Using self-organizing maps to investigate environmental factors regulating colony size and breeding success of the White Stork (Ciconia ciconia)

TL;DR: The self-organizing map algorithm (SOM) proved a relevant tool to help determine actual dynamics in White Stork colonies, and thus to support effective conservation decisions at a regional scale.

Abstract: We studied variations in the size of breeding colonies and in breeding performance of White Storks Ciconia ciconia in 2006–2008 in north-east Algeria. Each colony site was characterized using 12 environmental variables describing the physical environment, land-cover categories, and human activities, and by three demographic parameters: the number of breeding pairs, the number of pairs with chicks, and the number of fledged chicks per pair. Generalized linear mixed models and the self-organizing map algorithm (SOM, neural network) were used to investigate effects of biotic, abiotic, and anthropogenic factors on demographic parameters and on their relationships. Numbers of breeding pairs and of pairs with chicks were affected by the same environmental factors, mainly anthropogenic, which differed from those affecting the number of fledged chicks per pair. Numbers of fledged chicks per pair was not affected by colony size or by the number of nests with chicks. The categorization of the environmental variables into natural and anthropogenic, in connection with demographic parameters, was relevant to detect factors explaining variation in colony size and breeding parameters. The SOM proved a relevant tool to help determine actual dynamics in White Stork colonies, and thus to support effective conservation decisions at a regional scale.

Summary

Introduction

• Environmental conditions are significant determinants in breeding habitats, and may influence the breeding success of birds and contribute to the variability of breeding populations (Lack 1968).
• Most demographic studies on this species have been conducted in temperate areas, mainly in Europe, where environmental conditions and life history traits (e.g., clutch size, colonial or solitary nesting) differ from those encountered in northern Africa.

Methods

• (6) Annual mean of maximum temperatures (°C). (7) Approximate flight distance between the colony and the closest urban area (in m, ±10 m).
• (12) Type of colony [monospecific for the colonies occupied only by White Storks; plurispecific for the colonies occupied by storks and Cattle Egrets (Ardea ibis)].
• Secondly, the authors aimed to emphasize the relationships between environmental variables and the three breeding parameters recorded for each colony (the number of breeding pairs ‘‘HPa’’, the number of pairs with chicks ‘‘HPm’’, and the number of fledged chicks ‘‘JZG’’).

Results

• Breeding parameters and numbers of nests found each year are shown in Table 1.
• The mean number of fledged chicks per nest varied between years (being higher in 2006 than in other years), but was not affected by the number of pairs in the colony or the number of pairs with chicks (Table 2).
• The majority of Stork colonies were distributed in the north-eastern part of the wilaya, particularly on the plains of El Madher, Malel, Belezma and Ain Touta.
• Cluster B and C included colonies located in areas with low inhabitant density, relatively close to urban areas and refuse tips, and intermediate altitude, temperature and precipitation.
• These areas corresponded to the regions where intense farming uses irrigation.

Discussion

• The authors results suggest that the largest colonies were established close to urban areas and refuse, and consequently in the most human-populated zones.
• In their study, the higher number of fledged chicks per nest in colonies situated in areas with relatively high precipitation may reflect an indirect effect of precipitation on food abundance, as suggested by other studies on this species (Denac 2006; Nevoux et al. 2008).
• The geographical location and the average colony size of these 62 colonies are reported in Fig 1. b Gradient analysis of the value for each habitat variable on the trained SOM represented by a shaded scale (light low value, dark high value).
• The authors study thus supports the idea that identifying the variables which significantly affect the breeding parameters of White Storks should be a research priority for conservationists and environmental policy makers.

