UVM Theses and Dissertations
Format:
Print
Author:
Zalik, Nathan J.
Dept./Program:
Natural Resources
Year:
2007
Degree:
MS
Abstract:
Invertebrate prey is an essential food resource for most breeding songbirds. For grassland birds such as Savannah Sparrows nesting in hayfields, this resource may be affected by the harvesting process, which likely destroys and removes invertebrates as well as reduces the amount of vegetation on which invertebrates live and feed. Thus, for birds whose first nests fail due to the harvesting of hay, renesting may take place in a dramatically altered habitat that may be less suitable for raising young.
In this study, I investigated the composition of invertebrate prey over the course of the nesting season and their use in the nestling diet in both harvested and unharvested hayfields in the Champlain Valley of Vermont. The difference between use and availability of invertebrate prey types was analyzed as an indicator of prey selection. Additionally, I examined total invertebrate biomass in harvested and unharvested fields as well as potential effects of clutch size, food provisioning by adults, and growth of nestling Savannah Sparrows.
The relative abundance of invertebrate pray types differed between early and late in the nesting season on unharvested fields, as did their use in nestling diets. Late season harvested and unharvested fields also differed in invertebrate prey composition, but nestling diets between the two field types were not significantly different. Adult Savannah Sparrows consistently fed holometabolous larvae and spiders to their nestlings in greater proportions than were available. Other important components of nestling diets were Orthoptera, Homoptera, and late in the season, adult Lepidoptera.
Total invertebrate biomass as measured by sweep net samples declined by 36 - 82% after harvesting, compared to continual increases throughout the nesting season on unharvested fields. Nestling provisioning rates obtained through video observations differed between treatments in nestling mass. Although estimates of total field biomass indicated a decline in the energy available from prey after harvesting, this reduction was insufficient to induce food limitation based on the energetic requirements of Savannah Sparrows. My results suggest that adult Savannah Sparrows must have compensated for deduced food availability on harvested hayfields, possibly by increasing the total time spent foraging.
In this study, I investigated the composition of invertebrate prey over the course of the nesting season and their use in the nestling diet in both harvested and unharvested hayfields in the Champlain Valley of Vermont. The difference between use and availability of invertebrate prey types was analyzed as an indicator of prey selection. Additionally, I examined total invertebrate biomass in harvested and unharvested fields as well as potential effects of clutch size, food provisioning by adults, and growth of nestling Savannah Sparrows.
The relative abundance of invertebrate pray types differed between early and late in the nesting season on unharvested fields, as did their use in nestling diets. Late season harvested and unharvested fields also differed in invertebrate prey composition, but nestling diets between the two field types were not significantly different. Adult Savannah Sparrows consistently fed holometabolous larvae and spiders to their nestlings in greater proportions than were available. Other important components of nestling diets were Orthoptera, Homoptera, and late in the season, adult Lepidoptera.
Total invertebrate biomass as measured by sweep net samples declined by 36 - 82% after harvesting, compared to continual increases throughout the nesting season on unharvested fields. Nestling provisioning rates obtained through video observations differed between treatments in nestling mass. Although estimates of total field biomass indicated a decline in the energy available from prey after harvesting, this reduction was insufficient to induce food limitation based on the energetic requirements of Savannah Sparrows. My results suggest that adult Savannah Sparrows must have compensated for deduced food availability on harvested hayfields, possibly by increasing the total time spent foraging.