j RaptorRes. 38(1):26-34 ¸ 2004 The Raptor Research Foundation, Inc. MOVEMENTS AND SURVIVAL OF FLEDGLING COOPER'S HAWKS IN AN URBAN ENVIRONMENT R. WILLIAMMANNAN, 1 WENDY A. ESTES,AND WILLIAM J. MATTER Schoolof RenewableNatural Resources,University of Arizona,7•tcson, AZ 85721 U.S.A. ABSTP,ACT.--Cooper's Hawks (Accipitercooperii) nest in urban and suburban areasacross North America, but little is known about movements,habitat use, or survivalof fledglingsin thesesettings. We followed 40 radio-tagged,fledgling Cooper'sHawks hatched in Tucson,Arizona in 1999 or 2000, for up to 6 mo to estimatesurvival, and describepatterns of movementand the environmentsthey use while dispersing. The typical pattern of movementfor hawkswe tracked through early winter consistedof sedentary behavior in the natal m'ea,followed by relativelylong movementsbeginning 11-13 wk after hatching, and finally sedentarybehavior again when they settledinto a fall/winter home range. Distancesbetween relocationsof individual hawkswere, on average,greater for females (/= 6.8 km, range = 0.02-51.7 km, SD = 9.8) than males (œ= 3.8 km, range = 0.05-20.8 km, SD = 5.4; t-test,P = 0.02). Home range size for nine hawksduring their first fall/winter averaged771 ha (SD = 403). Distancefrom center of home range to natal site averagednem'ly twice as far for females (œ= 10.9 km, range = 4.2-19.5 km, SD = 6.4) as males (œ= 6.0 km, range = 2.2-13.3, SD = 5.0), but the difference was not significant (t-test,P = 0.23). Survivalof radio-taggedhawks was 67% through 180 d. Hawks used a vm'ietyof environments prior to settling for the winter, but were found most frequently (35% of locations) in riparian areas.We found no discernablepattern of habitat selectionfor land usecategories inside winter home ranges.We speculatethat the abundanceof food may facilitatesurvival of post-fiedging,dispersing hawks in Tucson. KEYWORDS: Cooper'sHawks; Accipter cooperii; dispersal;habitat selection; home range size;, urban environ- ments; Tucson, Arizona. MOVIMIENTOS Y SUPERVIVENCIA DE POLLUELOS DEL GAVILAN DE COOPER EN UN AMBIEN- TE URBANO RESUMEN.--E1gavil•tn de Cooper (Accipitercooperii) anida en fireasurbanas y suburbanasa lo largo de Norteam6rica,y se conoce poco acercade susmovimientos, uso de h•tbitat,o sobrela supervivenciade losjuveniles en estaslocalidades. Seguimos 40 gavilanesde Cooper juveniles equipadoscon radios de telemetria empollados en Tucson, Arizona en 1999 o 2000, pot cerca de 6 mesespara estimar su supervivencia,y describir los patrones de movimiento y los ambientesque ellos usan durante su dis- persi6n. E1 patr6n tipico de movimiento pm'a los gavilanesque seguimosa principios del invierno consisti6de un comportamiento sedentarioen el firea natal, seguidopot movimientosrelativamente lm'gosque comienzanen la semana 11-13 luego de romper el cascm'on,y finalmente un comporta- miento sedentm'iode nuevo cuando se establecendentro de su rango de acci6nde la temporadaotofio/ invierno. Las distanciasentre las reubicacionesindividuales de los gavilanesfueron, en promedio, mils grandespara las hembras (/= 6814 m, rango = 16-51 673 m, SD = 9752) que para los machos (i = 3776 m, rango = 46-20 759 m, SD = 5356) (test de T, P = 0.02.) E1 tamafiodel rango de acci6npara nuevegavilanes durante su primer otofio/invierno promedi6 771 ha (SD = 403.) La distanciadel centro del rango de acci6n al sitio natal fue en promedio cerca de dos vecesmils lejana para las hembras (œ = 10.9 km, rango = 4.2-19.5 km, SD = 0.387) que para los machos(/ = 6.0 km, rango = 2.2-13.3, SD = 5.0), pero la diferencia no fue significativa(test de T, P = 0.23). La supervivenciade los gavilanes monitoreadosrite del 67% pm'a 180 dias. Los gavilanesusm'on una variedad de ambientesantes de establecersepara el invierno, sin embargose encontraronmas frecuentemente (35% de lasubicaciones) en zonasriparias. No encontramosningfin patr6n discernible en la selecci6ndel h•tbitatpara las cate- gorias del uso del suelo dentro de los rangosde acci6n invernales.Especulamos que la abundanciade alimento puede facilitar la supervivenciade los gavilanesjuveniles que se dispersanen Tucson. [Traducci6n de G6sarM•trquez] E-mail address:[email protected]. edu 26 MARCH 2004 POST-FLEDGLING COOPER'S HAWKS 27 Natal dispersalin birds is the movement of fledg- nests in their first fall and winter (Boal 1997), but lings away from their nests and often involves a most reported movements during natal dispersal search by dispersingindividuals for a place to re- are considerablyless than this distance (e.g., me- side and potentially breed. Distancestraveled by dian = 6.4 km for males, N= 10; 14.4 and 790 dispersingbirds and their survivalcan significantly km for two females; Rosenfield and Bielefbldt affect the genetic structure, demography, and via- 1992, Rosenfieldet al. 1996). Thus, the initial stag- bility of bird populations (e.g., Pulliam and Dan- es of natal dispersalby Cooper's Hawks hatched •n ielson 1991, Payne and Payne 1993, Globert et al. relatively large metropolitan