Anthropogenic Subsidies and Wildlife: The Good, the Bad, and the Unintended Consequences of Food and Shelter Subsidies for Wildlife


Symposia will be available on-demand on their scheduled date, then again at the conclusion of the conference.

Since the beginning of our relationship with wildlife, humans have provided food and shelter subsidies that shaped the abundance, distribution, and behavior of wildlife populations across the globe. Anthropogenic subsidies may include food waste, bird feeders, indirect feeding activities, supplemental water, or unintended access to homes or buildings that provides shelter. Some subsidies meant for birds and other ?watchable wildlife? may ultimately subsidize nontargets such as carnivores or invasive species. Subsidies may also be directly antithetical to the intended purpose, as food and water subsidies may contain contaminants that are fatal to target species. These anthropogenic subsidies have both direct and indirect effects on the species that utilize them as well as their predators or prey. This symposium will bring together scientists to present a broad spectrum of research on the beneficial and harmful effects of anthropogenic subsidies on wildlife in urban and suburban settings, including impacts to rare and threatened species inhabiting adjacent parks or refuges. Anyone attending our symposium will benefit by learning about the varied impacts of subsidies and develop collaborations with other professionals focused on this topic.

Influence of Anthropogenic Foods on the Behavioral Ecology of Coyotes in the Chicago Metropolitan Area
Stanley D. Gehrt; E. Hance Ellington; Katie E. Robertson; Ashley M. Wurth; Seth D. Newsome
A prominent feature of urban ecosystems is the presence of anthropogenic foods, and these subsidies are often used to explain patterns of wildlife responses to urbanization. Subsidies may have profound impacts on generalist mammalian species in various ways. Coyotes have become common throughout the Chicago Metropolitan Area (CMA) in recent decades, although the role of subsidies in their apparent success remains poorly understood. Here, we expand our previous work using stable isotopes to characterize coyote use of anthropogenic foods in their diets, with a particular focus on coyotes residing in the most heavily urbanized area, the urban core. We used radiotelemetry to determine residency and social status of each coyote and analyzed whisker segments to determine intra- and interindividual variation in diet. Similar to suburban coyotes (n=121), we observed substantial interindividual variation in diet among urban core coyotes (n=29), and only 34% of the coyotes had an anthropogenic-dominated diet. Although a majority had a largely natural diet, they also exhibited variable use of human foods. This variability allowed us to use the full dataset for coyotes across the CMA and further explore the extent to which subsidies may influence aspects of urban coyote ecology. Use of anthropogenic foods was associated with limited space use, and we also report on associations with body condition and cortisol levels (n=198) as indicators of stress. The substantial interindividual variation in use of anthropogenic foods was a surprising finding given their locations in the urban core, and reveals how urban coyotes are using variable strategies for exploiting the urban environment.
Anthropogenic Resource Use by Urban Coyotes in Los Angeles
Justin Brown; Rachel Larson; Tim Karels; Seth P.D. Riley
Coyotes (Canis latrans) have shown the ability to persist in urban areas across North America, including in places that are intensively developed and support few other carnivores. It is important to understand how they use the urban landscape, what resources they are using, and specifically the role of anthropogenic resources. In 2015, we started a project to address these questions in Los Angeles, one of the largest and most urbanized cities in the world, where we GPS collared coyotes across the urban landscape and studied diet using two different techniques: scat dissection (n = 3,147) and stable isotope analysis (n=58). Location data has shown that coyotes are extensively using the urban matrix, including dense residential areas, although they use remnant vegetated areas, even if very small. The diet data indicated that anthropogenic food sources, such as domestic cats, human trash, and anthropogenic fruits made up 65-75% of the diet of coyotes in urban Los Angeles. Both diet techniques showed coyotes anthropogenic food use decreased as urbanization decreased. The scat data also showed little change in anthropogenic food use in urban coyote diets between wet and dry seasons, while suburban coyotes saw a 93% increase in use of anthropogenic food sources between wet and dry seasons. From preliminary data we have also seen home range sizes smaller than what has been previously documented in the suburban areas. It seems likely that this reduction in home range size is tied directly to increased levels of anthropogenic food sources available in urban areas of Los Angeles. We provide information from this study to local communities to help them understand why coyotes are using their neighborhood and provide suggestions on how to reduce coyote use of their neighborhood by looking for potential coyote food sources.
Impacts of subsidized ravens on greater sage-grouse populations within sagebrush ecosystems of western North America.
Shawn O’Neil; Peter Coates; Seth Dettenmaier; Brianne Brussee; Pat Jackson; Jonathan Dinkins; Joseph Atkinson; David Delehanty
