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Lake Xau comes up to expectations

Thousands of Ruffs have now discovered Lake Xau.

Lake Xau has been a dry dustbowl for the past three decades. However the exceptional 2011 floods from the Okavango coursed down the Boteti River for over 250 kilometres beyond Maun to reach Lake Xau late last year. Birds have been rather slower than expected in finding this huge, shallow waterbody, but waterbird counts conducted by BirdLife Botswana member, Chris Brewster, over the Christmas period, show that it is well on its way to achieving recognition as an Important Bird Area (IBA).

One of the criteria for an area to achieve IBA status is that it should harbour significant numbers of globally threatened birds. In this regard, the key dryland bird species such as Bateleur and Martial Eagle, and Lappet-faced and White-backed Vultures (long resident in the area) are now being joined by globally threatened waterbirds such as Wattled Crane and Black-winged Pratincole. Congregatory waterbirds have not yet built up to numbers which exceed the critical threshold (0,5% of the global or regional population) but numbers of Ruffs and Great White Pelicans are already notable.

At present, it is the number of Black-winged Pratincoles at the lake (2,000) which is of special interest. In a recent article in Africa Birds and Birding magazine, Phil Hockey (Director of the Percy Fitzpatrick Institute of African Ornithology) suggested that this species might be in serious trouble. Very few pratincoles relative to 20 years ago are now being seen (cf the sighting of 10,000 by Penry and Tarboton at Lake Ngami during the 1980s). Phil Hockey suggested that the pratincoles may have shifted their non-breeding range northwards into northern Botswana but this is unlikely to be the case given the few sightings we have. Chris Brewster's count of 2,000 at Lake Xau is the best news we have had for this species in recent years, and highlights the importance of this 'new' wetland.

Apart from the pratincoles, there is much of interest to be seen at Lake Xau - it is certainly a spot worth watching!

Birds and People #31

Open publication - Free publishing

Alive and well - Ross's Turaco in Botswana

In a previous blog (26/7/11), a challenge was issued to birders to look out for Ross's Turaco, which has only been recorded once in Botswana - in 1974. Well, some serious guides working for Okavango Wilderness Safaris have risen to the challenge, and followed up the sighting made by Victor Horatius in the Linyanti Concession recently.

Russel Crossey saw a single Ross's Turaco in the same vicinity shortly after Victor (possibly the same bird), and this prompted Dave Luck to keep a sharp look out for it when he was there during August. Whether it was Dave's skill or just luck that he saw one at Boscia Lagoon not far from the previous sightings is immaterial: this is now the third reputable guide reporting the species from the same place, and a proper submission has been made to the BirdLife Botswana Records Sub-committee.

Although the official verdict is not yet out, word has spread among the birding fraternity and the information has caused quite a stir. Rumours started that this is the first record for the Southern African Sub-region, that of Tim Liversedge in 1974 having been "thrown out" because it was subsequently proved to be a joke and not a genuine record. I contacted Tim Liversedge for his comment - he just laughed and said that it was after much deliberation that he 'collected' the bird he saw, and sent it to MPS Irwin at the Bulawayo Museum, because he knew that no-one would believe him - there can be no more concrete evidence than the specimen in a museum! However, he was thrilled that the bird had been seen again, not least because now no-one could accuse him of having shot the first and last one!

At the time of the first record, it was predicted that there would be other sightings and that this was not just an isolated bird. Tim believes that Ross's Turaco, being a forest bird, is likely to move down the riparian woodland of the Kwando River during wet times. However the long intervening period between sightings shows that it is unlikely that the species is resident or even a frequent visitor to Botswana. The current high flood levels in the Kwando-Linyanti system are quite comparable with those of the 1970s, so the wetter conditions may result in other individuals coming into the region. It should be looked out for in northern Botswana, the Caprivi Strip and western Zimbabwe.

So, well done to Vic Horatius, Russel Crossey and Dave Luck for re-confirming the presence of this species in the region. Many keen birders, like myself and Dave Luck, have seen Ross's Turaco in Uganda, and it is an awesome bird. It is however very difficult to photograph, so we are still encouraging photographers to keep an eye out for these magnificent birds, and to send their images to BirdLife Botswana.

Vultures curb spread of disease

With the recent news headlines in northern Botswana focused on a possible anthrax outbreak, I become nervous lest some misguided person try to implicate vultures in spreading the bacteria. This has happened in the past, so it is worth reading the views of anthrax expert, Peter Turnbull, below:

Nature's clean-up squad in action (Photo: J Bestelink)

"At the time of death in an animal dying of anthrax, the blood and body fluids are loaded with anthrax bacteria: there are more bacteria than red blood corpuscles in the blood. On exposure to the oxygen of the air, these start to form spores - the hardy forms of the anthrax agent which can survive for decades in the soil where blood and body fluids from such an animal have spilled. Vultures, in demolishing the dead animal before much of this sporulation can occur, contribute to reducing the environmental contamination left by the carcase. In theory, the faster the carcase is consumed, the less the chance of sporulation and residual contamination. And, at least to a point, more vultures = faster consumption. Faster consumption aldo reduces the chance of spread of the disease by flies.

