The absence of brown adipose tissue in birds.
D002001:Adipose Tissue, Brown / Q000032:analysis*; D000818:Animals; D001011:Aorta / Q000033:anatomy & histology; D001717:Birds; D001808:Blood Vessels / Q000033:anatomy & histology; D001833:Body Temperature Regulation; D004947:Esophagus / Q000033:anatomy & histology; D005260:Female; D008297:Male; D011667:Pulmonary Veins / Q000033:anatomy & histology; D013045:Species Specificity; D014132:Trachea / Q000033:anatomy & histology; D014684:Venae Cavae / Q000033:anatomy & histology