Final answer:
Parrots can be harder to handle than other birds due to their higher intelligence which requires more attention and stimulation. The legislation that prohibits importing certain species of parrots as pets in the United States is CITES.
Step-by-step explanation:
Higher intelligence for the first question and C. CITES for the name of the legislation that prohibits certain species of parrots to be brought into the United States to be sold as pets. Parrots are known to be harder to handle than other birds primarily due to their higher intelligence. Parrots have a large brain relative to their body size, which is indicative of their advanced cognitive abilities, including their capacity for problem-solving, mimicking sounds, and understanding complex social dynamics. This intelligence can lead to them being more demanding of attention and stimulation, and potentially more prone to behavioral problems if their needs are not met.
Regarding the legislation, CITES, or the Convention on International Trade in Endangered Species of Wild Fauna and Flora, regulates the trade of specific parrot species to protect them from overexploitation. Parrots that are endangered are listed on CITES appendices, which restricts their international trade, including their sale as pets in the United States.