migration in birds

Question

migration in birds

Mridu Yadav · Accepted Answer

Birds migrate to move from areas of low or decreasing resources
to areas of high or increasing resources The two primary resources
being sought are food and nesting locations

Birds that nest in the northern hemisphere tend to migrate
northward in the spring to take advantage of burgeoning insect
populations, budding plants and an abundance of nesting locations
As winter approaches, and the availability of insects and other
food resources drops, the birds move south again Escaping the cold
is a motivating factor but many species, including hummingbirds,
can withstand freezing temperatures as long as an adequate supply
of food is available
The term migration is used to describe movements of
populations of birds (or other animals) One way to look at
migration is to consider the distances traveled

Short-distance migrants: May move only a short distance, as
from higher to lower elevations on a mountainside
Medium-distance migrants: Some species may cover distances that
span from one to several states
Long-distance migrants: Birds that typically have ranges that
extend from the United States and Canada in the summer to Mexico
and further south in the winter

The 
pattern of migration can vary within each category, but is most
variable in short and medium distance migrants
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The term migration is used to describe movements of populations of birds (or other animals). One way to look at migration is to consider the distances traveled.