benefits of migration
-increased access to resources-escape deteriorating (climate) conditions
cost of migrations
increased risk of -higher predation risk -flying over large bodies of water
mitratory behaviour
energetically demanding
migrants
need to gain extra weight or energy to reach destination
red knots
need horseshoe crab eggs during migration to arctic breeding grounds
less well fed red knots
more likely to die (less likely to be re-captured next year)
mortality rates
in raptors are 6x higher during migration season than when stationary
common blackbird
migrants had 16% higher chance of surviving the winter than resident staying behind is worse!
red-eyed vireos
birds w/ low fat reserves would be less likely to cross the large waterbody
blackpoll warbler
successfully complete the overwater trip have reduced costs of getting to their destination -duration half as long-fewer predators -cold front + westerly breezes
differences in migration strategy
red knots use flapping flightsuse large fat reserves on migration
shorebird species
migrate at night to avoid predation
sockeye salmon
pop. reduced while migrating; -migrate @ night (favoured)-waiting in predator-free areas for other individuals to travel as group (dilution effect)
top-down forces
more daylight hours (change in resources)-more food growth-predation -reproduction
bottom up forces
decline in water and increase in saltiness of the water in drying rivers/shrinking water holes
multi factors impacting migration
bottom-up and top-down forces can interact to shape migratory behaviour
diff in migration strat
monarch migration not driven by food
monarch butterflies
killing freezes occur regularly @ night throughout eastern NA during winter-freezes rare in Mexican mountains
why not go to lower elevations in mexico?
monarchs use up their water and energy reserves in warmer drier areas (higher is moist and cool)
conditional strategy
choose whether to migrate depending on their social status
socially dom individual chooses
subordinates left w the option of lower fitness (but better than trying to behave like dom) ex. area limitation