of indigenous birds. They suggested that these results reflected competition, mainly
for food.
The Japanese white-eye (Zosterops japonicus) became the most abundant land bird
in Hawaiian islands after being introduced to Oahu in 1929 and to the island of Hawaii
in 1937. It feeds on a wide variety of foods and is fairly catholic in its choice of habi-
tats. It shares the range of at least three native species with similar food habits. Although
causality cannot be demonstrated conclusively, particularly in retrospect, there is strong
inference that the Japanese white-eye was implicated in the decline of the Hawaii
creeper (Oreomystis mana) in the 1940s.Rachel Carson’s (1962) classic book Silent Springraised the alarm about the effects
on birds of DDT (dichlorodiphenyltrichloroethane) and other organochlorines. In par-
ticular, these chemicals caused eggshells to become abnormally thin and fragile (Ratcliffe
1970; Cooke 1973). Because these chemicals accumulated in the food chain it was
the species at the top of the food chain, the raptors, which suffered the effects most.
Nesting success declined precipitously and so raptor populations collapsed (Hickey
and Anderson 1968; Cade et al. 1971). The chemical industry initially denied these
unwelcome side effects but by the 1970s the evidence was overwhelming and DDT
was banned in most countries. As a result, we have seen a rebound in the popula-
tions of several species of raptors, such as peregrine falcon (Falco peregrinus) in North
America and common buzzard (Buteo buteo) in Europe.
The issue of contaminants remains with new pesticides and herbicides. For exam-
ple, the so-called second generation of anticoagulants, such as brodifacoum, are both
highly toxic to birds and mammals and persistent, so that they increase the risk of
secondary poisoning of non-target species (Eason et al. 2002). Monofluoracetate (1080)
is commonly used in baits to kill mammal pests in Australia and New Zealand, but
there are impacts on non-target birds and mammals (Spurr 1994, 2000).
We give two examples.The Indian vultures
In Pakistan and India cattle and water buffalo (Bubalus bubalus) are treated with a
non-steroidal anti-inflammatory drug, diclofenac, to counter the effects of trauma and
disease. When vultures feed on carcasses of these domestic animals they die from
the toxic effects of diclofenac, to which they appear particularly sensitive. Three spe-
cies are affected, the white-backed vulture (Gyps bengalensis), the long-billed vulture
(G.indicus), and the slender-billed vulture (G.tenuirostris). The evidence suggests
renal failure in the birds.
Between 1990 and 2003 vulture populations have declined from tens of thousands
to a level where captive breeding is now required. At least 95% of the populations
have died in 10 years. Research is now required to identify alternative drugs that are
safe for vultures but remain effective for livestock (Green et al. 2004).The California condor
The story of the California condor (Gymnogyps californianus) reveals a little about
the realities of conservation: the gaps between theory and practice and the overwhelming
need to determine, not assume, the causes of the decline.
The California condor was probably abundant and widely distributed in southern
North America during the Pleistocene. Later it figured in the ceremonies and mythsCONSERVATION IN PRACTICE 319
18.2.8The effect of
environmental
contaminants