Saturday, April 03, 2010
The Scarlet Ibis Is What it Eats
The Scarlet Ibis is a rather small wading bird - about two feet in length, weighing less than 1.5 pounds. Its long decurved beak is pink; its legs and feet are reddish pink. Its plumage is brilliant, bright red. Only the tips of the wings are black, a feature which gives added strength to the long primary feathers.
As impressive as this evening congregation is, I was most taken during the couple of preceding hours when our guide directed the flat-bottomed boat slowly through the marsh’s channels in search of the ibis, other wading birds, and other creatures of the marsh. The ibis was not difficult to spot. Imagine a brilliant, bright red basketball balanced on a tree branch. Even deep in the tangled mangroves, it is not difficult to spot.
Next imagine those brilliant, bright red basketballs strung together as illuminated lights decorating a carnival tree. As we moved slowly along a quiet channel, we saw more and more of those red lights strung through the branches, resting and preening before their final flight to the roosting area. If the boat drifted too closely, they flew. It was easy to follow the flight of the brilliant, bright red body and wings as the birds wove their way through the mangrove swamp.
The Scarlet Ibis does not need to hide itself from its food. Its long bill probes for food in mud and shallow water. It is guided by touch, unseen by its prey except for the brief time when the prey is pulled from the darkness by the tip of the beak and flipped into the gullet.
Like most birds, the ibis diet is varied. The Scarlet Ibis feeds on frogs, fish, reptiles, and crustaceans. But it has a favored food, and that favored food is what gives the Scarlet Ibis its brilliant scarlet-red. The young Scarlet Ibis is a gray and white bird, looking very much like a young White Ibis. The ingestion of red crabs gradually produces the scarlet plumage. There are some scientists who consider the Scarlet Ibis, Eudocimus ruber, and the White Ibis, Eudocimus albus, to be the same species with diet making the difference. The crabs which are the favored food of the Scarlet Ibis are rich in carotenoids; the more carotenoid-rich crabs the ibis eats, the redder it becomes.
Now I am venturing into a new area for me, one which I still have much to learn about. But basically, birds cannot produce red, orange, or yellow feathers on their own. They are what they eat, and they must have the right diet to produce the plumage that will be most attractive to a mate. For birds like the Scarlet Ibis of Central and South America, or for more familiar birds closer to home, like the Northern Cardinal, or Purple Finch, in order to have the bright plumage which will attract a mate, they need a diet rich in carotenoids.
Carotenoids are a class of organic pigments that are produced by plants. These red, yellow, and orange pigments help plants to absorb light energy for photosynthesis and prevent degradation of chlorophyll. Animals that eat plants rich in carotenoids, or which eat other animals rich in carotenoids, enjoy numerous benefits from these compounds just as the plants do.
The coloring agent which makes carrots orange is a carotenoid. Some of us may have been told to eat our carrots so that we would have good eyesight. Aviation crews during World War II were given carrot juice to improve their night vision.
The benefit to eyesight of the carotenoid in carrots is not just a ploy of vegetable growers. Researchers at Arizona State University have learned that in birds, as in humans, carotenoids are deposited in the retina, improving their eyesight - in particular, their ability to see color; “the more carotenoids you eat, the better you can see color, the better mates you choose, and the redder the foods you choose, thus giving you even more carotenoids for health, attractiveness and vision.” There also seems to be evidence that carotenoids enrich the testes and seminal fluid, preventing sperm cells from oxidative damage and resulting in greater fertilization ability of males.
What this means in our northern climes is that the cardinal with the brightest red is most likely to attract the best females; in addition he probably mates with females which are socially paired with other males. He is more likely to sire more young, and more healthy young that survive.
With regards to the brilliant, bright red Scarlet Ibis of Central and South America, it seems to me that color no longer creates an “attractive” edge. It is simply an evolved and long-established given, although their diet high in carotenoids may keep their eyesight keen to danger and their young strong and more likely to survive.
And so you see, good birding is good for lots of things.