Meaning: Birds use their beaks as a means of defense against predators and rivals, protecting themselves from harm and securing access to food and territory.
Choice of Words: The sentence describes the defensive role of beaks. "Beaks" are the hard, pointed parts of a bird's mouth, "defend" means to protect or guard against attack, "birds" are flying creatures with feathers, "predators" are animals that hunt and kill other animals for food, and "rivals" are competitors for resources such as food or territory.