Going mad, help needed - Blackbirds sing Addams Family theme tune

Hi all

I'm finding one of the upsides to lockdown is being able to focus on the important things in life, like trying to solve the mystery of whether the blackbirds in our garden really do sing the Addams Family theme tune (seven main notes of) or have I finally gone mad. This has bothered me for years and I now think I have the answer.
It started at least 25 years ago when our son had a phase of singing it (with rude lyrics) and I couldn't stop whistling it in the garden. I noticed at the time that the blackbirds started whistling it too, but I can't remember whether I thought they were copying me or if it was their normal song and I was just copying them.  
Blackbirds are renowned mimics and the web is full of them imitating ambulances and ringing phones but the Addams Family song seemed a bit of a stretch (though no problem for parrots and the like). However, I've just found a Youtube clip of one doing just that https://www.youtube.com/watch?v=_o7LlSjgqgU   
My theory is that a blackbird did copy me all those years ago and the call has been passed down the (maybe 6 - 10) generations. If so, that's pretty amazing. 
Anyone have any knowledge in this area?
Thanks,  Andy