It’s a day for the wearing of the green. It’s also a day to recognize just how few of our birds appear to be Irish.

Green is abundant in nature, primarily because chlorophyll is abundant in nature. It’s the green pigment that converts sunlight into plant food. However, if birds want to wear green, they need to be a little more creative. You’ll recall that green is the combination of two primary colors, blue and yellow. Yellow and red pigments are found in foods that birds eat. These pigments are carotenoids, which make berries red and carrots orange.

Melanin is the pigment that produces dark colors. Animals can make this pigment. Even humans make it when tanning.

Blue pigments, however, are uncommon in nature. Even where there are blue pigments in plants – blueberries, for instance – birds generally are not able to metabolize them for use in coloring their feathers.

As loyal readers know, the color blue in feathers is not the result of pigments. Bluebirds, blue jays, indigo buntings and a host of other bluish birds attain their hue through structures in the feathers that bend light. Sunlight passes through the feather, and reflects back from the dark melanins below. The light refracts as it returns, producing the color blue.

To quote that famous Irish frog, Kermit, “It’s not easy being green.”

Producing the color green is trickier than blue. The same structures that refract blue light are present in green feathers, but the structures are tinted by yellow carotenoid pigments. The combination of blue refraction and yellow pigment creates the green color. It’s why frogs are green. Frogs have even taken it a step further. They can adjust the shape of the cellular structures in their skin to alter the shade of color being produced, so they can look greener in bright light and duller in dull light. They’re not consciously color-shifting. Evolution just favors those frogs that do it best automatically.

So going green takes extra work, but the advantages are obvious. In a marsh or a tree full of green, it’s a lot easier to hide from predators when you’re the same color. You’ve no doubt wondered why all parrots in the jungle are green. Hummingbirds are green. The question becomes, why aren’t more birds green?

At the same time birds want to blend in, they also want to stand out. Bright colors are a tool in attracting a mate and warding off rivals. Some bird species try to have it both ways. Male cardinals are bright red, but the female who has to hide on the nest is a more subdued color. Scarlet tanager males are even brighter red than cardinals, but the females are exactly the color of leaves.

A few green birds take it to extremes. The green jay in Texas clearly has no intention of blending in. One look at a green jay and you know that his feathers are refracting light in the showiest manner he can manage. Of all the birds in North America, he is the clear choice to lead the St. Patrick’s Day parade.

Humans also possess the ability to turn green. Come along with me on Saturday, April 1, and I’ll point out a few passengers doing it. That’s the day the Isle au Haut Ferry is motoring out of Stonington Harbor to search for colorful, but unusual, harlequin ducks. We’ll depart at 11 a.m.

I think this is the fifth year in a row that the Island Heritage Trust is offering this rare winter excursion. There are too few chances to get offshore in the offseason. Most tour boats are dry-docked or shrink-wrapped. But winter is a great time to venture out for sea ducks, and this trip has been really blessed with good weather over its first four years. The islands, coves, and ledges that extend from Stonington to Isle au Haut are prime wintering areas for birds that don’t mind getting salty, and the harlequin duck is the star of the show. Find more information at www.islandheritagetrust.org.

Harlequin ducks are very bright in color, but not very bright in intellect. They breed on raging whitewater rivers in Canada, and then winter in the most dangerous surf they can find along the rocky coast of the North Atlantic. They go where no other bird dares, taking advantage of food that no other duck can reach. They often get injured, but they have an amazing ability to heal quickly.

I get green just thinking about it.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.