Life forms that live all around us but that we never (or almost never) detect may be kind of freaky to think about. Viruses, bacteria, prions—those microscopic living (or maybe not really living, in the case of prions) things can seem strange, maybe even a little and scary. Some can make us sick, which is the only way we would normally detect them, if not for sophisticated scientific tests.

We’ve been reading lately about another group of living things that are also mysterious and often hidden from human eyes: fungi. Mushrooms are, of course, one of the more visible manifestations of fungi. They are actually the fruiting bodies of often very large underground network of cells. This  network of cells  does the work of the fungi, using enzymes to dissolve organic matter and convert it to sugars for fuel. Some of these networks (technically each one is called a mycelium) can be massive. One mycelium of a honey mushroom in Oregon is estimated to occur underground over an area of more than 2,000 acres, weigh more than 25,000 pounds, and to be at least 2,400 years old. Those last facts are courtesy of a fun book called “Fungipedia” by Lawrence Millman that we heartily recommend.

Lichens are fungi that can’t survive without algae and/or cyanobacteria living within them. Unlike many fungi, we can often see lichens. But often, except for really obvious ones like the boldly red-capped British soldier lichens or the long strands of beard lichens hanging off trees, we don’t even notice them. We’ve been amazed as we’ve begun to look more closely at how many different lichens you may find on a single tree or rock.

Birds and other segments of the animal world are completely dependent on fungi in so many ways.

The underground mycelium of fungi is critical for the survival of most trees and other plants as they share nutrients back and forth between them. Beneath the soil of every forest (really, under every tree) is a massive network of mycelia of various kinds of fungi. When we walk around a forest and see mushrooms, those are just the fruiting bodies showing the tip of the iceberg of something much bigger under our feet.

Some animals eat mushrooms and other fungi. Canada jays are known to eat and cache away mushrooms, slime molds, lichens, and other fungi. Spruce grouse and ruffed grouse at least occasionally eat mushrooms and lichen. Some bird species in other parts of the world focus on various fungi as food sources even more. Northern flying squirrels are well known for eating lots of mushrooms and other fungi. Some mice and voles do the same. Caribou are one of the most famous lichen specialist mammals. Whenever we see thick carpets of lichens in spruce-fir forests here in Maine, we wonder if that would have been a favored place for woodland caribou before they disappeared from the state in the early 1900s.

Some fungi can also harm or kill trees. Others are decomposers of wood that can make it possible for a woodpecker or a chickadee to excavate a nest hole in a tree. Bigger cavities are used by barred owls and wood ducks.

Some birds use lichens in other ways. Northern parula warblers build their nests in the hanging strands of beard (Usnea) lichens. Hummingbirds place lichens on the outside of their nests, presumably to camouflage them.

The ways in which birds and other animals use and are interconnected with fungi remain little known and understudied. One can imagine, for example, how hard it is to even detect if a bird has eaten a mushroom or lichen. So much more remains to be learned. We are trying to learn a little ourselves as we look more closely at the forms of fungi that are all around us.

As our friend, the late poet Archie Ammons from Cornell University, wrote: “Attend to mushrooms and all other things will answer up.”

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology and Vice President of Boreal Conservation for National Audubon. Dr. Wells is one of the nation's leading bird experts and conservation biologists. He is a coauthor of the seminal “Birds of Maine” book and author of the “Birder’s Conservation Handbook.” 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 nonprofit membership organization working statewide to protect the nature of Maine. Both are widely published natural history writers and are the authors of the popular books, “Maine’s Favorite Birds” (Tilbury House) and “Birds of Aruba, Bonaire, and Curaçao: A Site and Field Guide,” (Cornell University Press).