Ibis (2008), 150, 606–618
The origin of out-of-range pelicans in Europe: wild bird
dispersal or zoo escapes?
Blackwell Publishing Ltd
F. JIGUET,* A. DOXA & A. ROBERT
Centre de Recherches sur la Biologie des Populations d’Oiseaux, UMR 5173 MNHN-CNRS-UPMC, CP 51, Muséum
National d’Histoire Naturelle, 55 rue Buffon, F-75005 Paris, France
We tested whether spatial and annual patterns of occurrence of out-of-range Great White
Pelecanus onocrotalus, Dalmatian Pelecanus crispus and Pink-backed Pelicans Pelecanus
rufescens recorded in Europe between 1980 and 2004 supported a natural vagrancy theory.
Candidate variables tested were those likely to influence dispersal and escape probability
(distance to the usual breeding/wintering range, national captive stock), and wild breeding
population sizes and their movements (size of breeding colonies, climate conditions on
wintering grounds or during dispersal). Spatial vagrancy patterns supported the hypothesis
of wild birds dispersing from their normal range, with decreasing national totals with increasing distance to the usual range for the three species. Annual out-of-range numbers of Great
White Pelican were predicted by breeding colony size and breeding success in Greece, with
a further effect of Sahel rainfall during the previous year. Annual numbers of Dalmatian
Pelican were related to the North Atlantic Oscillation index and to breeding success in
Greece. Finally, annual numbers of Pink-backed Pelican were predicted by summer Sahel
rainfall, which is known to drive dispersal of the species northwards into the sub-Sahelian
steppes during wet summers there. Hence, annual vagrancy patterns in Europe were well
predicted for all three species by population size indices, reproductive success and/or climatic
components, which presumably influence survival and/or dispersal. We therefore consider
that vagrancy patterns were driven by wild birds, whereas escapes – even if potentially
numerous – do not create sufficient ‘noise’ to hide these patterns.
Keywords: dispersal, North Atlantic Oscillation, Pelecanus, Sahel, vagrancy.
The origin of rare birds observed in Europe is of
concern for authorities maintaining national lists of
naturally occurring species (e.g. Dudley et al. 2006).
Whilst genuine vagrancy can be assumed for most
Siberian or Nearctic passerines (Gilroy & Lees 2003,
McLaren et al. 2006), the case of waterbirds raises
more doubts, as large collections of such species breed
in captivity throughout Europe, either in zoos or in
smaller private collections. Anecdotal ringing recoveries have proven trans-Atlantic vagrancy for some
duck species (e.g. Baroteaux et al. 2005), whereas
progress in isotopic analyses has recently assessed the
Siberian origin of a first-winter Baikal Teal Anas formosa collected in Denmark in 2005 (Fox et al. 2007).
However, a more general approach is to examine the
observed vagrancy pattern in relation to ecological
*Corresponding author.
Email: [email protected]
© 2008 The Authors
Journal compilation © 2008 British Ornithologists’ Union
variables affecting wild populations, including climatic
components suspected of affecting dispersal or survival on breeding and wintering grounds and along
migration flyways (Dubois & Luczak 2004, McLaren
et al. 2006).
Three species of pelican occur annually and naturally in the Western Palaearctic (Del Hoyo et al. 1992):
the Great White Pelican Pelecanus onocrotalus and
the Dalmatian Pelican Pelecanus crispus breed in
Europe (the latter is rarer) with large numbers in
Romania (Danube Delta), but colonies also exist
in other countries such as Greece, Albania, Bulgaria
or Ukraine. In Northern Africa, the Pink-backed Pelican
Pelecanus rufescens is an annual spring and summer
visitor to southern Egypt at Abu Simbel on Lake
Nasser, close to the Sudanese border, sometimes in
large numbers (over 90 in 1990 and 1994), and it
also breeds just outside the Western Palaearctic in
Saudi Arabia (over 300 pairs; Newton & Symens 1996).
Vagrancy of pelicans to Europe
Outside their usual breeding grounds, migrating
flyways or dispersal ranges, pelicans are regularly
reported in western and northern Europe. Such
out-of-range birds are generally considered to be of
doubtful wild origin, because all three species are
kept in captivity, with some free-flying breeding
parties in a few zoos. As examples, in France for the
last 15 years there have been free-flying Dalmatian
Pelicans at Parc des Oiseaux of Villard-les-Dombes,
Ain department, eastern France (c. 50 birds with up
to eight free-flying adults), and a free-flying colony
of Pink-backed Pelican has been present at the
African Reserve of Sigean, Aude department, Mediterranean coast (c. 30 pairs with, for example, 18
chicks fledged in 2004) since 1974. These birds are
known to wander a few tens of kilometres around
their breeding sites. Therefore, casual pelicans observed
in western and northern Europe, far away from the
known ranges of wild populations, could have originated
from captive stocks, and obviously some do. Nevertheless, pelicans are very good flyers (Weimerskirch
et al. 2001) and are able to disperse over large areas
(Izhaki et al. 2002), so the possibility of natural
vagrancy far away from their usual quarters is entirely
plausible.
For this study, we gathered official records of outof-range pelicans from Europe and Israel between
1980 and 2004, to test predictions that could support
a natural vagrancy instead of an escape theory. We
first examined among-country variation in out-of-range
total numbers during the whole period for each
species, and tested for the effects of population sizes
officially kept in captivity in each country and of the
distance to the closest breeding colony (Great White
and Dalmatian Pelicans) or the only regular occurrence site in the Western Palaearctic (Pink-backed
Pelican). If spatial patterns in out-of-range pelican
occurrences are mainly due to local escapes we
should find a positive effect of the size of national
captive stocks on national totals, and if they are
driven by the dispersal of wild birds the number of
out-of-range birds should decrease with increasing
distance to the usual range.
