From Baja to Oregon, disturbing reports abound of brown pelicans lying sick in backyards, staggering across highways, or washing ashore dead. Hundreds of birds have been brought into wildlife care centers for treatment — and many others for autopsies.

Even to those of us who aren’t bird enthusiasts, these images are haunting. That’s because for Californians, our magnificent coastline is part of our natural identity, and the majestic brown pelican is a treasured part of that.

Researchers are scrambling to figure out what’s causing this widespread problem with the pelicans, but, in the end, the lesson we’re most likely to learn is just how precarious are the marine ecosystems that support these glorious birds. It’s a lesson we seem to have to keep learning over and over again, much to the detriment of the pelicans and other birds and wildlife.

The irony in all this is that these are supposed to be great times for the brown pelican. After DDT drove the bird to near extinction in the 1970s, the bird was designated as endangered. Under protected status, the brown pelican has rebounded beautifully, numbering more than 140,000 along the Pacific coast.

This success has prompted the U.S. Fish and Wildlife Service to move forward with delisting the bird, a moved that Audubon California and several other conservation organizations support as a victory for the Endangered Species Act.

Another vexing aspect of this mysterious incident is that we may never be able to satisfactorily identify what is making the pelicans sick.

Whenever birds that rely on the ocean for food, such as pelicans, suddenly start dying like this, one of the first causes that scientists suspect is domoic acid, which can cause deadly neurological effects in birds. Birds and sea mammals ingest the acid by eating fish and shellfish that consume small organisms, like algae with domoic acid. The acid builds up in the fish and then the birds.

While some of the pelicans tested thus far have come up positive for domoic acid, no one is saying that this is the main cause of the problems. Many of the affected birds show none of the normal signs of domoic acid poisoning, and if there was a widespread increase in domoic acid in the food chain along our coastline, we should see similar impacts on other birds and mammals, which we haven’t.

Which brings us back to a discussion of the precarious nature of the coastal ecosystem itself, and the continued threats that species like the brown pelican face every day. Even though its numbers have rebounded, its breeding grounds face near constant threat from human activity, particularly in the form of development and pollution. Moreover, the brown pelican needs fish to survive, which links the species to the continued health of marine fisheries.

When something is wrong in the environment, it is often the birds that are the first to tell us.

But since birds can’t speak English, they are left with only one simple way of sending us a message — dying.

Like many other sensitive species, the brown pelican is tightly boxed in, and all it needs is a nudge from something like domoic acid, a virus outbreak, a food shortage, an oil spill, or a poorly planned shoreline development to squeeze it out of existence.

It’s entirely possible that we’ll never be able to find a specific human cause for these illnesses. And if that’s the case, we’ll be letting ourselves off the hook too easily.

We’re the ones who put the pelican in that box, and we’re the ones who — despite our best intentions — never quite seem to truly set it free.

— Gary Langham, Ph.D., is director of bird conservation for Audubon California. He is also a lecturer at U.C. Berkeley, most recently teaching ornithology.