AUTHORS’ PAGE PROOFS: NOT FOR CIRCULATION
CSIRO PUBLISHING
Wildlife Research, 2009, 36, 1–10
www.publish.csiro.au/journals/wr
ON
LY
Selective piglet feeders improve age-related bait
specificity and uptake rate in overabundant
Eurasian wild boar populations
Cristina Ballesteros A, Ricardo Carrasco-García A, Joaquín Vicente A, Jesús Carrasco A,
Angelo Lasagna A,B, José de la Fuente A,C and Christian Gortázar A,D
A
Instituto de Investigación en Recursos Cinegéticos (IREC) (CSIC-UCLM-JCCM), Ronda de Toledo s/n,
13005 Ciudad Real, Spain.
B
Dipartimento di Produzioni Animali, Epidemiologia ed Ecologia, Facolta di Medicina Veterinaria,
Universita degli Studi di Torino, Via L. da Vinci, 44 10095 Grugliasco (TO), Italy.
C
Department of Veterinary Pathobiology, Center for Veterinary Health Sciences,
Oklahoma State University, Stillwater, OK 74078, USA.
D
Corresponding author. Email: [email protected]
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Abstract. The Eurasian wild boar (Sus scrofa) is a reservoir for pathogens that affect both humans and domestic animals.
The control of these diseases requires the development of strategies such as oral vaccination of the reservoir species. The aim
of the present study was to determine the species-specific visitation and removal rates of cereal-based baits under field
conditions in an overabundant wild boar population. Two different field trials were conducted at a hunting estate. In one trial,
baits were placed at track stations set up either randomly in the undeveloped portions of the estate or close to permanent wild
boar feeding places. In the second trial, baits were placed in feeders that were selective for use by wild boar piglets. Both trials
were conducted in summer 2007 and repeated in spring 2008. No evidence of attractant effect by the bait was found when
comparing baited against control stations. A close proximity to the feeders was associated with an increased probability of
being visited by wild boars, and piglet feeders were shown to be highly selective for young wild boars. Baits disappeared
faster in summer than in spring (i.e. ~70% consumption after the first day in selective feeders in summer, and 40% in spring).
Therefore, a combination of a summer season and selective feeders was found to be a potentially reliable bait-deployment
strategy for wild boar juveniles under Mediterranean conditions. These results support the use of selective feeders for oral
delivery of baits to 2–4-month-old wild boar piglets, which is the preferred age for vaccination. Our delivery technique
based on selective piglet feeders also has potential for other uses in the Eurasian wild boar and wild pigs under different
management conditions.
Introduction
The Eurasian wild boar (Sus scrofa) naturally inhabits vast areas
of Europe and North Africa, extending to Sri Lanka, Indonesia,
Japan, Taiwan and Korea. As a result of introductions, this species
is also found in areas far from its original distribution (Lever
1994). In most areas where the wild boar has been introduced,
hybridisation with the closely related free-roaming domestic or
feral pigs has led to cross-breeding. Introduced wild pigs are
common in the USA, Australia and New Zealand (Ruiz-Fons
et al. 2008a). The Eurasian wild boar is increasingly abundant and
extensively distributed in the Iberian peninsula (Acevedo et al.
2006) and elsewhere in Europe (Sáez-Royuela and Tellería 1986;
Schley and Roper 2003). This species is a valuable part of many
Eurasian ecosystems (Melis et al. 2006).
However, overabundant wild boar populations may cause
agricultural crop damage, traffic casualties, negative effects on
other wildlife species and the environment, and health problems
(Gortázar et al. 2006). In Europe, wild boars are a key wildlife CSIRO 2009
reservoir host for diseases affecting livestock, such as classical
swine fever (Kaden et al. 2000, 2002, 2003, 2005; Kaden and
Lange 2001) and Aujeszky’s disease (Ruiz-Fons et al. 2008a,
2008b), as well as for several zoonotic diseases including bovine
tuberculosis (bTB) (Naranjo et al. 2008). Thus, the control of wild
boars (as well as wild pigs and hybrids between these two forms)
is an increasingly common goal for wildlife managers. In Spain,
the use of lethal means other than shooting to control wild boar
damage and diseases is not allowed. Along with hunting, livetrapping and habitat management, both wild boar and feral-pig
control has been carried out with baits containing either poison
(McIlroy et al. 1989; Saunders et al. 1990; Cowled et al. 2006;
Twigg et al. 2007) or contraceptives (Linhart et al. 1997).
