Spatial distribution of nests of the European pond turtle, Emys orbicularis (Reptilia: Testudines: Emydidae), from long-term studies in central Poland

Abstract

Nest sites of the European pond turtle Emys orbicularis were marked in the Borowiec Nature Reserve (central Poland) from 1987 to 2002. In this area the turtle could lay eggs once a year. For 13 females, four to 12 nest sites per individual are known from the period studied. Spatial distribution of the sites is presented on maps. Only a small proportion of the female turtles displayed fidelity to a particular nesting sites, whilst others changed their nesting area. Even if there are nesting areas near water bodies, some of the females opt to use other sites. The results of the study suggest that, to gather accurate data about nesting areas used by the turtle, long-term studies are needed. Protection of the used as well as potential nesting areas (on which during short term studies laying was not recorded) could be important for conservation of the turtle.

Full text

95
Zoologische Abhandlungen (Dresden) 55
© Zoologische Abhandlungen, ISSN 0375-5231, Dresden 25.05.2006
: 95–102
: 95–102
Spatial distribution of nests of the European pond turtle,
Emys orbicularis (Reptilia: Testudines: Emydidae), from
long-term studies in central Poland
SŁAWOMIR MITRUS
DEP ARTM ENT OF BIOSYSTEM ATICS, DIVISION OF ZOOLOGY, UNIVERSITY OF OPOLE, OLE S K A 22,
45-052 OPOLE, POLAND, E-MAIL: EM YSPL(AT)YAHOO.COM
Abstract. Nest sites of the European pond turtle Emys orbicularis were marked in the Borowiec
Nature Reserve (central Poland) from 1987 to 2002. In this area the turtle could lay eggs once
a year. For 13 females, four to 12 nest sites per individual are known from the period studied.
Spatial distribution of the sites is presented on maps. Only a small proportion of the female turtles
displayed fi delity to a particular nesting sites, whilst others changed their nesting area. Even if there
are nesting areas near water bodies, some of the females opt to use other sites. The results of the
study suggest that, to gather accurate data about nesting areas used by the turtle, long-term studies
are needed. Protection of the used as well as potential nesting areas (on which during short term
studies laying was not recorded) could be important for conservation of the turtle.
Kurzfassung. Nester der Europäischen Sumpfschildkröte, Emys orbicularis, wurden in der Zeit
von 1987 bis 2002 im Naturschutzgebiet Borowiec (Zentralpolen) markiert. In diesem Gebiet
legen die Schildkröten einmal im Jahr Eier. Von 13 Weibchen wurden in diesem Zeitraum vier
bis 12 pro Individuum gefunden und untersucht. Die räumliche Verbreitung der Nester wird in
Karten dargestellt. Nur ein kleiner Teil der weiblichen Schildkröten zeigte eine Bindung an den
Nistplatz, während andere den Eiablageplatz wechselten. Besonders wenn sich die Nistplätze nahe
von Wasserfl ächen befanden, neigten einige Weibchen zur Nutzung anderer Plätze. Die Ergeb-
nisse lassen vermuten, dass Langzeitstudien notwendig sind, um zuverlässige Daten über die, von
den Schildkröten genutzten Nistplätze zu erhalten. Der Schutz der genutzten und potenziellen
Nistplätze, die in den Kurzzeitstudien nicht erfasst werden konnten, können wichtig für den Schutz
der Schildkröte sein.
Key words. Reptilia, Testudines, Emydidae, Emys orbicularis, behaviour, distribution of nests,
freshwater turtle, nesting area fi delity, reproduction ecology, Poland
1. Introduction
The European pond turtle, Emys orbicularis, lives in North Africa, the Iberian Peninsula, most
parts of South and Central Europe, as well as in Asia Minor and Central Asia (FRITZ, 1998).
It is an endangered species in many parts of its range (cf. FRITZ & ANDREAS, 2000). Now it
is an intensively studied species (OTA, 1999; HÖDL & RÖSSLER, 2000; FRITZ, 2003), although
most reports about the natural history of the turtle are based on short term research. However,
turtles are considered as long-living organisms (WILBUR & MORIN, 1988; SHINE & IVERSON,
1995) and as such, for planning protection of the European pond turtle, the value of such
studies are limited.
SCHNEEWEISS & STEINHAUER (1998) reported that three females of the European pond turtle
migrated probably to the same areas as 24 years previously. However, data concerning the
localities of freshwater turtles’ nests in subsequent years are scarce (cf. MITRUS, 2006). Such
information is important for understanding the ecology of the species, as well as for making
plans for its conservation. If nesting areas are used during long periods, knowledge about their
localities could be essential in order to protect populations of the turtle. However, as turtles
are long-living animals it is very probable that during their life, the ecological parameters of
nesting areas could change and females would be forced to look for new nesting areas.

