The Goldcrest is the smallest bird in Europe. It's only half the weight of a blue tit and it's egg only weights about 1 gram!
The five smallest bids in the world (length / weight):
1) The Bee hummingbird (5-6 cm / 1,6-1,8 gram)
2) The Weebill (8-9 cm / 6 gram)
3) The Pardolates (9-11 cm / 8-11 gram)
4) The Golden Headed Cisticole (10 cm / 10 gram)
5) The Goldcrest (8,5-9,5 cm / 5-7 gram)
The song of the Goldcrest actually looks most like the squeak of a mouse. Very high tones that sound like "see-see-see". The tones are so high that older people sometimes can't hear them.