Hunting wild boar is a very common recreational activity in
Spain, and may contribute to population regulation. However, it is
important to assess other options to reduce the numbers of wild
boar, especially in protected and urban areas where culling is not
viable. Fertility control has been demonstrated to be an effective
10.1071/WR08127
1035-3712/09/030001
Wildlife Research
C. Ballesteros et al.
were to determine (i) the species-specific visitation and (ii) the
removal rates of cereal-based baits under field conditions in
an overabundant wild boar population. For these purposes, we
compared two different delivery systems, namely track stations
(set up either randomly or close to wild boar feeding places) and
piglet-selective feeders.
Materials and methods
Experimental design
The field trials described here were conducted at a hunting estate
in the province of Ciudad Real, Castilla–La Mancha region,
south-central Spain (38550 N, 0360 E; 600–850 m above sea
level). The 938-ha study area has a high density of wild boars,
the estimated total number of animals being ~200 (Acevedo et al.
2006), which were fed daily at nine stations (a 10 by 10 m
vegetation-cleared area were food is provided on the ground).
These stations are evenly distributed across the estate. At six of
the nine stations there also exists a selective piglet feeder nearby
(see Fig. 1). Baits consisted of piglet feed, paraffin, sucrose and
cinnamon-truffle powder attractant (Ballesteros et al. 2009).
A 0.2-mL polyethylene capsule was placed inside each bait to
introduce vaccine formulation. Because no vaccine formulation
was used in these experiments, the capsules were filled with water.
The baits had a hemispherical shape (ø3.4 1.6 cm). The field
trials were conducted in summer 2007 and repeated in spring
2008 (Table 1).
PRO
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ON
method of reducing the size and growth of wildlife populations
(Massei et al. 2008). Massei et al. (2008) tested a GnRH vaccine
in female wild boars and demonstrated that this vaccine could
suppress reproduction of the wild boar. Baits could also be used to
deliver immuno-contraceptive vaccines for managing wild boar
populations.
Baiting is also used for disease control. Control of
economically important animal diseases in domestic livestock
has reduced their impact in many developed countries (Phillips
et al. 2003). However, the total eradication of a disease is almost
impossible if a wildlife host is able to serve as a natural reservoir
of the pathogen (Gortázar et al. 2007). Hence, the eradication
of diseases shared between livestock and wildlife may require
the development of control strategies that reduce pathogen
transmission between wildlife and domestic animals (Brauer
et al. 2006; Ballesteros et al. 2007; Cross et al. 2007). Oral
vaccines for wildlife were first proposed for oral immunisation of
foxes and dogs against rabies (Baer et al. 1975; Baer 1976). Oral
vaccination against rabies was the first successful attempt to
control a disease in wildlife through vaccination (Brochier
et al. 1996). More recently, oral-bait vaccination has been
considered for controlling classical swine fever in wild boar in
Germany (Kaden et al. 2000). Vaccination of the wildlife species
has advantages over other approaches such as population
control and is far more acceptable to the public. Vaccination
may be the only option that can be applied to native animals
(Kaden et al. 2005; Cross et al. 2007). However, effective and
efficient field vaccination of wildlife species requires
development of stable and species-specific baits as delivery
vehicles for pharmaceuticals, such as oral vaccines (Brauer
et al. 2006; Ballesteros et al. 2007), and appropriate baiting
strategies (Vos et al. 2008).
The pathogen Mycobacterium bovis or bTB is one of the most
important animal-health problems in the world. This major
livestock disease is very difficult to eradicate because of the
existence of wild reservoir hosts (Gortázar et al. 2008). Wildlife
species that have been identified as reservoir hosts for bTB
include the African buffalo (Syncerus caffer) in South Africa,
the Eurasian badger (Meles meles) in Ireland and the United
Kingdom, the brushtail possum (Trichosurus vulpecula) in
New Zealand and the Eurasian wild boar in Spain, among
others (Naranjo et al. 2008). Several experiments to develop
an oral system to deliver Bacillus Calmette-Guerin (BCG) as an
immunogen for vaccination of wildlife against bTB are being
conducted (Wedlock et al. 2005; Buddle et al. 2006; Lesellier
et al. 2006). Aldwell et al. (2003a, 2003b) developed a lipidbased formulation that serves as a vehicle for oral delivery of the
BCG vaccine. Live BCG is incorporated into a lipid matrix that
can store the bacteria in a live (but non-replicating) state for
weeks at room temperature (Aldwell et al. 2003a, 2003b).