96 MITRUS: Distribution of nests of the turtle Emys orbicularis
In a previous article (MITRUS, 2006) I have shown that some females of the European pond
turtle from central Poland, do display a long-term fi delity to a specifi c nesting area, but that
other individuals do not exhibit such behaviour. However, I provided a map showing the
spatial distribution of all known nest sites from the period 1987–2002 only; without data for
those sites were used by specifi c individuals (cf. MITRUS, 2006). I think that precise data about
the spatial distribution of nest sites of different individuals is important. Such information
could be very useful for planning research on populations of the turtle, and plans to establish
new protected areas. In this article, I provide precise data about nest site localisations during
the period 1987 to 2002, of individuals for which four or more nest sites are known.
2. Materials and Methods
Fieldwork was conducted from 1987 to 2002 in the Borowiec Nature Reserve (Zwolenka
River valley, central Poland, the Radom district). The location of the study site is presented in
MITRUS & ZEMANEK (2004), and more information about the reserve – in ZEMANEK (1992).
Turtles were marked by notching the marginal scutes (PLUMMER, 1989) or – before 1991 – the
numbers on the second vertical scute of carapace were engraved (MITRUS & ZEMANEK, 1998).
For each year during the egg-laying period (mid May to mid June, depending on the weather),
the European pond turtle females were observed with binoculars on their way to nesting areas
or while nesting. The age of most females is not known (cf. MITRUS, 2006). Nests were marked
by placing four pegs at the corners of a 50 cm square centered on the nest. In all sites marked
as nest sites, eggs were deposited (abandoned digs were very rare during the study, and were
not included in the analysis): the egg-laying process was observed, hatchlings were taken for
rearing as part of an active protection program (MITRUS & ZEMANEK, 1998), and/or pieces of
eggshells from disturbed nests were observed.
The sites were located on a map in the scale of 1 : 5.000, drawn on the ground on the basis of
an aerial photo from 1997. Due to the precise descriptions given in the fi eldwork notes it was
possible to show nest site localities with precision to within 10 m.
Statistical analyses were done using the software package Statistica, ver. 5 (STATSOFT INC.,
1999). Between-stand similarities of nest sites distribution were identifi ed using cluster analysis
with three methods of agglomeration: unweighted pair-group average (UPGA), weighted pair-
group average (WPGA) and Ward’s (MANLY, 1989; HAIR et al., 1992). Euclidean distances were
used. In the analysis data were used for females for which three or more nest sites are known.
Arbitrarily, a distance of 20 m or less between consecutive nests for a given female was taken
to indicate that the female displays nesting area fi delity.
3. Results
Each year (from 1987 to 2002), in the studied area, from 2 to 15 nest sites of the European
pond turtle were marked. No multiple nesting by one female during one season was observed.
A total of 118 nests for the turtle were marked: 115 nest sites of 23 different females, and three
nest sites of unknown females.
The nests of six females were found a total of 29 times (range 4–6 per female) during the
16-year study (Fig. 1.). For the next seven females, 65 nest sites are known (range 8–12 per
female; Figs 2A, B). For another four females three nest sites per individual are known.
The three dendrograms obtained by clustering sites according to the nests’ localities were
quite similar for the different agglomeration methods used. All the methods divided nest sites
in similar groups, although, there were differences with the aggregations of the groups. The

