What are these things I can see crawling in my chickens feathers

If you can spot some abnormal looking critters in the base of the feathers of your chicken they could be suffering from an infestation of Poultry Lice or Northern Fowl Mite. Because these parasites live on the chickens, if there is an infestation you will be able to see the Lice or Mites themselves or their eggs if you regularly examine your chickens. It is always useful to check the fluff around the vent area as Lice and Mites love to hang here where it’s nice and toasty!  Lice are small brown critters; Northern Fowl Mites are smaller and black. Both Lice and Northern Fowl Mites feed off your chickens’ blood, which makes them irritable and grumpy; they may even peck each other or pull out their own feathers. Infested chickens may also look pale and may stop laying for no reason.