Experimental release of an Iberian lynx
(Lynx pardinus)
ALEJANDRO RODRIGUEZ*, LUIS BARRIOS and MIGUEL DELIBES
EsgaciOn BiolOgica de Donana. Consejo
Sevila, Spain
Superior de
Investigaciones Cientificas, Avda. Maria Luisa s/n, 41013
Reintroduction to the wild of threatened species has become a modern additional justification for
captive propagation. This conservation procedure is costly. and both economic resources and the
absence of optimal conditions in the field limit the IUCN recommendations for reintroduction to a
small proportion of potential candidate species. Furthermore reintroduction attempts often fail. In
carnivores, reintroduction failure is attributed to unsuitable adaptation in the field by captive-reared
animals, due to their lack of hunting skills, their tendency to leave the target area, their inadequate
interaction with conspecifics or their excessive confidence in humans. This list of causes is based on
very few studies of carnivore adaptation after reintroduction. In very rare and endangered species.
monitoring individual case-histories is the only way to evaluate reintroduction success. We report a
successful experimental release of an Iberian lynx (Lynx pardinus) which grew up in captivity.
Careful feeding—training and avoidance of human contact during the captive phase. as well as good
habitat quality and correct interaction with other wild lynx in the release site, seem to account for the
observed success. Permanence of the lynx within the release area might be related to the availability
of territory vacancies in the receiving population. Our results allow some optimism for future
reintroductions of this endangered species in areas where it has become extinct recently.
Keywords: experimental release: pre-release training; adaptation to the wild of captive animals:
Lynx pardinus.
Introduction
Reintroduction and restocking, as defined by the IUCN (1987), are important tools for
conservation, either for reinstalling extinct populations or for reinforcing weak ones.
Careful reintroduction projects are costly (Kleiman etah,1991) and, beside the availability
of economic resources, their success depends on a set of biological (status and knowledge
of the species’ biology), environmental and bio-political requirements (Kleiman et al.,
1994). These preconditions are rarely satisfied, leading to a low rate of recommendation
for reintroduction programmes (4.5% of the 418 threatened species covered by the
IUCN/Species Survival Commission Action Plans; Stuart, 1991). Although many
reintroductions have been made success has been achieved only in a few cases. For
example, Beck and colleagues (1994) document 145 reintroduction projects, only for
conservation purposes, where captive-born animals (mainly birds and mammals) have
been involved, but the success rate was only the 11%, success being defined as the
maintenance of a self-sustainable population. Reintroduction has usually been undertaken
in extreme cases of species closeness to extinction (e.g. the Arabian oryx Oryx leucoryx,
Stanley Price, 1989; and the golden lion tamarin, Leontopithecus rosalia, Kleiman et a!.,
1986), or when species have been extirpated from most of their original ranges (e.g. the
peregrine falcon Falco peregrinus in the United States or the European lynx Lynx lynx in
western and central Europe; Campbell, 1980; Breitenmoser and Breitenmoser-Würsten,
1990). Wild populations of such threatened species are so small that extracting individuals
for translocation is often inadvisable (Stanley Price, 1991). This lack of a suitable wild
source of animals is an especially common problem in carnivores (Yalden, 1993). Then,
attention is drawn to animals born in captivity: along with their genetic reservoir function,
it is considered that the final objective of captive propagation is species reintroduction to
the wild (Seal, 1986; Foose, 1989; Chivers, 1991; Wilson and Stanley Price, 1994).
The deficient adaptation to wild conditions is considered as one of the main reasons of
the reintroduction failure (Foose, 1987; Stanley Price, 1989; Kleiman et aL, 1994). Among
carnivores, unsuitable adaptation in the field by captive individuals is due to five main
reasons (see Yalden, 1993). First, they are unable to hunt their natural prey, probably
because of shortcomings in the learning of complex behaviour when captive (Kleiman,
1980; Ginsberg, 1994); one reported consequence is a switch to hunting domestic prey,
increasing mortality caused by conflict with humans (Breitenmoser and Haller, 1987).