Recently, we developed baits to deliver pharmaceuticals to
the wild boar. Bait-acceptance studies in the field showed that
baits were accepted by 2–3-month-old animals, this age being
the preferred age for vaccination (because of the developed
immune system and low probability of contact with pathogens,
Naranjo et al. 2008). Orally immunised wild boar piglets
developed antibody titres to the recombinant protein used, thus
confirming that vaccine was released and that it triggered
an immune response (Ballesteros et al. 2009). Our objectives
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Track stations
In July 2007, we set up 36 track stations (18 with bait and 18
controls without bait) around the estate. Each track station
consisted in a 0.79-m2 area of bare soil in which we could
record, by examining the track impressions left in the soil, the
animal species that had visited the station. Control track
impressions of three fingers were left on each station to check
for adverse effects of wind or other casual agents. Two stations
(one station with bait inside and one control station without bait)
were set up close (<10 m) to each of the nine wild boar feeders.
Two more stations (with and without bait) were set up 80–100 m
apart. In all, 3 of the 18 track stations with bait were monitored
with digital game cameras with infrared illumination (Leaf River
Outdoor Products, Taylorsville, MS, USA). Cameras were set on
either native vegetation (e.g. tree trunks or branches) or artificial
structures (e.g. fence posts). The stations were checked every
morning to record complete or incomplete bait consumption and
note any track impressions in the soil. The relative frequency of
visits to the track station by different animal species (visits were
defined as the presence of the animal species until the bait was
removed) was evaluated according to sampling season, baiting
and proximity to feeders. We determined species-specific bait
contact and removal by track impressions in the soil and by
examination of the pictures. If the bait had not been consumed
during the first night, the station was reconstructed to erase the
track impressions and checked again the next day. Monitoring at
the control station ended when the checking of its paired bait
station was terminated. This procedure was repeated across a
4-day period. These 36 trials were repeated three times,
alternating the stations with bait and control to prevent animals
Wildlife Research
3
ON
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Selective piglet feeders improve bait specificity and uptake rate by the wild boar
Fig. 1. Selective piglet feeder to supplement free-ranging wild boar piglets. Baits placed inside
the cage are not accessible to adult wild boars.
Table 1. Summary of the field trials carried out during the study
Track stations
Track stations
Selective feeders
Selective feeders
Date
No. of stations
or feeders
No. of
baits
No. of
cameras
July 2007
March 2008
July 2007
April 2008
108
55
6
5
54
40
150
125
3
55
3
5
OF
Field trial
Selective feeders
In the summer of 2007, field trials were carried out at six selective
feeders for wild boar piglets distributed around the estate (Fig. 1).
These selective feeders were close to the adult wild boar feeders.
Each selective feeder consisted of a metal-grid cage in which
artificial feed for the young wild boars was delivered. The grid
width was sufficiently small so that only wild boars younger
than 5 months could get into the feeders, owing to their small size.
This was assessed by photo trapping, attending to the striped
coat coloration of the juveniles, which is characteristic of piglets
and disappears approximately at the age of 5 months (Sáenz de
Buruaga et al. 1991). In all, 25 baits were placed at each selective
feeder in a uniform way and mixed with the feed. Bait uptake was
evaluated by monitoring the feeders overnight with infrared
cameras (at three selective feeders) and by inspecting the place
every day to record complete or incomplete consumption of the
baits and the number of chewed or intact capsules found that were
expelled by animals.
These field trials were repeated in April 2008 to evaluate how
the seasonal variation in the use of selective feeders and the ages
of visiting wild boars affected the bait consumption. Because
most wild boars are born in late winter or early spring (Vicente
et al. 2004), it would be expected that wild boar piglets would be
too young to use the feeders at this time of the year. The same
procedures were used as described for the summer trials;
however, only five selective feeders were used for the spring
trials. Infrared cameras were placed at all five selective feeders.
PRO
from becoming accustomed to finding the bait at the same
locations. Our experimental design allowed for preventing the
effects of internal pseudo-replication regarding the use by the
same animals because the control and bait stations were
experimentally pair allocated (1 control and 1 bait station at
each location). Also, a preliminary investigation of the data
(foot prints and picture traps) indicated that the distance
between the two pairs of stations (positioned 80–100 m apart)
would be sufficient to guarantee that they would work
independently. However, the use of three sampling periods in
a relatively small area meant that the same animals could have
been sampled three times. This limited the external validity of
the results because 36 was a relatively small sample.
