Positive signs

During the last couple of days, the Robin has been twittering if not singing while waiting for his biscuit and this is the first time he has done this since I started feeding him some months ago. Is it a sign that Spring might be on he way, or is he practicing a territorial tune to keep other Robins away from the biscuit? I think generally there is a little more birdsong to be heard than say,  a month ago. A very mizzly day here, not cold but just grey and uninviting.