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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
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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