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!

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.

Waterbirds arrive at Lake Xau

The arrival of waterbirds at Lake Xau since it started filling has been less than spectacular! However, there is no doubt that the lake is Botswana 13th Important Bird Area (IBA) in the making.

The extent of flooding of the lake in 2010 (Photo: P Hancock)

By mid-November, the Boteti floodwaters, over 250 kilometres south of Maun and still moving, trickled out onto the long dry bed of Lake Xau. They extended about eight kilometres into the huge sump – the river’s natural terminus – and then spread out laterally and formed a shallow, open mudflat before stopping flowing. This waterbody has been colonized by a few dozen Red-billed Teal and Southern Pochard, and lesser numbers of Little and Cattle egrets and Grey Herons.

A Grey Heron drops in for a bit of fishing (Photo: P Hancock)

Wader numbers and diversity are still low, with a few Ruffs, Common Greenshanks, Wood Sandpipers and a single Black-winged Stilt being present. Other species seen at this time include Blacksmith Lapwing, Glossy Ibis and two Yellow-billed Storks.

The shallow mudflats are suitable for waders, including the Common Greenshank (Photo: P Hancock)

There have been quite good rains in the general area of Lake Xau, so that there is standing water on small pans and mudflats between Rakops and Mopipi, and this may have diluted the number of birds. However, the area is still worth a visit as it is likely to attract large numbers of waders still. The habitat is ideal for the incoming Palaearctic migrants and species such as Black-winged (and Collared) Pratincole and Caspian Plovers could reach good numbers. Birders visiting the area are requested to keep good records, and to send this information to Pete Hancock at birdlifemaun@gmail.com.

Water reaches Lake Xau

Earlier this year, it was predicted that the Okavango floodwaters would reach Lake Xau at the end of the Boteti River. By September, the water had already flowed under the bridge near Mopipi, and it finally reached Lake Xau on 16th October. Pete Hancock was there to witness this momentous occasion.

The Boteti River near Mopipi during September 2009 (top) and 2010 (bottom) (Photos: P Hancock)

In an area where ambient temperatures soar above 40 degrees, and the grass is so desiccated and dry that it seems ready to spontaneously burst into flames, the arrival of fresh, flowing water is nothing short of miraculous. Shimmering mirages turn to real water as I advance into the long dry lake-bed of Lake Xau, to witness the return of the Okavango floodwaters to this distal terminus for the first time in 40 years.

A huge twister lifts the fine dust from the dry part of the lake-bed (Photo: P Hancock)

A towering dust-devil sweeping across the dry plain suddenly collapses as it reaches the water’s edge. As the flood waters slowly advance, they fill small holes and burrows and flush insects and rodents and other small creatures, but as yet there are no waterbirds present to capitalize on this bounty. Only a few wily Pied Crows wade in the shallows enjoying this unexpected bounty.

A Pied Crow catches a spider flushed by the water (Photo: P Hancock)

This is quite different from the first recent flooding of Lake Ngami in 2004, where Marabou Storks, Blacksmith Lapwings and other waterbirds followed the advancing floodwaters to the lake, making an ‘instant’ birding spectacle.

However, it is expected that there will be some similarities between the rebirth of the two lakes. Currently, Lake Xau is heavily overgrazed, so there are extensive, open, shallowly inundated mudflats which will soon attract the incoming summer migrant waders. Lake Xau, like Lake Ngami, is a nutrient sink, and all the accumulated cattle dung, once dissolved, will fuel food chains for aquatic invertebrates, fish, amphibians and ultimately birds. BirdLife Botswana is committed to monitoring these changes in the hope that Lake Xau will substantially boost local and migrant bird populations.

Birds of Lake Xau - 1964

Reading Smithers (1964) Checklist of birds of the Bechuanaland Protectorate and Caprivi Strip gives one an insight into conditions in the country during the middle of the last century. Particularly fascinating is his account of birds at Lake Dow (Xau) – the frontispiece of the book depicts a Gull-billed Tern foraging over Lake Xau, a Category A rarity (seen less than 10 times in recent years). Here are some of the waterbirds seen at the lake during the late fifties and early sixties, and which may be seen there again when the lake floods in future:

Pink-backed Pelican – January 1959 many were seen in immature plumage
African Darter
Black-crowned Night-Heron
Squacco Heron
Black Heron
Great Egret
Yellow-billed Egret
Little Egret
Grey Heron
Goliath Heron – individuals in immature plumage seen in January
Saddle-billed Stork
Marabou Stork – seen in flocks of 50 at a time
African Sacred Ibis
Glossy Ibis
African Spoonbill
Lesser Flamingo – no nests of this species found at the Lake
Fulvous Duck – occurs in large numbers, January 1959, flocks of 200 at a time
Egyptian Goose
Spur-winged Goose
Comb Duck
Cape Teal – a few seen on Inkokwane Pan near Lake Dow
Red-billed Teal – in huge flocks
Hottentot Teal – common, occurring in flocks of upwards of 50
Southern Pochard
African Fish-Eagle
Purple Swamphen
Red-knobbed Coot
Wattled Crane
Grey Crowned Crane
African Jacana
Water Thick-knee
Kittlitz’s Plover
White-fronted Plover
Chestnut-banded Plover – an immature, hardly able to fly, taken on 18 January
Caspian Plover
Greater Painted-snipe
Black-winged Pratincole
Grey-headed Gull
African Skimmer
Gull-billed Tern – recorded in January 1959
Whiskered Tern – in breeding plumage December 1962 and January 1963
Kurrichane Buttonquail – breeding 15 January 1959, c/4 fresh
Yellow Wagtail – particularly common at cattle kraals
Sedge Warbler
Lesser Swamp-Warbler
Southern Red Bishop – in breeding plumage
Yellow-crowned Bishop – in full breeding plumage in January
African Quailfinch

This variety of birds needs a diversity of habitats, including open water, reeds and sedges, aquatic waterweeds, and short grasslands near water, all of which would have been found around the lake fifty years ago. Difficult to imagine, isn’t it?

Will Lake Xau fill?

The flow of the Okavango’s waters down the Boteti River this year have been nothing short of spectacular, with the front of the flood approaching Rakops (over 200km from Maun) at present.

While predicting the future is fraught with all sorts of risks, it seems likely that it is a question of when, not if, the water will once again reach Lake Xau, which is the terminus for the Boteti. This assumes of course that Debswana will remove the structures they built previously to channel water into the Mopipi Dam, but given their recent track record (where they removed the bund blocking the Nhabe Channel leading to Lake Ngami), this looks likely. During wetter decades, Lake Xau was a substantial waterbody, and supported spectacular birdlife; the front cover of Smither’s 1964 Checklist of Birds of the Bechuanaland Protectorate depicts a Gull-billed Tern flighting over Lake Xau, and this is the type of rarity that may well turn up at the Lake again when it floods.

Since the Lake has been dry for several decades now, the lakebed has grassed over, and it is currently not unlike Lake Ngami was before the recent floods. Lake Xau is also similar to Lake Ngami in being a nutrient sink with rich soils that, when flooded, will result in nutrient-rich, eutrophic waters in an otherwise dry area. Lake Xau will almost certainly attract and support a diverse suite of waterbirds – in large numbers – when it finally floods. However, it will not be a destination for ‘armchair’ birders – the location is quite remote, there are no facilities in the area, and access will be difficult. For serious birdwatchers, though, it will be worth watching this Blog for updates on the status of the area.
View of the dry bed of Lake Xau (in distance) from Kedia Hill