The secret of carrier pigeons'uncanny ability to find their way home has been discovered by scientists: the feathered navigators follow the roads just like we do.

Zoologists now believe the phrase "as the crow flies" no longer means the shortest most direct route between two points. They say it is likely that crows and other diurnal birds also choose AA-suggested routes, even though it makes their journeys longer.

Researchers at Oxford University spent 10 years studying homing pigeons using global positioning satellite (GPS) and were stunned to find the birds often don't navigate by taking bearing from the sun.

Instead they fly along motorways, turn at junctions and even go around roundabouts, adding miles to their journeys.

"It really has knocked our research team sideways to find that after a decade-long international study, pigeons appear to ignore their inbuilt directional instincts and follow the road system," said Prof Tim Guilford, reader in animal behaviour at Oxford University's Department of Zoology.

Guilford said pigeons use their own navigational system when doing long-distance trips or when a bird does a journey for the first time.

"But once homing pigeons have flown a journey more than once, they home in on a habitual route home, much as we do when we are driving or walking home from work," said Guilford.

"In short it looks like it is mentally easier for a bird to fly down a road. They are just making their journey as simple as possible."

信鸽有高超的认路归巢的本领。科学家们已经揭开了信鸽认路的奥秘：这些鸟类飞行家像人类一样沿着公路前进。

动物学家现在认为“as the crow flies”（笔直地）这个短语不再表示两点之间最短、最直接的路线。他们说乌鸦和其他一些白天活动的鸟类可能也会根据公路的路线飞行，尽管这样会增加飞行的路程。

牛津大学的研究者们花了十年的时间用全球卫星定位系统来研究信鸽。他们惊讶地发现信鸽飞行时往往不是通过太阳来辨别方向的。

相反，它们是沿着汽车路线飞行的。他们在路口处转弯，甚至还绕行环岛，多飞很长的路程。

牛津大学动物学系动物行为学教师提姆·吉尔福德教授说：“经过长达十年的国际研究，我们发现鸽子似乎忽视了它们天生的识途本能，反而沿着道路体系飞行，这着实让研究小组大吃一惊。”

吉尔福德说鸽子在长途飞行或者第一次飞行新航线时依靠的是它们自身的导航系统。

“但是，信鸽一旦多次飞行同一条路线时，它们就会沿着习惯的路线回家，就像我们从单位开车或走回家一样。”吉尔福德说。

“简而言之，对于鸟类来说，沿着道路飞行似乎更节省脑力。它们不过是让旅途越简单越好。” s