March 14, 2006 — Some birds blush, and now researchers believe they know how and why.

According to a recent paper in the journal Comparative Biochemistry and Physiology, blushing appears to cool down physically and/or emotionally heated birds. It also likely indicates the condition or status of the blusher.

Lead author Juan José Negro told Animal Planet News that there probably are similarities between bird and human blushing.

"Young girls going to balls used to pinch their cheeks to enhance facial redness," he explained. "Some women today wear rouge, as they want to show men that they are beautiful and in good condition. Birds also attempt to look good for their mates, so there is a parallel."

Negro, a scientist at the Estación Biológica de Doñana at Pabellón del Perú, Spain, and his colleagues began by documenting all bird species that are known to blush. Birds with a penchant for blushing include ostriches (Struthio camelus), the crested caracara (Polyborus plancus), the hooded vulture (Necrosyrtes monachus), and the pied-billed grebe (Podilymbus podiceps), as well as pelicans, turkeys, and other birds.

The researchers determined that most blushers are dark-colored, large species that tend to live in hot climates.

The scientists then analyzed in detail the facial skin of crested caracaras and hooded vultures. Samples were taken from both feathered and bare skinned portions of the birds' faces.

Under high magnification, the bare skin revealed numerous arteries, veins, and anastomoses, which connect arteries to veins. These are all separated by dense connective tissue and elastic fibers, similar to what is found in a turkey's wattle. As for the wattle, the structure allows the skin to fill with blood and turn red. In contrast, the feathered skin revealed few vessels that were immersed in connective tissue.

"Since a recognized function of blood is to dissipate heat through the skin, we hypothesize that birds blush to help control thermoregulation, and that this evolved function developed into a second mechanism involved in signaling status, willingness to mate and other visual cues," said Negro.

He explained that ostriches, for example, often blush when they are mating. Male ostriches especially turn red in their necks and faces when they are excited by a female.

Like humans, birds also turn red in the face when they become hot and bothered in emotional situations.

"I've witnessed different species of vultures fighting for food, such as over a dead cow carcass," said Negro. "You should see them. They get so red in the face. We also have turkey vultures here at our facility in Spain that perch themselves when it's very hot, sometimes over 100 degrees Fahrenheit. With red faces, they extend their wings and try to dissipate their body heat."

Gary Bortolotti is a professor of avian biology at the University of Saskatchewan in Saskatoon, Canada. He told Animal Planet News that he agrees with the findings and that he has witnessed big vultures blush.

Bortolotti said, "This area of study has largely been ignored and Negro has done some innovative work exposing an interesting aspect of avian coloration and signaling."

He added, "What surprises me is just how this seems to have been overlooked for so long."