Namibian Birds, their challenges and how they over come them
Birds, and indeed any living organism, must have a range of adaptations to survive their given environment. Dry environments present distinct challenges and make it an interesting subject matter to ponder while birding in Namibia.
The main ecological challenges in desert areas center around heat and water. If you visit these places in summer, this problem is really obvious. But the temperature problem doesn’t go away in winter…in some ways it gets worse. Why?
Well, for a start, any rain that will fall, falls in summer. That’s not the whole problem, however. Cold itself is a problem. Though Namibia’s deserts don’t get as cold as many other regions in the world, in Namibia’s dry areas there is very little of the way of food in those times. There are very few insects and almost no flying insects. This great source of food disappears during the time that birds (and some mammals) could use them most.
Despite the challenges, these dry areas are truly full of life. The birding doesn’t compare in numbers with wetter areas, but the birds that are found here have had to overcome some significant obstacles.
There are various ways to deal with problems, and some birds do it the easy way…they leave. Local and regional migration is very important to desert birds. However, there are other bird species that stay put in the desert and it’s these that make a birding experience in the desert so rich.
Below we discuss some of these adaptations.
Being big – Ostrich
If you live in the desert, being big is a problem. Yet, in areas with very few birds at all, deep in the desert, lives a big bird, the biggest bird of them all, the Common Ostrich. How does this huge bird survive the challanges of the desert? This facinating bird has a number of adaptations, both physiological and behavioral.
Ostrich use their feathers to insulate their body, as do all birds. In the hot times, this allows Ostrich to trap air within their feathers and use it as a temperature barrier between their body and the outside air.
Many of the deserts birds are rather small. This give the great advantage of needing less food than a larger bird, but it creates it’s own problem. The smaller in size an animal is, the greater it’s surface area to volume ratio. What this means is greater loss of heat when it’s cold, and faster obsorption of heat when it’s hot. Therefor it is a greater challange to meet enegry and water requirements. An example is the Dusky Sunbird, which is a nectar feeder and breeds when the most reliable energy source is available to them…the flowering Aloes. They feed far more on insects than other Sunbirds to, in order to help meet these requirements. It is for this reason that there is a far higher proliferation of ‘cold blooded’ animals at that size (lizards and small snakes)
Being Social – Sociable Weavers
As the degree of aridity increase, it is rare to find birds that have a communal nature. However in the Karoo and Kalahari, and right onto the fringe of the Namib Desert, one finds a bird so communal that it’s reflected in its name…Sociable Weavers. These birds face the problem of gathering enough food in the cooler months to keep up with the energy requirements of dealing with the cold, just like any other bird in winter. In the desert the problem is the availability of food is obviously less, and therefore harder to meet those energy requirments. Living in a comminty would seem to make it all the harder to find the already scarce food needed for this purpose. In the dry months of early summer the problem is reversed, where water is the resource most needed to keep cool. Do a trip around Namibia and you will see some strange hay stacks piled in the trees. No, they are not placed there as food for Giraffes, they are the nests of the Sociable Weavers. These birds live in large communal nests, with a number of chambers going up from the bottom. The chambers are not interconnected, and only take up a small part of the huge nest.
These nests are used all year round as roosts by the birds (most birds, of course, simply use their nests as breeding sites.) With outside tempratures having huge flucktuations and reaching both rather cold and very hot tempratures, the temprature within the nest remains relativly stable. Sociable weavers therefore have a great escape mechanism, get away from the extreems of weather by taking refuge in the nest. Over all, it comes to a huge saving of energy and water requirement for these birds, and alows them to live in communities in these extreem environments.
Some inhabitants of the drier regions can’t handle the extremes of aridity or temperature. They resort to a rather simple solution, they escape. The sociable weavers do it in a local sence, but for many birds a nomadic way of life is the solution to living in desert habitats. Some birds migrate, such as the Lesser Grey-backed Shrike, but for many it’s more a matter of finding an overwinter spot. These birds are nomads. Within days of good rains, they are back in the desert. Two species that are great examples of this are the Larklike Bunting and Grey-backed Sparrow-lark.
[ref img from Peregrine’s Bird Blog]
In the really dry times deep in the desert not one single bird will be found. But a little good rain and many appear and breed up into the thousands. As conditons drop, their populations plumit as well, but many individuals simply leave. They may be on the fringe of the desert or even in the slightly better spots within the desert itself.
Perhaps so obvious as to not warrant discussion, seeking shade is a vital behavioral adaptation for many birds in arid environments. You only need to spend one day outside during the hot time of the day to understand the degree to which shade can make a difference for the desert inhabitants.
Part of the purpose of mentioning it here is that in an effort to be sensitive to wildlife during your Namibia travels, remember that birds that you see during the middle of the day in the desert should be disturbed as little as possible. This is especially true in areas where there are a lot of people.
Water is limited, by definition, in arid areas, and getting enough of it can be a huge challenge. There are different ways that birds deal with this issue. Many raptors get enough moisture from the bodies of their prey. Other birds, such as insect eaters may also get enough moisture from their food. Seed eaters have the toughest time as seeds contain very little water. One adaptation of certain seed eaters is to drink water often. Of course this is a serious problem, however in Southern Africa’s dry regions we have a group of birds that do exactly that. These are the Sandgrouse. The call of the Namaqua Sandgrouse is a sound synonymous with dry regions in Southern Africa. Each morning and afternoon these birds set off for water, and may travel huge distances to do it. The most clever aspects of the whole thing is that they are also able to carry water back to their chicks. They don’t do this in their mouths…rather they have chest feathers specifically adapted for the job, expanding to increase the space and waterproof on the outside.
Finding food, the role of Mobility
What vultures do we find in the Namib? The smallest ones in southern Africa? No, the opposite, in the Namib the most common Vulture is the Lappet-faced Vulture, Africa’s largest! So how does this bird find food? Simple, it flies really far. These Vultures ride thermals very high and then decend, expending very little enegry and traveling great distances. Their outstanding eyesight helps them locate food even from great heights. The Lappet-faced Vulture is perhaps the extreem of this type of behavior, but many other desert organisms do the same on a smaller scale. In this regard, of course, birds have the greatest advantage – they fly.
At times when it is dry there are regions in the desert where there are few birds. But a trip through many of Namibia’s dry regions will reveal the opposite…far more birds than one would expect, given the degree of aridity. It makes a birding trip through Namibia that much more interesting if you ponder “how do these birds make it out here?”