SUMMARY: This brief study covers the counting and behaviour description of wintering Black Storks (Ciconia nigra) in a precise area of rice fields which surrounds the river Guadalquivir at southwestern Spain during three seasons. This small area has been highly transformed by intensive agriculture. It seems to hold one of the most important population of wintering Black Storks in Europe and it has remained relatively unknown as a wintering quarter until now.
Keywords: Black Stork, wintering, rice fields.
INTRODUCTION:
Spain has a stable wintering population of black storks (San Segundo, C., 1991). Doñana National Park and its surroundings has always been a well known wintering area for black storks (García L. et al., 1996; González , J.L. 1987) however this specific zone kept relatively unknown as an important winterground for this ciconiforme.
The information that appears in this study has been gathered over a 3 year period starting 7.11.1998 when the African Odyssey project from the Chezch Republic asked us to monitor the movements and behavior of David, a male Black Stork equipped with Argos and VHF transmitters, when it choose the rice fields which surrounds the Guadalquivir river as his wintering quarters in southern Spain.
On monitoring David we started to notice an important number of wintering black storks during the mentioned period. During this time we also release one of David's offspring, Jonas, on 31.12.98 (Parkes, C. 1999) who joined the group of storks including his father.
The observation and data, although continuous, has been irregular due to lack of funding and the great distances from our places of residence.
METHOD OF PROCEDURE
In this period we visited the zone in 32 journeys, using receivers (AR 8000), telescopes and GPS.
During every expedition we covered with cars the total area, criss-crossed with numerous tracks that divide the rice fields and canals. As obstacles are few, the sightings of the birds was on occasions easy, especially when we got signalled from the tagged birds. However, when they were out of sight inside the canals, we had great difficulty in locating them as they are very shy and fly off at the slightest human presence.
DESCRIPTION OF THE AREA:
This extremely flat area consists about 3,750 hectares and lies at N37° W6°, between one of meanders of the river Guadalquivir, known as Brazo del Este, and the town of Las Cabezas de San Juan, province of Seville, opposite the National Park of Doñana. However it lacks any level of legal or administrative protection.
The natural vegetation is practically non-existent, where few short eucalyptus are the only trees. The whole area has been completely transformed by intensive agriculture, especially the growing of rice. As usual in the cultivation of rice-fields there is a criss-cross pattern dividing the numerous canals for irrigation and for the water drainage. All these man-made canals are open, some being at ground-level, others above the ground, like aqueducts, made of concrete. There is also a huge infrastructure of access tracks that join the crop fields and the farm buildings that are scattered throughout the area. These are the only inhabited areas, although the resident population is minimal as the buildings are mostly used for storing rice, cotton and all the machinery and equipment; the actual movement of vehicles and machinery is specially intense during the months when the crops are being sown or harvested.
Few medium and low voltage power lines run the area, usually following the tracks.
The winter weather is mild with moderate temperatures although there is a high level of humidity. The rainfall is very high during some winters and sometimes with intense storms taking place.
This area holds a large number of birds like Grey Herons (Ardea cinerea), Little Egret (Egretta garzetta), Cattle Egret (Bubulcus ibis), Purple Gallinule (Porphyrio porphyrio), gulls and waders. During rice harvest, at the end of September and beginning of October, there are huge concentrations of White Storks (Ciconia ciconia)
RESULTS
Countings
During these 3 periods, the total birds observed has varied very little with yearly maximums of 57 birds being sighted during 1998-1999; 58 during 1999-2000 and 54 during 2000-2001. Nevertheless, we have noticed differences according to the seasons and the advance of the winter period, when generally the number of wintering birds starts to increase. (see fig.1). The last observation of the season was done in May where we saw various sub-adults and young together.
On this 3 year period the first observations were noted end of September. This data, however, has not been taken into consideration due to the possibility that some of these birds may have been using the area as a resting place before their migratory journey to Africa. Previous studies show that the tail-end of the black stork migration period carries on until mid-October across the Straits of Gibraltar (Bernis, F. 1980; San Segundo, C. et al., 1993, 1994; Parkes C. et al. 1998).
Ageing of birds.
