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 Herring Gull into American Herring Gull and Vega Gull as an example of the first kind of split (note that this is a four-way split but we'll only look at two of the species), and the split of Brown Booby into Cocos Booby and Brown Booby 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 Herring Gull and Cocos Booby.
You only need to prepare in advance for the first kind of split, so here we'll only talk about Herring Gull. 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 Herring Gull sightings are in the range of American Herring Gull, rename the species to American Herring Gull. To rename a species, highlight its name (by clicking on it), click on Edit->Edit Species/Family Name, change the name, and click OK.
For the Brown Booby/Cocos Booby type of split, there is nothing to prepare in advance.
How to do this is described here.
If you have only seen American Herring Gull but not Vega Gull, you are done with that split now. Likewise if you have only seen Brown Booby but not Cocos Booby, 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 Vega Gull 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 Vega Gull. Just click OK here. Then do a List Records of all of your sightings of American Herring Gull in the range of Vega Gull. Change each of these records to Vega Gull. 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 Vega Gull, and then on OK and Finished. You have now changed the species associated with this sighting from American Herring Gull to Vega Gull. 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 Cocos Booby type of split, the process is similar. Do a List Records showing all of your Brown Booby sightings that should be changed to Cocos Booby (e.g., select by Place) and move them all to Cocos Booby using the same procedure as described above.