What is a group of geese in flight called?

A skein in the air, a gaggle on the ground, and a plump or a wedge if you want to be difficult about it. Most of these collective nouns come from a fifteenth-century English fashion for inventing terms of venery - a book of them was printed in 1486, and a good many were jokes that no hunter ever used, which is where a murder of crows and an unkindness of ravens come from.

The V formation is doing real work. The bird in front sheds a swirling vortex off each wingtip, and inside that vortex the air is moving upward. A bird sitting in the right place gets lift for free, and measurements on ibises fitted with data loggers show they position themselves within tens of centimetres of the optimum and even flap in time to catch the rising part of the wave.

The lead bird gets none of that benefit, so the position rotates. Bar-headed geese also hold the altitude record for the family, crossing the Himalayas at heights where a human would lose consciousness in minutes, on a haemoglobin that grips oxygen unusually tightly.