Academic journal article The American Midland Naturalist

Reproductive Success and Habitat Selection in Black-Crowned Night-Herons (Nycticorax Nycticorax) in a City Park

Academic journal article The American Midland Naturalist

Reproductive Success and Habitat Selection in Black-Crowned Night-Herons (Nycticorax Nycticorax) in a City Park

Article excerpt

Introduction

As urbanization progresses it becomes increasingly important to understand the role of human-modified landscapes as wildlife habitat (Dearborn and Kark, 2010). Some wildlife populations thrive in urban areas, but for other populations urban areas are ecological traps in which wildlife choose low-quality habitat over high-quality habitat based on faulty or incomplete information (Battin, 2004). Black-crowned Night-Herons (BCNH; Nycticorax nycticorax) increasingly occupy urban areas (e.g., Kelly el al., 2006) but it is unclear if such areas provide suitable breeding habitats because anthropogenic disturbance potentially disrupts BCNH breeding (Tremblay and Ellison, 1979; Parsons and Burger, 1982). Therefore it is unclear whether BCNH colonies which select urban areas for breeding have found refugia, or have unwittingly fallen into ecological traps.

BCNH have colonized human-modified landscapes including cities and suburbs for decades (Hothem and Hatch, 2004; Kelly et al., 2006). For example a suburban colony in Penngrove, California has been active since the 1930s (Kelly et al., 2006). Other suburban colonies in California include West 9th St. of Santa Rosa and the Napa State Hospital campus (Kelly et al., 2006). BCNH also colonized Alcatraz Island in California, a popular tourist attraction with over a million visitors per year (Hothem and Hatch, 2004; Kelly el al., 2006). Examples of urban colonies can be found on the East Coast of the United States as well; BCNH colonized an urban estuary in New York Harbor (Craig et ai, 2012) and forage on and around Staten Island, New York (Bernick, 2004). Erwin et al. (1991) describe a colony of more than 300 BCNH pairs in Baltimore Harbor, Maryland and posit the colony benefits from proximity to urban lights which attract fish. Some colonies of egrets and herons (family Ardeidae), including BCNH, become so successful in urban areas that they are considered nuisances because of their odors, guano, loud vocalizations, and the perception they pose a health risk (Grant and Watson, 1995; Parkes et ai, 2012).

BCNH choose to colonize urban areas in a variety of scenarios but it is unclear if such areas are suitable for breeding. Evidence suggests urban areas become ecological traps for some BCNH colonies when colony abandonments result from nest tree removal by private residents in suburbs (Kelly et ai, 2006), similar to an oft-cited ecological trap in which grassland bird nests are mowed over (Best, 1986; Schlaepfer el ai, 2002; Battin, 2004; Sih et ai, 2011). Even in the absence of direct management against breeding colonies, BCNH are susceptible to human disturbance which can result in nest abandonment, nest failure, behavioral changes in nestlings, young mortality, and inhibition of egg laying (Tremblay and Ellison, 1979; Parsons and Burger, 1982; Kelly et ai, 2007). Femández-Juricic el ai (2007) determined nestling BCNH increase vigilance and decrease maintenance behaviors such as grooming in response to disturbance by pedestrians and boats. Consumption of environmental contaminants is also of concern for BCNH foraging in industrialized areas (Newman et ai, 2007; Levengood and Schaeffer, 2010; Padula et ai, 2010). In Illinois where this study occurred, the selection of urban areas by BCNH may in part reflect their limited alternatives. BCNH have been listed as endangered in Illinois since 1977 based on small population size, a history of decline, and extensive wedand habitat loss (Illinois Natural History Survey and Illinois Department of Natural Resources, 2011; Illinois Endangered Species Protection Board, 2011).

Differences in behavioral flexibility can provide insight into why some wildlife populations thrive under human induced rapid environmental change (HIREC), including urbanization, and others do not (Sih et ai, 2011). Generally the more behavioral flexibility exhibited by a wildlife population, the better their chance of initially surviving HIREC, and of subsequently adapting to novel conditions (Sih et ai, 2011). …

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