Team eBird has basically stated that to make data even more concise they've changes a few things. Historical would be used in place of incidental, or either traveling or stationary counts. Here is what they have to say about historical data:
The value of entering historic data into the eBird database cannot be overstated. These records help build historic perspective in the database, and allow us to look farther back in time when conducting analyses. In these cases it's good to have as much supporting documentation available for the old records as possible, and be prepared to field questions from our regional editors about the validity of the data. All eBird records are treated the same way, going through our data-vetting procedures, and historic data are no different.
Historic data entry does have a few caveats though which you can read about here.
But there is more. Team eBird apparently also wants all counts to be either stationary or traveling. If you are birding, or a heavy portion of what you are doing is birding, they want you to use those count types. Here is a quote directly from an email that was forwarded to me about the change:
Our goal is to encourage people to use Stationary and Traveling counts. These are the two principal types of surveys that provide the most useful data (aside from some specific surveys we may have in the drop down menu for particular projects). When we have start time, duration, distance, we can do much more with the data particularly when coupled with a yes to the question about whether all species were detected.
After looking through a large amount of data, it became clear that there are two different ways that people were using the "old" Incidental protocol. One was for historical data entry where people were simply missing values but had made an attempt to survey an area for a reasonable amount of time. The other was for current checklists. Of current checklists, we found tens of thousands of records with one or two species where people said they were answering yes to the question, are you reporting all species. This is NOT the intent of that question and we needed to address it.
The question that I'll paraphrase as "Are you reporting all birds" has a temporal component. In order to report "yes" to the question of are you reporting all species of birds, there must be a dimension of time, otherwise the answer doesn't make much sense. If someone spends 5 minutes surveying for birds or 10 hours, there will be very different number or birds detected. The same is true for distance. If we have no information on this, it doesn't help much to have an answer of Yes to this question.
You'll now see this message near the submit button on your checklist if you select incidental--and you can't change it to "complete checklist". This means that even if you stop for 1 minute to bird a location--and you are really birding and only see 2 species, you would submit a stationary count as opposed to incidental. It's a great way to improve data quality.
I talked with some friends recently about dozens of old field notes from when I did field work in Wyoming. 99% of those notebooks aren't in eBird--along with 10+ years of birding before that. I have 1,000's of historical checklists just laying around that one day I want to enter in eBird--and now there is a count type specifically for them! To that I say hooray! I will also have to start using the stationary and traveling more often when I make a quick stop while birding. I guess those minutes are important data not to be dismissed as incidental after all!