Everyone knows that vultures eat carrion, and Andean condors (Vultur gryphus) are no different from their scavenging brethren. The world’s heaviest soaring bird survives on a steady diet of rotting sheep, goat, rabbit and red deer, with the occasional horse or cow thrown in the mix. A group of researchers studying carotenoids — red and yellow pigments found in plants — in these birds, however, have come to the conclusion that condors are likely also eating a lot of vegetation. (The study was published last week by PLOS One.) That might mean they’re munching on some kind of plants, or it could be that they’re finding, as the scientists put it, “vegetal content” in the herbivores they eat, that is, whatever the birds come across in the stomach and intestines. Yum.
Andean condors may have need for carotenoids in their diet: Males of the species (above, a) have a brown iris in the eye, and neck wattles and skin on the head that can vary in color from gray to yellow. Females (b) have a red iris and less yellow skin (and no comb). During arguments over carcasses, the bare skin of grown and nearly grown condors can change in a moment from pale to deep yellow or orange or red (c and d). All that color requires pigment.
But how do they get that pigment, the researchers — a team from Spain and Argentina — wondered. They took blood samples from 22 wild Andean condors and 17 American black vultures in Patagonia in 2010, along with 27 captive condors from the Buenos Aires Zoo. The American black vultures are a much plainer species, and they wouldn’t seem to have as great a need for carotenoids. And the captive condors were fed a diet of meat only; if they had fewer of the pigments in their blood, then it would mean the wild birds were getting their colors from something other than herbivore flesh.
The wild condors and the black vultures, living in the same area, ate pretty much the same meals, but the condors had three times the concentration of carotenoids in their blood. The wild condors also had higher concentrations than their captive counterparts. The captive birds did have some carotenoids in their blood, but it was at lower levels.
The researchers concluded that the captive condors are getting some carotenoids solely from the herbivore meat they eat. But the wild birds are probably getting a lot more by eating “viscera and vegetation.” The Andean condors may also be biologically more competent at taking up or accumulating the chemicals than the black vultures, a necessity since they have a greater use for them.
But an analysis of 135 pellets (i.e., regurgitated food) taken from communal roosts gives added evidence that the wild birds are getting their carotenoids from vegetal matter of some sort: About 35 percent of the pellets consisted of 80 percent or more vegetal remains.
If Andean condors do indeed have a taste for veggies, they wouldn’t be the first vultures to snack on the green stuff. Egyptian vultures, which have their own need for carotenoids to color their bright yellow faces, get their fix by eating herbivore poo.
Image used under Creative Commons license, from Blanco G, Hornero-Méndez D, Lambertucci SA, Bautista LM, Wiemeyer G, et al. (2013) Need and Seek for Dietary Micronutrients: Endogenous Regulation, External Signalling and Food Sources of Carotenoids in New World Vultures. PLoS ONE 8(6): e65562. doi:10.1371/journal.pone.0065562