Abstract
BackgroundEarlier breeding is one of the strongest responses to global change in birds and is a key factor determining reproductive success. In most studies of climate effects, the focus has been on large-scale environmental indices or temperature averaged over large geographical areas, neglecting that animals are affected by the local conditions in their home ranges. In riverine ecosystems, climate change is altering the flow regime, in addition to changes resulting from the increasing demand for renewable and clean hydropower. Together with increasing temperatures, this can lead to shifts in the time window available for successful breeding of birds associated with the riverine habitat. Here, we investigated specifically how the environmental conditions at the territory level influence timing of breeding in a passerine bird with an aquatic lifestyle, the white-throated dipper Cinclus cinclus. We relate daily river discharge and other important hydrological parameters, to a long-term dataset of breeding phenology (1978–2015) in a natural river system.ResultsDippers bred earlier when winter river discharge and groundwater levels in the weeks prior to breeding were high, and when there was little snow in the catchment area. Breeding was also earlier at lower altitudes, although the effect dramatically declined over the period. This suggests that territories at higher altitudes had more open water in winter later in the study period, which permitted early breeding also here. Unexpectedly, the largest effect inducing earlier breeding time was territory river discharge during the winter months and not immediately prior to breeding. The territory river discharge also increased during the study period.ConclusionsThe observed earlier breeding can thus be interpreted as a response to climate change. Measuring environmental variation at the scale of the territory thus provides detailed information about the interactions between organisms and the abiotic environment.
Highlights
Earlier breeding is one of the strongest responses to global change in birds and is a key factor deter‐ mining reproductive success
We found a standard deviation of 10.6 days between the territories, while the within-territory standard deviation was 23.0 days
We found a significant interaction between territory and female identity that affected the timing of breeding, i.e., certain combinations of individuals and territories were associated with earlier breeding and others with later breeding
Summary
Earlier breeding is one of the strongest responses to global change in birds and is a key factor deter‐ mining reproductive success. This can lead to shifts in the time window available for successful breeding of birds associated with the riverine habitat. Earlier breeding in birds is one of the strongest responses to Nilsson et al BMC Ecol (2020) 20:70 the exposure of an individual to the current environmental conditions [11, 24]. Organisms experience the local weather and its direct effects on the availability of food and shelter. This determines whether resources are to be accumulated or if stored resources are depleted, and determines the allocation of resources to growth, survival and reproduction. The robustness to environmental variation such as droughts and floods might vary between territories. Environmental variation measured at the scale of the territory might affect individual life history decisions, such as the timing of breeding
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