THE SHELDUK <I>TADORNA TADORNA</I> (L.) IN SOUTHEASTERN SPAIN

Abstract

The Shelduck (Tadorna tadorna) is one of the most representative among the duck species in the wetlands of south-eastern Spain, and the only one of numerical significance in some of them. In our country, the species has changed its status from being considered an ocasional winter visitor to a regular winter presence, having also settled as a breeder in some localities. The south-eastern of Spain is one of the main winter quarters of Shelduck in our country, and the only area where it breeds besides the Ebro Delta. This paper summanzes a number of observations on Shelduck made in this area from 1976 to 1985, regarding the numerical evolution of the wintering and breeding populations, together with several data on its biology and ecology. The study area includes anumber of wetlands belonging to the provinces of Murcia (Salines of San Pedro del Pinatar, Marchamalo and Rasall) and Alicante (Salines of Santa Pola, La Mata Lagoon and El Hondo Reservoirs). Excepting for the latter, flooded with freshwatercomingfrom the Segurariver, al1 these areas are hypersaline lagoons transformed by man for salt production. The wetlands of south-eastern Spain set up the second or third winter quarter, in importante, in the Iberian Peninsula, after the Marismas of the Guadalquivir and the Ebro Delta. Data on wintering Shelduck are scarce until the winterof 1980-81, which may be partly due to a poor prospectingeffort. However, from this winter onwards the population has markedly increased, the presence of the wintering birds becoming more regular. The total winter figures show marked oscilations, both between and within years, but the general trend of the population is to increase. The main wintering localities are the Salines of San Pedro del Pinatar and La Mata Lagoon. The first evidence of Shelduck breeding in south-eastern Spain comes from the Salines of San Pedro del Pinatar, where a pair settled in 1976. From 1982 onwards, the species has also bred in La Mata Lagoon and, less regularly, in the Salines of Rasall (from 1982 to 1984), Santa Pola(at least two years) and El Hondo Reservoirs (only in 1985). The increase in the number of breeding pairs and the settlement of new breeding colonies usually occurs two years after a good breeding success, when the birds reared locally reach maturity. However, this increase may also be explained by immigration, mainly from the Camargue (France). Birds hatched in this locality have been reponed wintering in the spanish mediterranean coast, and the increase in the breedingpopulation of south-eastern Spain probably reflects the great success of the french breeding colony. The use of rabbit (Oryctolagus cuniculus) urrows by Shelduck for nesting has been confirmed in La Mata Lagoon, and there is strong evidende ofthe choice of similar sites in other localities. The number of Shelducklings per brood is low compared with the average figures given for the species. The occurrence of multiple nesting is rare. Ducklingsurvival changes markedly between localities, from almost 100% in La MataLagoon to the loss of al1 the ducklings of a pair breeding in the Salines of Rasall in three breeding seasons. In the Salines of San Pedro del Pinatar, duckling survival seems related to hatching date, the pairs breeding later in the season losing almost al1 their ducklings as an effect of human pressure, while the earliest ones fledge almost al1 their young. In other localities, like the Salines of Santa Pola, the absence of a regular breeding population is discussed in terms of the availability and interspecific competence for nesting sites.