Nasal salt secretion of Oriental Pratincole

[Samrat Sarkar]

The documentation of the behaviours of different birds may be carried out either on the assumption based on extended and minute observations or on some inferences made from some suddenly made behavioural activities. Generally, if we guess beforehand some habit of a bird we can analyze what their next movements are going to be. Again, a bird may, at some awkward times do something in such an awkward manner that it becomes really difficult to find out what that weird behavior suggests. In many cases some minute movements which evaded my vision in the first hand, later caught my attention while viewing their photographs and could make some surprising conclusions about those movements.

I went to Monglajodi, Orissa in the last winter season. There I was taking snapshots of a large flock of Oriental Pratincoles in the golden light of a fine clear morning and unawarely went very close to the flock. The Pratincoles were sitting on a dry earthen hillock in the middle of the water body. I chose a particular Pratincole as my target from the beginning. It was not because I saw some unusual behavior in the bird, but because it was favourably close to my camera. It was sitting there without much movement for quite a long time.

[Samrat Sarkar]

As I came closer it once shook its head vigorously but did not fly away. I primarily thought that it was trying its threat display, what the Pratincoles usually do when some opponents pose some threat to them. I immediately backtracked with my boat and left the place. And that was when I lost my chance of capturing a snapshot of flight of a Pratincole for that day.

[Samrat Sarkar]

But as I came home and started reviewing the pictures I noticed a peculiar thing. As the bird was shaking its head, which I mistook for its threat display, a sort of white liquid oozed out of its mouth. The frame of the snapshot froze in that very moment!

I was quite surprised to see this weird behavior of the bird. It was sitting there on a dry earthen hillock for at least ten minutes, if not more. I did not see it drinking water or eating any other thing in that period of time. I did not see it taking a bath either so that it will eject water which might enter in its nostrils during bathing. Then, what was that liquid which it discharged from its mouth? I searched for informations from the internet and rummaged many books and journals to find a suitable answer, discussed the matter with my wild life specialist friends. And at the end I came to a fascinating conclusion. What was that conclusion?

[Samrat Sarkar]

Some of us might have heard of a biochemical process called Osmoregulation. It is a method synchronizing different biological processes by which a living organism balances the amount of salt and water in its body in different weather conditions. The osmoregulatory organs in cases of the birds are chiefly four, namely, the kidney, cloaca, lower intestine and the salt gland.

There are some structural characteristics in the physiology of the birds which are not similar to the mammals. In birds, the urine coming out of their kidneys does not readily leave their bodies. The urine first come to a chamber named cloaca through ureter. This cloaca is situated just behind the anus of a bird. This cloaca is the final part of not only the excretory [urinal] system, but also the end part of the digestive system and the reproductive system. The urine coming to the cloaca from the kidney undergoes some sort of refinement.

In this process some common salt [NaCl] and then some water are absorbed from the urine. The water not absorbed from the urine is later utilized in some other physiological processes mainly when water becomes scarce in the nature. In the cases of Sparrow, Munia or domesticated chickens who feed mainly on cereals it has been found that upto 70% of salt and 10 to 20 % of water are absorbed from the urine that enters the cloaca. At the end of all these the birds sometimes find it difficult to maintain the required balance of salt in their bodies.

[Samrat Sarkar]

The kidneys of the birds like gulls, terns, auks, penguins, albatrosses, petrels, cormorants, Pelicans, gannets, herons and ducks living near the seas or rivers are not strong. The amount of salt absorbed from the kidneys of these birds is not sufficient to maintain the balance of salt and water. For that they use to take help from an extra pair of glands in their bodies. Rather, necessity has forced Mother Nature to create an extra pair of peculiar but very useful glands. They are called “salt glands”

These glands are situated just above the orbits of the eyes. Many birds living around the sea shores are on many occasions compelled to drink saline water from the sea. Also, many marine organisms such as crabs, squids etc. on which those birds feed contains excess salt. The salt glands absorb this excess salt of the food they eat and the water they drink and balances the amount of salt in their bodies and ultimately preserves the precious body water.

But why is it important to get rid of this excess salt from their bodies? The answer is very simple. The excess water in the body, if not disposed of properly, will require more water to dilute it to maintain the salt-water balance.

The birds then will have to drink more fresh water. In case the birds cannot manage to find that fresh water from its surroundings that water will have to be supplied from their body tissues only, and as a result the body tissues will wither. The birds then will suffer from dehydration. That is why it is so vital to dispose of excess salt from their bodies by some means or other.

How do salt glands function? They function like the kidneys only to a great extent. In the salt glands there are many blood capillaries from which highly concentrated salt water is absorbed and is oozed out through the nostrils. This is what the birds do by shaking their heads at some suitable moments. What the Pratincole did here was exactly that. The concentration of salt in the liquid thus oozed out is certainly higher than that of the liquid which enters the cloaca from the kidneys.

[Samrat Sarkar]

Now the usual question will be why a fresh water lake bird such as this Pratincole will eject salt water from its body this way. Its food stuff consists mainly of small insects hovering above the rivers or other water bodies, some insects living in the ground level, such as grasshoppers, moths, ants, flies, honeybees, Cricket and some invertebrate organisms.

Marine salt water animals are visibly absent in the list of the foods that the Pratincoles eat. In this connection we can mention the research work done by a scientist named Technau in 1936. He did his research work on 83 different species of birds and concluded that out of that 83 species of birds about 24 species had considerably large salt glands, all of whom had their habitats near the sea and were marine birds. And a more interesting thing was that the amount of salt secretion among the birds of a very same genus varied as a result of the change of place of their habitats.

The scientist Schildmacher described in his research work in 1932 that in the Berlin zoo that the salt glands of different ducks of the same species becomes larger when they live close to some saline water bodies than those of the other ducks who live in fresh water. Therefore, though the Pratincoles are generally fresh water birds as I saw them in Monglajodi, it may not be unusual for them to drink saline water from the nearby Chilika sea coast ore from some other parts of the sea.

But we cannot tell for certain that the salt glands are characteristics only of birds of saline or maritime habitat.

Active salt glands are also found in a number of birds such as Roadrunner, Savannah Hawk living in desert areas. Their nasal secretion takes place due to their habit of eating high protein food such as some insects and some vertebrate animals. The desert birds such as Sand Partridges or ostriches also have active salt glands which help them to balance the amount of salt and water in their bodies in high temperatures. This reason also might play an important role in the case of this Oriental Pratincole for its salt secretion.

Let me now come to my first point, osmoregulation. Whether a bird lives near salt water or not it continues its work of balancing the amount of salt and water in its body all the time. Perhaps this is the first time that the incidence of salt secretion by a Pratincole has been captured in the natural environment in a snapshot in the Indian Sub-continent.

Originally written in Bengali and Photography by Samrat Sarkar.
Translation into English by Biswajit Debnath.
Month of Observation - December 2016.
Technical sketch source - Internet.

Technical Papers helped to write this Article are -
1. THE FUNCTION OF THE SALT GLAND IN THE BROWN PELICAN BY KNUT SCHMIDT-NIELSEN AND RAGNAR FANGE.
2. The Salt-Secreting Gland of Marine Birds By KNUT SCHMIDT-NIELSEN, PH.D.
Special Thanks to Cornell Lab of Ornithology, USA

Comments, Inputs, Critiques are most welcome.