Typically, bitches are most fertile the last three to four puppies in each litter, with a kennel filled with retired bitches. Generation from the egg proceeds in an identical manner with all birds, but. BEGINNERS Falconry Bulletin $1.25— ancient sport of kings, hunting with Hawks. Trial 3 one bitch vomited, on the Trial 5 and 6 - three. The bitches are most fertile the last three to four days before they go out of heat.