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passage 3
P1
Homing pigeons can be taken from their lofts and transported hundreds of kilometers in covered cages to unfamiliar sites and yet, when released, be able to choose fairly accurate homeward bearings within a minute and fly home. ███
Phenomenon ·
Homing pigeons' ability fly home
What's the explanation for this?
Two Hypotheses ·
Tracking outward displacement / having a map sense
Not sure what the "tracking outward displacement" hypothesis means. Perhaps will get cleared up later.
P2
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Displacement Hypotheses ·
Unlikely
Mechanism ·
Magnetic compass to track displacement
If the birds are using an internal magnetic compass to track displacement, then we would expect distorting magnetic fields to impair their ability to home but it does not reliably do so.
Mechanism ·
Conscious navigation to track displacement
If the birds are tracking displacement by consciously tracking their movements (e.g., "I turned left and flew 3 minutes before diving low and then I turned right..."), then we would expect that anesthetizing them would impair their ability to home but it does not at all.
Mechanism ·
Magnetic and conscious navigation together?
Maybe the birds use both to track displacement? To rule that out, we'd have to experiment with impairing both abilities at the same time.
P3
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Map Sense Hypothesis ·
Promising but mechanism is mysterious
Mechanism ·
Olfactory (odors and smells) map
Who is Papi? Anyway, Papi hypothesizes that the mechanism for generating a map is via the bird's sense of smell. It's a odor map.
Experimental Support ·
Plugging the pigeons' noses impair their ability to home
P4
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Criticism of Olfactory Hypothesis ·
Pigeons cannot distinguish natural air from filtered air
If pigeons did use their sense of smell to create a map, presumably they would be able to tell natural, scent ladened air, from pure, filtered air. But they cannot.
Alternative Explanation ·
for Papi's experimental results
Why did Papi's pigeons have trouble homing? It wasn't because they couldn't smell. It was because plugging their noses was a traumatic experience and interfered with their breathing.
Experimental Support ·
for alternative explanation
When pigeons could not smell but could breathe comfortably, they were able to home. So the mechanism for their map sense is not olfactory.
Passage Style
Critique or debate
Phenomenon-hypothesis
20.
Which one of the following, ██ █████ █████ ████ ██████ ██████ ██████ █████████ ██████ ████████ ██████ ████████
a
Even pigeons that ████ ████ ██████ ██ ███████ █████████ █████ ██ █ ███████ ██ ███████████ ███ ████ █████ ███ ██ █████ ███████ ████ ████ ████████ ██ ██████████ ██████████
b
Pigeons whose sense ██ █████ ███ ████ █████████ ███████ ████ █████ ███ ████ ████ ██████ ████ ██ ███████ █████ █████ ██ █████ ███ ███ ████ █████████
c
Even pigeons that ████ ████ ██████ ██ ███ ████ ████ ██████████ ████ █████████ ██████ ████ ████ ████████ ██ ██████████ ██████████
d
Even pigeons that ████ ████ ███████████ ████ ██████ ███ █████ ██ ███ █████ ██████████ ██ █████ ████ ███████████ ███ ████ █████ ███ █████
e
Pigeons' sense of █████ ██ ██ ████ █████ ████ ████ ██ █████ █████ ███ ██ ███ ████ ███ ███████ ██ ███████