What triggers the birds to migrate?
The trigger for migration is part of that in-built mechanism that tells birds what to do and when to migrate, which direction to migrate and how far to migrate. It’s the changing day length that triggers the fat deposition all over the body of the bird over that two or three weeks before it starts its migration. And that fat is really like an aircraft taking on board fuel. Before a jumbo jet leaves Melbourne for Singapore it will take on sixty tons of fuel it will weigh 330 tons when it lands in Singapore it will only weigh 270 tons. An eastern curlew which is the largest wading bird in the world normally weighs about 750 gms when it leaves here it actually weigh 1200 or 1500 gms – a kilo and a half, almost twice the weight. What it will do when it leaves here is that it will fly continuously for two or three days non-stop and during that time all that fat will be converted into energy and when the bird lands, we don’t know exactly where, maybe Papua New Guinea or Indonesia, 3 – 4 thou
