One of the big bird stories of this nesting season is a mysterious epidemic that has led to widespread deaths of songbirds, which have been reported from Maryland, Virginia, West Virginia, Delaware, Pennsylvania, Kentucky, Ohio and Indiana.

Species that are particularly susceptible are blue jays, American robins, European starlings and common grackles. Juvenile birds are disproportionately affected. Infected birds show swollen eyes, often with crusty deposits around the eyes. Some tremble, twitch or stagger around, suggesting neurological damage.

So far, the epidemic has not reached Maine. But if you do see birds with the symptoms above, let people know through social media or by calling wildlife biologists or bird rehabilitators.

The epidemic began in May and seems to have peaked in June. We can hope it will pass soon. The peculiar feature of this epidemic is that we do not know the causal agent of this disease. The usual suspects have been eliminated: salmonella, chlamydia, West Nile virus and avian influenza virus. We don’t even know the general cause of the disease. It could be a virus, a bacterium, a fungus or some toxin in pesticides, herbicides or other chemicals.

From our shared COVID experience, we all appreciate the value of social distancing. If you should ever see ever see a sick bird from whatever cause at your feeder, you need to enforce social distancing among the birds by taking down your feeder. An active feeding station can be the base of a super-spreader event.

Several people have asked if humans should be concerned about contracting a disease from infected birds. There are a number of avian zoonoses, the fancy term for diseases that can be spread from one species to another. In some cases, a disease organism may not produce serious symptoms in a bird but may make infected humans quite sick.

Let’s take a look at some avian zoonotic diseases. Avian tuberculosis is caused by a bacterium called mycobacterium avium. These bacteria occur in the droppings of infected birds and soil that they contaminate. Humans acquire the bacteria by inhaling them from dried bird droppings or contaminated soil. In humans, the bacteria can cause lung disease, similar to tuberculosis.

Salmonella is a bacterium that affects the digestive system of birds. The greatest risk to humans is eating undercooked meat or eggs from infected birds. Although salmonella infects many species of birds, the ones we should be concerned about are poultry. Salmonella in humans causes gastrointestinal distress, abdominal pain and fever. Make sure the chicken you bake is well cooked and the chance of acquiring salmonella is very low.

E. coli bacteria occur in humans and many other animal species. Some strains in birds can be harmful to people. Digestive system problems and even kidney failure can be caused by the jump of some avian E. coli to humans. Like salmonella, the route of infection is eating undercooked meat from an infected bird.

Ornithosis, or parrot fever, is caused by the bacterium chlamydophila psittaci. It can occur in parrots, parakeets, turkeys, pigeons and other birds. In humans, it produces flu-like symptoms and respiratory problems. Humans acquire the disease by inhalation of dried droppings or feather dust of infected birds.

Birds and humans may be infected by West Nile virus and equine encephalitis virus. However, a human cannot contract one of these viral diseases directly from an infected bird. Rather, the virus is spread by the bite of an infected mosquito.

Lyme disease provides another example of an indirect link between birds and humans. Lyme disease is caused by the bacterium borrelia burgdorferi, which infects deer ticks. Borrelia is passed to a new host when the tick bites a host. Deer ticks are known to attach to birds as well as humans. With their ability to travel long distances, birds may be effectively spreading Lyme disease by ferrying deer ticks from place to place.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu