Multitrophic Effects of Migratory Birds on Herbivorous Insects In a Shrub Community

Abstract

I examined the effects of migrant birds on herbivorous insects and resulting plant damage in shrub communities on the Bard College campus. While studies have shown that insectivorous birds place downward pressure on insect and plant communities, there has been no research conducted into investigating possible changes to this pressure from the influx of birds during migration. I wanted to investigate the downstream effects of bird predation on insects and plants by recording changes in plant damage during the bird migration and resident periods from late spring to early summer. From May to July of 2017, I used a series of exclusion experiments to prevent bird predation, and insect traps to record the number of herbivorous insects present, as well as creating clay caterpillar models to record the presence of birds and insects in the system. In my vegetation damage assessments of the fraction of leaf removed and proportion of shrub damaged, I found that excluding birds from the system did in fact increase herbivory damage from insects. I also found that the fraction of a leaf removed was lower during the migratory period, suggesting that the presence of more birds in late spring has an even stronger predation effect, and is even more beneficial to plants. The multitrophic interactions between birds, insects, and plants need more attention to determine the response of local communities as the future of migrant bird species becomes even more uncertain