97
Zoologische Abhandlungen (Dresden) 55
1
2
1995
1997
1998
2000
2001
1995
1997
1994
1999
2001
1999
1993
1995
1989
1991
1992
1999
1997
2001
1993
1992
1995 1989 1998
1999
Nest sites of females
No 16
No 08
No 11
No 54
No 12
No 03
100 200 300
metres
0
N
1992
farms and farm buildings
water
forests
wet places with trees or bushes
field roads and paths
meadows
agricultural fields
xerothermic slopes and barrens
area increased on Figs. 2A,B
major area where turtles were
observed in reservoirs
Legend of the map
Zwolenka River
1995
1997
2001
Fig. 1. Nest sites localities in the Borowiec Nature Reserve (central Poland) and years of laying;
data for the females of the turtle Emys orbicularis for which 4 to 6 nests per female from the 16-year
period (1987-2002) are known. Different fi gures represent the nest sites of different individuals.
The “E” numbers are the identifi cation numbers of the animals.

98 MITRUS: Distribution of nests of the turtle Emys orbicularis
No 13
No 15
No 10
Nest sites of females
No 01
No 23
No 14
No 06
100 m
A
B
1999
1998
1997
1994
1993
2001
2000
2002
1997
1993
1994 1996
1998
1999 2000
2001
1991
1992
1998
1993
1994
2000
1995
1997
199920012002
1995
1997
1993
1992
1998
1999
2001 2000
2002
1997
1998
2002
2001
1993
19941995
1999
2000
1988
1991199419951996
1997
1999
1990
1997
19992000 2001
2002
1994
1995
1988
1987
1992
1990
1991
Nest sites of females
Fig. 2A, B. Nest site localities in the Borowiec Nature Reserve (central Poland) and years of laying;
data for the females of the turtle Emys orbicularis for which 8-12 nests per female from the 16-year
period (1987-2002) are known. Different fi gures represent the nest sites of different individuals.
The “E” numbers are the identifi cation numbers of the animals. Map legend – see Fig. 1.

99
Zoologische Abhandlungen (Dresden) 55
dendrogram based on UPGA agglomeration corresponded to distances between nesting areas
in the fi eld, so I have printed this one (Figs 3A, B).
Two females (E13 and E14; the “E” numbers are the identifi cation numbers of the animals)
displayed nesting area fi delity during throughout the studied period (Figs 2A, B and Figs
3A, B). Some others showed nesting area fi delity over a shorter period – from two to four
consecutive nestings (e.g. E06, E10, E15, E23; Figs 2A, B and Figs 3A, B). However, other
females did not show such behaviour (e.g. E11, E54; Fig. 1 and Figs 3A, B).
4. Discussion
During the study, no multiple nestings by the European pond turtle during one season were
observed. This supports the results of other studies; namely, that in central Europe the turtle
lays eggs once a year (ANDREAS & PAUL, 1998; JABŁOŃSKI & JABŁOŃSKA, 1998; MITRUS &
ZEMANEK, 1998; SCHNEEWEISS et al., 1998).
In order to show the spatial distribution of nest sites, I have chosen the nesting sites of females
for which 4 or more clutches are known. Some of the females display long-term (> 10 years)
fi delity to a nesting area (Figs 2A, B and Figs 3A, B – females E13 and E14; cf. MITRUS, 2006),
whilst for others the fi delity period is shorter (Figs 2A, B and Figs 3A, B – E06: 1997–1999,
E10: 1999–2002, E15: 1993–1995; cf. MITRUS, 2006). Knowledge about used nesting areas
could be important for protecting a particular turtle population. However, some females do
not show fi delity to a particular nesting area (Fig. 1 and Figs 3A, B; cf. MITRUS, 2006); thus,
for population conservation, protection of known as well as potential nesting areas could be
essential.
In the studied population most turtle nests were localised in a distance shorter than 150 meters
from water bodies (MITRUS, 2006). Such behaviour was reported earlier for the European pond
turtle (ROVERO & CHELAZZI, 1996; PAUL & ANDREAS, 1998). However, in the studied population
there are also females that deposit their clutches distinctly farer away from shorelines (about
150 m from the closest water bodies, in the studied population e.g. females E03, E16, Fig.
1), and during nesting migrations they crossed nesting areas of other turtles (e.g. female
E03 during breeding migrations crossed areas used by females E01 and E15, cf. Fig. 2A, B;
S. MITRUS, M. ZEMANEK – unpublished data). The reason for such behaviour is not known.
However, it could be important for plans to protect the turtle: even if there are good nesting
areas close to water bodies and some individuals lay eggs on these areas, other individuals
could use different areas (sometimes a long distance from water).
Some individuals of the European pond turtle in the studied population displayed fi delity to
a particular nesting area, but changed the nesting areas when vegetation grew larger and the
original site was overshadowed by growing trees, e.g.: areas used by female E10 in years
1987–1992 (Fig. 2A), by female E06 between 1993 and 1999 (Fig. 2B), as well as by female
E08 in years 1989, 1991, 1992 (Fig. 1; S. MITRUS & M. ZEMANEK – unpublished data). Thus, as
proposed by LINDEMAN (1992) in his model, the females probably changed nesting areas when
certain ecological characteristics changed and were no longer suitable for egg incubation. In
the model, a female selects a nest site, and then returns there on subsequent nesting forays as
long as the site retains the features for which it was selected; the site is changed, when they are
disturbed by man or shaded by growing trees and bushes (LINDEMAN, 1992).
However, some of the female turtles changed nesting areas without visible changes in the
environment. Sometimes, it was observed that a female visited the nesting area used in the
previous year, started to look for place to lay her eggs, but after some hours changed the
nesting area: in 2000, female E23 initially visited nesting area used in years 1992–1999,

