Thursday, October 28, 2010

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.

Friday, October 15, 2010

If at first you don't succeed ...

… try, try again!

With the water of Sua Pan evaporating fast, Dr Graham McCulloch’s chances of capturing several Lesser Flamingos to fit them with satellite tracking devices were fading too (see previous post dated 21/06/2010). However, the Independence Day long-weekend provided near ideal conditions for a last chance at flamingo capture – the remaining water was restricted to small pools in the Nata River, and four adult flamingos were present together with a number of immatures and juveniles. The challenge was to catch these adult birds before they left the area, so that data would become immediately available on their regional movements, but the window of opportunity to catch them was small ….

One of the few pools of water remaining in northern Sua Pan (Photo: P Hancock)

Long trap-lines were set in the remaining pools with the help of Nicky Bousfield, a qualified bird ringer with years of experience handling and caring for birds of all shapes and sizes. Success was immediate with one adult and several young birds being caught on the first day; the adult was fitted with a PTT backpack and ringed and then released. It remained in the area with the other flamingos, thereby enabling us to see how it reacted to its new hardware; the device fitted comfortably and apart from scrutinizing it closely and preening the feathers around it, the bird seemed quite unconcerned by its presence.

#50 with backpack slightly visible and its antenna protruding backwards (Photo: P Hancock)

The young birds were not targeted for the exercise as they are too small to comfortably carry the satellite transmitter; their capture was purely incidental, but nevertheless they were ringed before being released in the hope that they may still provide information on longevity and sources of mortality.

A juvenile Lesser Flamingo sports identifying rings (Photo: P Hancock)

After the initial success, the remainder of the flamingo group – particularly the adults – was wary, so the team (supplemented by a few local community members) tried a different capture technique. A long mist net, borrowed previously from researcher Tim Osborne in Namibia, was submerged in one of the pools with the aim of triggering it manually as the flamingos walked over it.

The net being quietly set at one of the remaining pools (Photo: P Hancock)

This however was not successful, and with time running out, we reverted to our original method of using the long traplines. Several more immatures and juveniles were caught, but unfortunately no adults.

The way the project stands at present, there are three adult Lesser Flamingos in total with satellite transmitters, and another three spare transmitters that will have to be fitted to flamingos next season. Some information is already coming in from the project, so watch this space for regular updates.