PESTICIDE-RELATED EGGSHELL THINNING IN AUSTRALIAN RAPTORS

Eggshell thickness of 32 species of Australian raptors, relative to DD T use, was investigated. Nine species showed a significant reduction i n shell thickness since DDT was introduced to agriculture in 1946: Whi stling Kite Haliastur sphenurux; Brahminy Kite Haliastur indus; White- bellied Sea-Eagle Haliaeetus leucogaster; Marsh Harrier Circus aerugin osus; Collared Sparrowhawk Accipiter cirrhocephalus; Peregrine Falcon Falco peregrinus; Grey Falcon Falco hypoleucos; Australian Hobby Falco longipennis; and Southern Boobook Ninox novaeseelandiae. Average redu ctions in thickness ranged from 2% (Collared Sparrowhawk and Australia n Hobby) to 10% (Peregrine Falcon). These levels are unlikely to be ca using widespread population declines. However, several clutches from t hese species were so thin (maximum thinning ranged from 15% for the Gr ey Falcon to 45% for the Whistling Kite) that they were likely to brea k during incubation. Thus, localised breakage of eggs and reproductive failure has probably occurred. In general, bird-eating raptors and th ose living in areas of intensive agriculture were worst affected. Oste nsibly, DDT consumption declined from a peak in 1973 to none in 1989. Reduction in shell-thickness occurred as early as 1947 and was greates t throughout the 1970s and 1980s. The uncontaminated eggs of owls were thinner than those of other raptors, perhaps partly reflecting the ow ls' lower absorption of dietary calcium (bone).