You can see the small spike of something (a broken feather?) sticking out of her left side.
She is undoubtedly female. Here she is doing a nesting wriggle.
She also spends a lot of her time messing about with nesting material - an exclusively female preoccupation.
This is Hugh, a male, her mate.
When Spikey comes in . . .
. . . Hugh departs!
So far, so good.
It is now 45 minutes later and Hugh is in the box again.
Again, an incoming bluetit means that Hugh departs straight away.
But who is it? It looks far too smart to be Spikey!
Here it is in close-up. It has smooth unruffled head feathers and there is no sign of any spike sticking out of its left hand side.
It jumps up to the hole and spends nearly a minute looking out before flying off.
However, apart from some desultory tweaking at the nest material, it didn't give any definite signs of what sex it is. Nonetheless, I cannot see Hugh leaving the nest box the way he did if this bird was another male!
A couple of hours later, again Hugh is in the box, when another bluetit enters.
This time Hugh doesn't leave quite so quickly.
There is a distinct pause before he goes.
It is also clear that this is Spikey . . .
. . . who promptly does a nesting wriggle.
Again, a couple of hours later Hugh is in the box when another bluetit enters.
Again, Hugh doesn't immediately fly out of the box . . .
. . . but depart he does. He gives no hint of a challenge to the newcomer who is clearly not Spikey.
To begin with, the newcomer just watches the exit hole . . .
. . . but then she too does a nesting wriggle!
Hugh seems to have two partners! Is this the same trio that used this box last year?
As before, she spent some time looking out of the box.
In this close-up of her head taken when she was on the hole, you can see that her head feathers are much smoother and tidier than Spikey's. The same was true of the two females last year - one was smooth and sleek and the other looked older and rougher.
Eventually she went back to the floor of the box when suddenly Spikey came in!
There was no hesitation before Spikey launched a fierce attack of the other female.
The newcomer (if she stays around after this, we shall have to name her!) put up no resistance but just tried to keep out of the way.
However, her options were limited as Spikey was between her end the exit hole.
Finally she managed to squeeze past and leave the box.
Mission accomplished for Spikey I suppose.
Spikey celebrated with another nesting wriggle.
This was the box towards the end of the day.
The nest still needs some work doing on it - for example, its base is still not fully covered and there are no feathers in it yet!
Still, there is plenty of time for that!
It would be quite amazing if we had two females sharing a single nest again this year!