What is the most common cause of frounce in raptors?

Frounce, also known as trichomoniasis, is a disease caused by the protozoan parasite Trichomonas gallinae, which primarily affects birds, including raptors. Among the options provided, the most common cause of frounce in raptors is indeed through the consumption of infected pigeons and doves. These birds often serve as hosts for the parasite, allowing it to proliferate within their systems. When raptors prey on these infected birds, they can easily contract the parasite, leading to the development of frounce.

This connection highlights a critical aspect of raptor ecology, as these birds often rely on pigeons and doves as part of their diet. Therefore, understanding the dietary habits of raptors is essential for managing their health, especially regarding diseases like frounce that can be transmitted through prey. The other options, while potentially relevant to a raptor's diet, do not serve as the primary vectors for this specific disease. Contaminated soil, fruits, vegetables, and other birds of prey may contribute to various health issues but are not the main transmission route for the organism responsible for frounce.