The Tropics, if you are a bird, is paradise. What bird wouldn’t want to live here? Evergreen forests, eternal spring, food available every day of the year and everywhere… (and a lot to choose from, too); no dramatic fluctuations in temperature due to changing seasons… But living all year in the Tropics is not as easy as it sounds. This is a crowded, albeit warm, house. A recent study (published in Nature, Ecology & Evolution) theorizes that the saturation of tropical avifauna and the extreme competition that exists within ecosystems in places like Ecuador, could be behind bird migration as a whole (or for a great majority of bird species in the world).
It could, in short, be an important reason why some species have preferred to fly long distances to take advantage of warmer summers in less “popular” places than the tropics (in the eyes of a bird, at least). More “simple” ecosystems in the north and south of the planet offer more food, more space, less competition during their respective summers… When the cold arrives, these sites become unlivable, or require an unnecessary adaptation process for a bird… unnecessary because birds have wings and can leave just as they came. Other birds, of course, will adapt and prefer to stay put rather than globetrot. It’s a bit like deciding between living in the suburbs and commuting, or living full-time in the city. In large cities, the distribution of inhabitants is essential. The same occurs with bird distribution: it’s Natural Selection at work.
About 15 percent of the world’s bird species are migratory. Small birds, large and medium birds … a migratory bird can be of any size. For birdwatchers, migratory birds always represent very special encounters. Some migratory birds are expected, but many aren’t and strange records arise when an individual bird has accidentally veered from its path or when groups are testing, perhaps, new migration routes.
In Ecuador, migratory birds arrive from two places and at two opposite times of year: during the southern hemisphere’s winters (austral migrants) and during Arctic winters (boreal migrants). They always travel from north to south or south to north (never or very rarely from Europe or Asia). They reach different parts of our country, through three general routes. One that passes along the coast, another through the Andes and another through the Amazon Basin. Some birds arrive and reside here for several months, others just pass through, heading farther south or north to their preferred wintering grounds, while others show up in the country only by accident.