering at Northwestern University, believes that this measure has only limited benefit. Instead, he and his colleagues have come up with a new measure that allows the comparison of animals as small as bees or zebrafish with animals as large as albatrosses or blue whales.
The new measure has two implications. First, among those species that engage in typical swimming and flying motions, which include most fish and birds, each animal is as energy efficient as it can be. This means that, given their size and shape, each animal is able to spend a minimal amount of energy to move the most distance. Second, this measure confirms a previous finding that jellyfish are unusually energy efficient, beating all the thousands of fish and birds Patankar studied.