migration and orientation Flashcards
what animal spends the highest percentage of its life in sunlight
arctic tern
migration patterns: do they take the same route back and forth?
no, north and south routes can be different
why do birds migrate?
- exploit seasonal food resources
- find good breeding sites
- avoid predation
- avoid climatic extremes
relationship of migration and food availability
- obligate if food is abundant and predictable
- low predictability but high variability means migrants are irruptive
trade-offs in survival and repro success of residents and migrants
-lower reproductive success correlates with higher adult survival,whereas high reproductive success correlates with low adult survival
2 main questions regarding migration
- how do birds navigate
- how do the know where to go? learning/instinct?
ways of studying migration
observation/bird counts, banding recoveries, genetic data, radar, displacement experiments
Emlen cages
-birds stand in ink, and so their movement is recorded as they try to leave their cage, thus we can tell how they navigate by changing variables
birds navigate ussing
- vision, star/sun compass, landmarks
- magnetic field
- olfaction
- infrasound
- coordination between many cues
solar compass
- elmen cages with blocked sun demonstrate this, conducted by Gustav Kramer examined migratory restlessness in starling, noted activity was not random
- those who could see the sun would move in the direction of migration, while those who could not moved randomly
-in order to use the sun birds must be able to both determine the sun’s position, and have an internal clock
other experiments testing vision navigation
-translucent contacts over pigeons eyes found that when they could not see landmarks, but still the sun on clear days they could navigate back to their nests
testing internal clock
-by changing bird’s internal clock their movement based off the time they thought it was
orientation at night
- birds will orient themselves based on the sunset
- birds can navigate using stars
Elmen’s indigo bunting experiments
using star maps of different seasons, elmen found that buntings oriented in with the north stars placement, so they were not confused by time-shifted sky in different seasons
-young birds learn the north stars placement based on it being the centre of rotations
Wiltschko’s magnetic field experiments
-under overcast skies he rotated magnetic fields, cause robins to orient in the opposite direction
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