Blackcap waiting on a branch

I love these little birds. A pair of blackcaps arrived late last year to over winter in our garden, and started gingerly coming to the sunflower feeder, and then carefully waited for an opportunity on the suet feeder, which can get crowded with other birds. 

Within a week or two I noticed a second male, the ones with the black caps, also flying into the tree from which feeding sorties are made down to the feeders. Then a second female was spotted, the one with the light brown cap on its head, but they females were much less obvious and tended to keep out of sight when possible.

Now about two months later, the females are very prominent and bullying, chasing other birds away with the best of them. Only the nuthatches seem to be scare them, and the great spotted woodpecker of course, which is becoming a more regular visitor again.

The pairs are also now beginning to escort each other although it sometimes appears that the female is chasing the male. how roles and behaviour can change in such a short time. Might it be springtime hormones?