In a second approach, we made species-specific
predictions derived from the published descriptions
of dispersal and migration strategy as found in the
Handbook of the Birds of the World (Del Hoyo et al.
1992; see below). The predictions were tested for
each species on national annual numbers recorded in
18 countries. Candidate variables tested are those
most likely to influence wild population sizes, and
therefore the pool of birds that are available for
607
dispersal: breeding colony size (either because
breeding birds cannot disperse while breeding, or
because larger population size implies a higher overall probability of some birds dispersing further
(Veit 2000) or of detecting one bird dispersing further);
breeding success (because larger breeding failure
might lead to more opportunity for failed breeders
to disperse before normal migration); climatic conditions (temperature, precipitation) during the previous year or winter (which could affect individual
survival and therefore the pool of birds available for
dispersal) or during the current year (which could
affect the dispersal amplitude).
SPECIES-SPECIFIC PREDICTIONS
In autumn, European populations of Great White
Pelican undergo long-distance movements across
Turkey and the Middle East into Africa (Crivelli et al.
1991a, Izhaki et al. 2002): pelicans arrive in the
Danube Delta late March–April and leave September
to early November, whereas African breeders are
generally sedentary. Many Asian breeders winter in
Pakistan (up to 25 000 individuals) and India (up to
10 000 individuals); 11–17 000 birds are found in
Senegal and Mauritania, and 75 000 in eastern Africa
(Del Hoyo et al. 1992). European populations winter
in eastern Africa, possibly in Kenya and/or in Sudan
(Izhaki et al. 2002). There are only two accepted
records from Morocco (Thévenot et al. 2003), which
supports the theory that the resident African breeders
are unlikely to be the source of out-of-range European
records. Breeding population size in Europe could
drive the stock of individuals ‘available’ for European
vagrancy, as well as the water conditions during the
previous winter in the winter quarters (eastern
Africa and India), which is possibly influenced by
annual precipitation during the previous year. Indeed,
the amount of annual rainfall is known to influence
the abundance of the species in some African wetlands
(Guillet & Crowe 1987). We therefore considered
breeding population size and breeding success in
Greece (the available data), the annual North Atlantic
Oscillation (NAO) index in the current year, and
annual standardized Sahel rainfall, Indian rainfall,
Monsoon index, annual rainfall in Sudan, all four
later climatic components in the previous year, as
potential predictors of out-of-range Great White
Pelican numbers in Europe.
The Dalmatian Pelican is really only dispersive,
rather than truly migratory, except in Asia; European
birds move short distances, staying mostly in the
© 2008 The Authors
Journal compilation © 2008 British Ornithologists’ Union
608
F. Jiguet et al.
eastern Mediterranean zone (Crivelli et al. 1991b).
Recoveries of birds ringed in former USSR suggest
movement to the west or southwest, but recoveries
of birds ringed in Greece suggest movement to the
southeast and also to the north (Bulgaria), with a few
recoveries in Israel, with pelicans arriving on breeding grounds in February–March and leaving in August
(Del Hoyo et al. 1992). Breeding population size in
Europe could drive the stock of individuals available
for long-distance vagrancy. As European birds are
resident or dispersive, local winter climate conditions
could influence local survival, and affect the pool of
live birds that could potentially disperse the following year. Indeed, preliminary analyses of ringing data
indicated an effect of winter temperature and of the
NAO index on survival rate in Greece (A. Doxa
unpubl. data). We considered the breeding population size of six colonies in four countries (Greece,
Albania, Bulgaria and Turkey) and breeding success
in Greece (the available data), winter temperature at
two wintering sites in Greece, annual NAO index in
the current year, and the Indian monsoon index and
winter Indian rainfall (if Asian populations disperse
westwards) in the previous year or winter as potential
predictors of out-of-range Dalmatian Pelican numbers
in Europe and Israel.
The Pink-backed Pelican breeds in sub-Sahelian
Africa, and makes regular movements north into
sub-Saharan steppes to coincide with the short summer wet season there; local movements are possibly
related to water conditions or beginning of breeding;
the species can breed all year round, mostly starting
late in the rainy season (Del Hoyo et al. 1992). Data
on annual variation in breeding numbers are not
available for this species, but annual spring and
summer rainfall in the Sahel could well influence
northward dispersal to Europe. Furthermore, rainfall
conditions on breeding grounds could influence
dispersal, so we considered spring (March–May) and
summer (June–August) rainfall in the Sahel, summer
rainfall anomaly in Sudan, as well as annual rainfall
in Kenya during the previous year, and the annual
NAO index as potential predictors of out-of-range
Pink-backed Pelican numbers in Europe and Israel.
If out-of-range pelicans are mostly escapes, we
should not find any significant correlation between
breeding numbers or climatic components and
temporal observation patterns, as long as the escape
probability of captive-bred pelicans in Europe does
not depend on the size of wild breeding colonies or
climatic conditions in Africa or Asia, which seems
intuitive. If out-of-range pelicans are local escapes,
© 2008 The Authors
Journal compilation © 2008 British Ornithologists’ Union
we should also find a positive link between the
number of national records and the number of birds
kept in captivity in the country. If most of these
pelicans are of a wild origin, some of the speciesspecific predictions should be validated, as long as
escapes do not create sufficient ‘noise’ to hide the
natural vagrancy pattern. In other words, temporal
variation in out-of-range pelican numbers should be
well explained by some of the proposed predictors,
while it would not exclude that at least some individuals had a captive origin. In this case, we should
also find a negative link between national number of
records and the distance to the closest breeding
colony (or to southern Egypt for the Pink-backed
Pelican), suggesting a diffuse dispersal from the usual
range.
