the great tits (yes the birds) sing tu-tit tu-tit tu-tit

all of them, and it's been like that for ages

it's just that 35 years ago, i remember them singing tit-tit-tu tit-tit-tu tit-tit-tu

again, all of them

i discussed this with my mom and other bird listeners and they remember the same song. i looked it up online and both songs are described and given recorded examples of

so sometime during my teens and/or early twenties, they all just changed their song