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Abstract Relocations of species have become a tool widely used in nature
conservation, but insects have rarely been considered as targets. Here, we present a
translocation project of the field cricket (Gryllus campestris L. 1758), which is a
threatened species at the northern edge of its range. Only ten populations were left
in Lower Saxony (Germany), illustrating the need for urgent conservation measures.
After 10 years of monitoring and management of an isolated population, 213
nymphs were captured and released at another nature reserve in summer 2001. The
size of the new population increased significantly from 27 singing males in spring
2002 to 335 singing males in spring 2005. The occupied area increased from 5.66 ha
to 33.14 ha. Altogether, the translocation project was evaluated as successful, but the
inland dune proved to be not as suitable for the species as initially expected. Our
results indicate that translocations of highly reproductive insect species are prom-
ising, as long as the release locality contains sufficiently large areas of suitable
habitat and a high number of wild juveniles from a closely located and large source
population are released in a climatically favorable period. Management and resto-
ration of habitats, as well as continuous monitoring are of crucial importance for the
success of the translocation project. Moreover, the importance of a high quality of
cooperation between conservationists, authorities, foresters, farmers, financiers and
scientists cannot be overstated.
Keywords Heathland ÆInsect conservation ÆOrthoptera ÆRe-introduction Æ
Relocation ÆRestoration
A. Hochkirch (&)ÆK. A. Witzenberger
Department Biology/Chemistry, Division of Ecology, University of Osnabru
¨ck, Barbarastr. 11,
Osnabru
¨ck D-49076, Germany
e-mail: hochkirch@biologie.uni-osnabrueck.de
A. Teerling ÆF. Niemeyer
BUND Diepholzer Moorniederung, Langer Berg 15, Wagenfeld D-49419, Germany
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Biodivers Conserv (2007) 16:3597–3607
DOI 10.1007/s10531-006-9123-9
ORIGINAL PAPER
Translocation of an endangered insect species, the field
cricket (Gryllus campestris Linnaeus, 1758) in northern
Germany
Axel Hochkirch ÆKathrin A. Witzenberger Æ
Anje Teerling ÆFriedhelm Niemeyer
Received: 3 February 2006 / Accepted: 29 August 2006 / Published online: 27 October 2006
ÓSpringer Science+Business Media B.V. 2006
Introduction
Animal relocations have become a widely used tool in conservation management.
However, most re-introduction projects so far have focused on large vertebrates,
such as birds and mammals (Sarrazin and Barbault 1996; Fischer and Lindenmayer
2000). In spite of the fact that invertebrates constitute a substantial proportion of the
species richness and biomass, and play a significant role in ecosystem functioning,
they rarely have been considered as relocation targets and are even often discounted
in conservation management as a whole. Thus, invertebrates need to receive much
more attention in nature conservation (Pyle et al. 1981; Dunn 2005). Relocation
projects of highly reproductive invertebrates are much more promising than those of
large vertebrates due to their small body size, the low costs, and the small spatial
requirements (Pearce-Kelly et al. 1998). The few documented cases of invertebrate
relocations mainly deal with Lepidoptera species (Rawson 1961; Dempster et al.
1976; Duffey 1977; Va
¨isanen et al. 1994; Witkowski et al. 1997), but some examples
of Orthoptera relocations have also been published (Pearce-Kelly et al. 1998;
Sherley 1998; Berggren 2005).
Four different types of relocations are commonly distinguished (IUCN 1998):
Re-introductions (attempts to establish a species within its historical range), trans-
locations (attempts to establish new populations within the range), supplementations
(addition of individuals of different genotype to an existing population), and
conservation introductions (attempts to establish a species outside its natural range,
but in an appropriate habitat). The aim of translocation projects is usually to reduce
the risk of extinction for an endangered species by creating more self-sustaining
populations (Sherley 1998). Fragmentation of habitats and loss of (sub-)populations
have been recognized as main threats for many species (Primack 2002). The artificial
establishment of new populations is, therefore, a consistent method for enhancing
the survival probability of a species. However, only 26% of the relocation trials
analyzed in a recent review have been classified as successful (Fischer and
Lindenmayer 2000). There is a strong need for more thorough management of
relocation experiments, with careful background research, choice of suitable release
sites and release stocks, as well as monitoring before and after the relocation (IUCN
1998; Fischer and Lindenmayer 2000). Here we present the results of a translocation
experiment of the field cricket (Gryllus campestris L. 1758) in northern Germany.
We evaluate the success of the translocation project by using a strong criterion
(significant increase in population size) as indicator of the success.
