Long-term trends in timing of breeding of the Barn Swallow Hirundo rustica L. in Croatia

Climate change is known to have number effects on plants and animals. Several studies have indicated advances in laying dates of birds in the last ca. 40 years, which could be attributed to air temperatures. The research was conducted in the village of Mokrice, a part of the Hrvatsko Zagorje region (northwestern Croatia). We studied the long-term variation in the laying date of Barn Swallow Hirundo rustica in order to examine their breeding phenology in relation to mean spring temperature. The Barn Swallow is a common bird species in the study area. We found a significant correlation between the first laying date and year. The coefficient of regression (slope = – 0.36) for Barn Swallows indicates an earlier breeding by 0.36 days per year, or 10 days over the period of the study (1979–2007). Our studies suggested that date of clutch initiation in the studied population is influenced by spring temperatures.