Birdsong dialects

I don't think I've got anything useful to say about THAT Craig Raine poem that hasn't already been said, so instead, let's talk about bird dialects.

The other night, at a site close to home, I was surprised and delighted to hear what sounded like a Corn Bunting singing. This once-common species has disappeared from large parts of the UK, and in Leicestershire, the only records these days are of a handful of birds around the Warwickshire border, near Twycross.

So, I was determined to actually see the singer, and perhaps my suspicions should have been aroused by the fact that it wasn't immediately visible, even though that distinctive 'jangling keys' song was clearly close at hand. When you see Corn Buntings singing on the continent, for example, they tend to be on very prominent perches - telephone wires, fenceposts, etc.

After checking such spots, and maybe five minutes of stalking around, peering into bushes, I realised that the song was actually coming from a Yellowhammer. This close relative of the Corn Bunting has also declined in recent years, but it's still present in reasonable numbers in my corner of Charnwood Forest. In fact, as I listened to it doing its Corn Bunting impersonation, I could hear another Yellowhammer further down the lane doing the more familiar 'little bit of bread and no cheese' song.

Now, I know that many if not all songbirds have dialects - the local Yellowhammers sound considerably deeper and a little slower than the recording of their song on my Collins Guide  app - but this seemed like something else altogether. Has anyone else come across anything similar?