Hydrology influences breeding time in the white-throated dipper

Long-term annual and spatial variation of polygyny in the white-throated dipper (Cinclus cinclus)

Mating strategies are key components in the fitness of organisms, and notably in birds the occurrence of monogamy versus polygyny has attracted wide interest. We address this by a very comprehensive dataset (2899 breeding events spanning the years 1978-2019) of the white-throated dipper Cinclus cinclus. Though the mating system of this species has been regarded as generally monogamous, we find that 7% of all breeding events were performed by polygynous males (approximately 15% of all pairs). The fraction of polygyny has been stable over the entire study period irrespective of population size. The assumption that polygyny is most common at low population density was not supported. Surprisingly, there was no difference between polygynous and monogamous males with regard to the quality of the territories they inhabited, ranked according to their overall frequency of use. The most common age group, first-year breeders, dominated among monogamous males, while among polygynous males second-year breeders were most common, followed by third and first-year breeders. The primary females were in general older than females mated to monogamous males, also when controlled for their general frequency in the population. The majority of the two females mated to a polygynous male, bred in the vicinity of each other. The probability for a male to be involved in polygyny more than once, was significantly higher than by chance, suggesting phenotypic quality differences among males.

Impact of Water Fluctuation from a Dam on the Mekong River on the Hatching Success of Two Sandbar-Nesting Birds: A Case Study from Bueng Kan Province, Thailand

Dam construction for the provision of hydropower and a stable water supply poses a major threat to freshwater biodiversity. Water fluctuation due to dam management has adverse effects on local people and biodiversity in downstream areas, including sandbar-nesting birds. The aim of this research was to determine the effect of water levels controlled by upstream dams on the breeding success of two sandbar-nesting birds, the little ringed plover, Charadrius dubius, and little pratincole, Glareola lacteal, along the Mekong River in Bueng Kan Province, Thailand. During January–May 2018, we found 160 active nests of only two species, the little ringed plover (n = 26 nests, 288 exposure days) and the little pratincole (n = 134 nests, 890 exposure days). Their nest success rates were 19.49 ± 7.52% and 5.54 ± 1.61%, respectively. Predation was a major cause of nest failure for both species (n = 82), followed by flooding (n = 44). We found a significantly increased probability of nest flooding when the water level was higher than when the nest was initiated for those located closer to the water, particularly during March and April, when water levels fluctuated. Our results indicate that dams threaten sandbar-nesting species.