Response of waterbird communities to habitat and landscape structure along an urban gradient

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Riparian areas and wetlands used by waterbirds have received relatively little focus in urban bird studies, despite their importance. Phoenix alone contains over 1,400 bodies of water, offering the opportunity to design and improve these areas to optimize potential habitat. Thus, our principal objective was to determine how aquatic, littoral, and landscape composition affect waterbird biodiversity components in an arid city. We surveyed 18 transects stratified across a gradient of urbanization and water availability along the Salt River, a CAP LTER long-term study system located in Phoenix, Arizona. Total bird abundance did not differ along varying levels of urbanization, but was affected by the amount of water in the habitat. Conversely, community composition was significantly affected by both degree of urbanization and water availability; both gradients influenced the suite of species found at a particular site. Some species, such as Brown Pelicans, were only found in urban habitats and others, such as Blue-Winged Teals, were only found in restored habitats with intermediate levels of urbanization. Environmental variables were reduced via Principal Component Analysis and used to model the responses of guild specific abundance. Diving ducks and fish eating birds were positively associated with large open bodies of water; however, diving ducks were the only guild negatively associated with urbanization. Wading and marsh species favored interconnected areas with large amounts of emergent vegetation. Dabbling ducks were the only guild primarily affected by vegetation density; whereas shorebirds preferred habitats with long, narrow stretches of cobblestone. Overall, our study showed that cities have the potential to maintain high levels of biodiversity, a heterogeneous land-use matrix can support regional diversity by harboring different species, and that waterbirds are tolerant of urbanization if resources are available. The implications of this study are relevant to urban planning in arid cities.