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Produk-inligting
Maart 2016
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Seed
Special
The Bushveld gerbil typically occurs in open woodland, thornveld
and bushveld, generally avoiding areas with less than 250 mm mean
annual rainfall. The Highveld gerbil has a higher tolerance for arid
conditions, can occur in areas with a mean annual rainfall of less
than 250 mm, and is typically found in vegetation ranging between
grassland and open woodland. The gerbils display a wide range of
environmental tolerance. They have been recorded in the natural
vegetation types of nine of the ten biomes in South Africa, from ar-
eas with a mean annual rainfall of 105 mm to areas with a mean an-
nual rainfall of 708 mm and mean annual temperature range from
13,9°C to 22,3°C.
Gerbils are nocturnal (active at night) and entirely terrestrial (ground
living, they do not climb). They excavate extensive burrow systems
in sandy soils. All the gerbil species have seasonal feeding habits:
During the wet season they feed on seeds and herbage and modify
their diet to include insects in the dry season. They do not hoard
food, but may cover seeds with sand.
Breeding is positively correlated with higher rainfall. The Cape ger-
bil tends to breed after winter rains. The breeding of the other two
gerbil species is in the summer rainfall months between October and
March, but areas delivering adequate and quality food resources
during the whole year, enable these rodents to breed consistently.
While the species is communal, males and females do not form pro-
longed associations during the breeding season. The males have a
home range of about 0,5 ha.
A high degree of tolerance exists between gerbil mothers and off-
spring (and between siblings) leading to the formation of family
groups even under high-density conditions when the habitat may
become saturated. When conditions, such as food abundance and
quality, favour breeding and also dispersal, females are reproduc-
tively active for longer and dispersal occurs earlier. The natural en-
emies of gerbils are predators such as owls (the barn owl and grass
owl), snakes and small carnivores. In agri-ecosystems, the effective-
ness of natural predation has been diminished by the reduction of
habitat, limited breeding sites and through hunting.
Gerbil damage
The Maize Trust funded project
Ecologically based rodent pest man-
agement in maize crop fields in the summer rainfall regions in South
Africa
focused on gerbil management research in maize, but other
crops were also affected by gerbil damage, especially groundnuts.
Gerbil damage is restricted to the crop planting stage when gerbils
forage on germinating seed and newly emergent seedlings. Dam-
age was noted in maize, groundnut and soybean fields, but all grain
crops may be affected.
In the Hoopstad and Wesselsbron districts of the north-western Free
State during 2013 to 2015, both the Bushveld and Highveld gerbil
species were trapped, with the latter the dominant rodent in the crop
field, especially at the beginning of the planting season.
Both species occurred in natural vegetation adjacent to crop fields,
but in thornveld where a higher diversity of rodent species was
found, the number of gerbils were relatively low in both natural veg-
etation and adjacent crop field. The Bushveld gerbil by far dominat-
ed the gerbil species complex collected in the Ottosdal study area
in North West Province during 2014/2015, while only the Highveld
gerbil was found in the Bethal maize study area in the Mpumalanga
Highveld at planting in 2015/2016.
In the Hoopstad and Wesselsbron study area, fields of groundnuts
had a higher number of gerbil burrows throughout the season than
adjacent maize fields. Groundnuts sustained high gerbil populations
during the season, as food was available over a longer period; at
planting, during seed formation, and at harvesting.
Where excessive wastage occurred at harvesting, food was available
during the dry or fallow season (winter) to sustain large gerbil popu-
lations into the next season, affecting the follow-up crop at planting.
The low bushy growth of groundnuts also provided adequate cover
for gerbil burrows during the season, as was evident at harvesting
when rows of burrows were exposed (
Photo 2
).
Fields of soybeans of which the seed pods were carried very close
to the ground, thus too low for the mechanical harvester to collect
and resulting in excessive wastage during harvesting, also appeared
to have high number of gerbil burrows at the start of the following
season.
In crop rotation programmes, where maize planting followed
on groundnuts, and to some extend on soybeans, higher gerbil
Gerbils:
Ecologically based rodent management
1: A young Highveld gerbil.
2: Rows of gerbil burrows under groundnuts exposed
at harvesting.
3a and 3b: Wastage at harvest: Sprouting maize, an
indication of abundance of food during dry season
that sustained gerbil colonies during the dry season.
1
2
3a
3b