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Neotropical Migratory Birds • Neotropical = ‘New Tropics’ – New World vs old world – Western Hemisphere • Neotropical birds breed in Canada and the United States during the northern hemisphere’s summer and spends the rest of the year in the tropics. – Defined as a species in which the majority of individuals breed north of the Tropic of Cancer (latitude = 23 degrees north) – About 200 species Migration Distance • Varies across species and within species • Shortest (a few hundred miles) are those birds that breed in the southern US and overwinter in Mexico. • Some of the longest are birds that breed in the arctic tundra in northernmost Canada and winter as far south as the southermost tip of South America – One way mileage = 10,000 • Arctic Tern – – – – Nests as far north as land extends Overwinters near the south pole Sees more daylight than any other species Round trip covers about 22,000 miles. Why Migrate? • They can take advantage of seasonally abundant food supply and avoid times and places that food supply is low. – Flying insects, caterpillars, fruits and nectar are abundant during our spring and summer, but not winter. • Ultimate reason is breeding success. – Can raise more young if they migrate than if they stayed in the tropics. – Abundant protein-rich food, longer daylight hours, more room, possibly fewer predators. When To Migrate? • Internal clock controls the onset of migration and the premigration preparations. • Environmental factors control this clock – Certain changes in a bird’s environment stimulate the production of certain hormones, which leads to changes in behavior and physiology. – Change in day length for example How To Get There? • Short migraters and waterfowl generally learn breeding and wintering locations from older more experienced birds – Often family members • Most long distance migraters are genetically programmed to make the trip. – First migration is completely under genetic control – Subsequent trips may incorporate previous experiences (return each year to good reproductive grounds) Migration Routes • Follow land through Mexico into the United States • Cross the Gulf of Mexico – First/last encountered land important to survival – Rest and refueling Seasonal Habitats • Wintering Grounds – Sufficient food for premigration preparations • Migratory Habitat – Fat reserves, nutrients, vulnerability to predation • Breeding Grounds – Reproductive success Habitat Variety Important • With the diversity of migratory birds, a diversity of habitats is needed in the migratory habitats. – Reduces competition