Weird. An Aussie band called Glass Towers have an album released last month called the halcyon days. No idea what halcyon means. A bird right?
"Halcyon Days" is a reference to greek mythology. In the myth of Alcyone, the Halcyon Days were the seven days in winter when storms never occur.
Just 'halcyon' is a genus of birds though, yeah (the word originating from the same myth, I believe)