Which mosquito-borne virus is most commonly associated with bird populations?

West Nile virus is particularly associated with bird populations, as it primarily cycles through a wildlife reservoir that consists of birds. Infected mosquitoes feed on these birds and, in the process, acquire the virus. Birds are crucial to the transmission dynamics of West Nile virus, allowing it to spread within the avian population and subsequently to humans through mosquito bites.

While other viruses in the list may also involve animal vectors, they do not have the same level of association with birds. Malaria is primarily transmitted through mosquito bites but is associated with humans and does not have a significant bird reservoir. Chikungunya and yellow fever are also transmitted by mosquitoes but are not directly linked to bird populations in the same way that West Nile virus is. In summary, the relationship between West Nile virus and birds is significant, making it the correct answer.