250 A. Diaz Agriculture, Ecosystems and Environment 78 2000 249–259
and Davy, 1984; Foran, 1986. Rabbits have a range of direct and indirect effects on plant community
composition. Direct effects can be caused by factors such as herbivory, scrapes, middens, trampling and
seed dispersal in faeces. All of these factors may also produce indirect effects such as changes in the
activity of other herbivores or changes in plant–plant competitive interactions. The effects of rabbit activity
occur at different scales — for example, scrapes and middens can result in dramatic but localised impacts
on vegetation composition Thomas, 1963; Dixon and Hambler, 1993, while the effects of herbivory may
be more diffuse and so affect a greater proportion of the vegetation at a locality. Recent investigations into
the influence of rabbits on vegetation have sought to distinguish the impact of the various effects Crawley,
1990; Prins and Nell, 1990; Hambler et al., 1995. Achieving this is difficult as many of the effects may
be impossible to separate experimentally Hambler et al., 1995 or may significantly interact, so impeding
interpretation. Direct measurement of the extent of herbivory on different plant species is very difficult
to obtain for free-living rabbits with open access to feeding areas. An index of relative herbivory can
be obtained by scoring the proportion of stems and leaves that have been nibbled Zeevalking and Fresco,
1977, but this gives no information on the amount of each stem or leaf that has been consumed unless
fenced controls are used. However, the use of fenced controls has two important weaknesses; i the cages
may cause micro-environmental changes Williams, 1951; Watt, 1957, 1960, 1962, and ii they may not
produce an accurate measure of herbivory as the rel- ative growth of different species may not be the same
under grazed and ungrazed conditions. Alternative techniques such as the analysis of rabbit stomach con-
tents Myers and Bults, 1977 or rabbit faeces e.g., Williams et al., 1974; Bhadresa, 1977 can establish
the proportion of different species consumed but not where they were consumed. Direct observation of
grazing can establish where species were consumed but not the proportion, unless combined with an anal-
ysis of gut contents immediately after the feeding event. Such data would be difficult to obtain for wild
rabbits in field conditions.
This study examines the potential for a non-invasive and non-destructive approach to estimating relative
herbivory by wild rabbits in the field. It investigates the relative palatability of a range of grasses and
forbs to wild rabbits and then examines the extent to which such data can be used to predict the difference
in abundance cover of these species in grazed and ungrazed swards. Included is an examination of
whether relative palatabilities are consistent when tested against a range of vegetation types.
2. Methods
2.1. Assessment of relative plant palatability In the early summer of 1996, seeds of plant species
commonly found on set-aside grassland in NE Scot- land were germinated on filter paper in Petri dishes
and then transplanted into top soil from ex-arable land. Two hundred plants of each of 22 species were grown
in seed trays in a glasshouse for 2 weeks. Each plant was then potted into an individual 100 ml pot, filled
with top soil, and moved outside to a gravel bed. Plants were kept well watered and grown to a simi-
lar above-ground size ca. 0.3 g dry weight. This took between 5 and 7 weeks, depending on the species. No
plants reached flowering stage during this time.