Second, they do not always establish a population in the target area. Some animals may
move away from the release site, as occurs with translocated wild animals both in suitable
(Pettifer, 1981; Slough, 1989) and unsuitable (McArthur, 1981) release habitats; a direct
management implication is an increase in expected mortality if wandering animals go
beyond reserve boundaries. Third, reintroduced individuals may home, as translocated
wild animals can do (e.g. Miller and Ballard, 1982; Fritts et aL, 1984). Fourth, they do not
interact properly with conspecifics. For example, Mills (1991) observed that reintroduced
cheetah (Acinonyx jubatus) males fought with resident cheetahs and then left the area.
Severe injuries were also reported by Pettifer (1981) for a reintroduced cheetah after
fighting with residents. Fifth, they do not fear humans, so released animals are more
vulnerable to hunting or road deaths than their wild conspecifics; as a consequence, for
example, captive red wolves (Canis rufus) suitable for reintroduction are separated as
much as possible from humans and are taught to be afraid of them (Moore and Smith,
1991).
As Rahbek (1993) states, there is a great gap between the theory and practice of
reintroduction of endangered species. Specific reports on mammal adaptation monitored
after reintroduction are scarce (Kleiman, 1989; Lindburg, 1992; notable exceptions are
reported by Kleiman et at., 1986, and Stanley Price, 1989). However, monitoring released
animals seems to be the only way to evaluate the factors affecting reintroduction success or
failure (Stanley Price, 1989; May, 1991). In very rare and threatened species, individual
case histories should be of a great value in evaluating the effect of such factors (Lindburg,
1992).
In a recent study, Rodriguez and Delibes (1992) show that the world population of the
Iberian lynx (Lynx pardinus) is only about 1100 adult individuals, distributed among nine
isolated populations. The Iberian lynx has been considered as the most threatened
carnivore in Europe (Mallinson, 1978), and one of the most rare cats of the world (IUCN,
in preparation). Here we report the results of an experimental release of a wounded young
lynx, which grew up and recovered in captivity.
The case history
On 6 July 1991, a wounded male kitten Iberian lynx (2.0 kg) was found on a road near
Cardeña, a locality within the Eastern Sierra Morena (southern Spain) nucleus, which is
considered currently as the most healthy population in the range of the Iberian lynx
(Rodriguez and Delibes, 1992). The lynx was anaesthetized with 0.5mg atropine and
50mg ketamine for veterinary examination. Superficial wounds were found on the right
foreleg and head, and radiographs showed a fracture of the proximal epiphysis of the left
femur. Injuries were cleaned and closed with absorbable sutures, and the fracture was
reduced under radioscopy. Before recovery from anaesthesia, a serum-diluted mixture of
antibiotics (40mg gentamicin and 50mg netilmicin) and a vitamin complex were
administered. On the following days the same treatment was applied with the food.
RECOVERY
In order to assure correct knitting of the bones, the lynx was put in a small cage, with
padded walls, which reduced its movements, especially jumping. The cage was placed in a
dark and quiet room, and the lynx was visited once a day for feeding and medication. In
the early days the lynx was only able to eat soft food (triturated meat), but small pieces of
meat were gradually accepted. This period lasted 43 days, sufficient time for the femur to
knit completely (Table 1).
TRAINING: FIRST PHASE
The lynx was moved to a 5 x Sm outdoor enclosure, provided with trunks and ledges at
different heights, in a quiet environment. The extremity affected by the fracture seemed
fairly weak and the animal clearly limped, as the other wounds healed up. Food consisted
of dead prey treated with vitamins and aminoacids. Food was set progressively at places
of difficult access to encourage exercise. Fifteen days after its arrival in the enclosure, the
first live prey (a rabbit) was provided. The lynx took 4 days to chase the rabbit; thereafter
it was able to chase living prey regularly. It also frequented several ledges, though it
preferred one at a height of 2.5 m. About 45 days after the beginning of exercises, limping
was nearly imperceptible.
TRAINING: SECOND PHASE
After 112 days in the small enclosure (Table 1) the animal was weighed (4.9 kg) and
provided with a radiocollar. Then it was moved (about 200 km) to an enclosure (1 ha)
with natural vegetation where wild rabbit density was first increased by releasing 100
individuals and supplying vegetables. Thus, the lynx could hide within dense vegetation
and it was forced to search and eat wild prey under seminatural conditions. Its physical
condition was monitored each few days by observation, and both rabbit remains and
analysis of its faeces indicated regular successful predation. The purposes of this phase
were to exercise the animal’s limbs and to improve its foraging behaviour. Human
contact and other disturbance were reduced to a minimum. This period lasted 83 days
(Table 1).
