The effects of conventional and organic cropping systems on food and reproductive success of Song Sparrows in eastern Ontario farmland.

摘要

Farmland birds have undergone population declines and range contractions in both Europe and North America, as a consequence of agricultural intensification. Understanding how conventional agriculture affects birds within farmland will help us move towards the goal of maintaining both agricultural productivity and farmland bird populations. I investigate the effects of food supply and foraging habitat availability in eastern Ontario on Song Sparrows (Melospiza melodia), a common farmland bird. I found that i) organic soybean cropping systems support higher nestling food abundance than conventional soybean cropping systems, ii) of the invertebrates I tested, hoppers (Auchenorrhyncha) and caterpillars (Lepidoptera) are the most important in the diet of nestling Song Sparrows, iii) the portion of nestling diet that came from semi-natural habitats, especially hedgerows, was higher than expected, based on habitat availability, iv) food availability does not have a measureable effect on mass of Song Sparrow nestlings, or on the number of fledglings produced and vi) that the amount of semi-natural habitat dose to the nest does not have a measurable effect on Song Sparrow nest survival. In addition, I have demonstrated a stable isotope approach for studying the diet and foraging habitat of farmland birds, when there is a contrast in carbon and nitrogen stable isotopes among food sources. My findings demonstrate the importance of hedgerows in providing foraging habitat for Song Sparrows nesting in farmland. In addition, my findings suggest that while conventional cropping systems do reduce food supply for birds in farmland compared to organic cropping systems, conventional cropping systems in eastern Ontario are relatively benign for Song Sparrows, and potentially other birds that nest and forage in hedgerows.