Hormones trigger the action of nest construction. Other variables like day span, migration, food availability, and territoriality additionally lead, though such actions are subject to hormonal influence. Once hormones kick in, a man’s testes and a female’s ovaries increase in size tremendously. On postmortem assessment, it’s easy to tell the reproductive status of a bird by simply assessing the size of these organs. Once the mating season is around, testes and ovaries shrink back to miniature small constructions found ventral with their kidneys.