Reproductive data and analysis of recoveries in a population of white stork Ciconia ciconia in southern Spain: a 24-year study

Changes in nest density and reproductive success of a free–ranging population of white stork (Ciconia ciconia) in the Gardens of ZooBotánico Jerez (Cádiz) were studied from 1990 to 2013. Reproductive data (number of nests and number of chicks per nest) and the effect of rainfall on the reproductive success were analyzed. In addition, a number of chicks were colour–ringed each year and the recovery data were also analyzed. The number of nests found in the area steadily increased during the study period and varied greatly from year to year from 2001 onwards (mean 19, range = 4–35, N = 22 years). Reproductive success also varied greatly among years. Overall, the mean number of chicks per nest was 1.78 ± 1.2 (range = 0–5, N = 439 nests).Reproductive success was strongly influenced by rainfall. It was highest (1.88) in years classified as rainy, medium (1.62) in years classified as normal, and lowest (1.24) in dry years. A total of 404 white storks were ringed, 110 of which were observed a total of 308 times (2.8 + 2.8 times per bird, range 1–12, all year data pooled). Recovery data show that with one exception, all ringed birds were recorded at different habitats of S Spain throughout the year. Remarkably, none was observed at traditional wintering quarters, south of the Sahara in Africa. Juveniles remained in the area (from July to October) soon after leaving our colony, and virtually all of them disappeared from November to January (their first winter) but were recorded again during their first breeding season. On the contrary, adults were repeatedly recorded at different sites in Cádiz, Sevilla and Huelva all year round. These birds showed a strong philopatry as some of them were recorded as breeders in our colony, up to 11 years after ringing. Our data emphasize the importance of both refuse damp and wetland areas for the species, especially in winter, and a shift in the timing of the reproductive season as birds were recorded from November to July each year. Our study provides evidence of the increase in the population, a significant effect of rainfall on their reproductive success, and the non–migratory habits of adult white storks in our colony. To our knowledge, this is the first time that such long–term reproductive data for a Mediterranean population of white storks is shown.