METHODS
Pelican records
We gathered data on out-of-range pelicans from
official records with identification validated by national
rarities committees. Therefore the data relate to
pelican records in countries where the species are
considered to be rare. We sent an e-mail asking for
national 1980–2004 accepted records to the mailing
list of the AERC (Association of European Records
and Rarities Committees). Members of national rarities committees who provided information are cited
in the Acknowledgements. We also collected official
records in annual reports of such committees, as
published in ornithological journals, e.g. Ornithos
(France), Limicola (Germany), Avocetta and Rivaria
Italiana Ornitologica (Italy), Dutch Birding (the
Netherlands), Ardeola (Spain), British Birds (the UK).
Data were obtained for 17 countries in Europe plus
Israel: Austria, Belgium, Cyprus (not for Great White
Pelican), Denmark, Estonia and Finland (but no
pelicans were identified to species in these two
countries), France, Germany, Hungary, Italy, Luxembourg, the Netherlands, Norway, Poland, Spain,
Switzerland, and the UK. Data from Israel (Dalmatian
and Pink-backed Pelicans only) were obtained from
Shirihai (1996) with the addition of two records of
single Pink-backed Pelicans observed in 1997 and
2000 (Smith & the IRDC 2007). Individual birds
that have obviously escaped from captivity (e.g. birds
with evidence of wing-clipping, wearing zoo rings)
are excluded from national counts by national rarities
committees if reported to them. We therefore
considered all records accepted as category A (wild
Vagrancy of pelicans to Europe
origin) or category D (wild origin possible but not
certain), but available data could not include relevant
comprehensive information on known escapes
(category E of national lists), which were therefore
not considered, except for the Pink-backed Pelican
for which we considered all documented records
even if not published by rarities committees (with
the exception of those obtained at close proximity to
the French free-flying colony, which are not considered by the French rarities committee). For the Great
White Pelican in Italy, we gathered records from
different sources with the help of Nicola Baccetti, a
member of the Italian RC, as the species is not
considered by this committee. Finally, different
rarities committees have different stances on what
they consider acceptable for a potential wild origin.
So the datasets we used certainly include escapes,
but the most obvious ones have been excluded.
However, as we are interested in temporal variation
in out-of-range numbers, our results should not depend
on such cases, as long as their annual distribution is
close to random.
In total, records included 216 Great White, 40
Dalmatian and 92 Pink-backed Pelicans. Pelican
numbers kept in European zoos have been found on
the web portal of the International Species Information System ISIS (http://www.isis.org/CMSHOME/):
there were 636 Great White, 367 Dalmatian and 167
Pink-backed Pelicans officially reported in captivity
throughout Europe in 2006.
Variation among countries
We examined variation in national totals among
countries for the whole period and for each species.
Raw data used were total number of out-of-range
individuals recorded in each country for the period.
As the information on presence or absence of records
was not available for each country in each year
between 1980 and 2004, we first controlled for an
effect of the number of years with available data (so
including years with information that there was no
record in that year). We also controlled for potential
effects of country size (as the total area covered by
the country: larger countries could receive more
pelicans just because they are large), total area covered
by wetlands in the country (as the amount of available
suitable habitat where out-of-range pelicans could
stop), and mean latitude of the country (as a proxy
for climate, related to the latitudinal gradient of
temperatures across Europe). Latitude is strongly
correlated with other climatic variables, such as
609
average monthly temperature in January (n = 18
countries, r = 0.82) or in July (r = 0.85). We then
looked for potential effects of national captive stocks
(as the number of birds officially kept in zoos in each
country, obtained from the web portal of the ISIS –
http://www.isis.org/CMSHOME/) and of the distance
from a country barycenter to the usual range, as breeding
colonies (either in the Danube Delta 45.2°N, 29.2°E
or in Greece 40.8°N, 21.1°E) for the Great White
and Dalmatian Pelicans, or as the regular occurrence
site within the Western Palaearctic for the Pinkbacked Pelican (i.e. Abu Simbel on Lake Nasser in
southern Egypt; 22.34°N, 31.72°E). For the latter
species, we also considered the distance to the large
free-flying colony in southern France (c. 80 birds at
the African Reserve of Sigean) as a fifth control
variable, as birds originating from this breeding population could well be responsible for some European
records. These analyses were conducted using loglinear models, first adjusted for the effects of the four
or five control variables, then for the effects of the
two predictors adjusted to each other (type III error).
We did not consider hierarchical partitioning analyses
as our data had first to be adjusted for the effects of
the number of documented years, total area, wetland
area and latitude. The number of captive birds (+1)
and distances (originally in kilometers, obtained
from GoogleEarth at www.earth.google.fr) were logtransformed before analyses.
In these analyses, we used all information available:
18 countries for Dalmatian and Pink-backed Pelicans,
but without Estonia, Cyprus and Israel for the Great
White Pelican.
Breeding numbers and success
Breeding colony sizes for the Great White Pelican in
Greece (Lake Mikri Prespa) were obtained for the
period 1983–98 from Crivelli et al. (2000). The
same reference was also used to obtain breeding
numbers of Dalmatian Pelican at six colonies: Greece
(two colonies), Albania (one colony), Bulgaria (one
colony) and Turkey (two colonies) for the period
1980–98. Additional data for the period 1999–2004
were also available for the two Greek colonies of
Dalmatian Pelican (D. Hatzilacou, G. Catsadorakis
& H. Nikolaou unpubl. data). As breeding numbers
were not reported for each colony each year for the
Dalmatian Pelican, we further estimated an annual
abundance index of breeding pairs. The abundance
index was obtained from a log-linear model that
accounts for missing data performed on the annual
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Journal compilation © 2008 British Ornithologists’ Union
610
F. Jiguet et al.
number of breeding pairs in each colony and calculated using the software TRIM (TRends and Indices
for Monitoring data; Pannekoek & van Strien 2001).
