Egyptian vultures exhibit strange mud-coloring rituals.{credit}Manuel de la Riva{/credit}

Scientists have discovered that Egyptian vultures engage in a peculiar “mudding” ritual that is one among a set of unique behaviors that not only distinguish the vultures from other birds of prey, but also, quite frankly, make them look a little “weird” in comparison.

In a new research paper in the journal Ecology, scientists Thijs van Overveld, Manuel de la Riva and José Antonio Donázar of the Estación Biológica de Doñana, Sevilla, Spain, describe the coloring ritual in detail, opining that the behaviour, where the birds dip their heads, necks and even chest in red soil, essentially bathing their upper bodies in mud, might represent a complex communication technique through which the birds relay social information.

Nature Middle East chats with Overveld about the intriguing mud bathing ritual, and what it tells us about the North African birds.

NME: What does knowing about this coloring ritual add to the body of knowledge we have about the bird?

Overveld: The situation of Egyptian vulture is not very good, and currently classified as critically endangered, so few birds are left and we actually know very little about their behaviour. What we do know is that the Egyptian vultures are among the most peculiar birds worldwide. The vulture has a unique behavioural reportoire, such as stone throwing to open eggs; it also eats excrement of ungulates which turns their face into yellow.

Our work adds a new, and unusual behaviour to their behavioural reportoire, which so far has only been described in its close relative, the Bearded vulture.

NME: What are some of the observations that you have made about the birds?

Overveld: These birds have a far more complex social life than previously assumed. Since these birds are non-vocal, we don’t rule out that mud bathing may be used to signal certain social information.

The most intriguing part of the painting behavior is the amount of individual variation.

I have been repeating the experiments in the last week, and the interest in the mud (and disinterest) is striking. We are just at the beginning of our work, so it is difficult to give a clear answer. We can rule out some options like social status, for instance; sanitary benefits also seem unlikely because some birds don’t use mud when it’s in front of them, but we cannot give an answer to why they do it.

NME: Is it as strange as it sounds? Is it atypical in any way?

Overveld: The bird is clearly a special case among birds generally, but most interesting, it’s a vulture that is general regarded as a filthy animal. This has been quite different in the past, given that many societies treat them as sacred animals. As you know, they have been providing essential ecosystem services by eating dead animals and thereby avoiding the spread of diseases.

The significance of our work is two-fold, we decsribe a behaviour that may tell us more about how [the birds] live and their adaptations, while meanwhile, we show that a highly threatened bird – with remarkable behaviors unique among birds worldwide – is disappearing.

NME: How does the coloring happen? What do the birds do exactly?

Overveld: When birds notice red mud, something happens. Some birds can stare or gaze at the mud for 20 minutes, only to scratch the mud and leave. Others step in the bowl and start to scratch, look at it very carefully and then typically swipe both sides of the head and neck in the mud.

The most important thing of our experiment is that we show birds get dirty on purpose. Some start with a bath in clear water and then go all the way in red mud.

The questions is why do some birds want to become so dirty, and why is it as if some birds look [like they’re about] to take the most important decision in their life before swiping their head [in the mud].

Currently we are describing in more detail the behaviour during different parts of the year in combination with experimental work to figure out whether they may signal other social cues we yet don’t know. They have a more social complex life than previously acknowledged so we currently don’t rule out any option.

Scientists have finally recorded the strange mud bathing rituals of Egyptian vultures.{credit}Thijs van Overveld{/credit}

If you’re curious about how Egyptian vultures bathe in mud, and would like to see the ritual in action, check out the following videos, courtesy of Overveld and colleagues: Video 1, Video 2, Video 3. According to the researchers, the videos are the first ever recordings of this specific mudding behavior.