Methods
The study object
The field cricket (Gryllus campestris) is a rather well-known insect. It is a compara-
tively large cricket species (17–26 mm), characterized by a shiny black body
coloration (Marshall and Haes 1990). The species mainly inhabits dry grasslands, and
is restricted to heathlands and oligotrophic grasslands at the northern edge of its
range (Kleukers et al. 1997), where it typically lives in burrows of approximately
30 cm depth (Regen 1906). The reproductive season of the univoltine species lasts
from May until the end of June. Nymphs hatch in mid July and overwinter during
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3598 Biodivers Conserv (2007) 16:3597–3607
their tenth or eleventh instar (Ko
¨hler and Reinhardt 1992). The final moult takes
place at the end of April or at the beginning of May. While males are territorial and
defend their burrows fiercely, females are vagrant and are attracted by singing males.
They lay their eggs in bare ground either close to a burrow or into the burrow. The
first instars can be found under bark or wooden pieces, but they also use old burrows
of adults. Populations of G. campestris are known to undergo extreme fluctuations
and are strongly affected by weather conditions (Remmert 1992).
The field cricket is a threatened species at the northern edge of its range, such as
the UK (Pearce-Kelly et al. 1998), Germany (Ingrisch and Ko
¨hler 1997), the
Netherlands (Kleukers et al. 1997), Denmark (http://redlist.dmu.dk, 2006) or
Switzerland (Thorens and Nadig 1997). In Lower Saxony it is listed as Critically
Endangered (Grein 2005), with only ten populations left (Grein 2000). The main
reason for its decline is believed to be habitat loss. Due to its well-known song, the
field cricket is a comparatively popular insect species. It probably represents one of
the scarce examples of ‘‘non-butterfly insects’’, which are suitable as flagship species.
For this reason, the species has been selected as Insect of the Year 2003 by the
‘‘Kuratorium Insekt des Jahres’’ of the German Entomological Institute
(Eberswalde) and the Federal Biological Research Center for Agriculture and
Forestry (Braunschweig) in Germany. In Lower Saxony, only one isolated popula-
tion remained west of the river Weser, at the eastern edge of the nature reserve
‘‘Neusta
¨dter Moor’’. This population has been monitored and managed intensely
during the last 15 years by the non-governmental organization BUND (‘‘Bund fu
¨r
Umwelt und Naturschutz Deutschland’’ or ‘‘Friends of the Earth - Germany’’).
From 1991 to 2001, the population increased from 32 to 949 singing males
(Hochkirch 1996; Teerling and Hochkirch 2002). In order to reduce the extinction
risk further, a translocation project was started in 2001, intending to establish a
second self-sustaining population in a nearby nature reserve (‘‘Renzeler Moor’’).
Although there are no former records of field crickets available for this nature
reserve, it consists of many seemingly ideal but unoccupied habitats for field crickets
and was thought to enable them to spread further. However, it is separated from the
source population by a distance of 3.5 km, with the river ‘‘Große Aue’’ and wet
grasslands acting as effective barriers for these flightless insects.
The study area
The two study sites are located in the central part of the natural region ‘‘Diepholzer
Moorniederung’’, an area between the towns Hannover, Bremen and Osnabru
¨ck
(Lower Saxony, Germany). The region is characterized by large peat bogs, wetlands
and dry alluvial sand ridges. These dry areas are naturally oligotrophic and were
heavily overgrazed from the middle ages to the 19th century. During this period,
heathlands, dunes and oligotrophic grasslands spread over northern Germany
(Webb 1998). After the invention of artificial fertilizers and massive changes in land
use, only small fragments of heathland have been left (Bakker and Berendse 1999).
All peat bogs are strongly degraded, either by cultivation, peat cutting or dehy-
dration. At the beginning of the 1970s, regional conservationists started a conser-
vation project in order to save the remaining peat bog fauna, which has been
continued by the BUND since 1983. With increasing experience the field of activities
spread to other types of habitat, such as wet grasslands, dunes and heathlands, which
surround the peat bog areas.
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Biodivers Conserv (2007) 16:3597–3607 3599
The nature reserves in the ‘‘Neusta
¨dter Moor’’ include the peat bog, as well as
adjacent heathlands and wet grasslands at the western edge. The main part of the
source population occurs east of these reserves, but it has spread into them during
the last decade (Teerling and Hochkirch 2002). We chose two release sites on a
former inland dune system in the northwestern part of the nature reserve ‘‘Renzeler
Moor’’ (established in 1970). This area was used as farmland and pine forest during
the past decades and transformed into meso- to oligotrophic grasslands at the
beginning of the 1990s. Both reserves are maintained by extensive sheep grazing,
which is also known to be advantageous for field crickets (Schmidt 1998).