TRIM is designed to analyse time-series of counts
with missing observations using Poisson regression
(log-linear models). Missing counts from particular
colonies were estimated (‘imputed’) from changes in
all other colonies. This abundance index was highly
correlated with the (log-transformed) breeding
numbers at Prespa in Greece (Pearson’s correlation,
n = 24, r = 0.94). Breeding successes of Great White
(1984–98) and Dalmatian (1984–2003) Pelicans at
Greek colonies were also considered as the average
number of fledged young per pair (Catsadorakis
et al. 1996, M. Malakou & H. Nikolaou unpubl.
data). Breeding success and (log-transformed) colony
size were highly negatively correlated for the Great
White (r = −0.584, n = 15, P < 0.01) and positively
correlated for the Dalmatian Pelican (data from
Prespa in Greece; r = 0.636, n = 20, P < 0.001).
Large scale climate indices
Some links to large-scale climatic variables were
found on the Climate Diagnostics Centre website
(http://www.cdc.noaa.gov/ClimateIndices/). The
selected variables were the annual NAO index
(http://www.cgd.ucar.edu/cas/jhurrell/indices.data.
html#naostatann), the monthly standardized Sahel
rainfall (http://jisao.washington.edu/data/sahel/), the
monthly Indian rainfall as well as the annual Indian
Monsoon index (http://www.cdc.noaa.gov/Correlation/indiamon.data). Data were initially obtained on
a monthly basis, but were also computed on an
annual (sum of monthly data from January to
December) or seasonal (December–February, March–
May, June–August and September–November) basis
when judged necessary. Annual rainfall at Nairobi,
Kenya, was obtained from http://envstudies.brown.edu/
thesis/2005/timothy_downing/Rainfall.htm. Spring
(March–May) and summer (July–September) rainfall
in Sudan were obtained from the Climate Explorer
of the Royal Netherlands Meteorological Institute
KNMI (http://climexp.knmi.nl/start.cgi?someone
@somewhere). Rainfall in Sudan was considered
because the Sahel rainfall index does not cover
Eastern Africa, although it covers a wide area and is
probably more representative of African rainfall
than data from Sudan. Winter temperatures used for
the Dalmatian Pelican analyses were those from
Amvrakikos Gulf and Lake Kerkini, two wintering
sites for the species in Greece; we considered the
© 2008 The Authors
Journal compilation © 2008 British Ornithologists’ Union
average December–January temperatures for each
year over the period 1980–2004, as the mean of the
two sites.
Statistical analyses on annual patterns
We used pelican data of annual national totals per
species for all countries, when data was available
(true absence of national records in a given year
being reported as zero). For each species, we tested
our predictions by performing a stepwise log-linear
model (Poisson distribution and log-link function)
on national number of out-of-range pelicans observed
each year, with an additive effect of country. Effects
of predictors were tested while being adjusted to
each other (type III errors). The annual colony size
of Great White Pelicans was log-transformed before
the analysis. All tested predictors were included in a
first model and we then performed a stepwise selection of the best model explaining the variance most
parsimoniously, i.e. with the smallest set of predictors using the Akaike Information Criterion (Akaike
1973).
There is a distinction between finding the best
model to describe the data and drawing inferences
about the likely causality of variables, and dealing
with multicollinearity is difficult in single-model
approaches. A possible solution is hierarchical partitioning, which uses all models in a regression hierarchy
to distinguish those variables that have high independent correlations with the dependent variable
(Chevan & Sutherland 1991). We therefore also
analysed our data with hierarchical partitioning
(MacNally 2002). For each species, we first performed
a regression on out-of-range numbers by considering
a country effect alone, and stored the residuals to
perform the hierarchical partitioning on them. We
obtained the independent (I) and joint (J) contributions of the predictors; Z-scores were obtained using
500 repeated randomizations (Walsh & MacNally 2003).
We performed these analyses using the hier.part
package of the R statistical software (R DCTeam 2004).
We are aware that performing regression or hierarchical analyses on residuals obtained from a preliminary regression model can be sensitive (Freckleton
2002), but we thought that this hierarchical partitioning could be an interesting complementary
analysis to the stepwise regression models we performed, though their results are to be considered with
some precaution. We did not consider hierarchical
partitioning approaches for studying spatial patterns
in out-of-range records, as the dependant variable
Vagrancy of pelicans to Europe
611
Table 1. Results of log-linear models performed on national totals of out-of-range pelicans (period 1980–2004) for countries with
available data. Models were first adjusted for effects of the number of years with documentation, total country area, wetlands area per
country, and latitude. After controlling for these variables, two predictors were tested: number of birds kept in captivity in each country
and shortest distance to the usual range. For the Pink-backed Pelican, we also (b) replaced the distance to the usual range by the
distance to the French free-flying colony, and (c) then tested the effect of distance to the usual range in a model initially also controlling
for the effect of distance to the free-flying colony. Significant P-values are in bold.
Species
Predictor
P. onocrotalus
(df = 8)
P. crispus
(df = 11)
P. rufescens
(df = 11)
Captive stock
Distance to closest breeding site
Captive stock
Distance to closest breeding site
(a) Captive stock
Distance to Lake Nasser
(b) Captive stock
Distance to French ‘colony’
(c) Captive stock
Distance to Lake Nasser
(df = 11)
(df = 10)
had first to be adjusted to four/five control variables,
and performing hierarchical partitioning on residuals
without accounting for error estimation for these
control variables would produce questionable results.
