Final answer:
A squirrel climbing up a tree is not a structural adaptation.
Step-by-step explanation:
The correct answer is a squirrel climbing up a tree. A structural adaptation is a physical feature of an organism that helps it survive in its environment. Camouflage and mimicry are both examples of structural adaptations because they involve physical features that help organisms blend in with their surroundings or mimic other organisms for protection. Spikes on a hedgehog are also a structural adaptation because they provide a defense mechanism against predators. However, a squirrel climbing up a tree is a behavioral adaptation, not a structural one. Climbing up a tree is a behavior that helps the squirrel find food and escape from predators, but it is not a physical feature of the squirrel itself.