Will Disease Decrease Turkey Numbers?
Wild turkey populations in Mississippi have increased significantly during the last few years. The increase in turkey densities has stimulated questions from turkey enthusiasts about the potential for disease outbreaks. Historically, disease related population reductions have been suspected to occur along the Mississippi River when turkey numbers were high. More recently, about 1991, significant disease mortality also was suspected in southwest Mississippi and southeast Louisiana. This region supported dense turkey populations and observations of more than 100 turkeys in a field were common. Within a short period of time, few turkeys were being observed and some landowners were concerned enough to stop allowing spring gobbler hunting on their property. A few dead turkeys were found and submitted to the MDWFP, but not enough to confirm a major disease outbreak. Disease does seem to be the logical reason for the population decline. Habitat loss, predation, and poor reproduction would not cause the population to crash. If poisoning was the culprit, it is extremely doubtful that it would impact such a large area.
Since the suspected disease outbreak in southwest Mississippi, the MDWFP has attempted to document wild turkey mortality caused by disease. Monitoring mortality will provide information to assess the impacts of disease and may lead to better management of the wild turkey resource. Documenting disease in turkeys is difficult since most debilitated birds will quickly fall victim to predation. Sportsmen can play an important role by immediately reporting sick or dead turkeys to their local MDWFP district office or to Dave Godwin, Turkey Program Coordinator at (662) 324-3798.
Avian Pox: The most common disease affecting wild turkeys in the southeast is avian pox. Every year the MDWFP receives multiple birds with pox. Avian pox is an infectious, contagious, viral disease that causes numerous wart-like lesions primarily on unfeathered areas of a turkey, such as the feet, legs, and head. Lesions also may be found in the oral cavity. Many of these lesions eventually develop overlying, dark-colored scabs causing some to incorrectly assume the bird has blackhead disease. Depending on the severity and location of lesions, infected turkeys may become weak and emaciated, develop vision problems, or have trouble breathing. Many turkeys are infected with avian pox without obvious evidence of disease. Avian pox does not always result in mortality. Lesions often spontaneously regress 6 - 12 weeks after infection. Lesions occurring in the mouth, trachea, or around the eyes generally result in higher rates of morbidity and death than lesions on the skin. In local areas high morbidity and mortality can occur. Also, turkeys that become debilitated by avian pox or other diseases are more vulnerable to predation.
Avian pox viruses are mechanically transmitted by blood-feeding arthropods, primarily mosquitoes. Mosquitoes can transmit the virus throughout the year, but the majority of infections occur during the warmer months when mosquito activity peaks. Annual occurrence of pox virus infections seem to depend on precipitation patterns since mosquito populations are related to rainfall. Infection also is possible by ingestion of virus-containing scabs shed from lesions.
Histomoniasis (Blackhead Disease): Histomoniasis is another important disease of wild turkeys in the Southeast and has been documented in Mississippi. It is caused by the protozoan (single-celled microscopic organisms) parasite Histomonas meleagridis. Turkeys with histomoniasis have a lack of energy and often stand with drooped wings and ruffled feathers. Infected turkeys may pass sulfur-yellow feces. The parasite causes tissue damage and hemorrhaging in the liver and ceca (a portion of the intestine where crude fiber is digested).
The parasite is transmitted within the eggs and larvae of cecal worms. Pheasants and chickens are carriers of the parasite but are tolerant of infection. Cecal worm eggs are passed in the feces of infected birds. When these eggs hatch, turkeys will eat the larvae and become infected with the parasite. Earthworms also play a role in transmission because they store cecal worm larvae in their bodies when they feed on soil containing droppings from infected birds. Therefore, turkeys also can become infected by eating earthworms. Mortality rates for turkeys infected with the parasite usually exceed 75%.
Since chickens are carries of the parasite and cecal worm eggs are passed in the feces of infected birds, the use of chicken litter as fertilizer on areas frequented by wild turkeys causes some concern. A 1992 survey of commercial broiler, breeder, and layer chickens in the southeastern United States was conducted. It evaluated the disease risk of using litter as fertilizer. The survey determined that commercial breeders and layers had very high infection rates, but that both H. meleagridis and its cecal worm vector were rare in commercial broilers. The essential absence of the parasite in broilers was attributed to the young age at which they are marketed. Based on these results, commercial broiler litter should pose no risk of as a source of histomoniasis, but litter from commercial breeders and layers could pose significant risk. The study also reaffirmed that noncommercial (backyard) chickens could be an important source of histomoniasis.
Disease Potential With Feeding:
Feeding wild turkeys unnaturally concentrates multiple birds at a specific site on an almost daily basis. Although feeding does not guarantee disease to occur, it certainly increases the potential for maintaining, transmitting, and introducing diseases within a turkey population. Concentrating turkeys at a particular site makes it easier for mosquitoes to feed on a turkey with avian pox and then pass the virus to another bird. Feed sites also are a common place for the scabs shed from pox lesions to be ingested by other turkeys. Droppings are concentrated at feed sites and create opportunities for ingestion of infected cecal worm eggs or larvae. Aflatoxins are found in spoiled feed, particularly corn and cereal grains. When turkeys ingest toxins present in grain they develop aflatoxicosis which affects their immune system, liver, and causes cancer.
Feeding turkeys potentially increases predation rates. Turkeys are a prey species and are always walking a fine line between survival and mortality. Feeding causes turkeys to habitually visit a specific site and allows them to be patterned by predators, thus tipping the scales in favor of predation. Even when feeders are placed in the open, predators have an advantage. Avian predators can easily find young turkeys out in the open, and mammalian predators can ambush turkeys where they enter a field. Because of increased potential for predation and disease, the MDWFP does not recommend feeding wild turkeys.
Report Sick Turkeys:
Diseases are always present in the environment, but significant outbreaks are unpredictable. With the current high turkey densities in most areas of the state, certainly the potential for a significant disease outbreak has increased. With your help, the MDWFP can monitor turkey morbidity and mortality and hopefully gain information that will help manage populations to prevent or decrease future outbreaks.