Why do some many animal species trouble themselves with extraordinary migrations often covering hundreds if not thousands of miles? For example, Blue Whales (seen in the South Ari atoll we just visited this past week) will eat nothing for 4 months during their polar migrations. It comes down to Breeding and Feeding.
In order to carry on the survival of the species, you need to survive to sexual maturity. The two most critical variables to such survival are eating enough and not getting eaten yourself. Normally it is a trade-off that governs much adaptation. The upside of eating and the downside of not getting eaten.
One strategy to optimise this balance is to do your eating in one place that great for eating, and do your breeding where you and you offspring are the least vulnerable. This strategy is called “Reproductive Migration” (there are actually nearly a dozen variations of migration). The Kelp Gull flourishes across New Zealand, but it makes the long flight to Antarctica in the summer, where there are no predators at all, for nesting. For the above mentioned whales, the polar regions are richer in food, but the warmer and calmer (shallow) waters of the tropics for birthing. Sometimes, the ‘migration’ is shorter, but more dramatic in their lifestyle. They will actually live in two completely different habitats each optimised for feeding and breeding. A prominent example is the penguin who eats in the aquatic world and breeds in the terrestrial world.
Leaders find bountiful feeding grounds. Managers find safe breeding grounds. Both together ensure the vitality of generations.