Take a LOT. It helps to have a quick camera (I
my Nikon D60 SLR) or at least one with continuos mode or sports mode. The chickens move so fast about 9 of 10 will be blurred.
Treats are great, but it helps to have them out of the picture so it looks more natural.
Taking them inside to a well-lit studio and putting them against a backdrop is good too.
Here's my photos, there's tons of chicken ones in there:
http://picasaweb.google.com/olivesphotography/PhotographyByOliviaCollins#
A shallow depth of field is nice but not TOO shallow or your pics will look kind of funky. Here's what I consider perfect DOF:
Sometimes you'll want PART of the bird to be blurred. You can do that on photo editing software or just get lucky. The latter is what made this photo of Olympia so appealing.
Light is also key. Morning is when my best photos were taken, as everything in the background seems sort of gray:
Snow makes for great pics too, even your chickens hate it like mine. But they stand very still in it and when they flap they make beautiful patterns.
Of course, they might get vengeful and come and kill you. Olympia below, charging:
Two or more birds doing the same thing makes for pleasing pictures too. (Please excuse Rita's scruffy back and the ugly background.)
Hope this helps. I do think it is nice to have a professional camera. The
D40 is only about $400 on Amazon . (My D6o was about $600.)