Male turkeys, often called toms, possess testicles, reproductive organs that develop internally rather than in an external scrotum as seen in many mammals. Located within the bird’s body cavity near the kidneys, this internal placement often leads to public confusion about their presence.
Internal Anatomy and Location
Male turkeys have a pair of testicles situated within their abdominal cavity, behind the lungs and in front of the kidneys. These organs are typically oval or bean-shaped. Unlike the prominent external testes of many mammals, a turkey’s testicles are not externally visible.
Their size is not constant; it changes significantly with the bird’s age and the season. For example, during early development, testicle weight can increase from a few milligrams to 60-100 milligrams, with substantial growth occurring after 15 weeks of age and peaking around 28 to 30 weeks.
The color of these internal organs can range from pale white to beige white, sometimes even exhibiting black areas. In many bird species, including turkeys, the left testis is often observed to be larger than the right.
Why Testicles Are Internal
The internal location of testicles in turkeys and other birds is a biological adaptation. This positioning helps maintain an optimal internal environment for sperm production. While mammals typically require external testicles for sperm development at a cooler temperature than their core body heat, birds perform spermatogenesis efficiently at their higher core body temperature. This ability to produce sperm at elevated temperatures is a unique characteristic among homeothermic animals.
The internal placement also contributes to the bird’s streamlined body shape, advantageous for flight. Additionally, housing the testicles within the body cavity offers protection from physical damage, which could be a risk for externally located organs in active birds.
Their Role in Reproduction
The testicles in male turkeys serve two primary functions: sperm production (spermatogenesis) and hormone synthesis. Spermatogenesis occurs within numerous tiny, coiled tubes inside the testicles called seminiferous tubules. Spermatozoa, the male reproductive cells, are first observed within these tubules around 15 weeks of age, with mature semen becoming present in the deferens ducts approximately at 26 weeks.
The testicles also produce hormones, most notably testosterone. This hormone regulates the turkey’s breeding cycle and influences characteristic male behaviors.
As the breeding season approaches, testosterone levels in male turkeys increase, leading to a significant enlargement of the testicles. This hormonal surge drives behaviors such as gobbling and displaying, important for attracting mates. The duration of daylight, known as photoperiod, is a major environmental factor influencing both testicular growth and the rate of sperm production in turkeys.