Figures

Fig. 1 The wilaya (department) of Batna, Algeria, with locations of the 62 colonies and densities of breeding pairs of White Storks (Ciconia ciconia) per colony (census 2008). Numbers refer to colony codes

Table 2 Testing for factors affecting breeding parameters of White Storks in the area of Batna (Algeria) between 2006 and 2008

Table 1 Annual variation (±SD) of the breeding parameters of White Storks (Ciconia ciconia) in the area of Batna, Algeria

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Using self-organizing maps to investigate environmental
factors regulating colony size and breeding success of the
White Stork (Ciconia ciconia)
Abdelkrim Si Bachir, Haroun Chenchouni, Nawel Djeddou, Christophe
Barbraud, Régis Céréghino, Frédéric Santoul
To cite this version:
Abdelkrim Si Bachir, Haroun Chenchouni, Nawel Djeddou, Christophe Barbraud, Régis Céréghino, et
al.. Using self-organizing maps to investigate environmental factors regulating colony size and breeding
success of the White Stork (Ciconia ciconia). Journal für Ornithologie = Journal of Ornithology,
Springer Verlag, 2013, 154, pp.481-489. �10.1007/s10336-012-0915-2�. �hal-00913174�

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and Santoul, Frédéric Using self-organizing maps to investigate
environmental factors regulating colony size and breeding success of
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Using self-organizing maps to investigate environmental factors
regulating colony size and breeding success of the White Stork
(Ciconia ciconia)
Abdelkrim Si Bachir
•
Haroun Chenchouni
•
Nawel Djeddou
•
Christophe Barbraud
•
Re
´
gis Ce
´
re
´
ghino
•
Fre
´
deric Santoul
Abstract We studied variation s in the size of breeding
colonies and in breeding performance of White Storks
Ciconia ciconia in 2006–2008 in north-east Algeria. Each
colony site was characterized using 12 environmental
variables describing the physical environment, land-cover
categories, and human activities, and by three demographic
parameters: the number of breeding pairs, the number of
pairs with chicks, and the number of fledged chicks per
pair. Generalized linear mixed models and the self-orga-
nizing map algorithm (SOM, neural network) were used to
investigate effects of biotic, abiotic, and anthropogenic
factors on demographic parameters and on their relation-
ships. Numbers of breeding pairs and of pairs with chicks
were affected by the same environmental factors, mainly
anthropogenic, which differed from those affecting the
number of fledged chicks per pair. Numbers of fledged
chicks per pair was not affected by colony size or by the
number of nests with chicks. The categorization of the
environmental variables into natural and anthropogenic, in
connection with demographic parameters, was relevant to
detect factors explaining variation in colony size and
breeding parameters. The SOM proved a relevant tool to
help determine actual dynamics in White Stork colonies,
and thus to support effective conservation decisions at a
regional scale.
Keywords White Stork  Ciconia ciconia  Algeria 
Breeding performance  Colony site  Conservation
Zusammenfassung
Welche Umweltfaktoren regulieren Koloniegro
¨
ße und
Bruterfolg beim Weißstorch Ciconia ciconia?—der
Einsatz von Selbstorganisier enden Karten
Untersucht wurden Unterschiede in Brutkoloniesta
¨
rke und
Bruterfolg bei Weißsto
¨
rchen Ciconia ciconia in Nordost-
algerien, in den Jahren von 2006–2008. Jede Kolonie wurde
anhand von zwo
¨
lf Umweltvariablen charakterisiert, welche
Auskunft u
¨
ber physische Umweltbedingungen, Land-
bedeckung und menschlichen Einfluss gaben, sowie anhand
von drei demografischen Parametern: der Anzahl der
Brutpaare, der Anzahl von Paaren mit Ku
¨
ken und der An-
zahl flu
¨
gger Junge pro Paar. Es wurden Generalisierte
Lineare Gemischte Modelle und der Selbstorganisierende
Karten-Algorithmus (Self-Organising Map, SOM, ein neu-
ronales Netz) angewendet, um die Wirkung biotischer,
abiotischer und anthropogener Faktoren auf die demogra-
fischen Parameter und die Beziehungen zwisch en diesen zu
untersuchen. Die Anzahl der Brutpaare und die der Paare
mit Ku
¨
ken wurden von denselben (hauptsa
¨
chlich anthrop-
ogenen) Umweltfaktoren beeinflusst. Dagegen wurde die
Communicated by P. H. Becker.
A. Si Bachir  N. Djeddou
Department of Natural and Life Sciences, Faculty of Sciences,
University of El Hadj Lakhdar, Batna 05000, Algeria
H. Chenchouni
Department of Natural and Life Sciences, Faculty of Exact
Sciences and Natural and Life Sciences, University of Tebessa,
12002 Tebessa, Algeria
C. Barbraud (&)
Centre d’Etudes Biologiques de Chize
´
, CNRS UPR, 1934,
79360 Villiers-en-Bois, France
e-mail: barbraud@cebc.cnrs.fr
R. Ce
´
re
´
ghino  F. Santoul
Laboratoire d’Ecologie Fonctionnelle et Environnement, EcoLab
UMR5245, Universite
´
Paul Sabatier, Ba
ˆ
timent 4R3-b2,
118 Route de Narbonne, 31062 Toulouse cedex 9, France
DOI 10.1007/s10336-012-0915-2

