Great tits started singing

Northern Illinois Birder: Great Tit

Great Tits Could be Global Warming's Next Victim (The Bird, That

Great tit: song, nest & eggs - Plantura

bird blue tit sings a song among the young green of the tree in

Great Tit BTO - British Trust for Ornithology

Timing of singing for urban and rural great tits: (A) Dawn chorus

PDF) Female great tits can identify mates by song.

Great Tit Bird Facts

Neighboring birds sing 'out of tune' (Constantine Alexander's Journal)