This experiment was repeated in March 2008 to determine
the differences in species-specific visitation rates during the
different seasons (and therefore in different age-population
structures) and in natural-forage availability (which becomes
maximum in spring in the Mediterranean habitats). During the
spring trials, 55 track stations (40 with bait and 15 controls)
were set up randomly in the undeveloped areas of the estate.
All of them were distant (>50 m) from the nine established
wild boar feeders. Infrared cameras were placed at all of the
track stations. The track stations were checked for four
consecutive days to record the presence or absence of baits,
bait condition, pictures taken and tracks present in each station
until the baits disappeared.
Statistical analyses
For each track station we recorded the animal species or the group
of species that visited during the monitoring period (from Day 0
until the bait was consumed, or Day 4 in the case where the bait
was not completely eaten). We considered that an animal or a
group of species visited the track station if characteristic
footprints were present; this was complemented with photo
trapping when available (see Table 1). The disappearance of
Wildlife Research
C. Ballesteros et al.
stations did not work; in one case, partridges used them as a dust
bath, and in another case, the wind had again erased the track
impressions. A similar field trial was conducted in March 2008.
During this trial, all stations (55) were monitored with cameras.
In only two cases did we note that the stations did not work
correctly, owing to the aforementioned wind impacts.
The relative frequency of track-station visits by different
animal species was evaluated and is shown in Table 2. Wild
boars were the species most frequently detected, most of the
times in combination with other species. Of the combinations of
wild boars and other animal species (n = 71), 79% involved birds,
49% other wild ruminants, 6% lagomorphs (wild rabbits,
Oryctolagus cuniculus, and Iberian hares, Lepus granatensis),
4% mice and 1% red foxes. In regard to combinations of nonwild boar species and other animal species (n = 10) during the
study period, 7 of 10 involved birds, six other wild ruminants,
five lagomorphs, one foxes and one mice. The presence of other
species alone (apart from ungulates and birds) was very low
(i.e. mice, foxes, rabbit and insects accounted for only five
presences in the 194 monitored stations). The frequency of
visits to baited v. control stations (i.e. bait attractiveness, this
analysis was performed for the summer trial) did not show
significant differences for any animal species or group of
animals. In addition, this was independent of the distance to
the feeder (Table 2). We found that a close proximity to the
feeders was associated with an increased probability of being
visited by wild boars (c2 = 27.71, P < 0.001, which was also
separately found for adult and young animals, c2 = 23.52,
P < 0.001, and c2 = 32.07, P < 0.001 respectively), wild
ruminants (c2 = 4.50, P = 0.03) and red-legged partridges
(c2 = 23.17, P < 0.001).
The relative frequency of bait consumption in the baited
track stations by different animal species was recorded
according to sampling season (Table 3), with the frequency
being >80% for wild boars in summer (both for close to and
distant from feeders). Once the animal found the bait, the
consumption was not statistically associated with the
proximity to a wild boar-selective feeder in any of the cases
(GLMs, P > 0.05 always).
We found seasonal differences in the relative frequency of
visits to track stations for only young wild boars and birds
other than partridges (c2 = 6.69, P < 0.01, and c2 = 7.65,
P < 0.01 respectively), which visited more frequently during
the summer period. Nonetheless, we did not find any seasonal
differences in bait consumption for any animal species.
Overall, as expected, the survival curve of baits in track stations
tested in summer differed (although marginally) with respect to
the proximity to the feeders (log-rank test, test statistic = –1.89,
P = 0.05) because the baits ran out quickly when they were in
track stations close to the established feeders. The main difference
was noted on Day 1, because ~15% of the baits were left in
stations close to the established feeders, whereas >30% still
remained in the track stations located far away from the feeders
(Fig. 2A). The bait-survival curve in track stations differed
between seasons in that baits disappeared at a more rapid rate
in summer than in spring (log-rank test, test statistic = 3.27,
P = 0.001). As indicative of this trend, ~30% of the baits were
left after the first day in summer, whereas this proportion was
>60% in spring (Fig. 2B).
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the bait (hereafter called consumption) was attributed to the
animal species or the group of species recorded the day that
the bait disappeared; also this was complemented with photo
trapping when available (see Table 1). This classification
included wild boars (adults and piglets separately), wild
ruminants, red foxes (Vulpes vulpes), lagomorphs and birds
(including red-legged partridges, Alectoris rufa).