The translocation procedure
From 1990 to 2001, the population at the Neusta
¨dter Moor was intensely monitored
and managed, leading to an approximately 30-fold increase in population size. In
2001 the population size was sufficiently large to start the translocation procedure,
which was oriented towards a previous re-introduction project for the field cricket in
England (Pearce-Kelly et al. 1998). The release sites at the Renzeler Moor were
inspected by the authors and an additional expert (G. Grein) and there was general
agreement that they represent suitable habitats for the field cricket. However, a
detailed habitat analysis was not performed. Two localities were chosen as release
sites: a meso- to oligotrophic pasture, which was managed by sheep grazing since
1992 and a restored inland dune, which was formerly forested with pines and
deforested in the winter of 1990/91. The great habitat-diversity of the surrounding
terrain was expected to allow further dispersal to suitable sites during the following
years. Since the success of translocations can be increased by using wild animals as a
source, releasing a large number of individuals and removing any detrimental factors
(Fischer and Lindenmayer 2000), we followed these recommendations. In contrast to
the breeding program presented by Pearce-Kelly et al. (1998), only wild nymphs
were released during the translocation. Although the source population could be
genetically rather invariable due to a bottleneck in 1991 (32 singing males), it was
chosen to gain nymphs only from this well-monitored area, which is also the closest
population to the release area. In order to increase the genetic diversity as far as
possible, nymphs were collected from different subpopulations at the Neusta
¨dter
Moor. The populations of both release and source area were monitored during the
following years.
A total of 213 nymphs (instar 7–8) were collected on 4 days in July 2001. They
were stored in boxes with swards of grass and heather to enable the nymphs to find
shelter beneath them during the transportation. Fish food was supplied until they
were released on 31 July 2001. Approximately half of the individuals (113 speci-
mens) were introduced directly on the inland dune, the other half (100 specimens)
on the pasture. Individuals from all subpopulations were released at each site to
increase the genetic variability. During the first days pieces of bark where placed on
the ground as shelter.
Monitoring of the field crickets
The population size of G. campestris in the Neusta
¨dter Moor and Renzeler Moor
was estimated by counting the number of singing males on each occupied site. The
characteristic calling song of the field cricket is well suited for monitoring, since it
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3600 Biodivers Conserv (2007) 16:3597–3607
can be heard up to 100 m, allowing a fast and comprehensive survey (Detzel 1998).
Females and non-singing males were ignored, to allow comparability of the data
between different years. Since not all males sing simultaneously, the data have to be
regarded as minimum values. The study sites were checked on dry, warm and
windless days during the main calling phase (from May to June). Densely populated
sites were mapped preferably during the highest activity in the late afternoon or in
the evening. All records were transferred to a map and analyzed with ArcView GIS
3.2. This method has been applied since 1990 in the study area (Hochkirch 1996;
Teerling and Hochkirch 2002).
Statistical analysis
We computed a linear regression model for population growth for the whole
population as well as for three different habitat types (pasture, dune, peat bog) and
tested for a positive increase in population size. All data were log-transformed prior
to statistical treatment to comply with the model assumptions. The tests were carried
out in ‘‘R 2.1.1’’ (R Development Core Team, 2004).
Results
In total, 27 singing males were recorded in the Renzeler Moor in the spring of 2002
(Fig. 1). Assuming a balanced sex ratio, this corresponds to a survival rate of 25.4%.
Considering that G. campestris is known to have a high mortality during the winter
(Remmert 1992), the survival rate was surprisingly high. This led to the decision, not
to supplement cricket nymphs in 2002. In the following year, 42 stridulating males
were counted and the population had spread also spatially compared with 2002
(Fig. 1). Most of the males were found between the dune and a degraded part or the
bog. After the unusual hot summer of 2003 (Ciais et al. 2005) the population
increased up to 107 stridulating males in spring 2004. The majority of individuals
(70%) were recorded on the pasture, whereas only 7% inhabited the inland dune
(Fig. 2). In 2005, the population had grown immensely, reaching 335 stridulating
males. Again the majority of crickets (77%) inhabited pastures and bog sites
surrounding the inland dune (Fig. 2). Some initial subpopulations colonized sites
approximately 250 m outside the nature reserve, such as adjacent fields and mead-
ows. The occupied area increased from 5.66 ha in 2002 to 33.14 ha in 2005 (Fig. 1).
