Adaptation or ecological trap? Altered nest-site selection by Reed Parrotbills after an extreme flood

Floods and other extreme events have disastrous effects on wetland breeding birds. However, such events and their consequences are difficult to study due to their rarity and unpredictable occurrence.

Here we compared nest-sites chosen by Reed Parrotbills (Paradoxornis heudei) during June?August 2016 in Yongnianwa Wetlands, Hebei Province, China, before and after an extreme flooding event.

Twenty-three nests were identified before and 13 new nests after the flood. There was no significant difference in most nest-site characteristics, such as distance from the road, height of the reeds in which nests were built, or nest volume before or after the flood. However, nests after the flood were located significantly higher in the vegetation compared to before the flood (mean ± SE: 1.17 ± 0.13 m vs. 0.75 ± 0.26 m, p < 0.01). However, predation rate also increased significantly after the flood (67% vs. 25%, p = 0.030).

Our results suggested that Reed Parrotbills demonstrated behavioral plasticity in their nest-site selection. Thus, they appeared to increase the height of their nests in response to the drastically changing water levels in reed wetlands, to reduce the likelihood that their nests would be submerged again by flooding. However, predation rate also increased significantly after the flood, suggesting that the change in nest height to combat the threat of flooding made the nests more susceptible to other threats, such as predation. Animals' response to rare climatic events, such as flooding, may produce ecological traps if they make the animals more susceptible to other kinds of threats they are more likely to continue to encounter.