Stunning shots of the mating Pied Kingfishers Elsa
Elsid, those are none too shabby! There is lots of discussion in some places about which is better for birds, the 200-500 or the 300PF + TC1.4E, so you are probably not as far under-gunned as you think.
As Elsa said, there is no such thing as a long enough lens for small birds. On the other hand you will find that atmosperic conditions (unless you live in a very cold climate) becomes seriously detrimental above the range where 500-600mm is "enough".