Some of us, if we live long enough, develop cataracts, the disease in which the clear lens of the eye becomes cloudy or opaque. We can have this common problem corrected with surgery.
Birds also develop cataracts, almost always species that live long enough. Raptors and parrots qualify. Discovery almost always depends on the birds receiving medical treatment for another problem.
It's assumed that birds with cataracts do not attract the attention required for admission to a facility like the Raptor Center at the University of Minnesota.
Birds so afflicted die because of diminished hunting ability; they starve. They also could die of other causes before cataracts become an issue.
The Raptor Center finds cataracts uncommon among raptors admitted and treated for rehabilitation, according to Dr. Dana Franzen-Klein, medical director at the clinic.
Beyond age "the other main risk factor for cataract formation is some sort of damage to the [bird's] eye, most often a traumatic injury, that either damages the lens itself or causes a prolonged period of inflammation inside the eye which can stimulate cataract formation," Franzen-Klein said in a recent interview.
If a wild bird has a complete cataract or a small cataract that is progressively worsening in care, we are unable to correct that defect and therefore will not release them to the wild, she said.
"However, if an adult wild raptor came in with a small, incomplete cataract that stayed stable throughout their stay and was not related to their reason of admission, we would release them back into the wild because it was not affecting their ability to survive at that point in time," she said.
Birds with cataracts will squint, tear, or rub the eye.
Cataract formation is a possibility for any animal with a lens in their eye, Franzen-Klein said.
Lifelong birder Jim Williams can be reached at firstname.lastname@example.org.