How Does Bird Flu Transfer From Bird to Bird?

Influenza viruses cause seasonal influenza for us every winter, but they can also grow in many animals. The usual source is a bird form of the virus that may have jumped directly into humans or come via an intermediate like farm livestock. H5N1 human infections have been lethal so far in up to 70% of cases. But how does avian flu transfer from bird to bird? Are there reports of H5N 1 getting into mammals anything we should worry about? I spoke to Glasgow University flu virologist Ed Hutchinson.