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.

顾名思义，地面鸟类通常大部分时间都在地面上觅食。无论飞行能力如何，地面鸟类都更多地使用腿而不是翅膀。对于那些会飞的动物来说，它们通常这样做是为了躲避捕食者或到达步行无法到达的区域。红腿鹬（ Cariama cristata； Cariamidae）就是这种情况，它是塞拉多（巴西稀树草原）的鸟类象征。鸬鹚身长可达 90 厘米，重量可达 1.5 公斤，在地面上寻找并捕食昆虫和小型脊椎动物（Rev Bras Ornitol 2016；doi.org/10.1007/BF03544333）。如果被追赶，seriemas 可以在起飞前以每小时 70 公里的速度奔跑。但这只雄伟的鸟类如何应对腿部肌肉疲劳呢？

在巴西米纳斯吉拉斯州的塞拉多，这只成年标本在寻找食物的长途步行后爬上白蚁丘，抬起右脚并将其放在左腿上后，保持静止约 15 分钟，同时观察返回狩猎之前的风景。据我所知，这张照片中捕捉到的行为以前从未在系列报道中报道过。

这种姿势是否可以让鸟在不需要支撑腿肌肉工作的情况下分散其重量？小鸟会轮流用每条腿站立吗？与火烈鸟（Phoenicopteridae）类似，单腿站立时消耗的能量是否比两条腿站立时消耗的能量更少（Biol Lett 2017；doi.org/10.1098/rsbl.2016.0948）？这种行为有助于调节体温吗？单脚站立可能是这些鸟类能量调节的重要策略。