 He spent over 30 years keeping birds and devoted two rooms of his house to swallows . One room housed a cage for the swallows . The other room was a training space with a balcony used for practice releases . He documented the age and health of each bird in a register , and marked each one by tying a colored silk to its leg . Red silk indicated a trained bird and blue silk indicated a partially trained bird . Trained swallows were allowed to roam outside their cages , while the others remained caged at all times . Untrained birds were sold as pets . 