Table 1. Summary of the recovery process, training, and post-release adaptation to the wild of the young male
captive-reared Iberian lynx
Phase
I
II
Post-release
Monitoring
Small cage
Recovery
Training
Place
I
II
111
IV
1—43
Quiet (5 x 5 m)
enclosure
Quiet (1 ha) pen
Field
Days
44—156
157—240
Intensive
(1—3)
radiofixes
per day
1—4
5—20
21—61
62—93
Events
Intensive care; bone knitting; healing of
injuries; ingestion of solid meat
Development of locomotion skills; hunting
training; isolation from humans
Contact with natural habitat; locomotion
and foraging skills; isolation from humans
Dispersive-like movements
Initial settlement
Exploratory behaviour
Definitive settlement; fall of the collar
00
LA
RELEASE
Movements and range
On 2 March 1992, the lynx (then estimated to be about 1year old) was recaptured, weighed
(6.0 kg) and provided with a new radiocollar, furnished with an activity sensor. A portion
of the collar was made of light rubber, whose resistance decreased with time, so that the
collar should fall when the animal’s neck reached the size of the collar perimeter or before.
Weight was within the normal values described for juveniles (individuals aged between 0.5
and 1.0 year; Beltrán and Delibes, 1993). The lynx was released in a pine stand 8.7 km east
to the point where it was runover 9 months before. Within such habitat, dense shrub cover
is available only locally. However, at a greater scale the main habitat types are scrubland
(Quercus, Cistus, Rosmarinus, Phillyrea) and grassland with scattered trees (Quercus
rotundifolia). The border between the two habitats is sharp.
The lynx was followed intensively during the first 3 days (Table 1). From the release site
it moved to the west through the pinewood as far as a dense patch of riparian vegetation, it
remained there for the rest of the daylight period but the sensor indicated continuous
activity. This site was only 300 m from the release point. Early in the night it moved along
the stream, still through the pinewood, to the border between pines and scrubland (Fig. 1).
It followed this border to a dense scrub patch where it was found in the morning of the
second day. The lynx remained there during the daytime; and the next night it contacted
the grassland habitat but avoided entering it. It skirted northwards along the edge between
grassland and scrubland. In the morning of the third day the lynx was near this edge, inside
the scrubland, where it showed some activity during the day and the following night. This
patch was the first area with high rabbit density it encountered, and probably it stopped for
foraging. Next day, still following the border between pastures and scrubland, it reached
the area where it finally established itself. This site is about 4 km north of the release site
(Fig. 1). The lynx travelled a minimum distance of 8.1 km and took 4 days to cover the
distance. During this period it was active 64% of diurnal and 50% of nocturnal monitoring
time. Activity level was about twice that reported for juvenile male Lynx in Doflana (SW
Spain; Beltrán, 1988). Thus, displacement was fairly slow and activity time relatively high,
suggesting, in addition to prey searching, a rather detailed habitat exploration.
From the fourth day on after release, lynx location was determined at least once a day.
From day 4 to day 20 (Table 1), fixes concentrated within a small area of scrubland (about
80 ha), near the grassland border (Fig. 2, area A). From day 21 to day 61 the pattern of
movements consisted of nine long and fast directional travels whose start and end were in
the A + B area (Fig. 2). After the first directional displacement the lynx enlarged his home
range to area B, i.e. it also used this area for daily movements and for diurnal resting.
Habitat characteristics of area B are similar to those of area A. The A + B area (Fig. 2) is
defined as the core area of the lynx home range because (1) it contains 79% of all fixes, and
(2) daily movements within it are rather short and slow as compared with those detected in
other parts of the home range.
The inter-journey periods within the core area were rather short. Distance, direction,
target area, dates and duration of these movements are shown in Table 2. Seven directional
travels reached a narrow valley covered with dense scrubland (the area C, Fig. 2), and the
other two were directed to the limit with the pine stand where the lynx was released,
namely the area D (Fig. 2). All directional travels were mainly directed to the south and
rarely reached the southern pinewood habitat strip.
Figure 1. The post-release movements (thick line) of the lynx. The polygon represents the lynx home
range, estimated by the minimum convex polygon method from daily fixes taken after the initial
settlement (i.e. fixes from the post-release dispersive-like phase were excluded). Pinewood and
grassland habitat types are avoided during the initial travel. Black circle: release point. Triangles:
lynx fixes every 24 h within the dispersive-like phase.
