In addition to this meteorological knowledge, birds also have an 'internal GPS' and a map of the vast ocean, according to the researchers. For example, birds adapt their departure from the northern hemisphere to the weather systems they will later encounter over the southern hemisphere. In addition to being efficient fliers, birds also appear to be good meteorologists to the enormous surprise of the meteorologists among the researchers. We therefore must conclude that the birds fly much more efficiently than what we calculate on the basis of known flight properties." We know this from research with satellite-tagged birds. "The truth is, they fly for an average of up to 9 days at a time. "When we start calculating from the energy content of the fat burned and the assumed air resistance of birds, it seems that a bar-tailed godwit can fly for a maximum of 4 days at a time," lead author of the paper, migratory bird researcher Theunis Piersma of NIOZ, Royal Netherlands Institute for Sea Research and University of Groningen says. Once it arrives in New Zealand, only 215 g of that remains. A bar-tailed godwit departing from Alaska weighs more than a pound (485 g) on average. The biggest unknown appears to be the energy consumption of the birds.
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