To test the attractiveness effect of the baits, with respect to the
effect of proximity to the established wild boar feeders, on the
frequency of visits to track stations, we used generalised linear
models (GLM) for each visitor taxon. As explanatory variables,
we included the presence of bait (0 = track station with no bait/
control station; 1 = track station with bait) as well as the proximity
to wild boar feeding places (binary variable: 0 = close,
1 = distant). We also included as an explanatory term the
interaction between the presence of bait and the proximity to
feeder. The presence of the animal (recorded as a binary variable
0 = absence, 1 = presence) was considered the response variable
in different models respectively. This analysis included animals
from the summer trial only because no track stations were set up
close to feeders in the spring trial.
For the analysis of consumption in baited track stations
(binary response variable: 0 = not identified, 1 = identified
during the trial), separate GLMs were conducted for each
group of animals where the explanatory variable was the
proximity to the feeder (binary variable: 0 = close, 1 = distant).
Visitation rates (binary variable: 0 = absence, 1 = presence)
were compared between seasons (explanatory binary variable:
0 = summer, 1 = spring) by the using different GLMs for each
group of animals respectively. This analysis included only the
track stations distant from the established feeders. A seasonal
comparison was also carried out for consumption (binary
response variable) in baited track stations (binary response
variable: 0 = not identified, 1 = identified during the trial) by
using separate GLMs for each group of animals.
Bait-survival curves (temporal rates of bait removal) were
compared among different treatments (Mantel Cox log-rank test,
Bland and Altman 2004). We first compared survival curves of
baits in track stations between seasons (season as an explanatory
factor, selecting the track stations located away from the feeders)
and then as a function of the proximity to the feeders (proximity as
an explanatory factor, selecting the track stations from the
summer trial). In regard to selective feeders, bait-survival
curves were compared between seasons. Finally, we compared
the temporal rates of bait removal between track stations and
selective feeders for each season separately (i.e. summer and
spring respectively).
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Results
Track stations
In total, 108 track stations were built during the first trial (summer
2007). In the first cycle, 51 survey checks of the stations were
carried out and in only two cases the stations were not working
correctly. In both cases, this was due to the fact that the wind had
erased the control track impressions. In the second cycle, we
carried out 42 survey checks and in two cases the stations did not
work correctly (again owing to the wind). In total, 46 survey
checks were carried out during the third cycle. In two cases, the
Selective piglet feeders improve bait specificity and uptake rate by the wild boar
Wildlife Research
5
Table 2. Frequency of visits to track stations (the unit is the presence of the animal species until the bait was completely
removed) by different animal species and/or age classes (in the case of wild boars), according to sampling season (spring v.
summer), presence of bait (baited v. control) and the proximity to a wild boar selective feeder (close v. distant)
%Wild boars, % of visits that included wild boars
Spring
Close to feeders
Control Baited
Adult wild boar
Young wild boar
Adult + young wild boar
Wild boar + otherA
Bird
Other ungulate
Combination with othersB
None
Destroyed
1
0
0
1
6
0
3
2
2
Total stations
15
Only wild boar
Total wild boar
1
2
%Wild boars
13.3
A
Summer
Close to feeders
Control Baited
Total
Distant to feeders
Control Baited
4
0
1
6
9
2
6
9
0
0
2
1
24
2
0
0
0
3
0
0
3
21
2
2
1
2
1
1
1
0
11
6
4
0
9
3
3
4
2
8
5
4
5
6
0
9
7
7
71
30
12
15
28
9
40
32
32
35
40
194C
5
11
3
27
3
24
3
14
11
19
26
97
27.5
84.4
75
40
47.5
51.9
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Animal species
Of the combinations of wild boars and other animal species (n = 71) during the study period, 79% involved birds, 49% other wild
ruminants, 6% lagomorphs (wild rabbits and Iberian hares), 4% mice and 1% foxes.
B
Of the combinations of non-wild boar species and other animal species (n = 10) during the study period, 7 of 10 involved birds, 6 other
wild ruminants, 5 lagomorphs (wild rabbits and Iberian hares), 1 foxes and 1 mice.
C
Data not shown for five presences concerning other species occurring alone (mice, foxes, rabbit and insects).
