Variation in Plumage Coloration of Northern Cardinals in Urbanizing Landscapes

—Biologists know relatively little of how one of the most important avian phenotypic signals, feather coloration, may be affected by anthropogenic changes resulting from urbanization. We examined the relationship between urbanization and carotenoid-based plumage color of Northern Cardinals (Cardinalis cardinalis) in 13 riparian forests distributed across a rural-to-urban landscape gradient in central Ohio, USA. Feathers and morphometric measurements were collected from breeding territorial males (n 5 129) and females (n 5 145) during March–August 2006–2008. Plumage brightness of males, but not females, increased with body condition (i.e., size-adjusted mass) and declined with amount of urbanization surrounding forests in which cardinals bred. The extent plumage coloration reflected condition was partially mediated by landscape composition. Specifically, the relationship between brightness and body condition was most pronounced in the most rural landscapes. The interdependency of male coloration and body condition may be more relaxed in urban than rural landscapes if carotenoid-rich foods from anthropogenic and/or invasive sources are more available, or are accessible to birds across a wide range of condition. Received 11 May 2009. Accepted 18 January 2010. Most studies of birds in human-dominated landscapes have described striking and relatively predictable patterns in response of species diversity and abundance to intensity of urban development (Blair 1996, Anderies et al. 2007, Devictor et al. 2007, Tratalos et al. 2007). Subtle consequences of urbanization, such as changes in behavior or coloration are less commonly examined. Biologists continue to have a poor understanding of how urbanization might influence plumage coloration, despite a century of interest in causes and consequences of this important phenotypic signal in birds (Andersson 1994, Bortolotti 2006). Most studies of avian coloration in urban systems have focused on detrimental effects of anthropogenic pollution upon levels of carotenoids in plant and animal matter (Sillanpaa et al. 2008) as well as plumage coloration, as in Great Tits (Parus major) (Eeva et al. 1998, Isaksson et al. 2005, Isaksson and Andersson 2007). The presence of certain exotic plants, some of which are positively associated with urban development (Borgmann and Rodewald 2005), also can affect coloration by altering access to diet-derived pigments. For example, Mulvihill et al. (1992) showed that access to exotic honeysuckle fruits (Lonicera spp.) containing rhodoxanthin, a carotenoid-group (xanthophylls) pigment, changed retrix-tip colors of Cedar Waxwings (Bombycilla cedrorum) from yellow to orange. However, the consequences of urbanization affecting avian coloration remain poorly understood despite these studies. One of the primary ways in which urban development might affect plumage coloration is by altering food resources. Cities generally contain a variety of novel food resources, including bird seed at feeders, fruit from exotic plants, and refuse that can change diets. These changes in food resources can directly affect coloration through increased availability of pigment-containing food sources. The link between diet and plumage coloration should be particularly strong for species that have carotenoid-based plumages, which are highly dependent on carotenoid pigments obtained from food sources (Møller et al. 2000, McGraw et al. 2001, Hill et al. 2002). However, access to pigments is not the sole determinant of coloration because individuals may differ in their ability to use ingested pigments (McGraw and Hill 2001). A variety of urbanassociated factors, such as abundant humancommensal predators, oxidative stressors (e.g., pollution), and high avian densities, may constrain the ability of individuals to acquire or physiologically sequester carotenoids for color production (Møller et al. 2000, Isaksson and Andersson 2007). Consequently, plumage quality is known to reflect general health or immunocompetence (Andersson 1994, Saks et al. 2003, Jawor and Breitwisch 2004, Dawson and Bortolotti 2006, Maney et al. 2008), individual quality (Hill 1991, Kristiansen et al. 2006), and quality of the environment in which birds live (Arriero and 1 The Ohio State University, School of Environment and Natural Resources, 2021 Coffey Road, Columbus, OH 43210, USA. 2 Current address: Massachusetts College of the Liberal Arts, Biology Department, 375 Church Street, North Adams, MA 01247, USA. 3 Corresponding author; e-mail: [email protected] The Wilson Journal of Ornithology 122(2):326–333, 2010