Standing on one foot

Abstract

As their name implies, ground birds typically spend much of their time foraging on the ground. Regardless of their capacity to fly, ground birds all use their legs more than their wings; for those that can fly, they usually do so to escape predators or reach areas that are inaccessible by walking. This is the case of the red-legged seriema (Cariama cristata; Cariamidae), avian symbol of the Cerrado (Brazilian savanna). Capable of reaching 90 cm in length and weighing up to 1.5 kg, seriemas search for and prey on insects and small vertebrates on the ground (Rev Bras Ornitol 2016; doi.org/10.1007/BF03544333). If pursued, seriemas can run at speeds up to 70 km per hour before taking flight. But how does this imposing bird deal with muscle fatigue in its legs?

In the Cerrado of Minas Gerais, Brazil, this adult specimen—after a long walk, in search of food—climbed onto a termite mound and, after raising and placing its right foot onto its left leg, remained static for about 15 minutes while observing the landscape before returning to hunting. To the best of my knowledge, the behavior captured in this photograph has not been previously reported in seriemas.

Does this posture allow a bird to distribute its weight without requiring muscle work by the supporting leg? Does the bird take turns standing on each of its legs? Do seriemas expend less energy when standing on one leg than when standing on two legs, similar to flamingos (Phoenicopteridae) (Biol Lett 2017; doi.org/10.1098/rsbl.2016.0948)? Does this behavior help regulate body temperature? Standing on one foot may be an important strategy for energy regulation in these birds.