Multiple nests

[PennyJ]

Hi all,
For approximately the last year there has been a trio of blackbirds in our backyard - 1 female & 2 males.
My husband and I sit in our little 'outdoor house' watching, and talking, to them daily. They have become used to us, I think, as they don't fly away when we are around anymore, and the males often come up to us in the outdoor house for a visit.
Over the last couple of months we have, to our interest and amusement, been watching the female building multiple nests. She started a nest in a standard camellia in front of the outdoor house but halfway through, she started building another nest, in the vine growing over the outdoor house. When that nest was completed she then began building a nest on top of a large wooden frame attached to the side of our house. After 2 days she went back to the first nest, in the camellia. After working on this for several days, she had built it to a height of 7-8 inches. Next she was back to the nest on the wooden frame. What she had already built she pulled apart and worked, for 2 days, on 2 nests side by side. That brings us up to this morning...which is when she began building another nest on the opposite side of the outdoor house. This evening my husband had a quick peek in the camellia nest and there are 2 eggs but have not seen her sitting on them.
Is this normal behaviour for blackbirds? We have spoken to family and friends and not one of them has been able to explain.
Can anyone help please?

[Jan]

There are historic reports of polygamy in Blackbirds in Australia and NZ according to the Handbook of Birds of ANZAB [Hanzab] but it says it isn't well documented. Nothing is detailed. The ratio of males to females is more for males, which may cause something like this??