RESULTS
Comparing zoo and out-of-range pelican
numbers
A chi-squared test revealed that numbers of captive
vs. out-of-range birds have different proportions
across the three species ( χ22 = 65.6, P < 0.001), with
the highest number of birds observed in the wild,
compared to the captive stock, for the Pink-backed
Pelican (the species with the highest number of freeflying birds), and the lowest for the Dalmatian Pelican
(the most sedentary species).
Estimate ± sd
t-value
P
0.83 ± 0.20
−2.72 ± 0.30
−0.86 ± 0.29
−4.04 ± 0.81
−0.12 ± 0.15
−1.27 ± 0.13
−0.11 ± 0.13
−1.56 ± 0.39
−0.14 ± 0.14
−2.46 ± 0.71
4.10
−8.99
−1.97
−4.97
0.86
−1.87
−0.83
−3.97
−1.01
−3.44
0.003
2.10−5
0.07
0.001
0.41
0.088
0.42
0.002
0.34
0.006
Great White Pelican only a positive effect of the
national number of birds kept in captivity.
For the Pink-backed Pelican, we also ran a similar
model but replaced the distance to Abu Simbel by
the distance to the free-flying colony in southern
France (43.03°N, 2.98°E). In this model, 79.6% of
variance was captured, and we found no significant
effect of the national captive stock but a significant
effect of the distance to the free-flying colony
(Table 1). We ran a final model for this species, first
controlling for effects of the four previous control
variables in addition to distance to the free-flying
colony, and further looked at adjusted effects of
captive stock and distance to the usual range. In this
model (Table 1), 86.7% of variance was captured,
and we found a significant effect of distance from the
usual range (Table 1; t = −3.44, df = 10, P = 0.002).
Inter-annual occurrence variation
Variation among countries
Results of log-linear models investigating among
country variation in national totals are presented in
Table 1. Proportion of variance captured by models
(with four control variables and two predictors) was
96.4% for the Great White Pelican, 72.5% for the
Dalmatian Pelican and 74.7% for the Pink-backed
Pelican. The four control variables alone captured
52.6%, 39.6% and 71.8% of total variance for the
Great White, Dalmatian and Pink-backed Pelicans,
respectively. For the first two species, we found a significant negative effect of the distance to the closest
natural occurrence site (see Table 1), and for the
Great White Pelican
We used data on out-of-range Great White Pelicans
in Europe from 1983 to 1998, including records
from Austria (three birds), Belgium (two), France
(30), Germany (four), Hungary (24), Italy (10), the
Netherlands (two), Poland (45), Spain (13), Switzerland (one) and the UK (one). The initial model
included colony size at Mikri-Prespa (Greece), NAO
index in the current year, standardized Sahel rainfall,
Indian Monsoon index, annual Indian rainfall, annual
Kenyan rainfall and annual Sudanese rainfall, all in
the previous year. The final log-linear model included
two predictors: colony size (t = −6.70, df = 151,
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Journal compilation © 2008 British Ornithologists’ Union
612
F. Jiguet et al.
df = 124, P < 0.001; Fig. 2) and the breeding success
(t = −2.71, df = 124, P < 0.001); 32.3% of the total
variance was captured.
Pink-backed Pelican
Figure 1. Correlation between annual number of out-of-range
Great White Pelicans Pelecanus onocrotalus observed in Europe
and breeding colony size in Greece. Each dot represents 1 year
between 1983 and 1998. Variables are log-transformed.
P < 0.001; Fig. 1) and standardized annual Sahel
rainfall during the previous year (t = 2.42, df = 151,
P = 0.017), which captured 55.5% of the total
variance.
We further ran the same stepwise model after
excluding records from Hungary and Poland, where
the species is considered to be of wild origin and
where records are most numerous (69, so more than
half of the total). The final model included the same
two predictors: colony size (t = −5.42, df = 121;
P < 0.001) and standardized Sahel annual rainfall
during the previous year (t = 3.52, df = 121, P < 0.001),
with 54.8% of total variance captured.
If also considering the reproductive success in the
initial model, the final model for all countries included
three predictors: colony size (t = −6.18, df = 142,
P < 0.001), breeding success (t = −1.90, df = 142,
P = 0.059) and standardized annual Sahel rainfall
during the previous year (t = 2.98, df = 142, P = 0.003),
for which 55.9% of the total variance was captured.
We used data on out-of-range Pink-backed Pelicans
in Europe and Israel from 1980 to 2004, including
records from Austria (one bird), Belgium (four),
France (28), Germany (nine), Hungary (nine), Israel
(three), Italy (24), Luxembourg (one), the Netherlands (one), Norway (two), Poland (one), Spain (14),
Switzerland (one) and the United Kingdom (three).
The initial stepwise log-linear model first included
the annual NAO index, annual, spring (March–May)
and summer (June–August) Sahel rainfall anomalies,
spring and summer rainfall in Sudan, as well as annual
rainfall in Kenya during the previous and current
year. The final model included three predictors:
standardized Sahel rainfall in spring (t = 1.64, df = 183,
P = 0.10) and summer (t = 3.46, df = 183, P < 0.001),
and annual rainfall in Kenya during the current year
(t = 2.37, df = 183, P = 0.019), which captured 50.8%
of the total variance. We ran this model again after
replacing the standardized spring and summer Sahel
rainfalls with a single combined standardized spring–
summer Sahel rainfall (as the sum of spring and
summer values, so from March to August). In this
case, the final model included this Sahel rainfall
variable, which was highly significant (t = 4.81,
df = 184, P < 0.001; Fig. 3), and annual rainfall in
Kenya (t = 2.23, df = 184, P = 0.027); 47.5% of the
total variance was captured. These results were
robust to the exclusion of a potential outlying year
(2001), as the Sahel received exceptional rainfall
during spring and summer in that year, while 12
Pink-backed Pelicans were recorded in southern
Europe (see Fig. 3): spring–summer Sahel rainfall
(t = 3.69, df = 171, P < 0.001; annual rainfall in
Kenya, t = 3.13, df = 171, P = 0.002); 43.0% of total
variance was captured.