100 MITRUS: Distribution of nests of the turtle Emys orbicularis
4
5
Fig. 3B
2000 E55
2001 E55
1999 E55
2001 E54
1999 E11
1995 E25
1994 E25
2001 E16
1999 E54
1997 E54
1995 E16
1994 E16
1999 E68
1999 E12
1995 E10
1997 E08
2001 E12
1997 E12
1994 E10
1995 E08
2001 E06
2001 E14
2000 E14
1999 E14
1998 E14
1997 E14
1996 E14
1994 E14
1993 E14
1991 E14
2000 E10
1999 E10
1997 E10
1997 E25
2002 E10
2001 E10
2000 E06
1991 E10
1990 E10
1992 E08
1992 E10
1988 E10
1987 E10
1989 E08
1999 E06
1991 E08
1998 E06
1997 E06
1994 E06
1993 E06
Linkage Distance
0
100
200
1993_E06
19
9
1997_E16
19
9
1992_E03
19
9
2002_E54
19
9
1995_E23
19
9
2001_E23
19
9
1998_E23
19
9
1999_E13
19
9
1996_E13
20
0
1997_E23
19
9
1988_E13
19
9
1995_E13
19
9
1989_E11
20
0
1993_E03
20
0
1998_E11
20
0
2000_E15
20
0
1999_E15
19
9
1993_E15
19
9
2002_E06
20
0
1999_E01
19
9
1995_E01
20
0
2001_E15
20
0
1994_E01
19
9
1998_E07
19
9
1998_E01
19
9
1993_E68
19
9
1998_E15
19
9
2001_E07
19
9
1992_E01
1999 E16
1997 E16
1995 E11
1992 E03
1995 E03
2002 E54
1990 E13
1995 E23
1997 E03
2001 E23
1999 E23
1998 E23
1992 E23
1999 E13
1997 E13
1996 E13
2001 E03
1997 E23
1991 E13
1988 E13
1998 E03
1995 E13
1994 E13
1989 E11
2000 E03
1993 E23
2002 E23
1998 E11
2000 E23
2000 E15
2002 E01
1999 E15
1995 E15
1993 E15
1994 E15
2002 E06
2001 E01
1999 E01
1997 E01
1995 E01
2002 E15
2001 E15
2000 E01
1994 E01
1993 E01
1998 E07
1992 E12
1998 E01
1995 E68
1993 E68
1993 E12
1998 E15
1997 E15
2001 E07
1999 E07
1992 E01
Linkage distance
0
100
200
300
400
500
0
100
200
A
B
Linkage distance
Fig. 3A, B. Clustering of nest sites of the turtle Emys orbicularis from central Poland (Euclidean
distances, unweighted pair-group average). As the distances were measured with a precision to
10 m, the true distances between nesting sites could be greater than presented on the fi gure. The
“E” numbers are the identifi cation numbers of the animals. The arrows show an example of two
females, which do not show fi delity to any one nesting area; braces – two females, which display
fi delity to a given nesting area during some successive seasons.

