Although this substance usually resembles pale-yellow cottage cheese, canthaxanthin colors this substance red in flamingos. For 10 points each:
[10h] Name this two-word suspension rich in fat and protein, which parents feed to newly hatched chicks. It’s regurgitated from a namesake sublingual pouch near the esophagus where some birds temporarily store food.
ANSWER: crop milk [prompt on bird milk; prompt on, but DO NOT REVEAL, pigeon milk]
[10e] Crop milk independently evolved in flamingos, male emperor penguins, and these birds, which may nest in columbaria. Historically, these birds have been bred for their magnetoreceptive, beak-based homing ability.
ANSWER: pigeons [accept doves; accept Columbidae; accept homing pigeons]
[10m] Pigeons secrete crop milk when the crop lining sheds epithelial cells named for these proteins during cornification. In mammals, the outer sheaths of follicular bulges are rich in isoforms 15 and 19 of these proteins.
ANSWER: keratins [accept cytokeratins; accept keratinocytes; accept keratinization] (In contrast to mammalian keratinocytes, avian keratinocytes are lipid-rich.)
<S, Biology>