Due to adverse weather conditions and their shyness, it was not always possible to determine their ages of but on 365 cases we determined 67 birds as first year (18.4%) and 298 as adults (81.6%). This rates has been virtually the same during the three seasons. (see fig.2)
Behaviour.
The birds generally remain in small groups in between 4-10 individuals although it is not unusual to see them solitary. We have also observed larger groups of up to 46 birds together. These groups disperse with great ease and thereafter may divide and form different groups with other birds completely separate from the original group. They sometimes integrate with white storks but this is not the normal case.
The black storks spent most of their time resting and feeding in the canals. Some will be perching on the aqueducts acting like surveillance, while others remain on the ground channels, interchanging positions. Their basic food was, introduced from North America, the red swamp crayfish. (Procambarus clarkii).
Origin of birds
The origin of these birds is not very clear. During our journeys, we have managed to see various ringed birds with PVC. Two of them were Portuguese, another Spanish with satellite transmitter (SEO, 1999), David and Jonas from Chezch Republic, and finally another one with green ring from Hungary or Chezch Republic. Both Portuguese birds were born from the same couple although on different years (Gonçalo Rosa, pers. comm.)
THREATS AND DANGERS
All the activities regarding agriculture, the use of pesticides, rodent poison, power lines (Ferrer. M, et al. 1999) and of course the continuous illegal and unstoppable shooting that takes place in this area (Andalus, 1987; Torés A. et al., 1999), like in whole Spain (Lucio, A.J. et al., 1992), are the greatest dangers for the population of black storks as all other birds using the Arrozales del Guadalquivir as their wintering quarters.
FIGURES
Figure 1. Average and maximum number of detected Black Storks by months on a single journey during all three seasons.
Figure 2. Age distribution.
REFERENCES:
ANDALUS. Matanza de cigüeñas negras y moritos en los arrozales de Doñana. Quercus 25: 20
BERNIS, F., 1980. La migración de las aves en el Estrecho de Gibraltar. Vol I: aves planeadoras. Universidad Complutense. Madrid.
FERRER, M., JANSS, G.F.E y varios autores, 1999. Aves y líneas eléctricas. Colisión, electrocución y nidificación. Ed. Quercus.
GARCÍA, L., CALDERÓN, J., RAMO, C., 1996. La Cigüeña Negra (Ciconia nigra) en Doñana y su entorno [Black Stork (Ciconia nigra) at Doñana and surroundings]. II Conferencia Internacional sobre la Cigüeña Negra. Trujillo, España.
GONZÁLEZ, J.L., MERINO. M. 1988. Primer censo de la población española de Cigüeña Negra. Quercus 30: 12-17.
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PARKES, C., LOBÓN, M., JIMENA, J.M., 1998. Censo migratorio postnupcial de la Cigüeña Negra (Ciconia nigra) en el Estrecho de Gibraltar en 1995 y 1996. [Postnuptial Black Stork (Ciconia nigra) survey across the Straits of Gibraltar. 1995 and 1996]. III Jornadas de Estudio y Conservation de la Flora y Fauna del Campo de Gibraltar. Almoraima 19:75-82.
SAN SEGUNDO, C., 1991. Selección de hábitat del género Ciconia en España. Areas de invernada de la Cigüeña negra. Convenio CSIC-ICONA. Informe inédito.
SAN SEGUNDO, C., 1993. Áreas de concentración e invernada de la Cigüeña Negra en España. ICONA (Informe inédito).
SAN SEGUNDO, C., FERNÁNDEZ, J.M., TRAVERSO, J.M., 1996. Recuento de Cigüeñas Negras en migración otoñal por Gibraltar [Autumn Black Stork census at Gibraltar]. Quercus 102: 13.
SEO, 1999. SEO/Birlife marca la primera cigüeña negra en España seguida por satélite. La Garcilla 106: 40.
TORÉS A., TORÉS A., PARKES, C., 1999. Una cigüeña negra de origen checo abatida junto a Doñana. Quercus 165:51.
Acknowledgments and thanks to the following for their help and collaboration: Mercedes and Rafael, Judit, Edward, our all friends who collaborate in this study.
