It's not goofy and yours is the second person to post to this forum that I can recall who was working on a bird watching database. You might search the forum for "bird watch" and see what pops up to see how the other discusson went.
What you have here is called a many to many relationship. A given county can list many species and a given species can be observed in many counties. This can be implemented with a Join Table:
Counties::__pkCountyID = County_Specie::_fkCountyID
Species::__pkSpeciesID = County_Specie::_fkSpeciesID
If this notation is unfamiliar, see: Common Forum Relationship and Field Notations Explained
This can work to provide what looks like a checkbox list of all species in a portal on your counties layout. Clicking the "check box" (really a button in this case) creates the needed record in the join table or (if you click it again), removes the same record to 'clear' the check box.
See this demo file to see a starting point for setting up such an interface: https://www.dropbox.com/s/oyir7cs0yxmbn6i/ManyToManywDemoWExtras.fp7
The check box list example shown here could be enhanced to list user selected groups of species to make it easier to select those that have been observed. Those groups might, for example, match the grouping of a bird watching resource such as the Peterson's Field Guide uses.