What caused the mysterious deaths of 27 bald eagles? Officials are now saying it appears to be due to the West Nile Virus. Lab tests revealed evidence of the mosquito-borne virus. The eagles exhibited symptoms like head tremors, seizures, wing paralysis, and weakness in the legs and feet. All the infected birds were from northern and central Utah. It wasn't a mosquito bite, however, that spread the disease. The eagles contracted the virus by eating Eared Grebes, a duck-like bird, that were infected and had recently died. The virus can be spread to the birds of prey if they eat infected animals. The Utah Department of Health said humans in the area should not worry, since it’s winter and mosquitoes, which normally spread the virus, are not around.