I do the adaptive thing too. It kind of creeps me out. I hope people don't notice, but honestly I can barely help myself. Sometimes I will do it on purpose, however - it's a survival thing when you live in the country, sometimes. Sure death to any budding relationship in many small towns is those five little words: "You're not
from around here?"
I took language in college and did some dialect coaching. I adore dialects. I have little interest in US accents but still am pretty good at picking out a number of regions and subregions. Native Californians do have an accent, by the way - it's just really hard to find a native nowadays. I can id several UK accents down to regions, and Scottish accents down to a 50 mile radius, because I've been exposed to more Scots than any of the other UK accents for some reason.
I can pinpoint Canadians within a few states, and I can spot a Manitoban or Nova Scotia resident at 200 paces.
I can ID two or three "'Stralian" accents, and at least two Kiwi, not counting First and immigrants.
I can usually spot non-native speakers of English and guess their native language (including Scots Highlanders and a few American First Peoples). I'm
not that good at the East Asian languages - beyond guessing at Japanese versus Korean versus Viet, Filipino, Islander, etc I'm a bit at sea. I only know that from my time in San Francisco.
I've been followed around by Scots my whole life, oddly. First, my grandparents on one side are Scottish immigrants and my father had just a teeny hair of their accent - the way the "d", "t", "L", "n" and a few other letters are pronounced. For a long time I thought I got this odd lispy way of speaking from my mostly Latina friends, but I never noticed that they actually did it! Then I started studying Scots dialects formally and realized where it came from.
So then my best friend in school's father was Scottish. A little later, we started going to a new church, and the pastor was Scottish! This was in SFO - not exactly a stronghold for Scottish culture, so, kind of weird.
After that, one of my friends in college was from Nova Scotia. She was heavily involved in the whole clan thing, heritage, etc. She had an accent but it wasn't Scottish as you can imagine!
Then I got involved with sheepdogging and now I've got one friend and two acquaintances from Scotland. To me their respective accents sound very different. Alisdair says "chyune" instead of "tune" and uses many of the stereotypical Scots phrases but his accent is flatter than you'd think. He is a native Gaelic speaker and it strongly influences his accent.
Tommy has a rather flat accent and uses almost no Scots anymore, but a peculiar turn of his vowels and consonants gives the clue as to his origin if you know what you are listening for.
And Jack has the very lyrical accent that you'd expect but switches freely between "Scots" type intonation of those key letters, and what you'd hear in the UK and what our own American dialects are mostly based upon.
Jack also freely switches between Scots, Northern English, and Americanisms. Sometimes he'll say, "I'm going now." (American), and sometimes, "I'll be going then," and sometimes, "I'll be gaeing t'noo."
It drives me crazy now to hear people talk about the "Southern accent" or worse, "drawl." Is there a "northern accent"? Well, southerners talk about that sometimes but it's chalked up to yet another stupid southern thing. To me, someone from the Appalacian region of NC talks profoundly differently than someone from this area, south of Richmond, VA.
The accent around here is a strange one and would be an interesting subject for study. Someone's probably done it, I just haven't looked it up. Anyway, this "mawhnin'" we just took our "cawh to the gerridge doon in Roxberreh t'see aboot the breks." It's not a "drawled" accent - in fact it's so clipped I can barely understand it with my bad hearing. Coastal accents tend to be similar all down to FL, then in FL you go back to a very softened accent again, similar to what you'd hear in LA.
The Appalacian accents have strong Gaelic and West of England influences (think pirate talk) on them. "Fix" and "sick" are very good English, no matter how people from Britain like to turn their noses up at it. So is "yonder" - it's the third piece in the locational triad, "here, there, yonder" - almost all languages have these or more, but we've gotten stuck with only here and there and no way to say, "not close to here." Ditto "Mine" "Your-en" "Their-en" and "His-en", a leftover from the days when we had analogous possesive singular. There was no "her-en" by the way, hissen is non-gender-specific.
There's a ton of books that have been written on this - some are better than others. My favorite is called "The Mother Tongue" can't remember the author, sorry. Should be in the library, it was well recieved when it came out.