Anthropogenic modification to ecosystems can result in the redistribution of higher trophic level species. Predator-prey dynamics have been altered by the removal of top predators, and the subsidization of generalist mesocarnivore species. Anthropogenic subsidies often involve resource inputs into ecological systems that can directly benefit some species (i.e., mid-level species), while indirectly harming others, such as lower-level species that are not well-adapted to increased predation rates. An example of a native avian predator that has experienced population increase following anthropogenic subsidization is the common raven (Corvus corax; hereafter, raven). In sagebrush ecosystems of the western U.S., elevated raven populations appear to be suppressing population growth in greater sage-grouse (Centrocercus urophasianus) through disruptions to reproductive behavior and demographic rates. Over the past 50 years, raven populations have expanded dramatically in distribution and abundance, in large part due to increased resource subsidies from human infrastructure and land use activities. Concurrently, some sage-grouse populations appear to be in decline where habitat conditions should be promoting species persistence. Using long-term monitoring data on sage-grouse and ravens in the northern Great Basin region, we observed that 1) ravens disrupt sage-grouse lekking behavior, 2) increased raven density is strongly associated with reduced sage-grouse nest success, and 3) negative trends in lek are linked with spatial variation in raven occurrence and density. Taken together, these results suggest urgency to address a growing management dilemma, as anthropogenic subsidies continue to facilitate raven population increases and expansion into the habitats of sensitive prey species. These findings are preliminary and provided to meet the need for timely best science.
Assessing the Effects of Anthropogenic Food Subsidies on Red Fox Ecology on Fire Island, New York
Kathleen Black; Sarah Karpanty; Daniel Catlin; James Fraser
Anthropogenic food resources have previously been shown to influence the diets, behavior, and population ecology of various predator species. These influences can become problematic in situations where predators populations negatively impact threatened and endangered species. We used fecal dietary analyses, den monitoring, and prey item surveys to determine whether anthropogenic food resources might be subsidizing the red fox (Vulpes vulpes) population on Fire Island, New York, where red foxes have been identified as a key predator of the federally threatened piping plover (Charadrius melodus). We found evidence of anthropogenic food consumption in 16% of fox scat samples examined, suggesting that foxes on the island are regularly exploiting these resources. Interestingly, the occurrence of anthropogenic food items in scats did not significantly differ by season, despite heavy seasonal fluctuations in human presence in the study area. During the denning season, we recorded anthropogenic food items outside of 48% of dens with food items, with these items comprising ~12% of all items recorded at dens. In addition, skates and other fish, which are frequently discarded as angler bycatch in the study area, made up a substantial portion (46%) of prey remains at dens. We conducted additional analyses to investigate den site selection relative to development, and examine relationships among proximity to development, the occurrence of human food items at dens, and red fox litter sizes. Based on our results, we make recommendations for managing the indirect impacts of anthropogenic food resources on shorebird conservation efforts on the island.
Risky Business: Northern Long-Eared Bat Persistence Is Linked to Their Novel Use of Anthropogenic Hibernacula in Coastal New England
Luanne Johnson; Carl Herzog; Samantha Hoff; Danielle O’Dell; Wendy Turner
Northern long-eared bats (Myotis septentrionalis) (MYSE) are one of the species most affected by white-nose syndrome (WNS), which has been killing hibernating bats since 2006. Due to greater than 90% population declines in the Northeast, and the rapid spread of the fungus (Pseudogymnoascus destructans) (Pd) that causes WNS, the species was listed as threatened by the U.S. Fish &Wildlife Service in 2015 and is listed as ‘endangered’ in many states throughout its range. Despite the severe population declines in the northeastern U.S., we documented year-round presence of this species on three coastal islands, Long Island, NY and Nantucket and Martha’s Vineyard, MA from 2015 to present. We investigated the mechanisms of persistence on these islands from 2017 – 2019, using spring and fall mist-netting, radio-telemetry, year-round acoustics and extensive community outreach. Community outreach and radio-telemetry led us to small groups of MYSE hibernating in a variety of anthropogenic structures that mimic the conditions of the caves and mines used by MYSE on the mainland. These structures include cinder block foundations with bulkhead door access, crawlspaces under homes, a cement military bunker, and a culvert. We also documented re-use of these hibernacula in subsequent winters. These remnant populations of MYSE surviving multiple winters of exposure to Pd may be developing resistance or tolerance to the fungus that could be passed to their offspring. However, their survival is entirely dependent on the good will of home or landowners because no federal or state regulations exist to protect bats hibernating in these anthropogenic structures. We propose some strategies to reduce risks to these unusual bat populations to ensure their survival.

Organizers: Luanne Johnson, BiodiversityWorks, Vineyard Haven, MA; Seth P.D. Riley, U.S. National Park Service, Santa Monica, CA
Supported by: Urban Wildlife Working Group

Location: Virtual Date: September 28, 2020 Time: -