根据教授所说内容 “But it lays its eggs in shallow depressions in the sand with very little protection around them. So if there are people or dogs on the beach, the eggs and fledglings in the nests are really vulnerable.” 可知，鸻鸟一般在沙滩的浅洼地产蛋，并且这些蛋周围没有什么保护措施。如果人们或狗在沙滩散步，那些巢里的蛋会或雏鸟就会受到伤害，而现在的加州海滩有很多人活动。所以衍鸟的巢穴安全和人类活动有关。选项 C 正确。

答案: C