I had seen totally unexpected landscape in the Thar desert: dry riverbeds with piles of broken rock, and vast stretches of level ground. Although large parts of the desert landscape was of this kind, there was a significant area full of sand dunes. I saw many dunes which were stabilized by plants specialized to grow in the desert, but there was a stretch of the great shifting dunes that deserts are famous for.
Dunes are formed by wind-blown sand. Sure enough, the air was dusty enough here that it felt comfortable if I pulled my tube scarf up to my nose to form a mask. Three kinds of sand dunes are commonly seen: barchans have horns facing away from the wind, parabolic dunes have horns facing the wind, and transverse dunes are perpendicular to the wind. What was I looking at? The great dune in the featured photo was clearly a transverse dune. I could sometimes see sand coming over its slip face. We were camped leewards of it. The ripples behind it were parallel to the edge. Eddies and gusts had formed smaller dunes, still pretty large, at its base. The photo above shows one of these. This was probably a blowout, or a parabolic dune. The horns at its end were not very long. In the picture above you can see that at the foot of the slip face the wind has tried to form yet another (tertiary) blowout dune. I guess this kind of fractal structure of dunes must be fairly common.
I woke up one morning to try to take photos of the dunes before sunrise, and found clouds blowing in. This was the first time I felt a strong wind. From the direction of the clouds it seemed that my guess was wrong: the clouds were blowing parallel to the dunes. The kind of clouds that you see in the photo are a high layer of cumulus clouds (altocumulus stratiformis). They form when ground-level winds carry moisture up where they freeze and then are carried in a different direction by high-altitude winds. So the direction of the movement of the clouds had nothing to do with the movement of the ground wind. In fact, because the ground wind had to be perpendicular to the movement of the clouds, my guess about the dunes had become more likely to be correct!
I had the warm fuzzy feeling which comes of the conviction of being right.
Evening, the golden hour, seems to be the time to see Bucanetes githagineus. The name does not roll off the tongue very easily. I prefer to call it by its common name: the Trumpeter finch. I saw a bunch one evening in a hill of broken rock in the middle of the desert. They were hard to spot because their colours match the rock so closely. The best light was over when we spotted them. I would see them by their movement, and then lose them when I zoomed in. It was a very unsatisfactory lifer.
The Trumpeter finch is rarely seen in India, but is common over the arid zones to the west: the Arabian deserts and parts of the Sahara, where they breed. The thick triangular bill is tuned to feed on oilseeds, but this finch will not sneeze at insects and grasses. Usually birds which live on dry food like seeds will need water some time during the day. I wondered where they would find water in that rocky desert in which we spotted them.
The next day, at the same time, we were surprised to find a bunch of these finches in the open near a village. They were there for water. The sightings were almost a hundred kilometers apart, so there must be many Trumpeter finches in the Thar desert. As you can see, the birds are gregarious. The colourful bills distinguish the sexes: the females have yellow bills, and the bills of males are more red in colour. Interestingly, these colours are derived from carotenoids in their food. The difference in colours is due to metabolic processing of the chemicals, which differ between males and females. The light pink colour at the chest which also distinguishes the male is likewise derived from ingested carotenoids. I found it hard to believe that if the bird is restricted to food without these chemicals it would change colour. But apparently that is how it is.
Since the 1970s Trumpeter finches have begun to breed in southern Spain. There has been speculation that this northward creep of the breeding range makes it a bellwether for the range deformations that climate change is bringing. These finches are also found to have very low counts of parasites in them. The first instances ever were found in the Spanish population. It is not known whether the lack of parasites is due to the absence of naturally evolved parasites in their original range, innate resistance to parasites, or lack of vectors. Whether the extension in range introduces new parasitic challenges is also something that one should watch for. After all, with climate change, and the resultant migrations of animals, new diseases could easily sweep through populations. It is sobering to think back on these sightings and realize how these small birds could relate to some of the largest changes in the world around us.
I saw this stretch of sand and did a double take. The pattern of light on it made it look like the bottom of a shallow sea It was not hard to imagine that the light refracted through ripples in water could make the caustics and dark patches that I saw. But the patterns were static. Things had walked across the desert, and then the wind has worked over their tracks to make the gentle ripples in the sand that you see in the featured photo. I looked around to check whether I could recognize from a new spoor what had made these patterns. The obvious guess was right: they were the footprints of camels.
