Wednesday 4 July 2012


There are few easier birdwatching tasks than studying White Storks in Extremadura. Almost by inertia, therefore, monitoring of the White Stork (Ciconia ciconia) population in Plasencia and roundabout began back in 1998. 2012 therefore saw the culmination of 15 years' work. Sadly, however, for natural and man-induced reasons, it has been the worst season since the series started, with an all-time low of 74 occupied nests recorded. This figure is 40% lower than the peak of 122 nests in 2005 and 12% lower than the start of the study in 1998 (84 pairs). The reason for this fall is basically the systematic removal of nests from powerlines and buildings, since the White Stork population has continued to grow in neighbouring areas. In the grid QE22, for example (Valle del Alagón) it grew by 63% from 2004 to 2011 (from 87 to 142 pairs; Corchero, 2011) and the colony of Mirabel landfill site by 210% in the same period (from 42 to 130 nests).


The study zone almost coincides with IBA 304 "Plasencia y Sierra de San Bernabé" and takes in the built-up area of Plasencia (56 pairs in 2012 - see distribution by buildings in the image above - peaking at 75 in 2001-2002), three powerline colonies (13 pairs in 2012, peaking at 45 in 2005) and five isolated pairs on the churches of Casas del Castañar, El Torno, Valdastillas, Barrado and Gargüera. All nests were built on artificial structures barring one rock-based nest (active for five years but never with breeding success) and another in a Cork Oak (active for eight years), both associated with a powerline colony.

The above graph shows the population trend. There was a big increase in pairs in the first three seasons(1998-2000) the rise levelling off in the next five (2001-2005). The upward trend finally came abruptly to a halt in 2006, when 19 pairs were lost after the removal of 20 nests from the powerline of the N-110 road (eight new nests were built and this same number remains in 2012 though with continual changes of site after further nest-removal campaigns) and 15 from the Centro Universitario-Cuartel de la Constancia (seven new nests were built). Further destruction followed in March 2008 when all the nests (25) were removed from the Cathedral, the biggest colony in the area. Fortunately local ginger groups forestalled new dissuasive measures and 18 nests were rebuilt, remaining occupied in 2012. Fifteen nests were also removed from the powerline of El Robledo, Malpartida de Plasencia; eight were rebuilt and only four remain in 2012. After slight dip in 2011 the biggest percentage reduction came in 2012 when all nests were removed from the powerline of Gargüera (none rebuilt) with only two occupied of the 15 that once existed on the Centro Universitario. It is paradoxical that it should be an ostensibly educational institution perpetrating this persecution of the storks. In this period many of the buildings of Plasencia have lost their nests, some on blocks of flats, others on property of the bank Caja de Extremadura (hotel, auditorium, offices), several in the bishop's palace and some from stately homes. In general tolerance is higher in religious buildings than in civil buildings.


If we factor in the poor weather conditions it is now easy to explain the extremely low breeding success in 2012. The situation seems to have been similar in the rest of Extremadura and in other regions of Spain, and also with the Black Stork (Ciconia nigra) in Cáceres too. White Storks began to breed in a poor physical state due to the dearth of food after a long and severe drought from November 2011 to March 2012. Untimely bursts of rain and cold snaps in April then exacerbated the situation and undoubtedly led to the death of small chicks in the nest, as shown by the graphs. The number of fledglings was the lowest ever, only 59, way below the 283 recorded in the exceptional year of 2001 and the mean figure of 162. This represents fewer than one chick per pair, specifically 0.8, half of the mean figure. The percentage of successfully breeding pairs (53%) is also the lowest in the 15-year series (mean of 75%); the same goes for the fledgling rate (number of chicks per successful pair). In 2012 only two pairs managed to rear three chicks. By way of comparison, in 2001 there were five nests with five fledglings and 21 with four. In general, the breeding parameters show a downward trend, especially after 2008; this might be bound up with the persistent removal of nests. In the last six years only three cases of four-fledgling nests have been observed, whereas this was fairly habitual up to 2006. Nonetheless, the breeding success is determined above all by the weather. The factors most detrimental to breeding success are wet springs (high chick death) low fledgling rate but with a high percentage of successfully breeding pairs; witness 2009) and drought (high nest failure, with a good fledgling rate, as in 2005). In 2012 both factors obtained, so the result was a dire breeding season across the board.


- Corchero, E. 2011. La cigüeña blanca en municipios de regadío del valle del río Alagón (NW Cáceres). Censo y parámetros reproductivos. Informe inédito.