You are probably searching for a name which is different from that used in HBW. Try searching for the scientific name, or looking for the species within its family. There is also an advanced search option under the top "Species" menu item.
Also keep in mind that some taxonomic changes were applied in September 2014 for non-passerine species and related orders, families and subspecies, derived from the recently published HBW and BirdLife International Illustrated Checklist of the Birds of the World.
We are also maintaining a list of Newly described species, regardless of whether we will accept them or not within our taxonomy in the future.
Watch our tutorial How to find Species, Families and Orders.