State of the Bay Report 2011-Final.pdf - Anchor Environmental

State of Saldanha Bay & Langebaan Lagoon 2011
Birds
the waders, plovers stand apart from the rest in that they have insensitive, robust bills and rely on
their large eyes for locating prey visually. Oystercatchers have similar characteristics, using their
strong bills to prise open shellfish. Most other waders have soft, highly sensitive bills and can locate
prey by touch as well as visually. Those feeding by sight tend to defend feeding territories, whereas
tactile foragers often forage in dense flocks.
Flamingos
2%
Cormorants
1%
Pelicans
0%
Herons,
egrets, ibises
1%
Gulls, terns
8%
Resident
waders
1%
Gulls, terns
15%
Herons,
egrets, ibises
7%
Resident
waders
7% Migratory
waders
30%
Waterfowl
1%
Waterfowl
0%
Summer
Migratory
waders
87%
Flamingos
37%
Winter
Pelicans
1%
Cormorants
2%
Figure 10.11. Average numerical composition of the birds on Langebaan Lagoon during summer and winter.
Waders require undisturbed sandflats in order to feed at low tide and undisturbed roosting
sites at high tide. In the 1970’s it was determined that the most important sandflats, in terms of the
density of waders they support, were in Rietbaai, in the upper section of Langebaan Lagoon, and at
the mouth, near Oesterwal. The important roosting sites were the salt marshes, particularly
between Bottelary and Geelbek (Summers 1977).
Gulls and terns are common throughout the area. Although their diversity is relatively low,
they make up for this in overall biomass, and form an important group. Both Kelp Gulls and
Hartlaub’s Gulls occur commonly in the lagoon.
Cormorants, darters and pelicans are common as a group, but are dominated by the marine
cormorants which breed on the Saldanha Bay islands. Great White Pelicans visit the bay and lagoon
to feed, but they breed beyond the area at Dassen Island. African Darters Anhinga rufa are
uncommon, and are more typical of lower salinities and habitats with emergent vegetation which is
relatively uncommon in the study area.
Waterfowl occur in fairly large numbers because of the sheer size of the study area, but they
are not as dense as they might be in freshwater wetland habitats or nearby areas such as the Berg
River floodplain.
Other birds that commonly occur on the lagoon include birds of prey such as African Fish-
Eagle Haliaeetus vocifer, Osprey Pandion haliaetus and African Marsh-Harrier Circus ranivorus, and
species such as Pied Kingfisher Ceryle rudis and Cape Wagtail Motacilla capensis.
10.3.3 Inter-annual variability in bird numbers
Irregular waterbird surveys were conducted at Langebaan Lagoon from 1934, but, due to the
large size of the lagoon, these early counts were confined to small areas. It was not until 1975 that
annual summer (January or February) and winter (June or July) surveys of the total population of
waders at high tide, when waders congregate to roost on saltmarshes and sand spits, were
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