TRANSLATED BY MARTIN KELSEY
Despite being a very attractive species for birdwatchers, the unusual and isolated Iberian population of Black Stork (Ciconia nigra) continues to be poorly known. Indeed, the only national census carried out in Spain took place way back in 1987. Since then, there have only been some compilations of information from varied sources. From these early estimates, the population in Extremadura (161-219 pairs over the period 1995-2013) has always been the largest. Portugal follows, with between 97-115 pairs in a national census carried out in 2004, and Andalucía, with 87 pairs in 2009, all of them in the Sierra Morena. With pre-2003 figures, we have Castilla y León (61 pairs), Castilla-La Mancha (24) and Madrid (12). Adding this all together, admittedly over a long time frame, produces 470 pairs for certain in the Iberian Peninsular, although it is likely that the real figure exceeds, probably by a margin, 500 pairs. If one takes into account published data, the Iberian population has apparently increased (Cano y Hernández, 2003, cited 405 certain pairs). If there had been a better coverage, it is probably wiser to consider the population as stable. For example, in the case of Andalucía, where a figure of 54 pairs (2006) and 52 pairs (1999, 2005, 2007) rose to 89 pairs (2009), an increase of no less than 70% in two years, which seems improbable under natural circumstances.
Focusing
on the population in Extremadura, the graph below shows the values
obtained in 17
regional censuses
that
we have been able to compile. Two phases can be seen, the first
between 1973 and 1989, when ornithology in Extremadura was in its
infancy and the data are partial, mainly anecdotal. And the second
phase from 1993m the government of Extremadura started annual counts.
The studies undertaken by Adenex (José Luis Pérez-Chiscano, Víctor
Pizarro, José A. Román, Juan J. Ferrero and others) have also
helped. The information of these last twenty years shows a stable
trend, with peaks and troughs most likely because of differences in
effort and coverage
(there are variations of up to 21% between consecutive years). The
maximum figure was 219
pairs in 1995,
followed by 195 pairs in 2011. In 2013,
the census recently made public reached
189 certain pairs ,
30 less than the maximum twenty years ago. By province, 116
pairs were found in Cáceres and 73 in Badajoz (in
2003 there were 101 and 82, respectively). Taking into account that
censuses almost always underestimate real populations, it
us very likely that there are more than 200 pairs in Extremadura,
perhaps
even 220.
The
map shows the breeding distribution of Black Stork in Extremadura.
The areas of highest breeding density are shown in red: the
dehesas
of
south-west Badajoz, Monfragüe, Alagón, the Tiétar pinewoods and
areas in along the Tajo and Guadiana rivers. This area of occupation
remains practically the same since the first censuses, being centred
along the Tajo river and its tributaries, and in some areas of dehesa
and mountains.
With
respect to
breeding,
we have information from 2002 and 2013. In
2013, 147 nests were monitored, from which 290 young fledged. The
reproductive indices are very similar in both years:
-
productivity (fledged young
per occupied nest): 1.97 in 2013, 2.05 in 2002.
-
fledging success (fledged young
per successful nest): 2.45 in 2013 and 2002.
-
Percentage of pairs which raise young successfully:
82% en 2013.
These
figures for Extremadura are very similar to the average for Spain
as whole (1.94) and
elsewhere in Europe (1.81 in Latvia, 1.96 in Lithuania) (Cano, 2012).
An
interesting aspect of
the Iberian population of Black Stork is the high proportion of nests
built on rock. The Black Stork normally nests in trees across its
wide range across Europe, although there are countries where use of
rocky sites is significant (Austria
28%, Bulgaria 52%). The distant population in southern Africa nests
exclusively on rock and the isolated Iberian population has a figure
of 55%, with 75% in the case of Portugal. For
Extremadura detailed information of nest substrate use is given for
the years 2003 and 2013 (table). Nests
on rock reach 55%, the same
as the Iberian population as a whole, with somewhat more use of this
substrate in 2003 than in 2013. It is noteworthy that whilst the
population, distribution and breeding success has remained stable
over the last decade, there
are important changes in best sites.
There has been a drop in the
number of nests in cork oak by a third,
compensated by an increase
in tree nests in general,
especially in holm oak and pine. With respect to rock sites, there
has been an increase in use
of rocky valleys, now the
habitat most often used, with a decrease in sites in mountain ranges.
These
changes in nest sites deserve a more detailed analysis to determine
the conservation impact of the Black Stork as well as the Cork Oaks
themselves (are there fewer Cork Oaks of sufficient size? Has
their management changed? Is there more disturbance?). Over
the last decade there at least has been more information on the
conservation of Black Stork. Some of
us remember that
in 2003, at a regional congress, Pizarro et
al. cited seven nests that were
destroyed by fire that year (three in the dehesas of Jerez, two in
the Tiétar pines, one in Cañaveral and one in Sierra de San Pedro)
or how the construction of the Alqueva dam apparently caused the loss
of ten active nests; also they stated that half the nests in cork oak
suffered disturbance during the cork harvest and during pruning; and
how sensitive nests were to boat traffic on rivers, indeed that there
were no nests on navigable stretches. And not forgetting the damage
caused by changing water levels on reservoirs, with 23 nests and 25
chicks lost in 1994.
Acknowledgements:
This post is based on information published in the sources cited
below. The 2013 data come from a press release from
DGMA-Junta de Extremadura,
apart from the nest site data which have been provided Ángel
Sánchez/DGMA (in litt.). The censuses in Extremadura are carried out
every year by some 250 rangers and other staff of the Environment
Directorate. We also would like to extend our thanks to personnel in
Portugal and other parts of Spain, as well as to other fieldworkers
and volunteers who have collaborated.
References:
- Anuarios Ornitológicos de Extremadura. 1998-2008.
- Informes de Medio Ambiente en Extremadura. 2006-2012.
- Censos oficiales de la CMA-Junta de Andalucía.
- Cano, L. S. 2012. Biología y conservación de la cigüeña negra en la península Ibérica. Tesis Doctoral. Universidad Complutense de Madrid.
- Cano, L. S. y Hernández, J. M. 2003. Cigüeña negra Ciconia nigra. En Martí, R, y del Moral, J.C. (Eds.).Atlas de las aves reproductoras de España. MMA y SEO/BirdLife. Madrid.
- DGMA. 2004. The black stork in Extremadura, Southwest Spain. IV Conferencia Internacional de cigüeña negra. Dávod-Püspökpuszta. Hungría. Abril 2004.
- Ferrero, J.J. y Pizarro, V. M. 2003. La cigüeña negra en Extremadura. Cuadernos Populares 61. Consejería de Cultura. Junta de Extremadura. Mérida.
- Pizarro, V. M., Fererro, J. J. y Gil, A. 2003. Conservación de la cigüeña negra en Extremadura. II Congreso de especies protegidas de Extremadura. 19-21 noviembre 2003. Cáceres. DGMA. Junta de Extremadura.