101
Zoologische Abhandlungen (Dresden) 55
but afterwards laid her eggs on a different area (Fig. 2B); likewise, female E06 in years
1997–1999 and 2001 (Fig. 2B; S. MITRUS & M. ZEMANEK – unpublished data). But in central
Poland no research on environmental parameters was undertaken, and it is not possible to
generalise the information.
I have shown that some females of the European pond turtle could use the same area during up
to 10 consecutive years, sometimes even more (e.g. E14, Figs 2B, 3A). JABŁOŃSKI & JABŁOŃSKA
(1998, p. 143) estimated that the length of time during which turtles use the same or nearby
nesting sites was a minimum of 60–70 years. However, the authors presented no empirical
data to support this conclusion, thus the information (and probably even the estimation of
the females’ age) are rather anecdotal. To understand the life history of freshwater turtles,
information about their longevity as well about the length of the reproduction cycle and long-
term distribution of the nest sites are needed.
5. Conclusions
1. To gather information about the selection of nesting areas by the European pond turtle, long-
term and concern on many individual studies are needed.
2. In central Poland only some female turtles displayed fi delity to a particular nesting area.
3. Even if there are nesting areas near water bodies, some female turtles use other ones,
sometimes a long distance from water.
4. Female turtles are able to change nesting area even if there are not easily visible changes
in the used nesting areas. Reason for such behaviour is not yet known, but for the turtle
conservation it is also important to protect potential nesting areas (e.g. on which laying was
not observed during short-term studies). It is probable, that after renaturalisation of disturbed
nesting areas, females (or part of them) return to lay eggs on the area.
However, as in different parts of the turtle distribution area, the reproductive behaviour could
be different; thus fi delity to nesting areas could also be different.
Acknowledgements
I am grateful to Dr. M. ZEMANEK for giving me access to the pre-1990 data she collected on nest
site locations, and to all my colleagues who helped with the fi eldwork, especially M. ZEMANEK and
A. KOTOWICZ. I thank R. TERTIL for help to edit the manuscript. The data used in the study were
collected during a program of active protection for the European pond turtle, supported by the
EcoFund – Polish Debt for Environment Swap, the Global Environment Facility (GEF/SGP
UNDP), the Kozienice Landscape Park, and the Environment and Agriculture Department of the
Mazowiecki Voivodeship Offi ce in Warsaw.
Literature
ANDREAS, B. & R. PAUL (1998): Clutch size and structure of breeding chambers of Emys o.
orbicularis in Brandenburg. – In: FRITZ, U. et al. (eds.): Proceedings of the EMYS Symposium
Dresden 96. Mertensiella, Rheinbach 10: 29–32.
FRITZ, U. (1998): Introduction to zoogeography and subspecific differentiation in Emys orbicularis
(Linnaeus, 1758). – In: FRITZ, U. et al. (eds.): Proceedings of the EMYS Symposium Dresden
96. Mertensiella, Rheinbach 10: 1–27.
FRITZ, U. & B. ANDREAS (2000): Distribution, variety of forms and conservation of the European
pond turtle. In: SOPTOM (ed), Proceedings of the 2nd International Symposium on Emys
orbicularis, June 1999. – Chelonii 2: 23–26.

