Black capped and mountain chickadee nestling fecal samples

Urban and suburban ecosystems are growing in size and number as the human population continues to increase. Not all cities are built the same, however, and it is still unclear how resident organisms are faring in increasingly urban habitats and whether cities are ecological sinks. To investigate how urbanization is affecting breeding success in insectivorous birds, we studied two species of chickadee, the black-capped and mountain chickadee[KG1]Â , along an urban-rural gradient in Boulder County, CO, USA. We used a citizen-science based experimental framework of nest boxes installed on private land throughout Boulder, CO, USA to local monitor breeding populations of chickadees relative to urbanization. Black-capped and mountain chickadees are two species of closely-related songbirds that co-occur broadly along an elevational gradient. Black-capped chickadees are considered to prefer nesting in low-elevation deciduous trees typically found in cities, while mountain chickadee prefer higher...