164
U. R. POTTS AND U. P. VICKERMAN
colchicus L.). The quail (Coturnix coturnix L.) was very scarce, except in
1972.
The short-term variation in the size of the grey partridge populations
and especially in their productivity is governed by the chick survival
rate (Blank and Ash, 1962; Blank et ul., 1967; Potts, 1970a, 1971a).
The variations in chick survival rate are broadly of two kinds, between
years and within years. Partridge chicks feed mainly on insects during
their first 15 days of life. The chicks are mainly to be found in cereals,
where their survival rates are higher than in other crops. Variation in
chick mortality during this period is largely due to annual fluctuations
in their food supply, except that adverse summer weather increases
the amount of food required.
In any one summer it is only the interregional differences in the
weather that are important in Britain (Potts, 197Ia). Intraregional, or
local, differences in chick survival are therefore not usually explicable
in terms of variations in the weather. These local differences are apparent
when one compares survival on adjacent farms or groups of farms. The
differences are due to changes in the availability of the food, and to
changes in the amount of chick predation and disease.
The biomass of insects of the kind that partridge chicks prefer
varies from one area of arable farming to another. For example ley
systems with undersowing (see p. 112) have more of these insects, such
as sawfly larvae (see p. 156). Detailed studies on the effect of the farming
system on the invertebrate fauna will be published elsewhere, and not
expanded here. Differences in predation and disease are mostly attributable to variation in the level of game management. The following
account mainly refers to predation.
B. M E T H O D S
The routine field work consisted primarily of extensive mapping,
first of the pairs in March-April, then of the chick food in June-July,
and finally of the broods and adults in August. The broods were aged
and the adults sexed. The partridge mapping was done from a Land
Rover, driven over the fields in a systematic manner, care being taken
to allow, so far as possible, for sudden changes in partridge distribution
caused by agricultural operations such as stubble burning. Each area
was counted at least twice in August and generally about 90% of the
pairs present in April were accounted for. Most of the counting was
done in the two hours from dawn, but some was also done in the
evening. It is important to note that partridges are remarkably
sedentary in the breeding season. The boundaries of the study area
U. R. POTTS AND U. P. VICKERMAN
colchicus L.). The quail (Coturnix coturnix L.) was very scarce, except in
1972.
The short-term variation in the size of the grey partridge populations
and especially in their productivity is governed by the chick survival
rate (Blank and Ash, 1962; Blank et ul., 1967; Potts, 1970a, 1971a).
The variations in chick survival rate are broadly of two kinds, between
years and within years. Partridge chicks feed mainly on insects during
their first 15 days of life. The chicks are mainly to be found in cereals,
where their survival rates are higher than in other crops. Variation in
chick mortality during this period is largely due to annual fluctuations
in their food supply, except that adverse summer weather increases
the amount of food required.
In any one summer it is only the interregional differences in the
weather that are important in Britain (Potts, 197Ia). Intraregional, or
local, differences in chick survival are therefore not usually explicable
in terms of variations in the weather. These local differences are apparent
when one compares survival on adjacent farms or groups of farms. The
differences are due to changes in the availability of the food, and to
changes in the amount of chick predation and disease.
The biomass of insects of the kind that partridge chicks prefer
varies from one area of arable farming to another. For example ley
systems with undersowing (see p. 112) have more of these insects, such
as sawfly larvae (see p. 156). Detailed studies on the effect of the farming
system on the invertebrate fauna will be published elsewhere, and not
expanded here. Differences in predation and disease are mostly attributable to variation in the level of game management. The following
account mainly refers to predation.
B. M E T H O D S
The routine field work consisted primarily of extensive mapping,
first of the pairs in March-April, then of the chick food in June-July,
and finally of the broods and adults in August. The broods were aged
and the adults sexed. The partridge mapping was done from a Land
Rover, driven over the fields in a systematic manner, care being taken
to allow, so far as possible, for sudden changes in partridge distribution
caused by agricultural operations such as stubble burning. Each area
was counted at least twice in August and generally about 90% of the
pairs present in April were accounted for. Most of the counting was
done in the two hours from dawn, but some was also done in the
evening. It is important to note that partridges are remarkably
sedentary in the breeding season. The boundaries of the study area