Very odd bird noise “callerrr” “caller”

Hi

My girlfriend and I have recently moved to a home in a woodland surrounded by nature ... its bliss!

yesterday around 6:30am we woke to a really odd sound coming from the bedroom window (slightly ajar) . we think it was a bird sound but initially it sounded like an american accent coming from an electric device

The sound was constant and repetitive and sounded like ... ”Callerr” ...... “Callerr” ......”Callerr”

it was really distinct and different from any birds sound i have ever heard mystery ?!?!

anybody any thoughts???