Characteristics of American Crow Urban Roosts in California

Abstract

American crows (Corvus brachyrhynchos) roost in urban areas across the United States creating problems resulting from fecal droppings, noise, and health hazards. With little information about roosts, managers have been unable to respond to questions from the public about roost problems or design control programs. We counted crows flying into Woodland, California, to roost, surveyed roosts for occupancy, and recorded features of 87 roost trees and 62 randomly selected nonroost trees from August 1992 through July 1994. Some crows roosted in town all year, with peak abundance from September through January. Roost trees had greater height, diameter at breast height (dbh), and crown diameter and volume than nonroost trees (P < 0.001 all cases). Most roost trees were located over an asphalt or concrete substrate (P < 0.001) in commercial areas of the city, rather than in residential areas (P < 0.001), and were subjected to greater disturbance from vehicles and people (P < 0.01). Ambient light levels and interior canopy temperatures during winter were greater at roost trees than nonroost trees (P < 0.001 both cases). There were seasonal changes in roost trees selected with an increased (P < 0.001) use of deciduous trees (elms [Ulmus spp.], mulberries [Morus spp.], oaks [Quercus spp.], and ashes [Fraxinus spp.]) in residential areas during summer months as opposed to the concentrated use of evergreen oaks, alders (Alnus spp.), and conifers (Pinus spp. and Sequoia spp.) in commercial areas during winter. We developed a logistic regression model with 4 variables that correctly classified status of 85% of roost or nonroost trees.