Lecture 8 Migration (unit 2) Flashcards
Migration Definition
Movement away from and then subsequent return to the same location on a regular basis (usually annual)
Dispersal Definition
Dispersal – movement away from a particular
area
Migratory Examples (3)
Monarch Butterflies, Caribou, Salmon
Bird Migration (3)
5 billion birds of 200 species migrate each year in from north down to Central or South America
> 80% of all bird species in the boreal region of Canada winter farther south
During winter, 50% of birds in
Mexico are migrants
Duck / Geese Migration (3)
– Use particular flyways
– Narrow & well defined
– Hunters shooting down banded birds provides useful conservation info
Songbird Migration (2)
– Less is know about flyways
– Appear to use weather fronts
Major Patters of Brid Migration (2 categories, 3, 2)
Birds that soar (eagles, hawks)
– Use updrafts & thermals
– Only fly in daytime
– Must stay over land
Birds that soar (eagles, hawks)
* Birds that flap (songbirds)
– Often fly over the ocean, Creates fewer updrafts, less turbulence
Why most birds migrate at Night (5)
*Avoid predators & can feed during the day
* Less turbulence caused by thermals and updrafts
* Cooler, thus avoid overheating (flight muscles generate lots of heat)
* Convective & evaporative cooling…no sweat glands but can secrete water through their skin & respiratory tract
* Night is more humid so less moisture loss
Arctic tern (6)
*Ultimate sun follower
* Fairly small bird (<125 g)
* Long-lived up to 34 years
* Opportunistic feeder small fish, crustaceans on top surface (50 cm) of ocean
*Biologists Used archival loggers placed on birds to follow them.
*19,000 km each way
Geolocators vs. satellite locators (2 pros and cons)
Geolocators are
* Smaller so they can go on small birds
* Cheaper
BUT
* Cannot transmit data (must be retrieved)
* Accuracy of location is within 185km
Ultimate vs Proximate explanations
Proximate explanations refer to causal
mechanism or developmental questions
* E.g., how is it triggered?
Ultimate explanations refer to the functional
or evolutionary history questions
* Fitness consequences
Why do Birds Migrate
Proximate – perception of day length, hormonal triggers
Ultimate – what is the purpose, and why now?
* What is the fitness benefit?
The Benefits must be > the Cost
The cost of migration (5)
Costs of Migration – HIGH
Energy
* V- Formation reduces drag by up to 50%
Predation
*Eleonora’s Falcon preys on migrants and has a breeding season during migrations
Getting lost
*Storms blow birds off course
Risk of starvation
* Get really fat & then long flight or Not so fat, short flights, stopover & feed
Why Breed in the north (5)
*Greater habitat available for breeding
* Long periods of daylight for foraging
* Superabundance of food in spring (higher resources)
* Fewer competitors
* Fewer predators
Caribou Migration (3)
6 migratory caribou herds in western Canada all trying to:
*Maximize access to abundant & high quality forage
* Minimize interactions with predators and insects
