Our son is enjoying fishing this summer, so we have been thinking a lot about different types of fish and their habits. While we have been fishing, we have seen lots of fishing birds as well. Obviously birds that eat only fish have to be skilled “fisherbirds” or they would not survive. A list of Maine’s obligate avian piscivores, as scientists like to call them, includes ospreys, most terns, northern gannets, belted kingfishers, Atlantic puffins, black guillemots and razorbills.

Many more species are largely dependent on fish for food but will eat other things as well. Bald eagles, for example, eats lots of fish when they can but they have no qualms about snatching an unwary duck or gull for dinner, or eating carrion or snacks from the dump. Great blue herons and other herons and egrets may prefer a fish meal but will eat crabs and other aquatic creatures; they’ll also take snakes, mice, and even birds if they can! We once watched a great blue heron that had been sitting stoically on a log imbedded in a mudflat that noticed an unsuspecting least sandpiper feeding below it. The heron, slowly and stealthily, moved into a striking position and suddenly shot its long neck out and struck the sandpiper at the base of the skull, killing it instantly. Another time, while in Florida, we watched and videotaped a great blue heron that spent more than 30 minutes struggling to eat a watersnake; the snake coiled itself around the heron’s head as it tried to escape. The heron did finally prevail but the snake kept fighting even as it was being swallowed!

People think of common loons as being only fish eaters, and certainly that is probably the bulk of their diet most of the time. But they will readily eat crabs while in salt water, and crayfish and small invertebrates in fresh water. Mergansers, those ducks that specialize in catching fish, will also take small crayfish, crabs, and invertebrates.

But the long-term survival of populations of all of these birds, even if they occasionally eat something else, is basically dependent on healthy fish populations. And healthy fish populations require clean waters with food sources for the fish themselves, including places for them to spawn and grow through their juvenile stages. Many of our marine fish can only spawn in rivers and streams, and after hundreds of years of dam-building by people, these fish have had fewer and fewer options for places to reproduce. From a fish-eating bird’s perspective, the mass movements of fish from the open ocean into the narrow confines of rivers and streams affords the best chances of easily catching lots of food for themselves and their young. Other fish require estuaries and salt marshes for breeding or as nurseries for the juvenile fish.

We have been fortunate here in Maine that over the last few decades, that the public and many of our leaders have recognized the need for clean waters and of the interconnectedness of our oceans and rivers. As waters have rebounded from the polluted excesses of decades ago and, more recently as obsolete dams have been removed from major river systems, many fish populations have also rebounded. These healthy fish, as they move back into the ocean, will provide food for other fish, making our Gulf of Maine healthier while helping bring back some of the commercial fish populations as they continue to provide for bald eagles, ospreys, herons, and other fish-loving birds.

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology. Dr. Wells is one of the nation's leading bird experts and conservation biologists. His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine, a statewide nonprofit membership organization. Both are widely published natural history writers and are the authors of the book, “Maine’s Favorite Birds.”