The palatability of these plants to rabbits was com- pared at 10 plots. These measured 5 m × 3 m and were
situated on homogeneous stands of self-sown vegeta- tion Table 1. Each plot was grazed by rabbits from
Table 1 Location and description of the plots into which grassland plant
species were inserted to test their palatability to wild rabbits Plot
Description 1
8-year old set-aside vegetation on Fintray Estate, Aberdeenshire
2 8-year old set-aside vegetation on Fintray Estate,
Aberdeenshire 3
8-year old set-aside vegetation on Fintray Estate, Aberdeenshire
4 8-year old set-aside vegetation on Fintray Estate,
Aberdeenshire 5
8-year old set-aside vegetation on Fintray Estate, Aberdeenshire
6 semi-natural acid grassland near Inverbervie, Kincardine
7 semi-natural acid grassland near Inverbervie, Kincardine
8 1-year old set-aside near Inverbervie, Kincardine
9 1-year old set-aside near Inverbervie, Kincardine
10 1-year old set-aside vegetation near Banchory, Kincardine
A. Diaz Agriculture, Ecosystems and Environment 78 2000 249–259 251
Table 2 The abundance cover of palatability-study species in the existing ‘background’ vegetation on each plot
Species Plot
1 2
3 4
5 6
7 8
9 10
Agrostis capillaris 8
30 40
12 2
Aphanes arvensis 2
10 5
1 1
Arrhenatherum elatius 4
Bellis perennis 1
3 28
15 1
Cerastium fontanum 8
5 8
1 1
2 1
2 6
Cirsium vulgare 5
1 1
2 5
1 Dactylis glomerata
4 10
Elymus repens 3
2 Festuca rubra
2 20
Geranium molle 4
1 Holcus lanatus
15 30
25 20
40 8
35 7
15 Lolium perenne
2 10
Myosotis discolor 1
1 2
1 Poa annua
5 2
12 1
70 90
80 Poa trivialis
2 10
5 Ranunculus repens
40 8
12 1
1 1
Rumex acetosa 1
1 1
2 Rumex acetosella
8 6
6 Senecio jacobaea
2 8
7 Taraxacum officinale group
2 1
2 Trifolium repens
30 50
15 10
1 1
2 Viola tricolor
1 1
1 2
18 25
a different warren. The plots chosen all had a high incidence of rabbits but varied in their floristic com-
position. This allowed a test of whether background vegetation had an impact on relative plant palatabil-
ity Table 2. Test plants were inserted into a regu- lar grid of 22 holes, cut into the turf at each of the
plots. The holes were spaced 1 m apart. This produced a grid of 24 potential holes, but as only 22 species
were available, at random, two corner spaces were ex- cluded from the grid of holes each time. A spacing of
1 m meant that test plants were placed sufficiently far apart for rabbits to chose between test plants and the
background vegetation rather than between test plants directly pers. obs..
The palatability of individual plants of each of the 22 species was tested simultaneously. At each plot, one
plant from each species was inserted into the grid of 22 holes. Plants were assigned to holes at random and left
for 24 h. At the end of this time, they were scored as either eaten if any part of the plant was taken or not
eaten. This procedure was repeated on 19 further days per plot between the second week of August 1996 and
the first week of September 1996. A count was made of the number of times out of the 20 replicate times that
each species was eaten at each plot. This was converted into a percentage palatability for each plant species at
each plot. All plots were sampled on the same day; very wet days were avoided in case heavy rain sub-
stantially reduced above-ground rabbit activity.
A check was made at each plot to see whether rab- bits were indeed responsible for the majority of the
herbivory of the test plants. Herbivory by roe deer and birds was checked for by running the above trial
with them excluded by netting hung 1 m over each plot. This was carried out for two 24 h periods before
the start of experiment and for two 24 h periods after the end of the experiment. The use of paired t tests
showed that netting plots caused no statistically sig- nificant difference in the level of herbivory and this in-
dicated that the plots were not being grazed by deer or birds. Herbivory by micevoles and by molluscs was
easily distinguished from that of rabbits as micevoles left clear tiny teeth marks and molluscs left rounded
edges and holes. Herbivory by both these groups was found to be minimal over the 24 h periods allowed for
each test run.
