130 T. H. BLANK AND J. S. ASH 



have occurred on an area where predators are partially controlled. Nest loss 

 due to predation has averaged 14- 6 per cent of all nests found, and has shown 

 considerable variation from 7-2 per cent in 1953 to 23-2 per cent in 1956. It 

 might be argued that high nest loss through predation would be followed 

 by a high chick loss, but by no means all the nest predators are chick predators 

 too. Trapping results have also shown considerable variation in the number 

 of predators caught, but it has been impossible to determine whether the 

 predator catch is in fact proportionate to the predator population. 



SUMMARY 

 Data are presented concerning a partridge population on a 4,000-acre area in 

 West Hampshire. 



Variations in breeding density have been less marked than the variations 

 which have occurred in the autumn population. Breeding density variations 

 have been reduced by controlled shooting (density dependent predation), 

 and emphasized by changes in crop distribution. Age (except indirectly 

 through sex-ratios) has had httle effect on breeding pair density. 



Autumn populations have shown marked fluctuations, and are primarily 

 dependent on the weather during June and July. In most years the weather 

 produces a relatively low survival rate. High survival rates occur only when 

 the weather in June and July is dry and sunny, and where the crop distribution 

 is suitable. Crop distributions that encourage a high breeding density are 

 often inimical to chick survival. 



The effects of disease, predation and the density of the breeding population 

 itself, although not accurately known, are considered to have had only minor 

 effects on the fluctuations recorded in September. 



REFERENCES 



Blank, T. H. & Ash, J. S. (1955). A population of Partridges {Perdix p. perdix imd Akctoris r. mfa) 



on a Hampshire Estate. Acta XI Congr. Int. Orn. (1954). PP- AM-7- 

 Blank, T. H. & Ash, J. S. (in press). Some aspects of clutch size in the Partridge {Perdix perdix). 



Acta. XI Congr. Int. Orn. (1958). 

 HoGLUND, N. H. (1955). Kroppstemperatur, aktivitet och foryngring hos tjadern Tetrao urogallus 



Lin. Viltrevy I (I), 1-87. 

 Lack, D. (1947). The significance of clutch size in the Partridge {Perdix perdix). J. Anim. Ecol., 



16, 19-25. 

 Mtodleton, a. D. (1936). Factors controlling the population of the Partridge {Perdix perdix) in 



Great Britain. Proc. Zool. Soc. Lond., 106, 795-8i5- 

 SnvONEN, L. (1956). The correlation between the fluctuations of partridge and European hare 



populations and the chmatic conditions of winters in South-West Finland during the last 



thirty years. Pap. Game Res. Helsingf., 17, 1-30. 



DISCUSSION 



G. C. Varley: The graphical representation you used in an attempt to 

 dentify the main causes of variation is similar to one I have used for insects. 