The overall population growth was significantly positive (linear regression model,
df =2,t= 7.55, p= 0.017, R2= 0.9661) and so was the increase of the occupied area
(linear regression model, df =2, t= 4.53, p= 0.046, R2= 0.911). However, after
analyzing the data for the three habitats (dune, bog, pasture) separately, the sub-
population growth on the dune was not significant (linear regression model, df =2,
t= 0.910, p= 0.459, R2= 0.293), while the subpopulations increased significantly on
the pasture (linear regression model, df =2,t= 8.695, p= 0.013, R2= 0.974) and in
the bog (linear regression model, df =2,t= 10.39, p= 0.009, R2= 0.982).
Discussion
Four years after the translocation of cricket nymphs, we evaluated the project as
successful. The population persisted and increased significantly, indicating a high
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Biodivers Conserv (2007) 16:3597–3607 3601
quality of the release area as habitat for Gryllus campestris. However, despite of these
overall results, the suitability of single sites (or habitat types) differed from our
expectations. While the population size increased strongly on the pasture and
degraded peat bog, the inland dune turned out to be much less suited than expected
(Fig. 2). A possible reason for this might be found in inappropriate conditions for
digging burrows (Ko
¨hler and Reinhardt 1992), due to either the dense cover of mosses
and plant litter or the soil structure of the dune. As initially intended, the increase in
population size also caused a considerable dispersal of the field cricket into adjacent
areas. Some of these habitats, such as peat bog sites or arable fields, might not be
Fig. 1 Dynamics of the new population of Gryllus campestris in the Renzeler Moor from 2002 to
2005 (black dots: singing males). The crossed squares represent the two release localities, the
southern of which was located on the inland dune, the northern on a pasture. Peat bog sites (striped)
are mainly situated southeast of the inland dune. The bold line marks the border of the reserve. Sites
north of the reserve consist mainly of conventional farmland
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3602 Biodivers Conserv (2007) 16:3597–3607
suitable as persistent habitats, but they may serve as stepping stones for future
expansion. In the source area (Neusta
¨dter Moor), degraded peat bog has been
colonized permanently during the last decade, allowing dispersal to remote heath-
lands. Continuous monitoring of the source population showed that the loss of 213
nymphs had no negative consequences. In 2005, the source population reached a new
maximum of 1945 singing males (unpublished data). We consider ten factors as crucial
for the success of the translocation method, which can be grouped into three major
classes: ecological factors, translocation procedure, scientific and administrative
support.
Ecological factors
Four ecological factors were probably of importance for the success. (1) The habitat
quality in the release area was rather high, due to an intense habitat restoration and
management since the end of the 1980s. Continuous management by sheep grazing
and mowing is needed to counteract the increased nitrogen deposition from the
atmosphere (Bakker and Berendse 1999). Although the dune was less suited for
G. campestris, deforestation and extensive sheep grazing supported the development
of large suitable habitats. The availability of high quality habitat is known to be the
major determinant for the success of relocation projects (Rawson 1961; Griffith et al.
1989; Wolf et al. 1996; Sarrazin and Legendre 2000). (2) The high habitat hetero-
geneity (grasslands, degraded peat bog, dune) in the release area supported the
success, as the field crickets were able to choose optimal sites and microhabitats.
Orthoptera are known to perform an active habitat choice (Whitman 1987).
Moreover, even less suited sites could be colonized in optimal years and serve as
stepping stones for future dispersal (Hochkirch 1996). (3) The weather conditions
were suitable for population growth from 2003 to 2005. This is probably of crucial
importance, since field crickets (as many insects) are highly dependent on favorable
weather at the northern edge of their range, which can influence the success of
translocation projects immensely (Pearce-Kelly et al. 1998). From 2002 to 2003, the
weather conditions were unfavorable (rainy), which is illustrated by a lower popu-
lation growth (Fig. 2). Apparently, the habitat quality of the pasture was even
Fig. 2 Comparison of the population development between the three main habitat types: grassland
(open circle), peat bog (closed square), dune (open triangle)
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Biodivers Conserv (2007) 16:3597–3607 3603
suitable under these conditions, since the population persisted and increased slightly
in that year. (4) Gryllus campestris is a univoltine species, which is known to produce
high egg numbers leading to rapid population growth (Remmert 1992; Pearce-Kelly
et al. 1998). Demography is generally thought to be of high importance for popu-
lation survival (Lande 1988).
