Grassland songbird productivity: Does the edge effect on nest predation vary between agricultural types?

Background/Question/Methods

Surveys indicate that grassland songbirds are declining more rapidly than other avian guilds including in the anthropogenically-fragmented landscape of the Okanagan-Similkameen, British Columbia. A common phenomenon in fragmented habitats is increased nest predation at habitat edges, and many species avoid edge habitats, reducing their habitat availability. Previous edge effect studies have not discriminated amongst agricultural types despite differences in vegetation structure and supplemental food source for predators. Over two breeding seasons, we studied the impact of fragmentation by orchards and vineyards on the reproductive success of Vesper Sparrows, abundance of nest predators, and avian community composition in the shrubsteppe of the Okanagan-Similkameen.

Results/Conclusions

Preliminary results from 2011 suggest an edge effect on nest predation is present in this habitat, with highest predation rates at orchard edges. Previously unconfirmed, nest camera work indicates snakes are the dominant passerine nest predator in this system and snake abundance was correlated with predation rate. Further, avian communities were different between edge and interior habitats with higher grassland obligate songbird abundance at habitat interior plots and vineyard edges. Our results identify potential contributing mechanisms of grassland songbird declines and will help land managers make decision about design and placement of grassland songbird habitat reserves.