09/01/2012
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Cuckoos spend Christmas in Congo

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The winter solstice has been and gone, Christmas has passed, and the New Year is upon us; and, with the BTO's satellite-tagged Cuckoos staying put in the same area around the Congo Basin throughout the period, it's tempting to think we might have located their wintering grounds. Kasper, the first Cuckoo to reach his present settled location, has remained in the same area since 23rd October; the last Cuckoo to arrive in the Congo, Martin, has been in his chosen location since about 16th December. Despite being separated by thousands of kilometres during their migration, the birds are now once again (just about) in the same country and separated by a mere 720 km (450 miles).


The location of the five Cuckoos at the start of January (Data: BTO/map: © Google Earth).

Now that the birds appear to be settled, it's possible to take a closer look at the habitat they're in and the area's climate. Four of the five Cuckoos are residing on the Téké Plateau, a grassland-covered area of Congo interspersed with humid closed-canopy forest. Climatically, it is within the wider humid closed-canopy tropical forest zone; but the sandy soils of the Téké Plateau, combined with frequent fires, mean the closed-canopy forest habitat is largely restricted to areas close to river courses. This seems to provide ideal conditions for Cuckoos; the satellite photos show how Clement is using forest patches with lots of edges in the northern part of the plateau.


December–January short-range movements by Clement (Data: BTO/map: © Google Earth).

For the three birds clustered around the northern part of the plateau in central Congo — Clement, Martin and Lyster — the weather has been sticky and wet: 80% cloud cover, 78% humidity, 24°C and with 11.2mm of rainfall on Tuesday.

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Kasper is the most southerly of the five Cuckoos, located at the southern end of the Téké Plateau 50km north of Brazzaville. He is in the start of the southern savannah, an area where the climate changes with rainfall decreasing and becoming seasonal, and the humid forests of the north give way to drier open grasslands.

At the other end of Congo, Chris — the most northerly of all five Cuckoos and, at 0.75°N, the only one in the northern hemisphere — is in an area of marshy forest that straddles the border with Democratic Republic of Congo. Unlike the mosaic patchwork of forest favoured by the other four birds, the wet forest in the north of Congo appears to be (from Google Earth satellite images) continuous canopy cover. The area is characterised by impenetrable swamps and forest that is flooded for several months of the year; it is also of interest to cryptozoologists, being the supposed home of the Loch Ness Monster-like Mokèlé-mbèmbé.

All eyes are now on what the Cuckoos will do next. It's expected that the next significant movement will be the start of their journeys back north, but when exactly these northbound movements are likely to start is still unknown; and with such a large gap between the first and last departure date from the UK last autumn, perhaps attempting to guess the timing of their spring migration would be foolhardy. As ever, the latest news from the Cuckoos can be found on each bird's blog on the BTO Cuckoo pages.

Written by: BTO