Dalmatian Pelican
We used data on out-of-range Dalmatian Pelicans in
Europe and Israel from 1980 to 2003, including
records from Cyprus (three birds), France (one),
Hungary (14), Israel (five), Italy (one), Spain (10)
and Poland (three). The initial stepwise log-linear
model first included annual estimates of breeding
pair numbers, breeding success in Greece, NAO
index, Indian monsoon index in the previous year,
winter rainfall in India (December–February) and
winter temperature in Greece. The final model
included two variables: the NAO index (t = 3.41,
© 2008 The Authors
Journal compilation © 2008 British Ornithologists’ Union
Hierarchical partitioning
Results of the hierarchical partitioning are presented
in Table 2, where independent and total (independent
and joint) contributions of predictors are given, as
well as the Z-scores (for the generated distribution of
randomized independent contributions of variables
Is) and their corresponding statistical significance.
For the Great White Pelican, we found a significant
independent effect of the breeding colony size but
not of the breeding success. The hierarchical partitioning for the Dalmatian Pelican identified independent
Vagrancy of pelicans to Europe
613
Table 2. Results of hierarchical partitioning of variance investigating the temporal patterns in out-of-range records of three species of
pelicans in Europe. The hierarchical partitioning is performed on residuals from a first regression model accounting for a country effect.
Independent (I) and total (independent and joint) contributions of predictors are given, as well as the corresponding Z-scores (obtained
using 500 repeated randomizations) and their statistical significance. Significant P-values are in bold.
Species
Predictor
P. onocrotalus
Colony size
Breeding success
NAO
Sudanese rainfall
Sahel rainfall
Indian rainfall
Monsoon index
Colony size
Breeding success
NAO
Winter temperature
Indian rainfall
Monsoon index
NAO
Sahel rainfall (spring)
Sahel rainfall (summer)
Sahel rainfall (spring + summer)
Sudanese rainfall
Kenyan rainfall
P. crispus
P. rufescens
contributions of NAO index and breeding success
(though the latter just short of statistical significance;
Table 2), and spring/summer Sahel rainfall and
Kenyan rainfall were significant independent contributions for the Pink-backed Pelican (Table 2).
DISCUSSION
Great White Pelican
National totals of out-of-range numbers during the
whole period were significantly positively correlated
with the number of birds kept in captivity; we
conclude that some of the out-of-range Great White
Pelicans observed in Europe were in fact escapes,
even if they were not obvious ones (obvious escapes
being excluded from national reports by rarities
committees). However, we also found a significant,
strong negative correlation with the distance to the
closest breeding colony, suggesting that out-of-range
records could also include birds dispersing from
European breeding sites.
When testing species-specific predictions (interannual occurrence variation), we found a highly
significant negative relationship between breeding
numbers in Greece and out-of-range numbers in
Europe, suggesting that, for a given pool of live birds,
I
I+J
Z-score
P
0.0717
0.0055
0.0005
0.0123
0.0045
0.0011
0.0009
0.0051
0.0314
0.0461
0.0034
0.0023
0.0019
0.0045
0.0090
0.0131
0.0182
0.0170
0.0312
0.0939
0.0223
0.0007
0.0324
0.0123
0.0004
0.0005
0.0093
0.0206
0.0361
0.0061
0.0004
<0.0001
0.0025
0.0243
0.0145
0.0320
0.0127
0.0158
7.88
−0.17
−0.68
0.74
−0.23
−0.66
−0.69
−0.29
1.42
3.33
−0.50
−0.85
−0.86
−0.11
0.39
1.23
2.52
0.89
1.68
<10–10
−
−
0.23
−
−
−
−
0.078
4.10–4
−
−
−
−
0.348
0.109
0.006
0.187
0.046
an adult Great White Pelican coming back from its
African wintering grounds faces an alternative, either
breeding or dispersing. Such a decision could depend
on local spring conditions or previous wintering
conditions, which could determine the opportunity
for such long-lived birds to invest in reproduction in
a given year (Stearns 1992). Moreover, we found a
negative effect of breeding success on out-of-range
numbers, revealing that for a given colony size
(because effects of predictors were adjusted to each
other in regression models, which means that the
effect of breeding success was measured on residuals
that were independent of colony size), vagrancy is
more likely when more breeders failed in their
breeding attempt. This suggests that more failed
breeders might disperse during the summer. In such
a scenario, we should expect out-of-range birds to
be mainly potential breeders, hence mature adults,
and to occur in late spring and summer. Indeed,
most out-of-range Great White Pelicans observed in
western and northern Europe have been reported
as adults (see Fig. 4a, 4b). The records for 1980–2004
concerned 37 adults, two subadults and 17 immatures in Poland; 15 adults, five subadults and five
immatures in Hungary; and 22 adults and four
immatures in France. For these three countries, two
abundance peaks were obvious in April–May, and to
© 2008 The Authors
Journal compilation © 2008 British Ornithologists’ Union
614
F. Jiguet et al.
a lesser extent in August–September, which probably
mirror the dispersion of adult-type non-breeders in
spring and of failed breeders in summer. Ageing
Great White Pelicans is difficult in the field, especially outside the breeding season, because 2- or
3-year-old immatures can look adult-like, although
the ages of birds reported here are as reported by
national rarities committees.
