A look at birds that take an earthy route to dealing with ectoparasites

Eurasian hoopoe sand-bathing near the Adyar Estuary. Photo: Prince Frederick  

Mannequins for sand-bathing — bee eaters may walk away with that title without a contest, where humans handle the adjudication.

A majority of us, particularly those who let birdwatching happen to them and hardly stir far from their lodgings and seek out birds, are prone to making that judgement.

The bee eater — and in our patches, the green bee-eater — is only a more visible symbol of a behaviour that runs in many other species.

Recently, on the earthern passage leading to the Adyar estuary, with the boundary of the Theosophical Society rearing up on one side in a tall wall, an Eurasian hoopoe seemed to make this point, suddenly pausing from an afternoon binge-eating session.

Call it what you will, a coincidence or a case of one-upmanship, the hoopoe stopped tapping the ground for insects, and engaged in a sand-bathing ritual, the highlight being that a green bee-eater had done a wriggle in the sands, only a few feet away and a few seconds earlier.

Away from the anthropomorphic lens that draws poetic but senseless inference of one-upmanship from a regular functional bird behaviour, it could be enlightening and fascinating to ask and explore the question: Why do birds have sand-baths? And possibly another too: Why do some have sand baths, and others don’t?

Ornithologist V Santharam observes: “Preen glands are essentially for oiling feathers. Mud baths are for dealing with ectoparasites. Preen glands may to some extent help deal with ectoparasites . But these birds that take mud baths do it more for getting rid of ectoparasites.”

On the other question, he points out that one notices a good number of hole-nesting species engaging in this cleansing ritual.

Santharam believes being hole-nesting birds may have something to do with this behaviour, possibly because their ectoparasite-load could be higher. The fact that hoopoes, the hornbills and bee-eaters are inveterate sand-bathers provides strong scaffolding for this thought.

On why a good number of birds do not view sand as a means to ridding themselves of free-loaders, there obviously cannot be an answer compact enough to be packed into one sentence, short and smart. Santharam notes that in some bird species, there could be other behaviours that may adequately compensate for the absence of this one. “In bird species that form social flocks and allopreen — the yellow-billed babbler being a classic example — the presence of the social group will take care of the ectoparasites.”

He also remarks how “anting” is for some bird species a way to try to be free of ectoparasites. By crushing certain types of ants picked up with their bills and rubbing the formic acid generated in this manner against their bodies, these birds seem to make short work of ectoparasites.

(Field Notes is a weekly column about the resident and migratory birds of Chennai)

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Printable version | Nov 29, 2021 9:18:06 AM | https://www.thehindu.com/sci-tech/energy-and-environment/a-look-at-birds-that-take-an-earthy-route-to-dealing-with-parasites/article37148317.ece

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