2. Many birds have the characteristics of seasonal migration along latitude. In summer, these birds breed in temperate regions with higher latitudes, and in winter, they spend the winter in tropical regions with lower latitudes. In late summer and early autumn, these birds move from the breeding ground to the wintering ground, and in spring, they return to the breeding ground and fly north. These birds that migrate north and south with the seasons are called migratory birds.
The advantage of breeding birds in temperate regions is that the days in summer are long and the nights in temperate regions are short, so young birds can be fed and nurtured in longer days, avoiding the competition between nests and food when breeding in tropical regions with many species. In addition, in summer, the number of insects in temperate regions is more abundant than that in tropical regions, while there are fewer natural enemies in temperate regions, and the predation pressure of natural enemies is relatively low. However, due to the cold winter climate, temperate regions often face the problem of food shortage. In tropical areas, on the other hand, the breeding season is faced with fierce competition between nesting sites and food resources, and the predation pressure of natural enemies is also relatively high, but the climate in winter is mild and the food resources in winter are much richer than those in temperate areas. Migratory birds breed in temperate regions in summer and winter in tropical regions in winter, and both places have advantages. In that case, why don't all birds become migratory birds? The answer is that immigrants must pay the price. For example, the migration process needs to consume a lot of energy, and may encounter bad weather, the migration direction is wrongly positioned, and it is necessary to adapt to an unfamiliar new environment and compete for resources with other migratory birds and residents in the region. At the same time, when all birds adopt a behavior pattern with high income (migration), the competition will become greater, and the behavior pattern with low income (non-migration) will become relatively favorable. Therefore, there will be different behavior patterns in evolution, and an evolutionarily stable strategy will be achieved, which is why some birds migrate and some do not.
Furthermore, individuals of the same ethnic group who do not migrate in winter may have to endure the crisis of food shortage, but they can occupy better breeding nests as soon as possible before the next breeding season, thus increasing the success rate of breeding; On the contrary, migrating individuals can obtain more abundant food sources in warm wintering areas, but there are risks of migration and the possibility of poor breeding nests. Whether to migrate or not is a question of individual survival and reproductive strategy. If the reproductive success rate of migrating individuals is much higher than that of non-migrating individuals, evolution will tend to migrate. On the other hand, if the reproductive success rate of migrating individuals is much lower than that of non-migrating individuals, the evolutionary direction will not be conducive to migration behavior; If the reproductive success rate of the two strategies is similar, then both behavior patterns will remain in evolution.