Animal species
Spring
Consumption/ Success
visits
(%)
8/11
1/3
Only wild boar
Total wild boar
Non-wild boar
4/12
4/6
1/1
3/6
33.3
66.7
100.0
50.0
9
9/14
9/14
12/25
Summer
Close to feeders
Consumption/ Success
visits
(%)
72.7
33.3
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Adult wild boar
Young wild boar
Young + adult wild boar
Wild boar + other
Bird
Other ungulate
Fox
Mouse
Rabbit
Insect
Combination with others
Indeterminate
OF
Table 3. Frequency of successful visits in relation to the total frequency of visits (the unit is the presence of the animal species
until the bait was completely removed) by different animal species and/or age classes (in the case of wild boars), according to
sampling season (spring v. summer) and the proximity to a wild boar selective feeder (close v. distant)
Non-wild boar, animals or combinations of animals excluding wild boar
64.3
64.3
44.4
Field trials in selective feeders and comparison
against track stations
We determined, on the basis of the pictures taken by infrared
cameras, that only wild boars younger than 5 months (hereafter
referred to as piglets) got into the selective feeders and consumed
the baits (Sáenz de Buruaga et al. 1991). Adult wild boars
triggered the cameras and were always detected roaming
3/3
18/21
1/2
85.7
50.0
1/1
3
100.0
3/3
21/24
2/3
100.0
87.5
66.7
Distant to feeders
Consumption/ Success
visits
(%)
3/3
4/4
2/2
5/8
0/5
1/4
100
100
100
62.5
1/2
0/1
4/5
5
50
9/9
14/17
6/11
25
80
100.0
82.4
54.5
around outside the feeders (Table 4). When detected, piglets
always entered the selective feeders. The survival curves of baits
(Fig. 2C) for summer and spring, respectively, differed
significantly from each other (log-rank test, test statistic = 3.40,
P < 0.001), with the survivorship of the initial baits being
higher in spring. For example, in the three feeders from the
summer trial, all 25 baits were consumed during the first night
Cumulative proportion surviving
(E)
(B)
Time
20%
30%
40%
50%
60%
70%
80%
90%
Time
OF
100%
0%
Selective feeder
Bait station
0%
10%
20%
30%
40%
50%
0%
Time
Time
60%
70%
80%
90%
100%
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>50 m from feeders
Close to feeders
10%
(D)
(A)
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Time
Time
LY
(F)
(C)
ON
Selective feeder
Bait station
Summer
Winter
Selective feeder
Bait station
Summer
Winter
Fig. 2. Bait-survival curve where time refers to days after distribution. (A) Track stations tested in summer: the number of baits was shown to run out quickly when they were in track stations located close to the
established feeders. (B) Track stations at different seasons, baits disappeared at a higher rate in summer than in spring. (C) In selective feeders for summer and spring. (D) Differences between track stations and
selective feeders in spring. (E) Differences between delivery methods in summer.
Cumulative proportion surviving
Cumulative proportion surviving
Cumulative proportion surviving
Cumulative proportion surviving
Cumulative proportion surviving
6
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C. Ballesteros et al.
Selective piglet feeders improve bait specificity and uptake rate by the wild boar
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Table 4. Presence of animals according to selective feeders at different days at spring 2008
Adults were detected outside the feeders
Day 1
Day 2
Day 3
Day 4
Day 5
A
Adult wild boar, young
wild boar and birds
Young wild boar and birds
Adult wild boar and
young wild boar
Mice and birds
Adult wild boar, young
wild boar and birds
Young wild boar and birds
Adult wild boar, young
wild boar and birds
Adult wild boar, young
wild boar, birds and mice
–
–
–
–
–
–
–
–
–
Adult wild boar and
young wild boar
Adult wild boar and
young wild boar
B
C
D
E
ON
LY
Feeder
PRO
Discussion
The results of the experiments reported herein confirmed that baits
are well accepted by Eurasian wild boar piglets living in a typical
hunting estate in south-central Spain, thus providing new
information about the application of oral baits to wild boars in
Table 5. Day of total disappearance of the baits and the number
of capsules found at each piglet-selective feeder (summer/spring)
Total number of baits per site and season was 25; –, not performed
Selective feeder for
wild boar piglets
A
B
C
D
E
F
No. of intact
capsules
No. of chewed
capsules
0/3
0/0
0/3
0/3
0/0
0/–
9/4
7/1
6/9
12/4
8/0
8/–
Adult wild boar,
young wild boar,
birds and mice
Young wild boar
Adult wild boar,
young wild boar,
birds and mice
–
the Mediterranean Europe. The use of selective feeders in summer
resulted in a good oral-bait delivery system for wild boar piglets,
at least under the conditions present in our study area.