Furthermore, wintering conditions seem to influence the potential for migrants to disperse into
western or northern Europe, as we found an effect of
Sahel rainfall during the previous year on out-of-range
numbers, although this effect was not confirmed by
the hierarchical partitioning analysis. Such rainfall
could affect the water conditions on the wintering
grounds, and then the ability of European individuals to survive the winter in Africa and to come back
to Europe the next spring. We obtained similar results
when excluding data from Hungary and Poland, two
countries with numerous records of vagrant Great
White Pelicans and where they are considered to be
of a wild origin.
The breeding population used here to estimate
breeding numbers is relatively small (between 54
and 139 pairs) compared with the larger populations
breeding, for example, in the Danube Delta (460–
2000 pairs; Schogolev et al. 2005), but it is not
inconceivable that factors affecting breeding numbers
in Greece could also affect those in Romania, and
the very strong relationship found here between
European vagrant and Greek breeding numbers
suggests that many Great White Pelicans observed in
western and northern Europe are genuine vagrants,
and indeed come from such European populations.
Greater confidence in this pattern would be supported by the use of breeding numbers in Greece
and in the Danube Delta, too, but annual surveys of
the species in the Danube Delta are not regular and
only started in 1996. Available censuses gave 1800
breeding pairs in 1996, 2000 in 1997, 460 in 1999
and 1700 in 2001 (Schogolev et al. 2005); only 2 of
these years were included in our analyses (available
censuses of breeding colony size in Greece from
1983 to 1998).
Dalmatian Pelican
National totals of out-of-range numbers during the
whole period were significantly negatively correlated
with the distance to the closest breeding colony,
suggesting that out-of-range Dalmatian Pelicans
observed in Europe could involve birds dispersing
© 2008 The Authors
Journal compilation © 2008 British Ornithologists’ Union
from breeding colonies, and probably were not
mainly local zoo escapes (we found no significant
effect of national captive stocks).
When testing species-specific predictions on interannual occurrence variation, we found, as for the
previous species, a negative relationship between
out-of-range records and breeding success in Greece.
This suggests that failed breeders might be prone to
disperse, which is in accordance with the abundance
peak of European records in late spring (Fig. 4c).
More interesting was the positive relationship found
with the annual North Atlantic Oscillation index,
suggesting that general atmospheric conditions in
Europe (a large NAO is generally linked to larger air
mass movements over the continent; Stenseth et al.
2002) might influence the survival or the dispersal of
the species in Europe. Interestingly, this pattern
approaches the one found for the Great White
Pelican: a negative effect of breeding numbers and/or
breeding success in the current year and a positive
effect of a climatic variable potentially enhancing
wintering conditions during the previous winter.
The observed phenology of out-of-range Dalmatian
Pelicans in Europe and Israel revealed two peaks
(Fig. 4c), in May (after breeding onset, probably due
to the dispersal of early-failed breeders) and in
October following autumn dispersal.
Pink-backed Pelican
Models for this species produced the most surprising
results, as it initially seemed fair to consider European
records as involving only zoo escapes. But as for the
other two species, national totals of out-of-range
numbers during the whole period were significantly
negatively correlated with the distance to the closest
regular occurrence site in the Western Palaearctic
(Lake Nasser in southern Egypt). However, these
national totals were also well predicted by the distance to the large colony of free-flying birds located
in southern France, so Pink-backed Pelicans observed
in the wild around Europe certainly include captivereared birds. When controlling for this effect in an
adjusted model, the number of national records still
increased with decreasing distance to Abu Simbel,
though the high totals from France and Spain strongly
suggest that most of these birds are escapes from the
French free-flying colony. However, beyond the
effects of variables controlled for, the correlations we
found seem to support the controversial hypothesis
of natural dispersal to Europe of a few African wild
Pink-backed Pelicans.
Vagrancy of pelicans to Europe
When testing species-specific predictions (interannual occurrence variation), we first did not expect
to predict variation in European annual records with
a climatic variable known to drive the northwards
dispersal of this species into the Sahel. However, we
found a strong positive effect of summer Sahel rainfall and Kenyan annual rainfall on the number of
Pink-backed Pelicans reaching Europe and Israel.
This pattern was not driven by vagrancy to Israel,
which lies closer to breeding sites in eastern Africa
and Saudi Arabia, as only three of the 80 records
came from this country. This result is in accordance
with the observed phenology of the species in Europe
and Israel, with more reports in August and September
(Fig. 4d), though this could also partly imply a postbreeding dispersal of European full-winged zoo
birds. The absence of records from the Middle East
(outside Israel) and south-eastern Europe (Turkey,
Greece) could well reflect a lack of detection of the
species, due to a low observation effort or little interest in verifying the specific identity of any observed
pelican. The phenology of records during the year,
with at least three to four birds recorded each month
(Fig. 4d), is probably a nice illustration of the potential
‘noise’ created by escapes.
Genuine European vagrants could find their origin
in eastern or western Africa (e.g. the record from the
Canary Islands), and as natural movements are
known to occur in Africa with northward dispersal
into the Sahel during the short wet summer of this
region, our results are consistent with a wild origin of
some Pink-backed Pelicans in Europe in some years,
driven by rainfall amplitude in the Sahel from June
to August. As examples, some of the records obtained
in 1990, 1994 and 2001 could well be attributed to
natural vagrancy from Africa; in these years unprecedented large numbers of Pink-backed Pelicans were
noted in southern Egypt on Lake Nasser (more than
90 individuals in 1990 and 1994, and at least 30 in
April 2001). Spring and summer rainfall in the Sahel
was exceptional in 2001 and in that year 10 birds
were seen in Italy (including a group of five juveniles
during September), one individual was reported
from Corsica (France), and one individual was sighted
in Andalucia (Cadiz province of Spain). Although
Europe could be regarded as having received unusual
numbers of Pink-backed Pelican in 2001, this year
falls well within the modelled pattern obtained if
2001 is excluded from the analysis (see Fig. 2), and
thus it is likely that some Pink-backed Pelicans
observed in Europe were of wild origin and not just
escapes.
