Long-term trends in wind speed, insect abundance and ecology of an insectivorous bird

Recent climate change has affected spatial and temporal patterns of temperature and precipitation, but also wind speed. Wind affects the abundance and the distribution of flying insects and can therefore influence the abundance of food for insectivores including insectivorous birds. I tested for temporal trends in wind speed, assessed the effect of wind speed on the abundance of flying insects, and tested for effects of wind speed on reproduction and adult survival rate, using long-term data on the barn swallow Hirundo rustica from 1971-2011. Wind speed varied largely independently among the months April-August, with a decreasing trend during 1971-2011 for July only. The abundance of flying insects decreased strongly with increasing wind speed during summer. Decreasing wind speed during July coincided with the pre-laying period of the second brood of the barn swallow, and years with stronger wind in July had lower abundance of food before laying during 1997-2011 and lower breeding success. Adult barn swallows had lower body mass in years with windy summers, and adult annual survival rate to the next year decreased both when wind speed increased and when body mass was reduced. These findings suggest that wind plays an important role in the ecology of insectivorous birds as shown by relationships with reproductive success and survival.