fighting hens

Just wondered if anyone could suggest why my girls have started fighting? I have six silkie hens and the oldest incumbents have started fighting from time to time.  There has been no change to their living arrangements since I added the three POL hens back in September last year - they tend to avoid the fights and are quite timid being the youngsters in the group.  They are let out to free range in the garden most days and otherwise live in a reasonably spacious run (8m2) with perches, logs, dirt for baths etc).  I don't quite know what has upset the pecking order but there is a definite fight going on to be top hen (lots of pecking at heads and squaring up).

I had been planning to worm them all over the next week but am concerned that by keeping them in their coop with nothing to eat other than treated pellets might worsen the situation?

This can happen if a hen wishes to become head honcho! If you can isolate, within sight of the run the instigator, and return to the main run after 2/3 weeks. It should settle. However, if she is really determined ......... .

The one thing I have learnt in my experience of hen keeping is that the spring and summer months are hormone crazy, it doesn't matter what size shape or breed, hybrid or not once they go into full production or reproduction mode hen life is unpredictable to say the least! Expect anything is my motto. Trying to introduce new birds is a particular nightmare. The battle for top spot is challenged, as well as the best spot in the nesting box! Which is going on in my lot at the moment. The grumbling for the best roosting position at bed time. Come the autumn and the onset of the moult things have really settled down. Phew why do we do it every year.....  in anticipation of next spring ?