Looking up from the sand it was clear what attracted the camels here: the acacia trees which were all around me. The Acacia jacquemontii is a common second wave of growth over sandy areas which have been stabilized by plants such as the khimp and phog. While writing this now, I had a moment of doubt about the identification. Was it really the local babool tree, A. jacquemontii? The shape of the canopy looked like that of the babool. But still, could it be the imported Israeli babool, Acacia tortilis, which the state government is partial to, since it grows faster? I looked at a photo I had taken of the leaves, and found that it was indeed the native babool.
I had a wonderful sighting of the female kestrel whose photo is featured in this post. It sat on a dry tree in the middle of the Thar desert for a long time, scanning the surroundings. I suppose it was looking for jirds or other rodents to eat. I loved that sideways glance with which she dismissed me as being of no consequence. I had no choice but to slink away.
The common kestrel (Falco tinnunculus) seems to be really common, being found over all of Asia, Africa and Europe, except only Siberia and the Sahara, Gobi, and a part of the Thar desert. Interestingly, it is found in the more inhospitable parts of Thar. One can speculate why. The common Kestrel evolved about 2 million years ago, after the Sahara and Gobi were formed. But the Thar desert developed later, so the Kestrel must have just acclimatized to the change. I wonder how this hypothesis could be tested.
The male differs from the female most visibly in the colour of its head: it is pale unlike the brown of the female. There are other differences in plumage as well: the markings are less prominent on the male. Interestingly though, it is in size that there is a very remarkable sexual dimorphism: the male is smaller. I’ve written about how gender politics shapes the bodies of raptors which pair bond. The combination of relatively drab colours and smaller size falls directly in line with the argument which I had explained at length: that this has to do with the female tending the brood while the male hunts for the family. I was happy to see that this has been put to observational test and the hypothesis does seem to hold.
The desert of full of spiny leafless green bushes. Leaves present a large surface to the sun and are great organs for photosynthesis, but they also lose a lot of water through transpiration. Green stalks can carry on photosynthesis while minimizing water loss. Of course, they also present a smaller surface to the sun. So this is a thorny problem (yes, I meant that) which plants have to solve: more photosynthesis or less water loss?
The local name for the green bush full of upright stalks which you can see in the photo above is khimp. The plant grows along the extreme arid zone which crosses from Mauritania to India through the Sahel, the Arabian desert and the Thar desert. A search for the origin of the botanical name Leptadenia pyrotechnica led me to this book, which claims that the name pyrotechnical comes from the observation that Bedouins use tinder to set alight the fibrous stems of this plant. Later compilations noted that the high fiber content of the stems has been used by people across its geographical range in various ways. Some have used it to make ropes, others in diet to cure anything from constipation to obesity. Although I never thought of breaking off a stem to look at the sap, I’m told that it gives a clear sap. This is probably one of the reasons why camels are said to be fond of it.
There is a claim that extracts from plant was found to be mildly damaging to liver cells in a lab. On the other hand it is said to be eaten. Browsing the net, I came across a recipe for cooking khimp. Here is a translation: “Cut the stems and boil them. Remove them from water and press to drain the liquid. Separately cook spices in oil and add the boiled stems. Add a little buttermilk to cook further, thickening it with besan (chickpea flour) as needed.” The double cooking of the stems probably serves not only to tenderize the material, but also to denature toxins. The pressing and draining may also remove any toxins.
They grow along with phog on dunes and other dry sandy places. In various countries around the world people are experimenting with using L. pyrotechnica as a biological barrier to the spreading of dunes. But when I stood on top some dunes and took the photo above, I did not know that this could also be a weapon against cancer.
The literal meaning of the word “pastoral” is the keeping and herding of sheep and other livestock. The metaphoric meaning extends to farming and country life. If you think only of the metaphoric meaning, then you will never describe the Thar desert as pastoral. However, when you give up metaphors and look at the real meaning of the word, then “pastoral” is the word you will use to describe the livelihood of people in this desert. Scenes like the one in the featured photo are common.
