STUDIES ON THE CEREAL ECOSYSTEM
175
in this species, due t o predation, are cited by Wagner et al. (1965).
Variable losses averaged 50% in the ruffed grouse Bonaaa umbellw, (L.)
(Bump et al., 1947); 40% was due to predation. Annual nest losses
to predators alone were up to 45% in the rock ptarmigan Lagopus
mutus (Weeden and Theberge, 1972), up to 36% in the willow grouse
Lagopus lagopus (Myrberget, 1972) and 37% in the bobwhite quail
Colinus virginianw (L.) (Stoddard, 1932).
Post-hatching predation is very much more difficult to record and
quantify than pre-hatching predation. There is, however, a positive
correlation between pre-hatching survival of clutches (where variations
in the losses are mainly due to predation) and the chick survival rate
(Potts, 1971b), and between the numbers of predators killed per ha and
the chick survival rate (Potts, 1971a).
Some of the predators probably confine their attention to eggs or
incubating adults and others mainly prey on the chicks. Each of the
four main predator groups will therefore be considered separately.
1. Fox
Prior to the epidemic of myxomatosis in 1954 the fox preyed mainly
on rabbits. Since then they have fed largely on voles and birds including
gamebirds (Lever, 1959). More recently, as the rabbit has recovered
some of its former status, these alternative items may have become less
important.
Even so the most important cauae of mortality among hen partridges
in the breeding season is predation by the fox, and the particularly
high losses in area (a) (Table XVIII) can be attributed t o foxes. Cock
partridges are not often caught because they do not incubate and keep
well away from the nest. Foxes would encounter both parents to the
same extent after the eggs have hatched since each parent broods the
chicks at night when fox predation takes place. However, high losses of
cocks did not occur on area (a), so that post-hatching fox predation was
possibly not important. Foxes did take larger chicks from time to time
and intensive studies on the summer food of the fox are required to
measure this effect.
2. Carrion crow and magpie
We have reliable records of carrion crow and magpie taking partridge
chicks, but little to put them in perspective. Out in the open young
chicks are vulnerable and there are several reports of small chicks
being taken when they are forced to abandon cover during grass
mowing. Middleton (1936) even considered that partridges produced
more chicks in cereal-growing areas because they were comparatively
free from the attentions of these predatory birds in fields of corn.
175
in this species, due t o predation, are cited by Wagner et al. (1965).
Variable losses averaged 50% in the ruffed grouse Bonaaa umbellw, (L.)
(Bump et al., 1947); 40% was due to predation. Annual nest losses
to predators alone were up to 45% in the rock ptarmigan Lagopus
mutus (Weeden and Theberge, 1972), up to 36% in the willow grouse
Lagopus lagopus (Myrberget, 1972) and 37% in the bobwhite quail
Colinus virginianw (L.) (Stoddard, 1932).
Post-hatching predation is very much more difficult to record and
quantify than pre-hatching predation. There is, however, a positive
correlation between pre-hatching survival of clutches (where variations
in the losses are mainly due to predation) and the chick survival rate
(Potts, 1971b), and between the numbers of predators killed per ha and
the chick survival rate (Potts, 1971a).
Some of the predators probably confine their attention to eggs or
incubating adults and others mainly prey on the chicks. Each of the
four main predator groups will therefore be considered separately.
1. Fox
Prior to the epidemic of myxomatosis in 1954 the fox preyed mainly
on rabbits. Since then they have fed largely on voles and birds including
gamebirds (Lever, 1959). More recently, as the rabbit has recovered
some of its former status, these alternative items may have become less
important.
Even so the most important cauae of mortality among hen partridges
in the breeding season is predation by the fox, and the particularly
high losses in area (a) (Table XVIII) can be attributed t o foxes. Cock
partridges are not often caught because they do not incubate and keep
well away from the nest. Foxes would encounter both parents to the
same extent after the eggs have hatched since each parent broods the
chicks at night when fox predation takes place. However, high losses of
cocks did not occur on area (a), so that post-hatching fox predation was
possibly not important. Foxes did take larger chicks from time to time
and intensive studies on the summer food of the fox are required to
measure this effect.
2. Carrion crow and magpie
We have reliable records of carrion crow and magpie taking partridge
chicks, but little to put them in perspective. Out in the open young
chicks are vulnerable and there are several reports of small chicks
being taken when they are forced to abandon cover during grass
mowing. Middleton (1936) even considered that partridges produced
more chicks in cereal-growing areas because they were comparatively
free from the attentions of these predatory birds in fields of corn.