Daily home-range size was estimated by measuring the area of cumulative convex
polygons. Home-range size increased with time but soon levelled out, even including sites
used through directional displacements (Fig. 3). After day 62 the lynx did not visit new
places. Maximum range size, including early movements through pinewood habitat, was
995 ha. From day 62 to day 93 (Table 1), when the radiocollar fell off, lynx movements
concentrated on a 220 ha area, within the northern half of its maximum range. These data
agree quite well with the average home range size for juvenile males (270 ha; Beltrán,
1988); maximum range size is within the nonnal values for adult males (1000 ha; Beltrán,
1988).
Habitat use
The relative availability of each habitat type was estimated inside a circle with radius equal
to the distance between the farthest lynx location and the release site, this latter taken as
the circle centre. Figures of relative abundance are 52%, 12%, 17% and 19% for
Figure 2. Directional travels of the released lynx from the core area (area A + B) of its home range to
other less used areas. Arrows indicate the beginning and the end of each outward journey. Letters
A—D show the progressive spreading of the home range with time. Black circle: release site.
pinewood, dense scrubland, open scrubland and grassland, respectively. The number of
independent locations (at least 24 h apart) within each habitat type was compared with
availability. The lynx selected scrubland and avoided pinewood (x2 test, p <0.0001). The
use of open scrubland and grassland was intensive (76% of fixes), while use of dense
scrubland (20%) and pine stands (4%) was rather occasional, mainly during the initial
establishment and directional displacement phases.
This individual seemed to select open scrubland for resting while activity fixes were
located near or into grassland. The Iberian lynx selects dense cover or a similar shelter for
resting (Beltrán, 1988), yet forages (>80% rabbits, Oryctolagus cuniculus, in the diet:
Delibes, 1980) in more open habitats. To investigate the influence that food distribution
may have on such unexpected habitat selection, rabbit abundance was estimated in the
three most commonly available habitat patches used by the lynx: dense scrubland, open
scrubland and grassland. Vegetation cover of these habitats is > 80%, 40—80% and <20%,
respectively. Rabbit relative abundance was estimated in each habitat by counting both the
number of pellets and latrines found in a lineal transect of 20 mm search effort. Five spatial
Table 2. Date of start, duration (days until return to the home range core area), minimum distance travelled
(km), and area visited (see Fig. 2) during the nine directional journeys made by the released lynx
Directional travel
Date of start
Direction
Duration (days)
Distance
Visited area
1
2
24 March 2 April
SSE
SE
2
2
7.6
5.5
C
D
3
5 April
SW
4
6.2
C
4
5
6
7
8
9 April 13 April 15 April 17 April 27 April
S
SW
S
SW
SW
2
1
1
1—3
1
4.0
6.2
3.8
6.8
6.2
C
C
C
C
D
9
1 May
S
3—5
7.6
C
00
ha
500
—
400
-
300
-
200
-
100
—
days after release
Figure 3. The size of the lynx home range against
the number of days after release. The home range
core area is defined as the area A + B (see Fig. 2).
random replicates were made within each habitat. Temporal replicates were considered
unnecessary because of the short lynx monitoring period (spring season) and the high
persistence of rabbit pellets (Simonetti, 1989), that reduces variability of pellet number
over time. Pellet and latrine abundance did not differ between open scrubland and
grassland. However, each of these habitats contained more latrines (x2 test, p <0.02) and
more pellets (p <0.001) than dense scrubland habitat. Moreover, rabbits are rare in pine
woodland. So, the lynx seemed to select the best food conditions, once shelter
requirements are satisfied.
Discussion
The five problems pointed out for general carnivore reintroductions seemed to be
overcome in the case presented here. The survival of this released lynx is the best evidence
of its ability to hunt. We assume that it preyed mainly upon rabbits, because of their
abundance and the relative scarcity of suitable alternative prey. We also think that the
training period with live rabbits may determine the subsequent lynx hunting success (e.g.
through formation of an appropriate prey search image; Dawkins, 1971). This result may
question, in some instances, the rules that, in some countries, prohibit the improvement of
hunting skills of captive animals by giving them live prey (Yalden, 1993; Shepherdson,
1994).
