Street trees are public resources planted in a municipality’s right-of-way and are a considerable component of urban forests throughout the world. Street trees provide numerous benefits to people. However, many metropolitan areas have a poor understanding of the value of street trees to wildlife, which presents a gap in our knowledge of conservation in urban ecosystems. Greater Los Angeles (LA) is a global city harboring one of the most diverse and extensive urban forests on the planet. The vast majority of the urban forest is exotic in geographic origin, planted throughout LA following the influx of irrigated water in the early 1900s. In addition to its extensive urban forest, LA is home to a high diversity of birds, which utilize the metropolis throughout the annual cycle. The cover of the urban forest, and likely street trees, varies dramatically across a socioeconomic gradient. However, it is unknown how this variability influences avian communities. To understand the importance of street trees to urban avifauna, we documented foraging behavior by birds on native and exotic street trees across a socioeconomic gradient throughout LA. Affluent communities harbored a unique composition of street trees, including denser and larger trees than lower-income communities, which in turn, attracted nearly five times the density of feeding birds. Foraging birds strongly preferred two native street-tree species as feeding substrates, the Coast Live Oak (Quercus agrifolia) and the California Sycamore (Platanus racemosa), and a handful of exotic tree species, including the Chinese Elm (Ulmus parvifolia), the Carrotwood (Cupaniopsis anacardioides), and the Southern Live Oak (Quercus virginiana), in greater proportion than their availability throughout the cityscape (2-3x their availability). Eighty-three percent of street tree species (n = 108, total) were used in a lower proportion than their availability by feeding birds, and nearly all were exotic in origin. Our findings highlight the positive influence of street trees on urban avifauna. In particular, our results suggest that improved street-tree management in lower-income communities would likely positively benefit birds. Further, our study provides support for the high value of native street tree species and select exotic species as important habitat for feeding birds.
(1) Street_tree_bird_foraging_walking_routes_EAP19-0535 --> Google Earth, kmz file of all 36 walking routes where all street tree and avian foraging data were collected. The walking routes were delineated into three categories (low-, medium-, and high-income), based on 2010 census tract data, from which 36 census tracts were randomly selected. The walking routes were established in residential neighborhoods with street trees and a walkway/sidewalk.
(2) Street_trees_EAP19-0535 --> 7636 street trees measured along the 36 walking routes. We identified and measured to dbh of all trees on all routes.
(3) Bird_foraging_EAP19-0535 --> 1546 bird foraging observations collected on street trees along the 36 walking routes.