At 3 weeks chicks are adolescents and are in an awkward stage between feathers and fluff. I just posted a bunch of pics of my 3-week-old chicks here if you want to compare them to yours:
http://cotehelefarm.com/2009/03/28/chicks-1-week-vs-3-weeks/
Unless they look significantly more feathered than these girls, I'd give them a heat lamp at night, depending on how cold it gets where you are. Even warm climates can have cold nights this time of year. Buff orps are pretty hardy chicks, but when they are babies they still like it warm.
http://cotehelefarm.com/2009/03/28/chicks-1-week-vs-3-weeks/
Unless they look significantly more feathered than these girls, I'd give them a heat lamp at night, depending on how cold it gets where you are. Even warm climates can have cold nights this time of year. Buff orps are pretty hardy chicks, but when they are babies they still like it warm.
