Ostrich (Shinya et al, J Virol, 2009)

Highly pathogenic H5N1 influenza viruses possessing mammalian-type PB2-627 were detected during the Qinghai Lake outbreak in 2005 and spread to Europe and Africa. …  Here, we report that H5N1 avian influenza viruses possessing mammalian-type amino acids in PB2-627 or -701 are selected during replication in ostrich cells in vitro and in vivo.

Shinya, K., Makino, A., Ozawa, M., Kim, J., Sakai-Tagawa, Y., Ito, M., Le, Q., & Kawaoka, Y. (2009). Ostrich involvement in the selection of H5N1 influenza virus possessing mammalian-type amino acids in PB2 Journal of Virology DOI: 10.1128/JVI.01714-09