London: Birds don`t have to bother about overcrowded roads, but they do stick to a speed limit to avoid hitting trees or other objects.
Researchers from the Massachusetts Institute of Technology (MIT) believe their findings could help the military fly unmanned drones as fast as possible without crashing.
They looked at birds such as the daredevil northern goshawk and developed mathematical models based on the way the animals travel through the air.
MIT professor and study author Emilio Frazzoli said: "If birds flew at speeds purely based on what they can immediately see, they wouldn`t go very fast."
Instead, he explained, they roughly calculate the density of the environment they are flying through and set themselves a top speed based on the likelihood of finding a gap between the trees or buildings, the Daily Mail reports.
Above that top speed, he went on, they are "sure to crash". But if they stay below it, they could theoretically remain in flight forever.
Frazzoli, who is currently testing his theory on pigeons, added: "There is no magic number for the critical speed. In fact, the critical speed depends on some parameters describing tree density and size, and the bird`s manoeuvrability and size.
"In other words, if the forest is too dense, the trees are too thick, the bird is too large or flying too fast, it will eventually collide with a tree," he added.
He said that mathematical calculations drawn from the way birds fly could eventually be used by scientists to increase the speed unmanned drones can safely fly at.