Length of the recovery period after extreme flood is more important than flood magnitude in influencing reproductive output of Brown Dippers (Cinclus pallasii) in Taiwan

Due to climate change, extreme weather events are becoming more frequent and severe. These extreme events have been documented to affect avian predators in stream ecosystems. To better understand the mechanisms behind this effect, we used a decade-long dataset from a mountain stream in Taiwan to assess the effects of extreme flooding caused by typhoons on invertebrate abundance in different periods of the year and the resulting effects on reproductive output of an avian predator of these invertebrates, the Brown Dipper (Cinclus pallasii). In this study stream, all extreme floods occurred between June and October, and these floods negatively affected invertebrate density. Consequently, average invertebrate density was lowest in October at the end of the typhoon season, and highest 4 mo later. Because invertebrate density increases over time after a flood, the length of the recovery period between floods that occurred between June and October was more important than each flood's magnitude in determining invertebrate density in October. October invertebrate density then positively correlated with invertebrate density, the number of dipper breeding pairs, and the proportion of breeding individuals in the following breeding season, which lasted from January to early April. The effects of lower invertebrate densities in October and then February percolated all the way through the system, affecting laying date, fledgling population, and the next winter's population. Given our results, an increase in the frequency of typhoons, especially late-season typhoons, will have a negative effect on Brown Dipper reproductive output through bottom-up effects in stream ecosystems.