Why is female blackbird calling?

Question

I live in the city centre of Newcastle and every year for the past 5 years between approx May and August a brown blackbird perches on a telephone pole and calls a shrill very loud call for about 20 minutes. It used to be around 7pm each evening, but is now sometimes midday and even 2.00am at night. 
 
 The bird has also been nesting in the basement car park of the buidling. 
 
 My question is, 
 
 I'm assuming this is the mother bird so why is she calling? Is it defending territory, or calling fledglings to feed them? 
 
 I had wondered if it was a brown fledgling calling for its mother for food? 
 
 Is there anything I can do to discourage it or encourage it to move elsewhere as call is painfully shrill? 
 
 Thanks

John B (not the sloop) · Accepted Answer

Hi Gus and welcome to RSPB Community. 
 Blackbirds have 3 grades of warning call that I can determine. 
 There's general anxiety - a kind of muted "chook chook chook" which they sit in a bush and do if something they're not happy about is nearby 
 There's "Danger" - a shriller "pink pink pink" which they do when mobbing something 
 And there's "Emergency - take cover!" A much accelerated "pinkpinkpinkpinkpinkpink" which nomally culminates in the bird departing in a big hurry. 
 All very different to their flutey song, and all in reaction to a perceived threat. 
 JBNTS