Problem:
Birds from the family Columbidae (e.g., doves and pigeons) produce a fatty, milk-like substance in their crop. The secretion is often referred to as "crop milk." They feed crop milk to their young through regurgitation.
Required:
Question 1: Does anyone know of another bird or reptile group (or even mammals) that has evolved such a mechanism; not regurgitation but secretion of a milk-like substance for feeding young?
Also, both male and female doves produce crop milk;
Question 2: Are there cases where males of a mammal species produce milk? Describe it.