252 A. Diaz Agriculture, Ecosystems and Environment 78 2000 249–259
Table 3 The total number of plants of each species that were nibbled by rabbits max = 20 per plot
Species Plot
1 2
3 4
5 6
7 8
9 10
Mean ± SD Elymus rpens
19 20
20 18
17 20
19 18
19 19
18.9 ± 0.99 Arrhenatherum elatius
18 20
20 19
17 17
19 19
20 20
18.9 ± 1.20 Dactylis glomerata
18 18
20 16
20 18
18 16
20 20
18.4 ± 1.58 Taraxacum officinale group
19 19
20 18
17 16
19 18
17 17
18.0 ± 1.25 Poa trivialis
20 15
17 18
19 16
15 20
20 19
17.9 ± 2.02 Ruumex aetosella
15 14
18 15
18 17
16 19
17 18
16.7 ± 1.64 Rumex acetosa
15 16
13 17
18 20
15 18
18 15
16.5 ± 2.07 Agrostis capillaris
16 13
14 18
12 16
13 15
12 16
14.5 ± 2.01 Festuca rubra
16 17
12 15
19 10
8 14
13 10
13.4 ± 3.47 Lolium perenne
13 13
9 17
15 14
10 14
12 15
13.2 ± 2.39 Poa annua
12 10
12 13
13 13
14 11
10 14
12.2 ± 1.28 Trifolium repens
16 7
13 14
10 14
12 12
11 10
11.9 ± 2.56 Holcus lanatus
11 10
8 11
13 10
11 7
12 12
10.5 ± 1.84 Geranium molle
2 10
8 7
4 8
9 4
4 8
6.4 ± 2.67 Aphanes arvensis
7 8
4 7
4 8
5 6
6 5
6.0 ± 1.49 Viola tricolor
3 2
4 6
5 5
3 5
4 2
3.9 ± 1.37 Ranunculus repens
2 6
2 4
6 4
3 1
4 3.2 ± 1.99
Cerastium fontanum 4
2 1
3 4
2 3
5 2
2.6 ± 1.51 Bellis perennis
2 3
2 3
4 2
4 2
4 2.6 ± 1.26
Myosotis discolor 2
1 2
1 1
2 1
1.0 ± 0.82 Senecio jacobaea
1 1
2 0.4 ± 0.70
Cirsium vulgare 2
1 1
0.4 ± 0.70
2.2. Survey of sites to determine floristic composition and incidence of rabbits
To test the extent to which estimates of relative plant species’ palatability, obtained using the above
method, could be related to the relative herbivory of species in grasslands, an examination was made of the
correlation between the incidence of rabbits and plant species’ abundance in grasslands across NE Scotland.
Fields surveyed were set-aside land that had been out of agricultural production for 8 years and had been al-
lowed to revegetate from naturally available seed and propagules. These fields were located in three sepa-
rate regions of north east Scotland: i near Dalcross, Inverness-shire, ii near Kirkton of Oyne, Aberdeen-
shire and iii Fintray Estate, Fintray, Aberdeenshire. All fields contained a mosaic of vegetation types. Most
vegetation types were dominated by grasses, but some were composed mainly of low-growing forbs. Rabbits
had formed burrows and variously-sized warrens in or around many of the fields studied.
In June 1996, a survey was carried out of the floris- tic composition and levels of rabbit incidence on sites
in these fields. Each site measured 25 m × 25 m. Thirty sites were located at Dalcross, 40 at Kirkton of Oyne,
and 40 at Fintray Estate. A total of 10 fields were sampled at Dalcross, 21 at Kirkton of Oyne and 22
at Fintray Estate. Sites were selected so as to sample all of the vegetation types found, except for vegeta-
tion types on the few marshy areas present. No site contained rabbit burrows or warrens. All sites were in
homogeneous stands of vegetation, but no stand con- tained more than one site. At each site, the total percent
cover of each vascular plant species present was es- timated by eye. Plant nomenclature follows Clapham
et al. 1987.
Rabbit incidence at each site was estimated using an index based on the number of faecal pellets de-
posited on the site in a week. The technique used was to first clear all rabbit faecal pellets from 25 2 m × 2 m
quadrats, spaced 5 m apart and positioned in a grid pattern within each 25 m × 25 m site. Pellets were also
removed from the ground immediately around each quadrat to reduce the possibility of nearby pellets
being blown or kicked into the quadrat. Occasional areas with latrines were avoided by making minor
A. Diaz Agriculture, Ecosystems and Environment 78 2000 249–259 253
Fig. 1. The range in faecal pellet counts per site in the three regions studied. Closed squares represent Fintray sites. Open circles represent Oyne sites. Closed triangles represent Dalcross sites.
adjustments to quadrat positions. The quadrats were revisited 7 days after having been cleared and a count
was made of all faecal pellets present. The differ- ences between the sites found by this method were in
agreement with those found using two other indices of rabbit incidence, night counts and the removal of
carrot bait Diaz, 1998.
3. Results
