Bird Migration

Why Migrate? Escape from -lack of food -bad weather Major North American Flyways

Examples Insectivorous birds such as warblers Fruit (berry) eating birds such As cedar waxwings

Types of Migration Seasonal North/South Primary pattern Elevational Migrations Summer/winter shift from high elevations to low elevations Latitudinal Movement from interior areas to shore areas Western Tanager

Preparing for Migration Molting New feather growth needed for long migratory flights Putting on weight - Some birds can double their weight in a period of 2 – 3 weeks.

Trigger for migration Day length -increase of day-length at the end of winter stimulates bird pituitary gland. -hormones produced trigger accumulation of fat, migration, courtship and mating, nesting and care of young.

Finding the way Visual -Topographical landmarks such as mountains, lakes, cities, rivers, etc. -Familiar routes learned along with flock Sense of time -Allows them to navigate by sun- azimuth orientation. Use the sun as a compass. As it moves across the sky, they keep on course knowing where it should be at a given time of day.

What if they cannot see? Night navigation by the stars orient to the north star Storms or cloudy weather orient to the earth’s magnetic field

2 Reproductive Strategies Altricial – Babies are hatched naked and blind - Cannot fly, walk or find food - Few eggs are laid (2 – 3) - Parents invest much energy in care -If young are preyed upon, the eggs are easily replaced (short incubation time) - Examples are robins, swallows wrens, hawks

2. Precocial -Young are hatched covered with down feathers -Many eggs are laid (6 – 15) -Parents invest a lot of energy in producing many large eggs -Young are well developed and can move and feed shortly after hatching -Difficult to replace if preyed upon -Examples are ducks, geese, swans, chickens