Schwa

https://m.xkcd.com/

It has to be some real weirdo dialect where all of those vowels can be replaced by a schwa.

To save you looking it up (like I did ;) ) if you aren’t up with all the language terminology – a schwa is an unstressed “uh” sound that you might say, such as in a word like “approximate” (uh-prox-uh-m-uh-t, though that’s not how I’d say it).

My firstname is often spoken with two schwas. Only in British English is the name ‘Bernard’ so devoid of clear articulation — quite unsuitable for shouting to either dog or human over a distance.

Only in British English is the name ‘Bernard’ so devoid of clear articulation

As with many things, that’s rather dependent on the dialect of English.
A wandering, zig-zag route down from the extremities of Northern Scotland to the tip of Cornwall will probably reap a few hundred variants.
Of those, it wouldn’t surprise me if Yorkshire and the Black Country came up with several variants within the length of a half mile.