The Custom Lists can be created one bird at a time, but I find it is much easier to use the ID Wizard to filter a list of birds and then add or delete individual birds there. I then click Save as Custom List. This is exactly the feature you are asking for.

I am adding your request to copy and paste birds from one Custom List to another to our to-do list for the next update.

The v3.1 user interface was rather clunky and hard to read. The new v3.9 is much easier to use.

We are very interested in hearing about new features you would like to see or about improving existing features. As in this example, there is often more than one way to accomplish the same thing -- we just need to do a better job of explaining it in our help files!