General Shrike Biology Symposium: Biology of Shrikes Convener: Reuven Yosef 287 Effects of Changes in Human Land-use on Great Grey Shrikes Reuven Yosef International Birding Center Eilat, P. O. Box 7741 Eilat 88106, Israel. The current biodiversity crisis and escalation of extinction rates of the world's biota have led to stopgap efforts to save the last, surviving individuals of endangered species. Groups of organisms that have not yet reached the verge of extinction, nor become endangered, but that nevertheless display population declines, are still largely ignored. A common theme of the In- ternational Shrike Symposium, held in January 1993, was that most long-term studies of shrikes have documented major population declines, mostly in the late 20th century, in previously robust populations. Previously inaccessible data from East European countries show declining trends in populations, and that use of pesticides and increasing farming intensi- ty are the major contributing factors. Further evidence of declining trends comes from the "Operation Baltic" research program that monitors autumn migrants in Poland. There a severe decline in Great Grey Shrike Lanius excubitor numbers occurred at the end of the 1970s and in the 1980s when the average number of the species trapped was only 4 % that of the 1960s. Two exceptions to the general patterns of decline were reported from Belorussia and Poland. An increase in the population in Belorussia was observed, ironically in areas that were evacuated by humans following the nuclear accident at Chernobyl in 1988, and shrikes have been observed breeding in abandoned villages and agricultural areas. The other exception was reported from rural Poland. It was suggested that this is a result of less agricultural mechaniza- tion and pesticide use there, compared to neighboring regions. It is believed that modern agricultural practices lead to a reduction in large invertebrates, adversely affecting shrike populations in western Europe. The following are probably the most important of causes of declines in European Great Grey Shrike populations: A) Human land-use changes. B) Diminished diversity and quantity of available prey caused by habitat alterations and by ex- cessive use of fertilizers and pesticides. C) Climatic variation becomes increasingly important with the decrease of prey populations. D) Decreased environmental heterogenity reduces availability of optimal nest sites and shelters and increases scarcity of hunting perches; the lat- ter results in a greater energetic requirement for prey captur~