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Unformatted text preview: Classic Example: Ravens – Bernd Heinrich- Ravens are highly intelligent birds o Heinrich studies foraging behavior of ravens in the north woods of Maine during winter o Huge vocabulary of quarks, quorks, queeks, yodels, screams, drums, etc Feed on carcasses in winter Carcasses are scarce, hard to find and hard to break open because they freeze Ravens are also very common- One day Heinrich saw 15 ravens eating a dead moose o Ravens yelled to attract other ravens (he thought) o But why would they do this? Why not just keep the food for themselves to eat all winter long? o How was yelling at the carcass adaptive? o Heinrich tested several different hypotheses to discover the answer HYP 1: Ravens are one big family • Prediction: birds yelling at carcass should then be related • Test/Results: DNA fingerprinting revealed that birds were not related HYP 2: Ravens yell to signal a bear or some other animal to come open up the carcass which would allow to eat it • Prediction: Ravens should only yell when they first find the carcass • Test: hauled out dead cows and watched what happened • Result: First raven to arrive didn’t always yell or sometimes yelled when the carcass was already open • Conclusion: Ravens are not yelling to signal another animal HYP 3: Ravens yell to dilute the r isk to the individual • Prediction: Birds should stop yelling once there are a lot of birds around • Test: Hauled out dead cows and watched what happened • Result: Ravens yelled even when lots of birds were around • Conclusion: Ravens are not yelling to dilute the risk to the individual o Breakthrough Observation Heinrich observed that a single bird or a pair of birds never yelled. Yelling only started when 3 or more birds had arrived at a carcass • He also knew that pairs defend territories but solo birds did not • These observations implied several predictions which led Heinrich to a solution to the mystery o Prediction: resident territory holders should never yell Prediction: non-resident birds should yell...
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This note was uploaded on 06/21/2011 for the course NPB 102 taught by Professor Hahn during the Spring '09 term at UC Davis.
- Spring '09