US EPA

2204270 

Journal Article 

Pesticides and the Rook Corvus frugilegus in Scania, Sweden between 1955 and 1970 

Malmberg, T 

1974 

1 

Oikos
ISSN: 0030-1299
EISSN: 1600-0706 

HEEP/74/10518 

24 

3 

377-387 

HEEP COPYRIGHT: BIOL ABS. Rook populations are usually found to be very stable, and only few cases of large fluctuations are known. The breeding numbers of the species in Scania, Sweden, based on nest censuses, decreased from approximately 11,100 in 1955-1957 to 5100 in 1964-1968 and 8300 nests in 1969. Chlorinated hydrocarbon analyses of 26 Rock specimens from 1965-1970 showed mostly low levels of lindane, dieldrin, PCB (polychlorinated biphenyls), DDT and its metabolites. Analyses of total mercury were made on 75 Rook specimens from 1887-1971 and showed high or very high levels in the period 1950-1966 and moderate or low before and after these years. This period corresponds to the time when alkyl mercury seed dressings were commonly used in Sweden, after which these chemicals were banned. The high mortality and pronounced population reduction found in Scania were not paralleled in Danish Rooks, which were not exposed to the same pesticides. The temporary decrease of the Swedish Rook population studied was probably by alkyl mercury, perhaps in combination with aldrin poisoning.