Also common, and becoming more so, are sights as in the photo above. You often find bleached bones of sheep gleaming in the dusty brown landscape. Carcases are sometimes left to lie where the sheep died, as the nomadic pastors move on, so one can get a whiff of a dead animal while driving across the desert. There are also municipal and village dumping grounds for carcases. A variety of scavengers pick the bones clean. Among them the ones I found most interesting are the vultures. In the Rajasthan desert seven of the species of vultures seen in India have been recorded. We managed to see a fair fraction of them.
The sighting to remember was of this red-headed vulture (Sarcogyos calvus) feeding. Historical reports of this species show that it was infrequent but widespread throughout southern and south-east Asia, including the southern parts of China. Habitat loss and change in methods of disposing of carcases of livestock has pushed it to local extinction over large parts of south-east Asia, with only a small population left in Cambodia and in eastern Myanmar. The largest pool is in India, Pakistan and Nepal. Even in this heartland, its numbers fell dramatically in a few years around the beginning of the 21st century. The cause of this decline was traced to the use of diclofenac in treating inflammation in livestock. It turns out that this chemical is fatal to vultures. With the ban on veterinary use of diclofenac and its replacement by other compounds, the population has begun to grow again. However, the IUCN red list still lists it as critically endangered. I might have seen it in 2005, but I have no record of it. So this could well have been a lifer for me.
One thing that strikes you immediately when you see the Egyptian vulture (Neophron percnopterus) is that it has a short and feather-covered neck. It is an opportunistic feeder, picking at the remains of a carcass after other vulture species have left, and eating small animals, insects, fecal matter, as well as eggs. It is among the very few tool using birds, using rocks to smash eggs. It used to be widespread over Europe, the Sahel and Arab desert, and India. In three generations of the bird (about sixty years) the European population crashed to about a half of what it was in 1960. Poisoning of animal carcases against predators first hit the European population. Then EU regulations on the disposal of carcases, implemented in the early years of the 21st century, hastened this decline. In India, the rapid die-off of other vultures increased the exposure of this species to diclofenac, so leading to a cascading decline in numbers. We saw a few of these birds in the two days we spent in the deep desert, so the Indian numbers have presumably stabilized. IUCN has revised its assessment of this species to vulnerable.
I saw very few of the dark, nearly black, Cinereous vultures (Aegypius monachus). They are widespread through most of Europe and Asia, and are winter visitors in Rajasthan. This was one of a large group of vultures which was waiting near an unmoving cow. From the smell it was definitely dead, but the vultures were not yet ready to attack it. One suggestion was that the hide was too thick, and they were waiting for a red-headed vulture, with its strong and hooked beak to open up the skin. Given that the population of red-headed vultures is so small (84 in 17 districts of Rajasthan in 2009), they could have had a long wait. Also, I’ve seen single Gyps indicus (the Indian vulture) opening up a carcass. There are always parts of a body with thinner skin, or none at all. So this behaviour remained a mystery to me.
In the same crowd I saw many White-rumped vultures (Gyps bengalensis) and Indian vultures. Their numbers had crashed massively due to diclofenac poisoning, but the population is recovering slowly. A detailed study of the vultures Rajasthan was published eight years ago, and makes for interesting reading today. Now that diclofenac is not as much of a problem as it was then, the numerous other conservation bottlenecks pointed out in the study have come to the fore. Habitat loss due to quarrying and mining was pointed out as one major cause. I saw that quarrying is widespread in the desert. Electrocution in power lines is another cause which has been identified. All large birds are subject to this problem.
The mixed flock of Indian and White-rumped vultures which we saw in our first morning in the desert seemed to indicate that some pockets of vulture populations still remain. The IUCN red list still classifies them as critically endangered. This was the largest crowd of vultures I saw since 2005, when I saw them stealing from a tiger. I can understand why some naturalists are interested in the population genetics of vultures. Recovery of numbers from such a tremendous bottleneck may cause vultures to lose much of their genetic diversity. The government’s action plan involves setting up captive breeding centers. But these need to also preserve diversity of genes. Vultures a really fighting for survival, and it is still hard to sat whether they will survive another human lifetime.
I kept seeing clusters of burrows below clumps of bushes in the desert. The Family asked me once, “Snakes?” I thought not, because it is usually a mammal which digs burrows. It turned out that many of these are dug by the Indian desert Jird (Meriones hurrianae), one of which you can see in the featured photo. This one was happily sunning itself until someone approached too close, and it darted into the nearby burrow. I didn’t get a look at its tail, which is supposed to be quite distinctive.
