Many times we see bird species that are not natives to the local environment. Sometimes these can be the result of variations that has occurred through thousands of years, but very often this happens due to the migrations in the birds.
There is a strong chance that author might see the migratory bird. Some birds from colder regions leave their homes to migrate to warmer areas in the months of winter. Such birds are called migratory birds. There are many other organisms that do seasonal migrations. Some of the migrations take the journey of thousands of miles. This is the common reason, why sometimes we spot a non-native bird in our backyards.