birds

i work in the evenings and just outside my office are some trees .the past few weeks around 6pm and again at 10pm bieds are singing as i no very little about birds i was wondering if any one of you could tell me what they might be.
what ever they are they are a joy to listen too.
happy new year everyone and looking forward to the start of the gardening season.

 

Robins are tuning up at present and setting out their territory you can hear them anytime in the night especially near artificial lighting

 

How big are the birds? They may be starlings which like to roost in trees near lights.