Breeding population trends and recent changes in the nesting behaviour of the White Stork Ciconia ciconia L., 1758 in Navarre, north of Spain

The white stork Ciconia ciconia is one of the most emblematic birds in rural habitats of Europe. Its populations showed a drastic decline during the 20th century, followed by a rapid recovery in the last decades. The population increase has led to a relaxation in the specie’s monitoring effort, the last Spanish national official census having been conducted more than 15 years ago. In order to update this knowledge, this study shows the results of a breeding population census conducted in Navarre during the spring of 2018, describing the preferences in nest location, and comparing the current breeding population size with that described in the literature published since 1960. Our results show a breeding population of 739 pairs, which is the highest value ever recorded. However, this increase in the number of pairs has not been associated with a significant expansion of the specie’s distribution area, which is still limited to the southern half of Navarre. The only relevant colonisation would be the 5 pairs established in the Pamplona district. Most pairs (86.3%) nested in colonies, with an average size of 9.2 nests. Most of the nests were located in trees (49.0%), followed by buildings (28.8%), cut trees (10.0%), pylons (6.9%) and other types of structures (antennas, chimneys, artificial nests, cranes..., 5.3%). A comparison of the current situation with previous censuses shows that there has been an annual population growth rate of 6.6%, with an important change in nesting habits, both in the percentage of pairs that nest in colonies and in the substrate selected to build the nest. The possible causes that could explain these changes and the conservation implications for the species are discussed.