So I have no professional recording equipment, and really had to improvise to get this bit of audio:
I recorded it in the first place by simply pointing the microphone of my Samsung Galaxy S2 at the tree containing the chattering birds.
I downloaded that recording to my computer in an unhelpful .3ga format, which I then converted to MP3 using Bigasoft Audio Converter (on a free trial). I used the same software to cut it down to the best 30 seconds of audio.
WordPress doesn’t support MP3 without an upgrade, so I uploaded the file to SoundCloud then used a little bit of HTML code to create and embed the player. First you put:
…inside square brackets [ ], then the link for the audio:
https://soundcloud.com/david-craven-5/siskins then /soundcloud
…again in square brackets 
Hope that’s clear?
It’s not great, but something I’m going to try more this year. If anybody as tips or suggestions of ways to better achieve this, I’d love to hear from you!