VANN - Evolutionary ecology and hydrology - the effects of stream flow dynamics on the white-throated dipper

By combining hydrology and biology, we aimed to understand how hydrological runoff at the scale of the territory affects the national bird of Norway, the white-throated dipper Cinclus cinclus (hereafter dipper). When biologists are concerned about how the environment influences a species, they often turn to large-scale environmental variables. This is exemplified by the frequent use of the NAO index (North Atlantic Oscillation) and other global meteorological data. The large-scale variables are however often not an appropriate measurement for what happens on a small spatial scale. Environmental variables on a small spatial scale are often non-existent or hard to measure. In our research project on the dipper, local water conditions are the most important environmental factor. The dipper is completely dependent on open water, because it feeds on submerged insect larvae and builds its nest adjacent to running water. Flooding, drought and ice conditions are therefore of the utmost importance for the dipper, especially during the breeding season where water flow acts as a defence against predators. The interdisciplinary collaboration between biologists at the University of Oslo and hydrologists at the Norwegian Water Resources and Energy Directorate (NVE) used a novel method of simulating daily hydrological runoff on a small spatial scale. This result was applied to a study population of breeding dippers, in order to understand how local runoff and other hydrological conditions affect dipper breeding success. We simulated a time-series of river discharge and other hydrological parameters at each dipper territory for the whole study period (1978-2015).These simulated hydrological time-series were a good representation of the real runoff and have been essential to understand the consequences of changes in runoff and hydrology for the dipper and other aquatic animals. Early breeding results in more offspring. Breeding time is in addition one of the strongest response to climate change among animal taxa. The dipper breeds on average ten days earlier now than at the start of the study 37 years ago. We found that river discharge and other hydrological parameters reflecting the local water conditions at the breeding site were important to the dipper. High discharge and groundwater levels and little snow shortly before breeding led to earlier breeding. Birds breeding at low altitudes bred earlier than conspecifics at higher altitudes, but over time this effect declined, and the difference in time between high and low altitude breeders became smaller. Warmer winters have probably led to more open water also at higher altitudes, rendering these sites available for early breeding. Also, breeding was delayed when the male partner was new to a territory. In animals defending territories, some territories are often more popular than others. We have indications that runoff is partly responsible for the variation in territory occupancy rates. Dippers at low altitudes lay more eggs and raise more young than birds at higher altitudes. Females lay more eggs now than at the start of the study. Warm springs and less snow contribute to more laid eggs. Warm springs and increased early spring variation in runoff and snow cover likewise lead to more young. On the other hand, high population density leads to a lower production of young. In addition, as part of the project we have also investigated the potential for interactions between recolonizing Atlantic salmon and brown trout. Surprisingly, we found that juvenile trout upstream, not downstream, the migratory barrier had a positive effect on the population of dippers. It is possible that the wider downstream reaches might have higher abundances of alternative food, rending juvenile trout unimportant as prey.

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In this project, we take an interdisciplinary approach and use a novel method of simulating daily hydrological runoff on a small spatial scale and apply it to an exclusive long-term study of breeding white-throated dippers Cinclus cinclus. This proposal p rovides a unique opportunity to understand how variation in the key local environment affects the ecology and evolution of a top predator of freshwater ecosystems. Floods, droughts and freezing of the river occur on a small spatial scale determined by the local hydro-meteorology and topography and can have severe consequences influencing the ecology and the evolutionary processes. Water flow dynamics also has potential to change due to climate change as well as due to riverine basin regulations caused by hydropower production. We therefore propose to analyse how environmental variation in terms of water flow dynamics (B1) affect breeding parameters and territory occupancy, leading to an understanding of how birds perceive habitat quality, (B2) determine t he amount of phenotypic plasticity and estimate selection and heritability, (B3) including knowledge of population age composition, influence the population dynamics, and (B4) influence the effects of liming and the subsequent competition of the recover ed salmonid population on territory occupancy and population dynamics of the white-throated dipper population.