Julie Mallon

Date of Graduation

2015

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Wildlife and Fisheries Resources

Committee Chair

Todd Katzner

Committee Co-Chair

Keith L Bildstein

Committee Member

Eungul Lee

Committee Member

Micheal P Strager

Abstract

Understanding how animals move in response to their environment is a fundamental question in ecology. Soaring species, which rely on environmentally generated uplift to forage and migrate, should be especially sensitive to changing weather and climatic conditions. Changes in uplift distribution or strength can have energetic implications and restrict movement capacity for soaring species. Poor weather conditions can shorten foraging time or slow migration progress. To increase mobility, birds can switch to flapping or soar using another uplift type. Use of uplift, however, is associated with certain flight altitudes and movement speeds. Switching uplift types will affect a bird's ecological interactions and how it moves through its environment. Understanding how species flight behavior is affected by variable conditions, therefore, informs how species movements change under varied environmental conditions.;Numerous studies have evaluated avian behavioral and movement responses to environmental variation. The greatest focus of these studies has been of migration movements. Yet, it is also important to study such responses during non-migratory periods; movements during the breeding and non-breeding seasons affect an individual's foraging behavior and inter-specific interactions.;To better understand how soaring species behaved under variable conditions, I observed flight behavior at local- and continental-scales. I first evaluated variation in flight behavior of black (Coragyps atratus) and turkey (Cathartes aura) vultures in response to variation in environmental conditions during the breeding season. I then evaluated the relationship between flight behavior and uplift availability at a continental-scale during the breeding and non-breeding seasons.;At the local-scale, I found uplift type use influenced flight behavior and species selected uplift resources differently under the same conditions. At the global-scale, I found that flight behavior again was driven by the uplift available, as turkey vultures exhibited variable flight patterns when multiple uplift types were available but exhibited a more singular flight pattern when only one uplift type was available. My local-scale observations documented the use of a previously unidentified uplift type to soar, which is likely used by other soaring species. I also documented behavioral response to climate-scale variation in uplift availability. Different responses to uplift availability by black and turkey vultures suggest that sympatry of these species may occur because they have species-specific flight strategies. Species-specific flight strategies should cause vultures to select certain carrion types, thereby diffusing competition for carrion resources. My findings suggest the functional roles of vultures as scavengers is ultimately linked to their movement behavior.

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