Linking Optimal Foraging Behavior to Bird Community Structure in an Urban-Desert Landscape: Field Experiments with Artificial Food Patches

Abstract

Urban bird communities exhibit high population densities and low species diversity, yet mechanisms behind these patterns remain largely untested. We present results from experimental studies of behavioral mechanisms underlying these patterns and provide a test of foraging theory applied to urban bird communities. We measured foraging decisions at artificial food patches to assess how urban habitats differ from wildlands in predation risk, missed-opportunity cost, competition, and metabolic cost. By manipulating seed trays, we compared leftover seed (giving-up density) in urban and desert habitats in Arizona. Deserts exhibited higher predation risk than urban habitats. Only desert birds quit patches earlier when increasing the missed-opportunity cost. House finches and house sparrows coexist by trading off travel cost against foraging efficiency. In exclusion experiments, urban doves were more efficient foragers than passerines. Providing water decreased digestive costs only in the desert. At the population level, reduced predation and higher resource abundance drive the increased densities in cities. At the community level, the decline in diversity may involve exclusion of native species by highly efficient urban specialists. Competitive interactions play significant roles in structuring urban bird communities. Our results indicate the importance and potential of mechanistic approaches for future urban bird community studies.

Invasion, Evenness, and Species Diversity in Human-Dominated Ecosystems

“…Efficient utilization of resources may also relate to behavioral aspects. In central Arizona synanthropic bird species, including several exotic ones, were found to be more efficient foragers than native species (Shochat et al, 2004a). Yet, under certain conditions, species that have such a potential to become invasive may remain in low profile in wild habitats, where harsh conditions favor native species.…”

“…However, agricultural development in such arid zones, that adds water holes and irrigation systems to the ecosystem, not only allows the establishment of seed-eating birds, but totally removes the restriction on their fast individual and population growth rates. This extreme change in the rules of the evolutionary game creates a new environment in which very few resources remain for the nocturnal rodents in the end of the day (Shochat et al, 2004a). …”

Oak Regeneration Before and After Initial Restoration Efforts in a Tall Grass Oak Savanna Conference Paper

“…Browers and Breland (1996) found higher rates of seed removal from experimental food stations near houses and buildings compared to stations in rural areas, which they suggest may be due to a higher density of squirrels in developed areas. The lack of large predators in urban areas can also lead to altered trophic dynamics (Shochat et al 2004), possibly leading to a higher abundance of seed predators and seedling herbivores.…”

“…In addition to altering the presence and absence of a species, urban areas often have a higher abundance of fewer species (Blair 1996, Shochat et al 2004, which may result in altered ecological processes. In the case of Oregon white oak, animal dispersers are also seed predators.…”

Foraging Behavior of Urban Birds: Are Human Commensals Less Sensitive to Predation Risk Than Their Nonurban Counterparts?

“…The food-enriched urban environment is thus predicted to support proportionally higher bird densities than adjacent wildlands. However, Shochat (2004) and Shochat et al (2004) suggested that the high level of predictability and continuous input of food and water resources into urban environments may actually result in overmatching (i.e., overexploitation of the richer, urban environments). The result is intense food resource competition in urban environments and scarcity of food at the individual level (Sol et al 1998, Marzluff 2001.…”