102 MITRUS: Distribution of nests of the turtle Emys orbicularis
FRITZ, U. (2003): Die Europäische Sumpfschildkröte. Bielefeld, Laurenti, 224 pp.
HAIR, J. F., JR., ANDERSON, R. E., TATHAM, R. L. & W. C. BLOCK (1992): Multivariate data analysis
with readings. – Macmillan, New York, pp. 265–291.
HÖDL, W. & M. RÖSSLER (2000): Die Europäische Sumpfschildkröte. – Land Oberösterreich, OÖ.
Landesmuseum, Linz, Stapfi a 69, 248 pp.
JABŁOŃSKI, A. & S. JABŁOŃSKA (1998): Egg-laying in the European pond turtle, Emys orbicularis (L.),
in Łęczyńsko-Włodawskie Lake District (East Poland). – In: FRITZ, U. et al. (eds.): Proceedings
of the EMYS Symposium Dresden 96. Mertensiella, Rheinbach 10: 141–146.
LINDEMAN P. V. (1992): Nest-site fixity among painted turtles (Chrysemys picta) in northern Idaho.
– Northwestern Naturalist 73: 27–30.
MANLY B. F. J. (1989): Cluster analysis. – In: MANLY, B. F. J. (ed.), Multivariate Statistical Methods.
Chapman & Hall, London, pp. 100–113.
MITRUS, S. (2006): Fidelity to nesting area of the European pond turtle, Emys orbicularis (Linnaeus,
1758). – Belgian Journal of Zoology 136 (1): 25–30.
MITRUS, S. & M. ZEMANEK (1998): Reproduction of Emys orbicularis (L.) in Central Poland. –
In: FRITZ, U. et al. (eds.): Proceedings of the EMYS Symposium Dresden 96. Mertensiella,
Rheinbach 10: 187–192.
MITRUS, S. & M. ZEMANEK (2004): Body size and survivorship of the European pond turtle Emys
orbicularis in Central Poland. – Biologia, Bratislava 59/Suppl. 14: 103–107.
OTA, H. (1999): A review of the European pond turtle, Emys orbicularis (Testudines: Emydidae), as
a subject for integrative population studies. – Japanese Journal of Herpetology 18: 30–36.
PAUL, R. & B. ANDREAS (1998): Migration and home range of female European pond turtles
(Emys o. orbicularis) in Brandenburg (NE Germany), fi rst results. – In: FRITZ, U. et al. (eds.):
Proceedings of the EMYS Symposium Dresden 96. Mertensiella, Rheinbach 10: 193−197.
PLUMMER, M. V. (1989): Collecting and Marking. – In: HARLESS, M. & H. MORLOCK (eds.), Turtles.
Perspectives and Research. 2nd ed. Robert E. Kreiger Publishing Company, Malabar, Florida,
pp. 45–60.
ROVERO, F. G. & CHELAZZI (1996): Nesting migrations in population of the European pond turtle
Emys orbicularis (L.) (Chelonia Emydidae) from central Italy. – Ethology, Ecology & Evolution
8: 297–304.
SCHNEEWEISS, N., ANDREAS, B. & N. JENDRETZKE (1998): Reproductive ecology data of the European
pond turtle (Emys o. orbicularis) in Brandenburg, Northeast Germany. – In: FRITZ, U. et al.
(eds.): Proceedings of the EMYS Symposium Dresden 96. Mertensiella, Rheinbach 10:
227–234.
SCHNEEWEISS, N. & C. STEINHAUER (1998): Habitat use and migrations of a remnant population of the
European pond turtle, Emys o. orbicularis (Linnaeus, 1758), depending on landscape structures
in Brandenburg, Germany. – In: FRITZ, U. et al. (eds.): Proceedings of the EMYS Symposium
Dresden 96. Mertensiella, Rheinbach 10: 235–243.
SHINE, R. & J. B. IVERSON (1995): Patterns of survival, growth and maturation in turtles. – Oikos
72: 343–348.
STATSOFT, INC. (1999): STATISTICA for Windows [Computer program manual]. – Tulsa, OK:
StatSoft, Inc., 2300 East 14th Street, Tulsa.
WILBUR, H. M. & P. J. MORIN (1988): Life History Evolution in Turtles. – In: GANS, C. & R. B. HUEY
R. B. (eds.), Biology of the Reptilia. Alan R. Liss, Inc., New York, pp. 391–440.
ZEMANEK, M. (1992): Rezerwat przyrody Borowiec w dolinie Zwoleńki. – Ochrona Przyrody 50:
173–195.
Received 01.11.05 , accepted 27.01.06.