In preparation for their 11,000km migration from Alaska to New Zealand, the Bar-Tailed Godwit builds up massive fat reserves to sustain it on its flight. In order to make space for this fat, and to save energy in flight, these birds absorb up to 25% of their digestive system, i.e. tissue comprising of their liver, kidneys, and alimentary canal. The organs are reformed upon arrival at the migratory destination. (http://bit.ly/2KcTy3Z)