Subcutaneous fat
A layer of fat just underneath the skin to provide energy during migration, also called 'pre-migratory fat'. Its development causes a very noticeable increase in weight in a bird preparing for migration and it enables a migrant to travel long distances without having to stop for food, an invaluable aid in sea or desert crossings.From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver