Duck Duck Go is a search engine, but Google Analytics doesn't include it in its default list of forty. However, you can change that. As explained on Customize Organic Sources:
- Navigate to a property. If you're not in the settings menu, click Admin. Select the account and property you want to edit.
- From the PROPERTY column, click Tracking Info > Organic Search Sources.
- Click +Add Search Engine.
- In the form, specify what the Domain Name Contains and the Query Parameter. You can also specify a Search Engine Name and what the Path Contains.
- Click Create.
There have been previous questions asking why Duck Duck Go appears as a search engine. I'm not asking that. I understand that this is based on Google's categorization. The point is that it is possible to change Google's categorization. This has been requested previously (e.g. here), but it's not clear that it has made its way to staff consciousness.
As an example of why I want this, look at the Politics.SE Site Analytics page (probably requires super permissions, either moderator or 5k rep on Politics). Currently, DuckDuckGo.com would be the third largest search engine after Google and Bing (and before Yahoo!).
Many of the forty search engines recognized by Google are not English language. As such, they may not appear much in referrals to Stack Exchange. Duck Duck Go may be more impactful for Stack Exchange than Russian language search engines. They offer this customization for a reason. Why not take advantage of it?
TL;DR: If it is unclear, I am recommending that the Stack Exchange person responsible for configuring Google Site Analytics to add DuckDuckGo.com as an additional search engine. Directions in the quoted material, with relevant information added immediately afterwards.