This page summarizes the general techniques for performing a taxonomic split in Avisys. There are two kinds of split; one where a species is split into entirely new species and the old species no longer exists, and one where part of a species is split into a new species but the old species still exists. We'll use the split of Willet into Prairie Willet and Saltmarsh Willet as an example of the first kind of split, and the split of Spotted Flycatcher into Mediterranean Flycatcher and Spotted Flycatcher as as example of the second kind of split.
Of course, you don't need to do anything at all if you have no sightings of the split species, so we'll assume here that you have sightings of Willet and Mediterranean Flycatcher.
You only need to prepare in advance for the first kind of split, so here we'll only talk about Willet. First, rename the species to one of the split species. If you have sightings of both of the split species, never mind that until later; for now just rename the species to the split species for which you have the greatest number of sightings. So, if most or all of your Willet sightings are in the range of Prairie Willet, rename the species to Prairie Willet. To rename a species, highlight its name (by clicking on it), click on Edit->Edit Species/Family Name, change the name, and click OK. Don't bother updating the scientific name, as that will be done automatically when you run the taxonomy update.
For the Spotted Flycatcher/Mediterranean Flycatcher type of split, there is nothing to prepare in advance.
How to do this is described here.
If you have only seen Prairie Willet but not Saltmarsh Willet, you are done with that split now. Likewise if you have only seen Spotted Flycatcher but not Mediterranean Flycatcher, you are done with that split. If you have seen both of the split species, you have a little more work to do.
First, find Saltmarsh Willet and click on the name to highlight it. Then, either press Ctrl-F3, or equivalently click Utilities->Save Species for Edit. Either way, this will bring up a "Saved Species" dialog listing Saltmarsh Willet. Just click OK here. Then do a List Records of all of your sightings of Prairie Willet in the range of Saltmarsh Willet. Change each of these records to Saltmarsh Willet. To do this, click on the first sighting and then click on Edit, and then on Species. Clicking on Species will bring up the Saved Species dialog that you saw before, and you then click on Saltmarsh Willet, and then on OK and Finished. You have now changed the species associated with this sighting from Prairie Willet to Saltmarsh Willet. If you have a second sighting, highlight it and press enter, and then choose Yes for the question "Do you want to do mass modifys?", and then simply press enter on each subsequent sighting to perform the rename. Repeat this process for each relevant Place. The whole process is simpler than it sounds.
For the Mediterranean Flycatcher type of split, the process is similar. Do a List Records showing all of your Spotted Flycatcher sightings that should be changed to Mediterranean Flycatcher (e.g., select by Place) and move them all to Mediterranean Flycatcher using the same procedure as described above.