Featured Bird: Great-tailed Grackle

Is that a bird, or an alarm-clock? (Photo © Ivan Gabaldon).

Great Tailed Grackle (Quiscalus mexicanus). Spanish: Zanate Mayor. Maya: X’kau.

Description: Large Grackle, keel-shaped tail is very long and graduated, golden yellow eyes. Male is iridescent glossy blue-black overall, purple sheen on head, chest and back, more greenish blue on wings and tail. Bill and legs blackish. On female, upperparts  are brown, underparts cinnamon-buff on breast to grayish brown on belly; less iridescent than male. Juvenile resembles female but eyes are brown, plumage is less glossy, some streaking on underparts. Immature males duller, with shorter tails and darker eyes.

Size: Male 34.5 – 47 cm (13.5 – 18.5 in) – Female 26.5 – 31.5 cm (10.5 – 12.5 in).

Voice: loud shrieks, clacks, whistles and chatters, including a bright, piercing, ascending whistle.

Status, habitat and range: widespread and common in Mexico, specially in open flatlands with scattered groves of trees and in marshes and wetlands. Also common in towns and villages, only absent or rare in deserts, heavy forest and high mountains. Gregarious, breeds in colonies, often sleeping on trees in parks and plazas, moves in large flocks.  Very adaptable to urban areas, but may display aggressive behavior toward humans if nests are threatened. Feeds mostly on the ground on almost anything, including garbage, pet food and also eggs and chicks of other bird species. Found from South of the U.S. to NW Venezuela and Peru.

A large flock of Great-tailed Gracles in Merida city, Yucatan. (Photo © Ivan Gabaldon).

No other bird is as common in Mexico as the Great Tailed Grackle. They are indeed everywhere, always active and noisy in city parks, gardens, on top of homes and buildings. But take some time to really look at them through binoculars or a telephoto lens, and their unique beauty will show through. For starters, “common” is not the best word to describe the magnificent, iridescent plumage of these “black birds”, which are really not plain black. Even the brown females, less iridescent than the flashier males, display different hues, their feathers changing colors as they bask in the sunlight.

A male Great-tailed Gracle in mid-flight, showing iridescent coloration in its underparts. (Photo © Ivan Gabaldon).

But what exactly is iridescent coloration? I couldn’t explain it if I tried, not having the scientific background to make sense out of this beautiful visual miracle. So rather than confusing readers with a blotched attempt at paraphrasing my sources, I’ll just quote from those who really know, in this case from the fascinating book Bird Coloration by Geoffrey E. Hill (National Geographic Books):

“The most familiar iridescent coloration is the shifting rainbow of colors frequently seen in oily puddles in parking lots. (…) Birds with highly reflective, iridescent feathers are often described as looking oily. (…) As daylight reaches the surface of the oil, some of the light is reflected from the surface and some light passes into the oil. Light that passes into the oil becomes compressed and slows down because oil has a higher density (refractive index) than air. Some light then reflects off the bottom of the oil layer and moves back to the surface of the oil, [where it] meets light reflected from the surface [which will have] moved a different distance and at a different speed, (…) most of the wavelengths of light that meet will be out of phase, canceling each other out. A few wavelengths will be in phase when they meet, and these will be amplified. Through this process (…) some wavelengths of daylight are subtracted while others are amplified. (…) The result is brilliant color display.”

A common bird? With such regal attitude? (Photo © Ivan Gabaldon).

Just as it works in oily puddles, it works in feathers:

“Feathers produce iridescent coloration by means of very thin films made of alternating layers of material. The simplest of these iridescent colors result from the cortex (the transparent outer layer) of a feather barbule acting like a layer of oil on water. Light either reflects from the surface of the cortex or penetrates the cortex and reflects from the base. Just as with oil on water, the two types of reflected light meet with most wavelengths out of phase. Wavelengths that are not cancelled create bright coloration. (…) The cortex only works as a thin film when a layer of black melanin creates a boundary at its base, without [it] light passes through the cortex without reflecting back to the surface and there is no iridescense. (…) Depending on the thickness of the cortex, the color produced by this simple mechanism can have a characteristic bronze, purple, blue or green hue.”

Parts of a feather: 1. Vane; 2. Rachis; 3. Barb; 4. Afterfeather; 5. Hollowshaft, calamus (Source: Wikipedia).

The effect changes with the viewer’s distance and position, as related to the angle of the light source on the feathers. The best position to observe or photograph the iridescent colors is with a 45 degree angle between the sun, the feathers and the observer.

A male Great-tailed Grackle, colors in full display. (Photo © Ivan Gabaldon).

Not to be left behind, a female Great-tailed Grackle boasts her colors as well. (Photo © Ivan Gabaldon).

So now you know: next time you see a group of Great-tailed Grackles, most common bird in the land, be aware that you are in the presence of a visual miracle, sponsored by the Laws of Physics and designed by Mother Nature herself. Hopefully, you’ll never see them as “just those black birds” again.

A juicy meal! (Photo © Ivan Gabaldon).

A couple of Tropical kingbirds (Tyrannus melancholicus) were at ease until this male Great-tailed Grackle arrived to claim the space. (Photo © Ivan Gabaldon).

At the end of the day, these Great-tailed Grackles travel in group to their roosting place. (Photo © Ivan Gabaldon).

I.G.H.

Sources:

National Geographic Field Guide to the Birds of North America (Fifth Edition), edited by Jon L. Dunn and Jonathan Alderfer.

Aves Comunes de la Península de Yucatán, by Eduardo Llamosa Neumann with illustrations by Gladys M. Rodríguez.

A Guide to the Birds of Mexico and Northern Central America, by Steve N.G. Howell and Sophie Webb.

National Geographic Bird Coloration, by Geoffrey E. Hill.