@Eggcessive always gives wonderful solid advice, so you've already received some wonderful advice. I am in my first year of keeping chickens. I picked up 3 silkies in August and 2 are cockerels and 1 Pullet. Bella, the Pullet tends to be very shy, and she's so petite and tiny. I noticed her being even more to herself so I started taking her inside and making her a bowl of mash (wet feed) a couple of times a day. This made a huge difference. She's still tiny but she has the energy to be a chicken and interact, plus she's growing, even though it's slow. I believe that even though feed is always available, she wasn't eating enough, whatever the reason was. I still do this usually once a day and her crop is rarely empty, except in the morning.