615
Figure 2. Correlation between annual number of out-of-range
Dalmatian Pelicans Pelecanus crispus observed in Europe and
Israel (first adjusted to breeding success in Greece, e.g. residual
not explained by this predictor) and the North Atlantic Oscillation
index. Each dot represents 1 year between 1984 and 2003.
Numbers of out-of-range pelicans have been log-transformed.
Figure 3. Correlation between annual number (log-transformed)
of out-of-range Pink-backed Pelicans Pelecanus rufescens
recorded in Europe and Israel and standardized spring–summer
(March–August) Sahel rainfall. Each dot represents 1 year
between 1980 and 2004. The dashed line represents the linear
trend obtained when excluding data from 2001, which could have
been an outlier.
In Saudi Arabia, four major nesting colonies of
Pink-backed Pelicans with 310 active nests were
discovered in 1995; the breeding season appears to
span October–February; the Saudi Arabian population
holds c. 1200 birds and a further 300–500 probably
occur along the Yemen Red Sea coast (Newton &
Symens 1996). Given the breeding phenology of
this population, the last chicks fledge just before the
beginning of the wet season in the Sahel and the
northward migration of Great White Pelicans through
© 2008 The Authors
Journal compilation © 2008 British Ornithologists’ Union
616
F. Jiguet et al.
Figure 4. Phenology of out-of-range records of pelicans, on a monthly basis. (a) Great White Pelican Pelecanus onocrotalus (for a total
of 215 birds observed between 1980 and 2004); (b) Great White Pelican, for all countries except Poland and Hungary; (c) Dalmatian
Pelican Pelecanus crispus (for the 40 birds reported in this study between 1980 and 2003); (d) Pink-backed Pelicans Pelecanus
rufescens (for a total of 91 birds observed between 1980 and 2004). Only the first date of observation is considered for birds that
remained at one site for a long time or for individual birds that were recorded switching between sites. Results are also presented
according to the age of the birds if reported (adult-type versus immatures).
Ethiopia, Sudan and the Middle East; hence it seems
conceivable that some Pink-backed Pelicans prone to
disperse may join migrating Great White Pelicans in
sub-Sahelian or Sahelian Africa and Saudi Arabia
and further disperse into Europe during the summer.
CONCLUSION
By regulation, captive birds of non-domestic species
should wear special rings to indicate their origin,
although this is often not the case. In France, fledged
Pink-backed Pelicans from the African Reserve of
Sigean have been ringed annually since 2002, but
were not marked before this time. There are certainly
© 2008 The Authors
Journal compilation © 2008 British Ornithologists’ Union
escaped pelicans wandering around Europe, either
wearing zoo rings or not. Indeed, our results on
variation among countries revealed that the data we
used should include escapes for the Great White Pelican (the larger the national captive stock, the more
records in a country) and for the Pink-backed Pelican
(with more records in countries closer to the French
free-flying zoo colony). However, as national numbers of out-of-range birds decreased with increasing
distance to usual ranges, and as annual variations in
out-of-range numbers have been well predicted by
meaningful ecological and climatic variables, our
results give strong support to a genuine occurrence
of all three pelican species in northern and western
Vagrancy of pelicans to Europe
Europe. However, determining the true origin of any
particular individual will never be an easy task, unless
it had been ringed in a wild population, and would
be mainly probabilistic, based on the analysis of
global pattern and climatic conditions whenever
relevant. Finally, such analyses could also be conducted to assess the potential genuine occurrence in
Europe of other African/Asian waterbirds. For example,
the Pygmy Cormorant Phalacrocorax pygmeus occurs
annually in western and central Europe outside its usual
range, while it shares a large range with Eurasian
pelicans. Among African species suspected to reach
Europe naturally, similar analyses could be developed
for Ruddy Shelduck Tadorna ferruginea, Fulvous
Whistling Duck Dendrocygna bicolor, Lesser Flamingo
Phoenicopterus minor, African Spoonbill Platalea alba,
Yellow-billed Mycteria ibis and Marabou Stork
Leptoptilos crumeniferus and Allen’s Gallinule Porphyrio
alleni.
Alain Crivelli provided invaluable help in gathering original
data and commenting on early analyses. D. Hatzilacou,
G. Sarigul, M. Malakou, M. Siki, P. Simeonov and H.
Nikolaou provided unpublished data on pelican censuses.
We wish to thank all authorities who provided access to
national records: Jean-Yves Frémont and Georges Olioso
(France), Nicola Baccetti, Daniele Occhiato, Luciano Ruggieri and Marco Zenatello (Italy), José Ignacio Dies (Spain),
Colin Richardson (Cyprus), Bernard Volet (Switzerland),
Patric Lorgé (Luxembourg), Johannes Laber (Austria),
Tamás Zalai (Hungary), Tadeusz Stawarczyk (Poland),
Vegard Bunes (Norway), Antero Lindholm (Finland), Uku
Paal (Estonia) and Laurent Raty (Belgium). Pierre-Yves
Henry provided an easy access to climatic databases, while
Julien Gonin and Pierre Crouzier helped with clarifying
the current status of captive but free-flying breeding pelicans in France. Pierre Camberlin provided data on rainfall
in Sudan from the Royal Netherlands Meteorological
Institute. Stuart Newson helped with improving the
English and three anonymous referees provided helpful
comments on a first draft of the manuscript.
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