This was my only view of this creature. They are said to be common; IUCN classes it as being of “least concern”. Little is known about them; for example, there is no estimate of how many there are. M. hurrianae are omnivorous, but mainly eat plants. Only in the hottest season, when plants are scarce, do they eat significant amount of insects. They probably get water from the food they eat. They are not travelers; they can spend a lifetime within 10 meters of their burrows.
I’ve seen them also being called the Indian desert hamster. It seems that hamsters are more likely to stand on two legs than their close relatives, the Jirds. Calling this desert species a hamster is a little inaccurate.
Burrows are fascinating. What would they look like? It turns out that Jirds’ burrows have been mapped in detail. They can be highly branched, dipping as low as a meter below the surface, with a major gallery which could be 2 to 4 meters in length. Jirds are safety seekers; there are multiple bolt holes in these tunnels, and lots of side galleries with stores of food. The inside temperature stays around 30 Celsius most of the year, but falls to about 20 degrees in winter. If this is the extreme of cold which adults can bear, then it would make sense that few pups are born in winter. Studies suggest that this is true. Interestingly, Jirds occassionally dig short and shallow tunnels where they can hide temporarily if needed.
Their tendency to bolt into tunnels makes them hard to see. I waited for about 20 minutes, but there were too many people nearby, and the Jird didn’t reappear near this bush.
As we drove through the Thar desert, I wondered about the mysterious landscape around me. India receives so much rainfall from the monsoon that it is hard to believe that it contains a desert. The popular belief that the monsoon winds are “depleted” of moisture by the time they reach the desert is false. The distance to the sea is rather small, and the air is generally moist. In just three winter months, when the rest of India is dry, the amount of water deposited by dew in the desert is between 30% and 40% of the total rainfall. Something prevents the western branch of the monsoon from penetrating into Gujarat and Rajasthan.
It is believed that this is the immense high-pressure anti-cyclone that exists over the Sahara and West-Asian desert. In fact, the claim is that the monsoon winds prevent the spread of this pattern to the rest of India. Evidence for competition between the two systems is what happens when a third factor occasionally intrudes. In the infrequent episodes when a Western disturbance hits India during the monsoon, causing immediate heavy rainfall and flooding over a wide area of the desert. This means that the monsoon winds are not depleted of moisture in this region, but are obstructed from flowing by the anti-cyclone. If this conjecture is true, then a weakening of the monsoon due to climate change could allow the anti-cyclone to extend across India, making it an arid habitat.
Our jeep had long wandered off the road. The flat landscape that I’d grown used to gradually gave way to undulations. There was still a strong wind blowing dust and sand into my face, so I had my mask on. But when I looked around, the ground had changed. Until a minute ago we were driving through hard packed sand (see the featured photo). Now, all around us I could see something different poking through the sand. The photo above shows the surface. The broken flat stones are made of a material called calcrete. This is formed by the action of water and atmospheric carbon dioxide on wet dust and sand (the word calcrete seems to be a portmanteau of calcium and concrete). The presence of calcrete means that wet lands turned to desert at some time in the past. Dating of calcrete in the Thar desert shows repeated cycles of wetness and desert starting from 1.5 million (15 lakh) years ago to 250,000 years ago.
I walked across this landscape in search of a wheatear, but my attention was on the landscape. A short walk through sand brought me to something that looked like a dry riverbed into which sand had trickled: calcrete was overlain with sand, as you can see in the photo above. Aerial and satellite photography shows evidence for a well-organized drainage system of interlinked rivers in the far past, disrupted by climate change. Successive surveys and dating showed brief re-emergence of local drainage systems over a period of a million years, which were disrupted within a few tens of thousands of years.
The wheatear perched briefly on a bush and I managed to take a photo. After it had flown off, I looked at the land behind the bush (photo above) and it became obvious that it had been shaped by flowing water. The surface was covered in calcrete, which it why it had not been reshaped by the wind. Studies of pollen around Didwana lake in the eastern part of the desert have established that about 6500 years ago the area was wet enough to support a large variety of grasses and flowering herbs and shrubs, of the kind which are usually pollinated by butterflies. This dried up around 4000 years ago. When these studies were first published, there was speculation in the press about the connection with the mythical river called Saraswati. More studies revealed a fluctuating boundary of the desert over human history and pre-history. Palaeolithic tools and sites have been found buried intact in the sand, showing that the desert shifts fairly abruptly. The gradual abandonment of Harappan cities could also have been partly due to such climate fluctuations.
