Chapter 54 – Behavioral Biology
54–80
94. If a behavior has evolved by natural selection, it must have ______________.
Ranking Questions
Tinbergen observed that after gull nestlings hatch, the parents remove the eggshells from the
nest. To understand why (ultimate causation), he painted chicken eggs to resemble gull eggs,
which had camouflage coloration to allow them to be inconspicuous against the natural
background. He distributed them throughout the area in which the gulls were nesting, placing
broken eggshells with their prominent white interiors next to some of the eggs. As a control,
he left other camouflaged eggs alone without eggshells. He then noted which eggs
were found more easily by crows. Because the crows could use the white interior of a broken
eggshell as a cue, they ate more of the camouflaged eggs that were near eggshells. Tinbergen
concluded that eggshell removal behavior is adaptive: it reduces predation and
thus increases the offspring’s chances of survival.
95. Rank these experiments from worst to best to study why gulls remove broken eggshells
from their nests.