Do Food Availability and Microclimate Determine Bird use of Forest Canopy Gaps?

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Title: Do Food Availability and Microclimate Determine Bird use of Forest Canopy Gaps?
Author: Champlin, Tracey B
Advisors: Dr. Clyde Sorenson, Committee Member
Dr. Christopher Moorman, Committee Chair
Dr. John Kilgo, Committee Member
Abstract: We investigated the influence of arthropod availability and microclimate on avian use of forest canopy gaps in 2002 and 2003. We used mist netting and observation of foraging effort (attack rates) to determine the influence of arthropod abundance on avian habitat use of three sizes (0.13, 0.26, and 0.50 ha) of 2- to 3-year-old group-selection timber harvest openings during four periods (spring migration, breeding, post-breeding, and fall migration). We sprayed a broad-spectrum insecticide to reduce arthropod abundance in six of 12 gaps (2 of each size) from April through October in both years. We used a D-Vac backpack vacuum to monitor treatment efficacy across the four seasons. We used four-channel HOBO® H-8 data loggers to measure temperature, light intensity, and relative humidity at netting stations in canopy gaps without arthropod reduction. Arthropods were effectively reduced in both years in treated gaps, but bird response to arthropod reduction varied among gap sizes and between years. In 2002, we generally captured more birds in treated than control gaps of the smallest size (0.13 ha) and fewer birds in treated than control gaps of the larger two sizes. In 2003, we recorded few differences between the number of captures in treated and control gaps. Relationships between bird captures and microclimate (temperature, light intensity, and relative humidity) were inconsistent. For example, fewer birds were captured where temperatures were higher during the breeding and post-breeding periods in 2002 and more birds were captured where temperatures were higher in spring 2003. We suggest that birds in bottomland forests of the relatively mild southeastern U.S. select gap habitats based primarily on the dense vegetation structure that provides protection from predators during times of vulnerability (e.g., post-breeding molts, migration). Other factors, including food availability and microclimate, likely play lesser roles in the habitat selection process, except during the breeding season when exposure to predators is less severe.
Date: 2007-04-18
Degree: MS
Discipline: Fisheries and Wildlife Sciences
URI: http://www.lib.ncsu.edu/resolver/1840.16/2583


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