Environmental Engineering Reference
In-Depth Information
80
70
60
50
40
30
20
10
0
Figure 3.8
Percent mortality of palaearctic birds
The highest mortality amongst palaearctic migrants was noted in the black-tailed godwit: 215 of
500 observed individuals succumbed to poisoning. Wood sandpipers were the second most poisoned
palaearctic bird, with 126 of 467 individuals poisoned. The green sandpiper (
Tringa ochropus
),
marsh sandpiper (
Tringa stagnatilis
), common greenshank (
Tringa nebularia
), ruff (
Philomachus
pugnax
) and ringed plover (
Charadrius hiaticula tundrae
) were poisoned in comparatively smaller
numbers (less than 100 individuals) but they are also less abundant. From these results we concluded
that the number of palaearctic individuals killed by poisoning is directly proportional to the fl ock or
group size of the species.
As shown in Figure 3.8, mortality rate expressing percentage losses per species was highest in
marsh sandpipers followed closely by the common snipe (
Gallinago gallinago
), black-tailed godwit,
ringed plover, yellow wagtail (
Motacilla fl ava
) and fi nally the wood sandpiper. Percentage mortality
in this case was highest in less common (or abundant) species. The values presented in Table 3.7
show that the wood sandpiper was the second most killed species, but suffered the lowest mortality
rate. In contrast, the marsh sandpiper endured 'negligible' total mortality but suffered the highest
mortality rate (Table 3.7). This indicates that the less common species were more adversely affected.
Table 3.8 summarises mortality against total numbers observed for resident and intra-African
migrant bird species. Of the resident and intra-African migrants, the African openbill was by far the
most poison-killed species. Two thousand two hundred and sixty one (2 261) of 5 848 individuals
exposed to poisoning died. In fact the openbill suffered the highest mortality from poisoning overall,
accounting for 26% of all mortality observed at the site. Mixed species of doves and pigeons were
the second most poisoned bird family (391 of 1 570 poisoned). These species were lumped together
because they associated closely and distinguishing one from another was diffi cult. The Abdim's
stork was the third most poisoned species while the rest followed regressively with mortalities of
less than ten individuals each. As was the case for the palaearctic migrants, the most abundant intra-
African migrant species were also the most poisoned.
The African openbill was poisoned using a 'unique' baiting technique that employed live decoys
whose beaks were fastened with string or a rubber band (to prevent them from eating the poison laced
bait (
Pila
sp. snails)) and whose feet were tied to restrict movement. The poachers went around disturb-
ing nearby fl ocks of openbills which then only had the option of settling around the decoys and baits
otherwise the disturbance went on and on. This practice increased the incidence of openbill poisoning.
In Bunyala (and undoubtedly elsewhere) decoy birds are captured and kept to lure other birds of
the same species (see Figure 3.9). The presence of the decoy suggests to the unsettled birds that there
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