Yup, I see a lot of birders here in California since I'm active in the local birding community and lead tours for the bird festival.
I have NEVER seen someone with a 42mm+ SLC in the field. I have seen a couple of older 30mm SLCs over the years, but that is highly unusual such that I notice. Almost nobody uses porros. Everyone using Swarovski has EL models (plenty of new SVs as well as 1st gen ELs still running). Swaro is the dominant high end brand, then Zeiss (a few SF users, some Conquests, and lots of old Victory FLs), and some Leicas (and then it's nearly always 32mm UV or Trinnie BA/BN). Only ever seen a few Meoptas or Kowas (although the Kowa 883 is by far the dominant alpha scope),
As to Nikon... only one guy I know uses an EDG, I've only seen a few MHGs in the field, but Nikon Monarchs are BY FAR the most common binocular overall as they dominate the under $500 zone with birders. On a bird tour the Monarch 5 and Monarch 7 are used by most of the "beginner/intermediate" types, and I know some really good birders who use Monarchs. Then Vortex is generally #2, with Vipers being the most common. So it seems that Nikon has a broad reputation for the cheap zone, and Vortex Vipers tend to be the "step up" for someone who wants to spend ~$500 for something better.... no doubt these tropes are reinforced by the many online reviews over the years with Vipers consistently topping the "mid level" tier.