The National Zoological Park has been battling with a spate of animal deaths since earlier this year. The zoo houses around 40 pelicans and 20 ducks. Bird flu, or avian influenza, is a viral infection spread from bird to bird. Currently, a particularly deadly strain of bird flu -- H5N1 -- continues to spread among poultry in Egypt and in certain parts of Asia. Technically, H5N1 is a highly pathogenic avian influenza (HPAI) virus. It's deadly to most birds.