Anzahl flu
¨
gger Ku
¨
ken pro Paar von anderen Faktoren bes-
timmt: Weder die Koloniegro
¨
ße noch die Anzahl von Ne-
stern mit Ku
¨
ken hatten hier einen Einfluss. Die Einteilung
der Umweltvariablen in natu
¨
rliche und anthropogen bed-
ingte half in Verbindung mit demografischen Parametern
dabei, die Faktoren zu identifizieren, welche die Variation in
Koloniegro
¨
ße und den Brutparametern erkla
¨
ren. Die SOM-
Methode erwies sich als geeignetes Werkzeug zur Bes-
chreibung der tatsa
¨
chlichen Dynamik in Weißstorch-Kolo-
nien und stellt somit eine Hilfe bei der Festlegung effekt iver
Schutzmaßnahmen auf regionaler Ebene dar.
Introduction
Many studies have investigated biological and socio-eco-
nomic factors affecting threatened species in order to
understand the current biodiversity crisis (Scott et al.
1995). In birds, studies on habitat selection are of growing
importanc
e for conservation policy and planning because
they deal with quantitative information affecting the
dynamics of bird popu lations (Caughley
1994). Environ-
mental conditions are significa nt determinants in breeding
habitats, and may influence the breeding success of birds
and contribute to the variability of breeding populations
(Lack
1968). The determination of the factors (natural or
anthropogenic) affecting breeding success is the main
target of many bird conservation studies, since breeding
success can often be more easily managed than other
demographic parameters (Pedrini and Sergio
2002;
Gil-Sa
´
nchez et al.
2004; Manning et al. 2004).
Strictly or usually colonial bird species exhi bit wide
variation in colony size, with the smallest and largest
colonies within a species often varying by several orders of
magnitude. Numerous studies used natural variation in
colony size to measure fitness consequences of breeding
with different numbers of conspecifics (van Vessem and
Draulans
1986; Møller 1987; Brown and Brown 2001). In
addition, environmental factors or ecological situations
surrounding breeding sites of birds have critical impacts on
breeding success in either direct or indirect manners
(Burger and Shisler
1980; Cody 1985; Yorio et al. 1995).
In its breeding range, the White Stork (Ciconia ciconia)
nests either solitarily or colonially (Cramp and Simmons
1977). Altho ugh several studies investigated the factors
affecting White Stor k colony size and fitness parameters,
such as breeding success, independently (van Vessem and
Draulans
1986; Carrascal et al. 1993; Barbraud et al. 1999;
Moritzi et al.
2001; Jovani and Tella 2004; Tryjanowski
et al. 2005a, 2005b; Denac 2006), variations in colony size
and fitness may be due to different environmental factors,
and few studies have aimed at disentangling these fac-
tors. In fact, the effect of one environmental factor
(e.g., ambient temperature) may become evident, some-
times with lagged effects, only when other environmental
factors (e.g., food availability) affecting reproduction are
taken into account (Tryjanowski and Sparks
2008).
Therefore, the aim of this paper was to investigate the
main environmental factors affecting the distribution and
size of breeding colonies and breeding parameters of the
White Stork in an ecotone area located between the arid
and semi-arid bioclimatic stages. Most demographic stud-
ies on this species have been conducted in temperate areas,
mainly in Europe, where environmental conditions and life
history traits (e.g., clutch size, colonia l or solitary nesting)
differ from those encountered in northern Africa. This
species is of high conservation interest and its populations
have experienced considerable changes during the last
decades (Thomsen and Ho
¨
tker
2006). Our approach is
based on artificial neural network analyses that enhance our
ability to determine the actual dynamics in colony sizes
and breeding performance, and to investigate how these
demographic parameters are associated to broad-type nat-
ural as well as anthropogenic inf ormation.
Methods
Study area
The study was conducted in the Wilaya (departme nt) of
Batna, north-east Algeria, in an area of 12,192 km
2
located
between 6° and 7°E and 35° and 36°N (Fig. 1). The general
climate is typically Mediterranean with a continental influ-
ence (semi-arid area with cool winters), but ranges from the
arid to the humid category according to Emberger’s (1955)
classification. This wilaya is characterized by predominance
of high montane vegetation forests including tree species
such as Holm Oak (Quercus ilex L.), Atlas Cedar (Cedrus
atlantica M.), and Aleppo Pine (Pinus halepensis Miller.).
Plains are mostly used for cereal crops (mainly Durum
Wheat Triticum durum L. and Barley Hordeum vulg are L.)
and livestock. Livestock mainly includes extensive sheep
grazing and intensive poultry farming.
Survey method
Colonies of White Storks were censused during 3 years
(2006–2008) from early January to early July. We defined a
colony of storks as a breeding site with at least two nests
built on the same suppor t or on two supports separated by a
few meter s (\10 m). Based on dates of first hatched eggs
(2006: March 10; 2007: March 24; 2008: March 20), col-
onies censuses were carried out from May 20 to June 8
2006, from June 2 to July 2 2007 and from June 14 to 30
2008, in order to ensure that when the counts were made no
chick had already fledged. These dates were dictated

