Date of Award:

8-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

S. Nicki Frey (Committee Chair), Michael Conover (Committee Co-Chair)

Committee

S. Nicki Frey

Committee

Michael Conover

Committee

Mark Chynoweth

Abstract

Independent foraging is needed for the reintroduction of a species to be successful, but it can cause cascades in interconnected ecological communities. California condors (Gymnogyps californianus) were reintroduced to the Colorado Plateau in 1996, and the population has continued to grow with yearly releases of captive individuals. However, little is known about foraging behavior of condors and their potential competitors. Carrion is a risky food source, and there is a tradeoff between vigilance and feeding. Altering behavior can maximize caloric intake while minimizing risk. Here, I investigate habitat selection, vigilance, and interspecific interactions among condors, golden eagles (Aquila chrysaetos), turkey vultures (Cathartes aura), common ravens (Corvus corax), coyotes (Canis latrans), and red foxes (Vulpes vulpes) on a high-elevation plateau in southern Utah. I assessed scavenger activity and measured habitat variables for 89 carcasses over the summers of 2022 and 2023 and obtained video of scavenger behavior for 76 carcasses. Condors selected for sparser understory cover, allowing easy access to lead-free carcasses on sheep bedding grounds, where most livestock mortality occurs. Eagles selected for sparse understory cover only when close to roads, and eagles and condors displaced each other when simultaneously present. Increased human activity could lead to more intense competition between eagles and condors. The presence of condors at carcasses can force eagles to increase their vigilance, especially when condors arrive in groups. Vultures did not select for any vegetation type, which may buffer against competitive impacts of condors. Vultures prioritize feeding over vigilance when arriving at large carcasses that are likely to attract condors and visit rates of vultures decline after condors have visited a carcass. Ravens, coyotes, and foxes did not display preference for any variable tested. Condors, eagles, and vultures used different environmental variables to modify their vigilance, suggesting several tactics to balance energetic demands and safety. Condors arrive at carcasses less than an hour after the first scavenger and on average consume over half the carrion, leaving little for other scavengers. The population densities of eagles and vultures may decline in areas where condors occur because of additional competition for carrion. This study offers insights into the impacts of condor reintroduction and aids the management of condors and their competitors. The potential for changes in avian scavenger community composition may lead to broader changes in carcass distribution on the landscape and could lead to trophic cascades in scavenger, predator, prey, and vegetative communities.

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Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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