180
a. R. POTTS AND 0. P. VICEERMAN
Tubbs, 1967). Kestrels (Falco tinnunczclus L.) occasionally take
partridge chicks (Ash, 1960; Cav6, 1968) but their breeding density
was even throughout the areas-approximately 1.8 pairs per 10 km2
(Shrubb, 1970). Most other raptors were scarce throughout the study
area and there was no suggestion that, at this density, they were a
significant hazard to wild partridges.
An analysis of the food of the barn owl (Tyto alba Scop.) and shorteared owl (Asio flammeus Pontopp.) showed that, as with the weasel,
Microtw agrestis was the preferred food (Table XX).
6. Predatoriprey relationships
It seems reasonable to assume that, other things being equal, total
losses of partridges to predators will be higher when predator densities
are greater, and higher when their normal prey is scarce. Various
methods were used to obtain indices of the densities of the most important prey species. Those species such as the hare and rabbit which can
easily be seen near dawn or dusk, were mapped during the March-April
and August partridge counts. Rabbits were abundant in area (a) until
the winter of 1969-1970 when an acute outbreak of myxomatosis
resulted in the virtual absence of this species for the next two and a half
years.
Standard mixed grids of 100 Longworth and “break-back” traps
were set for four-day periods in selected areas of rough grassland. This
work began in September 1971 and the population sizes of the small
mammals were estimated according to the methods of Hayne (1949).
Although the many ungrazed grass-covered Celtic terrace systems in
area (a) appeared to be good Microtus agrestis habitat, this species was
relatively scarce (Table XXI).
Other methods were used to meamre the relative abundance of the
predators. The locations of the predators were recorded whenever
they were seen and the distribution of crows and magpies was recorded
in June. Despite the lower densities of prey, all the indications were of
higher densities of predators in area (a) than elsewhere (Table XVIII).
Much the same situation persisted throughout 1972 when better
estimates of the abundance of Mustelidae were obtained.
In area (a) and in a closely comparable part of area B, known as (c)
(see Plate 4), ten Mark I V Fenn traps were set in tunnels on a grid from
10 June to 22 July 1972. The results, together with the standard procedure, are given in Table XXII; these show clearly the higher predatorprey ratio in area (a). Not surprisingly, perhaps, the 14 weasels had been
feeding mainly on birds and thebe included partridge chicks.
The production of each of the main game bird species was much
higher in the area, with the lower predator-prey ratio (Table XXIII).
a. R. POTTS AND 0. P. VICEERMAN
Tubbs, 1967). Kestrels (Falco tinnunczclus L.) occasionally take
partridge chicks (Ash, 1960; Cav6, 1968) but their breeding density
was even throughout the areas-approximately 1.8 pairs per 10 km2
(Shrubb, 1970). Most other raptors were scarce throughout the study
area and there was no suggestion that, at this density, they were a
significant hazard to wild partridges.
An analysis of the food of the barn owl (Tyto alba Scop.) and shorteared owl (Asio flammeus Pontopp.) showed that, as with the weasel,
Microtw agrestis was the preferred food (Table XX).
6. Predatoriprey relationships
It seems reasonable to assume that, other things being equal, total
losses of partridges to predators will be higher when predator densities
are greater, and higher when their normal prey is scarce. Various
methods were used to obtain indices of the densities of the most important prey species. Those species such as the hare and rabbit which can
easily be seen near dawn or dusk, were mapped during the March-April
and August partridge counts. Rabbits were abundant in area (a) until
the winter of 1969-1970 when an acute outbreak of myxomatosis
resulted in the virtual absence of this species for the next two and a half
years.
Standard mixed grids of 100 Longworth and “break-back” traps
were set for four-day periods in selected areas of rough grassland. This
work began in September 1971 and the population sizes of the small
mammals were estimated according to the methods of Hayne (1949).
Although the many ungrazed grass-covered Celtic terrace systems in
area (a) appeared to be good Microtus agrestis habitat, this species was
relatively scarce (Table XXI).
Other methods were used to meamre the relative abundance of the
predators. The locations of the predators were recorded whenever
they were seen and the distribution of crows and magpies was recorded
in June. Despite the lower densities of prey, all the indications were of
higher densities of predators in area (a) than elsewhere (Table XVIII).
Much the same situation persisted throughout 1972 when better
estimates of the abundance of Mustelidae were obtained.
In area (a) and in a closely comparable part of area B, known as (c)
(see Plate 4), ten Mark I V Fenn traps were set in tunnels on a grid from
10 June to 22 July 1972. The results, together with the standard procedure, are given in Table XXII; these show clearly the higher predatorprey ratio in area (a). Not surprisingly, perhaps, the 14 weasels had been
feeding mainly on birds and thebe included partridge chicks.
The production of each of the main game bird species was much
higher in the area, with the lower predator-prey ratio (Table XXIII).