When they are not breeding, they spend 99 percent of their time rising and sometimes not landing for several months. For the offspring, however, these diligent pilots have to look for solid ground. If the weather then changes and it becomes cold and damp, so that insect food becomes scarce, the animals rely on two strategies: temporarily switch to warmer areas at longer distances. Or they fall into a cold hibernation for hours to save energy. This is what Arendt Willbrook of the University of Siegen and his team describe in Biology Letters..
The working group observed dozens of fast nests over several breeding seasons, using temperature sensors on the birds, among other things. In more than 400 cases, it showed a sharp decrease in temperature at the breeding site: it decreased by an average of 8.6 ° C. The average body temperature of the animals at that time was around 24°C and thus was significantly lower for birds. On average, this cold snap, also known as hibernation, lasted approximately 11 hours. In one case, the injured bird rested in this state for 22 hours.
In this way, animals can drastically reduce their energy consumption and thus go longer periods without food. While a rapid metabolic rate typically drops by a third at night, it is down by 56 percent during hibernation. As a result, they also used up to 70 percent less oxygen and, conversely, produced 70 percent less carbon dioxide, as measured by scientists with the help of appropriate sensors in the nests.
This is very strong evidence that rapid rises can go into hibernation, and the first evidence of these birds when they have to, Willbrook and colleagues write Wild Animals.
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