A novel topic No 7: the birds' bath

One of the nice things about our house is that we have a birth bath in the back yard which is easily visible from the dining table and kitchen.  Hence, we often get to watch birds bathing while eating lunch.  (You can also see the bath from the main lounge area too.)   It's fun watching birds bathe:  everyone should have such avian facilities in their yard.

But, it has occurred to me - why do they bathe at all?   Does the water help remove lice?  Google is my friend, and leads me to some information:

When birds bathe in water or saturate themselves with dust they are actively maintaining their plumage. In well-watered areas bathing is most common, in arid ones dusting is more often observed. Experiments with quail show that frequent dusting helps to maintain an optimum amount of oil on the feathers. Excess plumage lipids, including preen oil, are absorbed by the dust and expelled along with dry skin and other debris. If quail are prevented from dusting, their feathers quickly become oily and matted. Dusting may also help to discourage bird lice, but no experimental evidence exists as yet showing that to be the case.

Wrens and House Sparrows frequently follow a water bath with a dust bath (one reason to suspect an anti-parasite function for dusting). Overall, the amount of time and effort birds put into bathing and dusting indicates how critical feather maintenance may be. Feathers are marvelous and intricate devices, but keeping them functional requires constant care.

A bird is considered to be bathing whenever it uses any of several stereotyped movements to wet its feathers. One pattern, wading, is commonly observed in birds with strong feet and broad, short, flexible wings. In a typical sequence a bird stands in the water, fluffs the feathers to expose the bare skin between their bases, and rapidly flicks the wings in and out of the water. The breast is submerged and rolled vigorously back and forth, and then, as the front end emerges, the head is thrown back, forming a cup with the partially elevated wings and tail, and dousing the feathers of the back. Those feathers are elevated so that the water reaches the skin, and then lowered, forcing the water between them. The sequence may be repeated, with the bird submerging farther in each cycle, until it is a mass of soaked disarranged feathers. Variations on this theme can be seen in different species, such as robins, thrushes, mockingbirds, jays, and titmice.

So, it seems the dust might be more important than the water in removing lice?  Oddly, I can't find, even via Google scholar, any papers on water itself removing parasites.   But preening is important:

After bathing, birds dry themselves using ritualized movements. Even swimming birds must force the surplus water from between their feathers to protect their insulating properties. Anhingas and cormorants, which often sit in a characteristic sunbathing posture with drying wings spread, are perhaps also thermoregulating. (Vultures take on similar sunbathing postures in the morning. Sunbathing, which occurs in many birds, may stimulate skin parasites into activity so they can be more readily picked off.) Songbirds shake themselves to throw off water by vibrating wings and tail and ruffling feathers. All birds normally follow bathing with preening.  

More on preening from another website: 

 Preening is the simplest and most common of feather care activities. It involves two different actions, nibbling and stroking. All other feather care activities seem to be a prelude to preening, or at least end in a bout of preening. Preening serves the function of returning feathers to their correct position and form and often involves the addition of oil to the feathers from the Uropygial gland. Wiping is simply wiping the feathers with the bill, pressing them into place and perhaps spreading some oil over them. Nibbling is a more serious attempt to put the feathers back into pristine condition. The bird uses its bill to nibble along the edges of feathers straightening them out and ensuring the barbules are all zipped up.

 One thing I am not sure I have heard about before, however, is "anting":

Many different songbird species have been observed picking up single ants or small groups and rubbing them on their feathers. Less commonly, other songbirds "ant" by spreading their wings and lying on an anthill, and squirming or otherwise stimulating the ants to swarm up among their feathers.

The purpose of anting is not well understood, but the most reasonable assumption seems to be that it is a way of acquiring the defensive secretions of ants primarily for their insecticidal, miticidal, fungicidal, or bactericidal properties and, perhaps secondarily, as a supplement to the bird's own preen oil. The former explanation is reinforced by a growing body of evidence on the biocidal properties of ant secretions and by an observation of a jungle Myna (Acridotheres fuscus) actively "anting" with a millipede, whose potent defensive secretions (evolved to fend off the millipede's enemies) could be smelled from 15 feet away. Likewise, the observed correlation of anting activity with high humidity might be explained by the documented fungicidal properties of ant secretions. Because the seasonal timing of anting and molting (spring and summer) often correspond, some have suggested that anting may soothe the skin during feather replacement. It seems more likely that the seasonal relationship simply reflects the greater activity of ants during those periods.

Interesting.

UPDATE:  here's another way birds deal with parasites - by lining their nests with cigarette butts!

Birds have long been known to line their nests with vegetation rich in compounds that drive away parasites. Chemicals in tobacco leaves are known to repel arthropods such as parasitic mites, so Monserrat Suárez-Rodríguez, an ecologist at the National Autonomous University of Mexico in Mexico City, and her colleagues wondered whether city birds were using cigarette butts in the same way.

In a study published today in Biology Letters¹, the researchers examined the nests of two bird species common on the North American continent. They measured the amount of cellulose acetate (a component of cigarette butts) in the nests, and found that the more there was, the fewer parasitic mites the nest contained.