I raise a few chickens and have for almost 4 years.  Chickens are natural grain eaters, whereas ruminants like cows and sheep should never eat grain.  That said, grain is a minor part of their diet and they can live without it.  Chickens eat bugs, meat, vegetables, fruits, nuts, seeds, grains and eggs.  They love it all.  I have a clear path round my compost bin free of grass, thanks to the chooks eating insect larvae.  Everyone should raise their own chickens if they eat the flesh or eggs.  Buying poultry from anyone but local friends is dodgy because the price fetched is so cheap, and thus, feeding and lifestyle practices will be cut.  And btw, also be careful of any large poultry operation.  They must have a good range and lots of bugs.  My eggs are super pristine with deep orange, perky, spherical yolks.  My 5 hens graze on 1 acre fenced without any restriction - they truly range free!  I could have 5 times as many do just as well, but any more than that, and the quality suffers.  Visit your poultry farm and ask questions.  But know that you will always do better raising your own!  Getting back to nature is a process.

I ate pheasant raw for the first time tonight, so my head was already in this topic.  By the way it was great. 

Even where 'grain' is not an option, pheasants in the US survive on seeds, because insects are not available year-round.  Does this make the meat bad for you?  Does it matter since they have so little fat?  Is the only difference between them and chickens (from a health standpoint) the fact that they are generally older when eaten?

I'm assuming wild birds here.