No attempt at homing behaviour was detected. Furthermore, there was a rather high
degree of fidelity to the reintroduction area, as a home range was established within 10 km
of the release point. When released the estimated age of the lynx was about 1 year. At this
age most lynx are subadult (see Fritts and Sealander, 1978). So, one might expect a typical
transient pattern of movements, with irregular displacements and less preferred habitat
use (Ferreras, 1994). Conversely, initial dispersive-like movements were shorter than
those reported in previous studies (up to 30km; Beltrán. 1988: Ferreras, 1994) and time to
settlement was also shorter (4 days vs several months for males in the Donana area:
Experimental release of an lberfan lynx
391
Beltrán, 1988; Ferreras, 1994). Resource quality within its home range can be considered
excellent (rather than poor, as predicted for transient individuals; Rolley, 1987) according
to the standards of food and cover reported for the species (Delibes, 1989; Rodriguez and
Delibes, 1990; Palomares et at., 1991).
A strong intrasexual competition for the highest quality habitats seems to exist (Delibes,
1989). Because we assume that the density of lynx within the release area is high
(Rodriguez and Delibes, 1992), such fast settlement can be viewed as the filling of a
resident male vacancy, as no study reports tolerance of resident males to dispersal males
(Beltrán, 1988). This hypothesis is supported by th observed small home-range size
(about half of the size reported for adult males; Beltrán, 1988), in agreement with
predicted values for relatively deilse populations (Rolley, 1987). Therefore, settlement of
reintroduced lynx may depend on the availability of vacancies near the release area. The
absence of exploratory travels northwards from the lynx range may also correspond with
the presence there of a resident male range. There were no signs of abnormal interactions
among the released individual and other resident lynx.
Although observed habitat selection agrees quite well with lynx preferences as
previously defined, because space use of resident population is unknown, we cannot
distinguish between two alternative mechanisms of range selection, one based on habitat
preferences, the other determined by avoidance of resident-occupied space. However, it is
unlikely that resident individuals defend the worst habitat type (Delibes, 1989), i.e. pine
stands. So, in this case, habitat preference-mediated movements may guide an initial
search phase, while further settlement may depend on distribution of resident conspecifics
of the same sex. Directional travels can be seen as exploratory behaviour to gain
information about neighbouring space occupancy.
Two farms are located in the northwestern border of the lynx home range. No attack on
poultry was detected, and human presence seems to be avoided, as the western limit of its
home range runs parallel (at several hundred metres) to a line of isolated farms.
It may be worthwhile to note, as illustrated in this paper, that the study of the
establishment process of reintroduced animals can be very useful in understanding the
genesis of home range after dispersal in carnivores.
A reintroduction can be considered successful if the population reinforced or created
resists extinction (Beck et al., 1994). At the individual level, this implies reproduction of
released animals. From this point of view we cannot yet state that the present attempt is
successful because lynx contact was lost before mating was detected. However, lynx
establishment in a stable range within a dense population suggest that future mating
opportunities are likely to occur.
The relative success of this reintroduction cannot be wholly attributed to the chance of
finding a vacant territory. The procedure has met a number of those criteria that Griffith
and colleagues (1989) associate with successful reintroductions: suitability and protection
of habitat (the area is within a natural park), as well as care and development of pre-release
physical and behavioural skills of the released animal (Box, 1991). Our results suggest that
recovered young wild lynx and perhaps, those born in captivity, may be good candidates
for future reintroduction, in order to extend the species range to areas where extinction has
occurred recently (Rodriguez and Delibes, 1990), after adequate habitat management.
New case studies are needed to evaluate the efficiency of reintroduction techniques for this
species.
Acknowledgements
We are grateful to R. Laffitte, 3. Aldama, and the staff of the DirecciOn Provincial de Ia
Agencia de Medio Ambiente de Córdoba for care and veterinary assistance of the lynx.
We thank also the wardens of the Parque Natural de Cardena y Montoro for their help with
radio-tracking. This research was supported by the Consejo Superior de Investigaciones
Cientificas (CSIC) and the Instituto Nacional para la ConservaciOn de la Naturaleza.
Personal support to AR and LB was provided by grants from the Junta de Andalucia and
CSIC, respectively. D.W. Yalden and an anonymous referee kindly made useful comments
on the manuscript.
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