Aaron N. K. Haiman Cooper’s Hawk Diet 8-May-2006p. 1Prey Selection of Cooper’s Hawks (Accipiter cooperii) Nestingin Urban Areas of Berkeley and Albany, CaliforniaAaron N. K. HaimanAbstract The Cooper’s Hawk is one of the few species of top predators that can persist in urbanareas. Little is known, however, on the dynamics between urbanization and the species thatadapt and persist in these areas. One requirement for the survival of Cooper’s Hawks in urbanareas is prey availability. To determine the prey species of the Cooper’s Hawk in the urban areasof Berkeley and Albany California, I analyzed the previously identified 579 prey remains of the2002 breeding season. To this dataset I added the 478 prey remains collected from Cooper’sHawk nest sites during the 2003 breeding season which had not been identified. In 2002, 16species of bird and 3 species of mammal were found. In 2003, 20 species of bird and 1 speciesof mammal were found. Of these species, Rock Dove, Mourning Dove, and American Robincomprised ~80% of the biomass of their diet. The percentage of non-native biomass of the dietwas higher, on average, in more urban nests (~65%) than in park nests (~25%). Most of thisbiomass was brought to the nest in the mid-section of the breeding season. Determining how theCooper’s Hawk is able to survive and reproduce in such close proximity to human activity anddisturbance can lead to better management decisions with respect to this species and others in thefuture.Aaron N. K. Haiman Cooper’s Hawk Diet 8-May-2006p. 2IntroductionThe amount of land covered by urban development, and the effects of urbanization onspecies distribution, are increasing throughout the world every year (Vitousek et al. 1997). Oneway that urbanization changes the natural environment quickly and disruptively is by thedisplacement of species (Beissinger and Osborne 1982, Mills 1989, Bell et al. 1995, Estes andMannan 2003). Urban habitats are usually very different from preexisting habitats in terms ofchanges in temperature gradients, precipitation levels, runoff patterns, and amount and quality oftopsoil (Herrick 1995). Many species of wildlife, such as the Bachman’s Sparrow (Aimophilaaestivalis) and the Striped Shiner (Luxilus chrysocephalus), cannot tolerate urban environmentsand are subsequently displaced (Schweizer and Matlack 2005, Dunning and Watts 1990). Somespecies, however, can cope with such disturbances and will persist in urban environments. Theseinclude the Cooper’s Hawk (Accipiter cooperii), the focus of this study, and the Eastern FoxSquirrel (Sciurus niger) (Salsbury et al. 2004, Barry et al. 1998).A. cooperii (Bonaparte) is a medium-sized raptor that occurs throughout southern Canada,the continental United States, and Mexico (Ferguson-Lees 2001). As a top predator, it feeds on awide variety of small to medium-sized songbirds, game birds, and small to medium-sizedrodents, and reptiles (Wheeler 2003, Roth and Lima 2003). It breeds in mature trees, and nestingcan begin as early as February and chicks can still be receiving food from the adults untilOctober. A. cooperii has a high tolerance for urbanized environments and has been asuccessfully breeding bird in numerous urban areas throughout the U.S. including Tucson,Arizona (Estes and Mannan 2003), Stevens Point, Wisconsin (Rosenfield 1996), and Berkeley,California (Pericoli and Fish 2004). For the purpose of this paper, success is defined as thefledging of at least one young at a given nest-site in a given year (Pericoli and Fish 2004).The survival of top predators in urban environments depends upon these predators findingsuitable habitat, large enough territories, and other resources one of which is food. The preyspecies of Cooper’s Hawks that live in urban environments will necessarily be tolerant of humanimpacts. Since all species cannot survive in urban landscapes, the number of species that areavailable to A. cooperii as prey in such landscapes will be more limited than in rural habitatswith lower levels of human disturbance (Peeters and Peeters 2005). It has been shown that moreomnivorous species are better adapted to survive in urban environments than more specializedspecies (Clergeau et al. 1998). However, a result of reduced prey diversity can be preyspecialization whereby a predator becomes very successful at capturing a limited number of preyAaron N. K. Haiman Cooper’s Hawk Diet 8-May-2006p. 3species but loses behaviors required for capturing a broader prey base (Kauffman et al. 2004).Such specialization can benefit a predator, but it can also expose the predator to stressors if oneor more of the prey species on which it specializes becomes scarce. Prey specialization canresult from anthropogenic effects or by natural processes. Regardless of how specializationdevelops the results can be the same. One of the results that can negatively affect a predator is ifthe prey acts as a vector for disease. Doves throughout the United States can carrytrichomoniasis, a disease that can prove fatal to Cooper’s Hawks (Stabler 1954). These doves canpass the disease on to young Cooper’s Hawks when the infected flesh is eaten (Estes andMannan 2003). If the Cooper’s Hawks depend too strongly on doves for food, they may beexposed to this disease at a higher rate than rural populations. The rates of infection vary acrossthe Cooper’s Hawk range, and it has been found that the infection rates in urban environmentsare higher than the infection rates in nearby rural environments (Rosenfield et al. 2002).As we come to better understand what the effects of urbanization on ecosystems are, we willbetter understand how and when to buffer habitats and species from the more harmful of thoseeffects (Mills 1989). By identifying the characteristics of a successful habitat of a target species,the specific conservation needs of that species can be better understood. More informedmanagement decisions can then be made to plan further urban development so that the aspects ofa habitat that are required for a species are left unharmed, and so preserve biodiversity. In thisway we can avoid degraded habitats and ecological
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