according to arrival dates of White Storks on one hand and
dates of the first hatched chick on the other hand. During
the survey period, the color of chicks’ beak and legs was
still blac k, thereby facilitating their detection in the nest
without confusion with the parents. According to Schu
¨
z
(
1936), Arnhem (1980), and Whitfield and Walker (1999),
at 6 weeks the black feathers on the wings appear, and in
the seventh week standing is regular and the chicks per-
form wing beats that prepares the muscles to fly. After the
ninth or tenth week, young chicks perform their first flight.
Censuses were carried out in all admini strative units of
the wilaya of Batna with assistance from the local staff of
the Forests Conservation Direction, who dir ected us
towards nesting sites of storks. Chick counts were often
made during the morning when chicks are fed more fre-
quently and are upright in the nest facilitat ing their count.
The number of chicks was estimated by eye or with
binoculars.
For each colony, the following parameters were
recorded:
(1) Site descripti on: name of the site, exact location
(longitude, latitude), census dates.
(2) The number of bree ding pairs (HPa), defined as a
male and female holding a nest with or without
chicks.
(3) The number of pairs with chicks (HPm), defined as a
male and female holding a nest with chicks, the
presence of chicks indicates the presence of a
breeding pair with chicks.
(4) The number of fledged chicks per nest (JZG). Fledged
chicks were defined as nestlings older than 7 weeks
which are still on the nest and about to fledge. At this
age, chicks are supposed to survive until fledging
since there is no or very slight mortality between the
census period and their fledging (Djerdali et al.
2008b). In computation, JZG was entered as the
average number of fledged chicks per breeding pair in
the colony.
Environmental variables
For each colony site we collected the following environ-
mental variables:
(1) Altitude in meters above sea level measured by an
altimeter (±1 m).
(2) Annual precipitation (mm).
(3) Cumulated precipitation (mm) recorded during
November, December, and January (winter rainfall)
corresponding to the pre-breeding period.
Fig. 1 The wilaya (department) of Batna, Algeria, with locations of the 62 colonies and densities of breeding pairs of White Storks (Ciconia
ciconia) per colony (census 2008). Numbers refer to colony codes

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Using self-organizing maps to investigate environmental factors regulating colony size and breeding success of the white stork (ciconia ciconia)" ?

The authors studied variations in the size of breeding colonies and in breeding performance of White Storks Ciconia ciconia in 2006–2008 in north-east Algeria.