The bird gone, I climbed a little bluff to join The Family, and saw immediately clear evidence that I had walked across the bottom of an ancient river. The photo above makes it very clear. How old was this? I’m sure it has been mapped out. The geological and climatic history of the Thar desert has been examined in great detail in the last 60 years by a large number of scientists working in India. There is a group in IIT Mumbai who examined the age of sand dunes, and found some as old as 160,000 years, and others as young as 11,000 years. In several of the photos above, you can see distant dunes. It gives me shivers to realize that they were being laid down at the same time as glaciers advanced across the north of Europe, Asia and the Americas. As water got locked up in ice, this part of the world turned dry.
Geology and climate sculpt the land over periods longer than our lives, even longer than our civilizations. As a result, it has been hard to see the forces which shape our societies. Walking across that river bed I thought that I had a tiny view of these forces. In the past our actions have been too weak to shape the planet. No longer. We need to understand the Thar desert to plan a way ahead as the climate changes.
The tall bush which you can see on the right hand edge of the featured photo is called phog in Hindi, and Calligonum polygonoides by botanists. Other clumps can be seen on further dunes. Each thicket can grow about as tall as a human, and spreads out in a circle. Unfortunately, I visited the Thar desert in winter, when one does not get to see the flower or berries of the phog. The flowers and buds are eaten as a raita, the shoot is used as feed for livestock and the root is used to make charcoal. The deep tap roots and lateral root system together contain a larger biomass than shoots.
As you can see from this panoramic shot, the plant grows very well in the extremely arid habitat of dunes where little else grows. As a result, it serves to stabilize the dunes. Over-exploitation of the plant to produce charcoal used by goldsmiths and local ironsmiths has begun to endanger the phog. There are attempts to propagate the plant through cultivation and replanting, but this has not been uniformly successful. Studies of competition between the phog and other varieties of desert grass shows that in more moist conditions the phog loses out. Consistent with this is the fact that growth of C. polygonoides changes soil properties less than other plants do.
Of more than 80 species of Calligonum recorded worldwide in arid areas of southern Europe, northern Africa, west and central Asia, only this one species grows in the Thar desert of India. A recent study found very high degree of genetic diversity in the phog population in Rajasthan. However, there was no geographical clustering of varieties. When I talked to an expert, I was told that the confused state of this first study makes this subject worth a second look. After reading the scant literature on this plant, I would be willing to do such a study if I had the expertise and the means.
We drove to a large pond in the desert close to the border with Pakistan. In the middle of a barren landscape broken only by acacia and small shrubs, the grass around the pond looked inviting. There was livestock grazing here: sheep, goats, cows and donkeys. We had a little breakfast and then hunkered down on the edge of the water to wait for chestnut bellied sandgrouse.
This bird can be found in a long arc of arid land from Senegal and Gambia in West Africa, through Saudi Arabia and Iran up to India. We sat near the easternmost range of this sandgrouse, Pterocles exustus. We did not have a long wait. Soon flocks of these birds showed up to drink water. We could hear their tritone calls as flocks of twenty to thirty birds wheeled around the pond and landed at the edge to drink. There was much movement, noise and fluttering of wings as each flock dropped to the pond, drank and took off. Soon after that, another flock would appear. I was busy trying to photograph them and did not keep count of the total number of birds, but over 20 flocks would have watered that day, meaning there must have been more than 500 sandgrouse. My count is so bad, that it could easily have been twice as many.
The birds feed on seeds, and so must drink water. At the time I watched the birds I was not aware of the spectacular way they carry water to their young. The male, which have yellow faces, sit in the water, and let their downy belly feathers soak up water. When they come to the nest, the young suck the water from the wet feathers. Since I did not know about this, I did not look for this behaviour. Nesting season starts by the end of winter in these parts. Even so, in my photos the males are generally in the water, whereas the females are at the edge of the pond.
The IUCN entry on the chestnut bellied sandgrouse says that the Egyptian subspecies, P.exustus floweri, is extinct. So I was happy to see a report about the rediscovery of the Egyptian sandgrouse population in 2011.