Translocation procedure
We distinguish four major parameters of the translocation procedure, which assured
the success. (1) Differently to the project of Pearce-Kelly et al. (1998) we had the
chance to gain specimens from a sufficiently large wild population. Relocation
projects using wild animals are generally more successful than those using captive
animals (Griffith et al. 1989; Fischer and Lindenmayer 2000). Moreover, transloca-
tion success of wild-caught animals correlates positively with the density and
increase of the source population (Griffith et al. 1989), which was also true for the
population at the Neusta
¨dter Moor. (2) As the source population was located close
to the release area, the translocated individuals were probably genetically adjusted
to the local conditions. The higher success of translocations using founder groups
from indigenous sources has been reported also from other taxa (Ebenhard 1995;
Sarrazin and Barbault 1996; Singer et al. 2000). (3) Another important factor could
be the use of nymphs for the translocation. Nymphs of Gryllus campestris are more
mobile than adults, since they do not show any territoriality. They do not start to dig
burrows before autumn (Detzel 1998). Results from population modeling suggest
that the use of juveniles in translocation projects is generally more efficient than
relocating adults (Robert et al. 2003). (4) We transferred a high number of indi-
viduals. It is noteworthy to mention that the relation between translocation success
and the number of animals released is asymptotic (Griffith et al. 1989). Pearce-Kelly
et al. (1998) introduced between 106 and 1200 nymphs of G. campestris, but the
survival depended more upon the habitat quality than on the number of released
insects. Although there is a minimum number of animals that should be released,
translocations have low chances of success without high habitat quality (Griffith
et al. 1989; Ebenhard 1995).
Scientific and administrative factors
Two factors within this class were of importance for the translocation project. (1)
Continuous monitoring of both source and release population has been performed
since 1990, allowing the assessment of the translocation method as well as the
influence of the removal of specimens from the source population. In many trans-
location projects, such intense monitoring measures are missing (Sarrazin and
Barbault 1996). Moreover, the experience of ten years of monitoring and manage-
ment facilitated the choice of suitable release sites. (2) The success of the translo-
cation project was also promoted by the excellent cooperation of the local and
regional administrations, foresters and farmers, financial supporters (see acknowl-
edgements), the executing organization (BUND) and the scientific consultants
(University of Osnabru
¨ck). There is a strong need for such a high quality of coop-
eration in nature conservation (Sarrazin and Barbault 1996).
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3604 Biodivers Conserv (2007) 16:3597–3607
Negative factors
Two factors could have had negative effects on the success of the translocation
process. (1) The transferred crickets were gained from only one population, which
passed through a genetic bottleneck at the beginning of the 1990s. It is rather likely
that the established population is genetically impoverished as has been shown for
other translocated populations (Stockwell et al. 1996). However, inbreeding need
not always cause inbreeding depression (Lande 1988; Hoelzel et al. 1993; Leberg
1993) and the consequences of genetics on survival or reproduction are difficult to
predict (Sarrazin and Legendre 2000). The strong population growth of the field
cricket indicates that currently the suggested loss of genetic diversity does not cause
any problems. Demography generally seems to be of higher importance for popu-
lation dynamics than population genetics (Lande 1988). Moreover, by transferring
specimens from a nearby locality, the risk of outbreeding depression is minimized
(Griffiths et al. 1996, Sarrazin and Barbault 1996). (2) There is another caveat, which
should receive a stronger consideration in future translocation projects. Based upon
the initial inspection of the release area, two sites (the dune and the pasture) were
regarded as suitable habitats for the field cricket. While the subpopulation on the
pasture increased continuously from 2002 to 2005, the subpopulation on the dune
decreased during the first three years (Fig. 2). The increase of the dune subpopu-
lation in 2005 might be caused by continuous immigration from the surrounding
sites. The success of the whole project was determined by the high performance of
the pasture and the surrounding bog sites. Had only the dune been chosen as a
release site, the project might have been less successful. Therefore, detailed habitat
analyses should be performed prior to relocation projects (Holloway et al. 2003).
Acknowledgements We are grateful to Till Eggers for statistical advice. We would also like to
thank Anselm Kratochwil for his constant support and encouragement throughout this project. The
Division of Ecology at the University of Osnabru
¨ck provided research facilities. Till Eggers, Julia
Gro
¨ning, Elisabeth Witzenberger and Anselm Kratochwil provided valuable comments on a
previous version of the manuscript. The local and regional administrations (Land of Lower Saxony,
district government Hannover, NLO
¨, NLWKN, Landkreis Diepholz) enabled us to carry out the
translocation and all associated surveys. Additionally our thanks go to the Forstamt Binnen and the
Sheep farm Grimberg, who supported and carried out habitat management measures. We owe great
thanks to our financial supporters (Land of Lower Saxony, Bingo Lotto, Deutsche Umwelthilfe,
Stiftung Naturschutz im Landkreis Diepholz, Arbeitsamt Nienburg, BUND, University of
Osnabru
¨ck).
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