The vultures do, of course, get the infected blood and gore on their beaks and feathers and they will go to nearby water to wash this off. However, unsporulated bacteria are fragile and die off quickly in water (they are also quickly killed within the vulture's digestive system). So, although the water may derive some anthrax spore contamination from bacteria that have started to sporulate, this will be low - bacteriological testing has proved how difficult it is to detect anthrax spores in such bodies of water. By the time the birds are airborne again, numbers of spores on their feet, beaks, feathers and in their guts is back to zero or very low.

Vultures are very clean, and bathe regularly (Photo: P Hancock)

Contrary to what you might expect, knowing the infamy of anthrax, it is not a highly infectious disease. That is to say, an animal generally needs to ingest or inhale a large dose of spores to become infected. So, small numbers of residual anthrax organisms on the feet, beaks, feathers or in the guts of vultures constitute essentially zero risk or threat to animals elsewhere. There is again scientific evidence for this.

The decline in the numbers of vultures around is probably already apparent to you where you live and you are probably well aware of the particularly catastrophic decline over the past two decades on the Indian sub-continent largely from inadvertent diclofenac poisoning, but also from other human-made causes also at play in Africa - habitat destruction, deliberate poisoning, capture for traditional medicines, drowning in reservoirs, powerline collisions and electrocution and so on. The apparent consequences of this population crash are not nice. Substantial increases in numbers of rats and of feral dogs have been attributed to the decline in vultures and with that, vastly increased numbers of cases of at least rabies and distemper. In addition to the health issues, there have been consequent costs to the economy estimated at billions of dollars. One British Medical Journal article has even suggested a link (albeit unproven) between absence of vultures and a rise in human anthrax cases.

In Africa, loss of our vulture populations can be expected to lead to similar disturbances in other scavenger popul;ations, again with possible concomitant increases in rabies, distemper and plague. Botulism from decaying carcasses is another strong possibility.

It also needs to be remembered that vultures rely on other vultures to detect carcasses; when vulture populations decline, their ability to find carcasses deteriorates at an accelerating rate.

So, as well as helping to reduce residual contamination at the site of an anthrax carcass and minimizing fly-borne transmission, thereby playing an important role in curtailing the spread of anthrax, the importance of vultures to the overall health of the ecosystem should not be underestimated.

Also not to be forgotten is that circling vultures have always been, and continue to be, the best signal to game managers and farmers that deaths have occurred within their boundaries, enabling prompt action as needed.

In summary, persecuting vultures as an approach to anthrax control is folly, and in the long run, can be expected to increase problems associated with both anthrax and other diseases."

Peter Turnbull, with thanks to Orr Spiegel, Hebrew University of Jerusalem, Steve Bellan, University of California, Berkeley, and Kerri Wolter, VulPro South Africa, for most helpful comments.

With water comes life . . .

It is a well-known fact that the 2011 Okavango flood is one of the highest on record - water has surged past Maun (especially when the bridge over the Xotego River broke!), down the Nhabe towards Lake Ngami, and down the Boteti for over 250 kilometres to Lake Xau. While this has had its downside (such as the escape of numerous crocodiles from flooded enclosures at the Sitatunga Crocodile farm!), the news for birds has been overwhelmingly good. BirdLife Botswana has long realised that Lake Xau is likely to become a birding hotspot as it fills, although this did not really materialise last year when the water barely reached the lake-bed. We have been monitoring the situation closely, and BirdLife members Pat Nurse and Ray and Val Lovett recently conducted a partial count of the now extensive lake.Marabou Storks are among the first birds to find new areas such as Lake Xau

Highlights of their count are as follows:
Little Grebe 6
Grey Heron 12
Goliath Heron 1
Great Egret 2
Yellow-billed Egret 9
Little Egret 20
Cattle Egret 20
Squacco Heron 3
Marabou Stork 15
Glossy Ibis 163
White-faced Duck 1
Red-billed Teal 65
Southern Pochard 19
Spur-winged Goose 2
Wood Sandpiper 2
Black Crake 1
Common Moorhen 2
African Jacana 1
Kittlitz's Plover 3
Crowned Lapwing 30
Blacksmith Lapwing 76
Wattled Lapwing 1
Common Greenshank 6
Black-winged Stilt 11
Collared Pratincole 18

The lake is still filling, and it is early days yet. The lake-bed is very uneven with ridges and channels so the water is spreading out into a system of fingers of water. Migrant waders are only just now returning, so it is going to be very interesting to keep an eye on this exciting new birding destination.

Dinner with Phil Liggett

Phil is the internationally acclaimed commentator of the annual Tour de France cycle race. He has agreed to address us on his other two loves, namely birding and cycling. His first love is obviously his dear wife who will accompany him. He is an outstanding raconteur and we can guarantee an exceptional evening. Please join us at the GICC on Friday night 28th October at 19:30. Better still, please consider reserving a table for ten. Tickets cost P375.00 per person, which is almost a giveaway considering the menu on offer. Tickets can be obtained from our Gaborone office at Kgale Siding, or phone 3190540 and ask for Dikabelo. In all seriousness, we are open to receive bids from those who would like to have Phil and his wife sit at their table for the evening. Please help us advertise this dinner among all birders and the cycling fraternity. The diner will also be of interest to those who like to travel. Come and join us for an evening of fun. Contact Harold Hester on 3190541 for more information.