areas could occur 2001). Natal dispersal usually is measured as the within these developed environments. straight-line distance between natal nestsand sites Knowledge of the patterns of movement and where birds first breed, if they survive (Howard habitat use of dispersingCooper's Hawks in urban 1960, Greenwoodand Harvey 1982). But dispersal settingscould be used to identify environments to generally takes place in landscapescomposed of protect or enhance as cities grow, assumingthat patches that vary in size and quality relative to the hawk populations are a desired feature of the ur- needs of dispersing individuals; thus, movements ban landscape. Furthermore, Boal and Mannan between natal and breeding sites are not likely to (1999) suggested that models of population be linear (Wiens 2001). Furthermore, selection of growth of urban Cooper's Hawks are needed to a place to reside by dispersingbirds may be con- understand whether some urban areas represent ducted in stages(e.g., search, settlement, residen- "source" or "sink" populations (Pulliam 1988). cy; Stamps2001), each associatedwith different be- Estimatesof survival of hawks during dispersalare haviors and patterns of movement. Identifying critical to such modeling efforts (e.g., Lande 1988, patterns of movement in all stagesof dispersalis Boyce1992, Beissingerand Westphal1998). We fol- critical to understandingwhy dispersingbirds set- lowed Cooper's Hawks hatched in an urban setting tle and breed where they do. Also, information for up to 6 mo after fiedging to: (1) estimate their about environments that facilitate movement and survival from late summer through early winter; survivalduring dispersal(e.g., Miller et al. 1997) and (2) determine how far they dispersefrom na- are important in the developmentof habitat man- tal sites,the kinds of environmentsthey use while agement plans for birds, especiallyif plans encom- dispersing,and the characteristicsof areasthey use passbroad spatial scales(e.g., Strong and Bancroft when they settle during their first winter. 1994, Miller et al. 1997) and fragmented land- STUDY AREA scapes(e.g., Temple 1989). Natal dispersalhas been studied in a variety of We marked and tracked fledgling Cooper's Hawks m bird speciesover the last decade, but information and near Tucson, Arizona (32 N ø, 111 Wø). The Tucson metropolitan area encompassesabout 70 000 ha with an about this process remains limited compared to estimated human population of 803 600 residents. Tuc- other aspectsof population demographyand other son includes developmentsranging from commercial dis- kinds of movements (Koenig et al. 2000, Walters tricts and high-density housing to suburban areas w•th 2000, Clobert et al. 2001). Among birds of prey, low-densityhousing. Parks, golf courses,and open space various stagesof natal dispersalhave been studied are scattered throughout residential areas. Tucson is lo- cated in the Sonoran Desert and supports remnants of primarily in speciesthat are the focus of manage- lower and upper Sonoran vegetation types and riparian ment and conservation efforts and in environ- corridors (Brown et al. 1979), but much of the natural ments that are relatively undeveloped or rural vegetation has been removed or replaced with nonnative (e.g., Wyllie 1985, Walls and Kenward 1995, Ganey plants. et al. 1998, Harmata et al. 1999, Restani and Mat- METHODS tox 2000). Cooper's Hawks (Accipitercooperii) nest in highly-developedenvironments (i.e., urban and We used bal-chatri traps (Bloom 1987) to capture fledgling Cooper's Hawks at nests monitored in a long- suburban areas) in several places across North term study (Boal and Mannan 1999, Mannan and Boal America (see Rosenfield and Bielefeldt 1993 for 2000). We captured fledglings when they were old review, Stewart et al. 1996, Boal and Mannan 1998, enough to hunt on their own and when their rectrices 1999), but little is known about the movements, were fully emerged (-->55 d old). We marked each cap- tured fledgling with a Department of Interior leg band habitat use, or survival of fledglings in these set- and a colored leg band with a unique alpha code, and tings. Existing information suggeststhat Cooper's attached a radiotransmitter (model RI-2C [5 g] in 1999 Hawks may move up to 100 km from their natal and model PD-2 [3.5 g] in 2000; Holohil SystemsLtd, 28 MANNAN ET AL. VOL. 38, NO. 1 Carp, Ontario, Canada) to a central rectrix (Samuel and dences/ha]; high-density residential areas [-->7.4 resi- Fuller 1994). Estimated life of transmitters was 6 mo dences/ha]; open spacewith low human use [e.g., cem- (model PD-2) or 9 mo (model RI-2C). No more than two eteries, neighborhood parks, and natural open space], fledglings (usually a male and female) from any nest open spacewith high human use [e.g., golf courses,dis- were radio-tagged,and nestsfrom which fledglingswere trict and regional parks, and schools],and other [e.g, marked were all >5 km from the edge of the metropol- roadways,and commercial,industrial, and agricultural lean area.