Breeding Biology of the Dipper Cinclus cinclus in Mountainous Riverine Ecosystem of Southern Slope of the Alborz Mountaian

The Dipper Cinclus cinclus is an inhabitant of the mountainous riverine ecosystem of Iran. There has been no official study on its breeding biology in this country. We conducted a study to investigate the breeding biology of this species in Lalun, Abnic and Ahar streams, situated in Northern parts of Tehran province during the 2013 breeding season. The Dipper bred in two subsequent periods. The first period started from late March to late April (16 and 18 days for the incubation and fledging periods, respectively). The second period started from early May to mid-June (15 and 16 days for the incubation and fledging periods, respectively). More than 80% of the 21 surveyed nests were built on artificial structures. The nests were spherical in shape with the average length of 24.1 ± 2.69 cm (mean ± SD) and the average width of 20.8 ± 2.87 cm. In average, the nests were located 140.7 ± 41.7 cm above water level and weighed an average of 273.6 ± 94.1 g. The average clutch size was 4.7 ± 0.48 with a mean brood volume of 4.5 ± 0.53, which was not significantly different between the two breeding attempts. The mean egg weight in the first and second breeding attempts were estimated to be 4.57 ± 0.054 g and 4.055 ± 0.078 g, respectively. Overall, 75% and 63% of the nestlings in the first and second nestling attempts had successfully fledged. The majority of the nest failures and offspring mortalities (c. 83%) were mainly attributed to human disturbance. Finally, hatching and fledging success rates were higher in the first breeding attempt, indicating the importance of the first breeding period (March and April) in the conservation of breeding populations of the Dipper.