Although identification of animal species by track impressions
allows the determination of the animal species visiting the
sampling stations, this method requires trained observers.
Hence, accurate identification of the animal species depends
on e.g. the researcher’s ability to identify the recorded
footprints and the weather conditions (Lyra-Jorge et al. 2008).
To improve species identification, we designed experiments
where track stations were combined with camera traps. The
combined system was shown to be effective for accurate
species identification and enhanced the efficiency, compared
with using tracks alone for species identification. Regarding
the attractiveness of the bait (which included a cinnamontruffle powder attractant), the frequency of visits to baited v.
control stations (i.e. bait attractiveness) did not show statistical
differences for any animal species or group of animals. However,
evaluation of the attractiveness of the composition of the bait used
was outside the scope of the present study and future experiments
are needed to evaluate this issue.
Our results concerning bait uptake (up to 70 and 90%
consumption after the first and second days, respectively, in the
selective feeders in summer) are comparable to the best results
obtained in other studies conducted to develop species-specific
baits to deliver pharmaceuticals to wild boars and wild pigs.
Cereal-based baits to deliver an oral vaccine against the classical
swine fever in wild boars have been used in Europe. Kaden et al.
(2000) distributed baits marked with oxytetracycline in Lower
Saxony (Germany) during 2 years, with bait-removal rates
between 72 and 100%. In Australia, similar baits (PIGOUT,
Animal Control Technologies, Somerton, Victoria) have been
used to control wild pigs (Lapidge et al. 2005) and cumulative
PIGOUT-bait removal rates as high as 98–100% have been
reported. Mitchell (1998) distributed baits in Queensland
(Australia) and, although a high proportion of wild pigs
consumed the baits, substantial proportions were taken by cattle
and other non-target species. Fleming et al. (2000) in New South
Wales found that non-target species such as birds and foxes
removed far more baits than did wild pigs. In the USA, Fletcher
et al. (1990) distributed biologically marked baits in Georgia
and found that 95% of the wild pigs captured after bait
OF
in the summer and ~30% of the total baits remained after the
first day, whereas >60% remained after the first day in spring
(Fig. 2C).
In all, 74 of the 375 capsules contained in the baits placed in the
feeders were found after exhaustive searches; therefore, 80% of
the capsules were not found. The number of chewed capsules
found around the feeder in relation to the number of capsules
found is shown separately for each trial (Table 5). Overall, 100
and 75% of the capsules found had been chewed in summer and
spring respectively. Only in two cases were intact capsules found
that contained liquid inside.
The survival curve of baits differed between track stations and
wild boar feeders in spring (log-rank test, test statistic = 5.55,
P < 0.001) because the baits ran out quicker in the selective
feeders than in the track stations placed in the close proximity
of the feeders (Fig. 2D). No statistical differences between
delivery methods were found in summer (Fig. 2E) (log-rank
test, test statistic = 0.88, P = 0.38). However, when considering
the first day only, the selective feeders performed better than the
track stations (log-rank test, test statistic = 1.97, P = 0.04), with
12% of the baits remaining after the first day in selective feeders in
summer, and 25% in track stations.
Adult wild boar,
young wild boar,
birds and mice
Adult wild boar,
young wild
boar and birds
Wildlife Research
C. Ballesteros et al.
bait. This confirmed that encapsulated liquids can be delivered
to wild boars within baits, and the vaccine would eventually come
to contact with the oral mucosa. Nonetheless, although eating or
chewing a vaccine capsule is a primary requirement, this may not
necessarily result in the actual vaccination occurring (Cowled
et al. 2008); this needs to be assessed under experimental and field
conditions. Placing the baits inside selective feeders for wild
boar piglets was found to be a much more selective method for
delivering oral vaccines to wild boars because only young wild
boars visited the feeders by night. This method ensured that only
wild boar piglets were in contact with the oral vaccine, making
active immunisation of younger animals possible.
