Research indicates birds have somewhat similar symptoms to people. Studies done with crows indicate that when crows are infected they have difficulty with balance and are lethargic sleepy, problems with the nervous system.

The University of Minnesota https://www.raptor.umn.edu/our-research/west-nile

https://corvidresearch.blog/2015/09/24/the-facts-about-crows-and-west-nile-virus/