FLUCTUATIONS IN A PARTRIDGE POPULATION 



127 



very sunny, while in Norfolk conditions were less favourable. In 1954 the 

 June and July weather in both Norfolk and Hampshire was wet and sunless, 

 while in 1959 the weather was more sunny in Norfolk than in Hampshire 

 (particularly during June). Table V shows how these weather conditions 

 have affected the recruitment rates on two comparable estates in Hampshire 

 and Norfolk. The failure of the chicks to survive may be due to the direct 

 effect of low temperatures and wet herbage, resulting in 'chilling' (as has 

 been, shown to occur in Capercailzie in Sweden (Hoglund, 1955)), or to 

 starvation resulting from a lack of, or the low availabihty of, the necessary 



Table V. The effect of weather on recruitment rates 



A and B are comparable estates in Hampshire and Norfolk respectively. 

 * Wet days = days on which 0-2 mm or more of rain fell in June and July, 



insect food. While the partridge chick appears to be most vulnerable to bad 

 weather during the first three weeks of life (i.e. when it is mainly insect 

 feeding and still down-covered), due to the normal spread of the hatching 

 period the weather is of critical importance during most of June and July. 



Changes in the relative acreages of grass-ley and corn-land have also 

 affected partridge survival rates in the different years. While the grass-leys 

 are necessary to maintain maximum pair density in March, they are also 

 the cause of heavy chick loss during June when the grass crop is being 

 harvested. Not only are large numbers of chicks killed by the hay-making 

 activities, but those that survive are left in an uncongenial habitat (cut grass 

 field) at a very vulnerable period of their lives. The effect of varying crop 

 distribution is most clearly seen when, in a period of a few years, a pre- 

 dominantly corn-producing area is grassed down. Under these conditions, 

 even if the weather is favourable, survival rates are relatively low. When 

 the weather, too, is adverse, then very few young can survive. In 1958 when 

 weather conditions in June and July were relatively unfavourable, young/old 

 ratios of 1-9/1 -o were recorded on a predominantly corn-producing beat 

 (corn to grass = 312/100), while on a beat where the corn/grass acreage was 

 84/100, survival rates were only o*3/i'0. From 1949 the acreage under 



