From barnyard to backyard, lowly hens have flown the country coop and joined the city chicken movement. A new generation of small-acreage farmers raising heritage breeds has inspired urbanites to install some poultry out back. This is not a how-to book on raising chickens but rather a wry, fascinating, sometimes startling appreciation of them, conveyed in compelling accounts by Susan Troller and striking prints and paintings by S.V. Medaris.