In summary, our results concerning the frequency of visits and
consumption rates by different species indicated that the baits
described herein can be used for oral administration of vaccines
and other pharmaceuticals to wild boar piglets during any time of
the year, especially in summer, and at least in places where
artificial feeders are used to supplement the feed to wild boar
piglets. These include many private and public estates in Spain
where wild boars are overabundant and the resulting risk of
disease is high (Acevedo et al. 2007; Gortázar et al. 2008),
and where the performance of portable oral-bait delivery
systems needs to be evaluated. Our delivery technique based
on selective piglet feeders has also potential for practical use in the
Eurasian wild boar, wild pigs and hybrid populations in extended
infected areas, and not only in private and public estates in
Spain where wild boars are overabundant. This is so because
piglets are a key age class in population dynamics (regardless of
the kind of pig) and therefore important epidemiological
targets for disease control or population control. We encourage
evaluating the safety, convenience and selectivity of this
technique elsewhere within the native and introduced portions
of the species range. Research is also needed to investigate the
potential of this technique not only as a vehicle for the delivery of
oral vaccine, but also in delivering toxicants or contraceptives to
wild pigs.
PRO
OF
ON
distribution had consumed baits, whereas only a low proportion of
the baits was taken by non-target animals. However in Texas,
Campbell and Long (2007) found high (17–29%) PIGOUT-bait
removal rates by cattle. Thus, oral-bait consumption and selectivity
is strongly dependent on habitat factors, the composition of the
local vertebrate community and the density of the target host
animals. The good performance in the present study is relevant
because reaching a high disappearance/consumption rate would
contribute to the viability of an eventually delivered live vaccine.
We are confident that our method is suitable for administering baits
successfully to wild boar populations under the circumstances
during the present study. Future studies are needed to establish
the bait-delivery effort required to reach a significant proportion of
the wild boar population.
Visitation rates to track stations by young wild boars
(and also birds other than partridges) were higher in summer
than in spring. As a consequence, the bait-survival curve in track
stations differed between seasons, in that baits disappeared at a
higher rate in summer than in spring. Bait removal from the piglet
feeders was also faster in summer. This is an important finding
because it identifies the appropriate season for oral-bait delivery
to this age class of wild boars. Several factors could contribute
to these results. First, summer food restrictions typical of the
Mediterranean habitats (Bugalho and Milne 2003) would favour
a more intense use of feeders by wild boars during that season.
Second, the increased density of wild boars after the spring
births would lead to an increased use of feeders in the
summer, and to a larger proportion of young animals. Ongoing
extensive trials using biomarkers (e.g. as used in Campbell et al.
2006) are assessing the rates of bait uptake by age class.
In regard to different delivery systems, releasing baits close
to or in piglet-selective feeders was advantageous, compared with
baiting further away from the feeders. A close proximity to the
feeders was associated with an increased probability of wild
boar visits, as well as with visits by wild ruminants and redlegged partridges. When the baits were placed in the piglet
feeders, a high proportion of the baits was consumed during
the first and second nights. Hence, the use of piglet feeders
enhanced selectivity, performing better than track stations,
which were more accessible to non-target species. In our study
location, placing baits directly in the field was not selective
enough for wild boars because other animals, e.g. birds, foxes
and other wild ruminants, were also attracted to the baits.
However, contrasting findings have been reported in wild-pig
populations from Australia and USA (e.g. Campbell and Long
2007), with the outcomes depending on several factors such as the
composition and attractiveness of the bait, particularities of the
delivery system and the prevalent animal community. However,
artificial feeders for wild boar piglets are not always present in
hunting estates and other places inhabited by the wild boars.
Future experiments with mobile feeders are underway, to test the
consumption of baits by wild boars in places where selective
feeders are not available. Future studies should assess whether
dispersed single baits are consumed at different proportions and
by a different number of wild boar individuals than are multiple
baits delivered at fixed stations (Cagnacci et al. 2007).
We gained some insights regarding the performance of
our baits as potential vehicles for delivering a vaccine. A high
proportion of the capsules was found chewed and eaten with the
LY
8
Acknowledgements
This work was supported by grants from Instituto Nacional de Investigación y
Tecnología Agraria y Alimentaria (INIA) (project FAU 2006-00017-C03-01),
Consejería de Educación y Ciencia, Junta de Comunidades de Castilla-La
Mancha (JCCM) (projects PAI 06-0046-5285 and PAI 07-0062-6611), the
Grupo Santander and the Fundación Marcelino Botín, Spain. Cristina
Ballesteros and Ricardo Carrasco-García are recipients of a JCCM fellowship.
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Manuscript received 9 September 2008, accepted 6 February 2009
http://www.publish.csiro.au/journals/wr