The purrs seem meaningless at this time.
It's Honk => Chittering => Purrs => Repeat
The chittering is where the morse is.
The chittering seems to be "enclosed" in a very fast stretched clicking, ie while the morse is occurring there's a constant "stretched" clicking which to me seems to just be there as an indicator "location block here" sort of thing.
Sometimes there's a bit of overlap, occasionally a first quieter purr will occur just as or just before the "location block" ends,
The above cycle repeats itself over and over.
For a given UA deployment, the chittering stays consistent (or at least appears to) over cycles, the purrs however change which each cycle.
It's around 4-6 purrs, sometimes it seems the last purr is squashed by the honk coming in over the top so it's not always clear how many they are.
The purrs don't seem obviously to be morse in that for a set of purrs the gaps between each purr seems to be consistent, like it doesn't SEEM like there's a letter gap.
Caveat : Between the purrs there sometimes seems to be a short piece of high/low alternating audio, this changes in position across cycles and changes itself across cycles, it may encode something itself or it may be a start/end marker.
Here's a example cycle, this particular one has multiple "in between purrs".
https://www.dropbox.com/s/wqgs48hto3ohpcy/between_purrs.wav?dl=0
It goes :
- Honk/Wail
- Chittering [Location block]
- Purrs
- Purr (Low)
- Purr (High)
- Inbetween purr (LHH?)
- Purr (L)
- Purr (H)
- Purr (H)
- Inbetween purr (HLH?)
- Honk/Wail
For the more curious, here's the full audio across multiple cycles the above was taken from :
https://www.dropbox.com/s/gywdxpskw2ta3s7/ross_154_first.mp3?dl=0
As mentioned above (2) Purr block varies each time.
Morse key