competitive commensalism mutualism parasitism
I gave my students this multiple choice question: In a desert environment, cactus wrens often build their nests in cholla cacti to avoid predators. This behavior does not hurt the cacti. Which type of relationship do cactus wrens and cholla cacti demonstrate?

Only one answer is correct among these 4 choices:
- competitive
- commensalism
- mutualism
- parasitism

Could you tell me which one is correct?

commensalism