Not eating their pellets

I have 6 hens, two hybrids and 4 breed. Ages 18-20 weeks for the hybrids, breed hens 17 weeks ish.

I've been watching them quite carefully for the last few days as whilst the hybrids seem quite happy to chomp away on their pellets the others do not seem to eat from either feeder.

The hybrids are quite a bit larger than the others but with two feeders I don't think there is any garding going on. It seems mainly that the feeders are being ignored and the breed hens are quite happy foraging. Obviously I cannot watch them all the time and be certian that they are not taking pellets however this would appear to be the case.

I give them some mixed corn in the afternoon and some greenery every other day.

Any thoughts?

BTW I will be starting to put photos on the poultry pics thread today in case anyone was going to shout "Pictures!" 

My three year old hens have gone off of their pellets too.  They scream indignantly if they don't get them in the morning, but walk off once they're there.  That said, if we through them all over the lawn for them to forage for, they wolf them down like little treasures.  Go figure!   

Hybrid 'egg laying machines' can have a higher metabolic rate than some less productive pure breeds.
My young goldline hen seems to always have her head stuck in the food dish while the old Light Sussex hen is chasing flies !

With my 3 chickens no two days are the same.   Sometimes we get home in the evening to find their food pot very nearly empty with them shouting at us for food and other days it hardly seems as if they've touched it.   I've noticed they actually seem to eat more pellets the more they are allowed out to free range, which isn't every day as it depends on weather and us being home or not.    

apart from two girls that were given to me to foster my free rangers are thinner than other peoples birds that are kept in runs. They have lots of feeders full with food and have mixed corn every day but they like to go wandering and travel quite a lot of miles chasing butterflies, frogs etc.