Many birds we have grown accustomed to seeing are actually species that visit us from the south for a brief appearance to breed. Seasonal migration presumably evolved as a means of increasing lifetime reproductive output. The extra daylight we enjoy in the spring and summer provide birds with more hours per day in which to gather food.
Thrushes, like this little one, are long-distance migrants.
It's nothing short of a miracle how birds fly long distances. They prepare for their long trek by accumulating fat to provide fuel for the prolonged flight. They can lose one-fourth to one-half of their body weight during overwater migration.
Most long-distance migrants, especially smaller birds, fly at night. They may travel continuously or land daily around sunrise to rest and forage. When traveling over water or unsuitable habitats, birds that normally stop each day may fly without a break for longer periods. For example, Blackpoll Warblers migrate overland in spring, but autumn migrants travel non-stop over open ocean from south-eastern Canada and the north-eastern United States to their wintering grounds in northern South America. Migrants that move only relatively short distances within our region usually travel during the day, generally spending only a few hours of the morning in migration. Aerial foragers, such as swallows and swifts, do not stop but simply feed in flight as they are migrating.
Preparing to migrate, hummingbirds eat lots of nectar and insects, and respond to hormonal changes that are triggered by the changing length of daylight.
The Rufous Hummingbird generally winters in Mexico and possibly as far south as Panama.
The process of migration has baffled humans for centuries and many theories have been developed. Is it the sun, stars or moon that helps to guide birds? Landmarks or the magnetic field of the earth have also been thought to be the answer.
Migration is derived from the Latin word migrare, to go from one place to another. It is a regular movement and refers to the spring movements of birds from their wintering to their summering or nesting places, and the fall movements from their nesting grounds to their wintering places. They migrate because of the greater availability of food and longer days in which to gather food for nestlings. These factors enhance their chances of survival. It also means avoiding the physiological stress associated with cold weather.
The migratory routes of birds are numerous, and while some of them are simple and easily traced, others are extremely complicated. Differences in distance traveled, in time of starting, in speed of flight, in geographical position, in the latitude of the breeding and wintering grounds, and in other factors all contribute to great diversity. No two species follow exactly the same path from beginning to end. The continued loss and degradation of stopover habitat is potentially a huge threat to the survival of bird species. As birds fly south, they may find fewer places to rest. As forests are being cleared and fragmented, it has a serious negative effect on migrating birds and other species.
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