R. William Mannan

Comparative Breeding Ecology of Cooper's Hawks in Urban and Exurban Areas of Southeastern Arizona

One step in assessing the quality of an urban environment as habitat for a species is to compare its breeding ecology and productivity in urban and exurban (i.e., undeveloped, natural) areas, We studied Coopers hawks (Accipiter cooperii) in Tucson, Arizona, and in exurban areas in southeastern Arizona, 1994-96. Urban pairs nested earlier (P < 0.001 and had larger clutches (P = 0.085) that exurban pairs. Nestling mortality was greater among urban nests (50.3%) than exurban nests (4.9%). The primary cause of death among urban nestlings was trichomoniasis (79.9%), which was a consistent mortality factor among vears (P = 0.402). An overall failure rate among urban nests (52.6%) was greater than at exurban nests (20.5%; P < 0.001). Although the role of bird feeding in the spread of trichomonias is remains unclear, promoting dove-proof feeders or abstinence from bird feeding may minimize the spread of the disease among prey species, thereby reducing mortality of nestlin g Coopers hawks. The greatest cause of mortality among free-ranging Coopers hawks in the urban area was collisions (69.8%), primarily with windows. Techniques to decrease window collisions should be promoted to reduce window-strike mortalities among both Coopers hawks and their prey. Coopers hawks also are occasionally aggressive when defending their nests from preceived threats hich may lead to fear and persecution by city residents. Hence, environmental education may be an important component of managing this species in urbat settings.

FEEDING BEHAVIOR OF COOPER'S HAWKS AT URBAN AND RURAL NESTS IN SOUTHEASTERN ARIZONA

Abstract We monitored 18 nests of Coopers Hawks (Accipiter cooperii) in Tucson, Arizona, and 18 nests in rural areas of southeastern Arizona from 1999–2000 to compare feeding behavior of urban- and rural-nesting hawks. We recorded the frequency of prey deliveries, the approximate size and type of prey items, and the behavior of hawks during each delivery. Differences between rates of prey delivery at urban and rural nests decreased as nestlings grew. Rate of prey delivery at urban nests exceeded that at rural nests most during the morning and least at midday. Urban hawks delivered 2.0 ± 1.2 times more prey biomass nestling−1 hr−1 to nests than rural hawks. The odds of males delivering prey directly to nests, and of prey items being refused, were 13.6 ± 2.3 and 2.5 ± 1.6 times greater, respectively, at urban nests than at rural nests. Male and female hawks also vocalized more at rural nests than at urban nests. Our data suggest that prey is more abundant and available to hawks in Tucson than in surrounding rural areas. Diet composition of urban- and rural-nesting hawks also differed. Doves comprised 57% of urban prey deliveries, but only 4% of rural prey deliveries, and may explain the high rate of nestling mortality from trichomoniasis, an avian disease caused by a parasitic protozoan, in Tucson. Comportamiento Alimenticio de Accipiter cooperii en Nidos Urbanos y Rurales en el Sureste de Arizona Resumen. Monitoreamos 18 nidos de Accipiter cooperii en Tucson, Arizona, y 18 nidos en áreas rurales del sureste de Arizona durante 1999–2000 con el fin de comparar los comportamientos alimenticios de gavilanes anidando en zonas urbanas y rurales. Registramos la frecuencia de entrega de presas, el tamaño aproximado y el tipo de presas, y el comportamiento de los gavilanes durante cada entrega. Las diferencias entre las tasas de entrega de presas en nidos urbanos y rurales disminuyeron con el crecimiento de los polluelos. La tasa de entrega de presas en nidos urbanos excedió a la de nidos rurales más durante horas matutinas que durante las horas del mediodía. Los gavilanes urbanos entregaron 2.0 ± 1.2 veces más biomasa de presas polluelo−1 hr−1 que los gavilanes rurales. Las probabilidades de entregas de presas por machos directamente en los nidos, y de rechazo de presas fueron 13.6 ± 2.3 y 2.5 ± 1.6 veces mayores, respectivamente, en nidos urbanos que en nidos rurales. Los machos y hembras de los gavilanes también vocalizaron más en nidos rurales que en nidos urbanos. Nuestros datos sugieren que las presas son más abundantes y disponibles para los gavilanes en Tucson que en áreas rurales circundantes. La composición de la dieta de gavilanes urbanos y rurales anidantes también fue diferente. Las palomas formaron el 57% de las presas urbanas entregadas, pero sólo el 4% de las rurales. Esto puede explicar el alto índice de mortalidad de polluelos por tricomoniasis, una infección parasitaria, en Tucson.

Nest-Site Selection by Cooper's Hawks in an Urban Environment

Loss of nesting habitat due to urbanization and development has been identified as a primary threat to Coopers hawks (Accipiter cooperii), but this species can successfully nest in some urbanized areas. Hence, understanding the features of urban areas that promote occupancy by Coopers hawks may become important in managing for the species. We measured nest tree, site, and area features at 49 Coopers hawk nests representing 33 breeding pairs in Tucson, Arizona, between 1993 and 1996. Introduced eucalyptus (Eucalyptus spp.; 70.8%), aleppo pine (Pinus halepensis; 25.0%), and native cottonwood trees (Populus fremontii; 4.2%) were used as nest trees to a greater extent than expected based on their availability (P 10 m tall when compared to random sites. Most nest trees were located in the yards of single-family residences (48.3%) and in high-use recreational areas (28.3%). ). Dominant land-use types in nest areas were high-density residential areas (65.9%) and high-use recreational areas (22.7%). Levels of human disturbance at nest sites did not appear to influence nest-site selection. Density of Coopers hawks nests in Tucson was higher than in exurban areas and probably was associated with the large trees, water, and abundance of prey in the city. Maintaining nest sites for Coopers hawks in Tucson will require maintaining groves of large trees.

EFFECTS OF RADIOTRANSMITTERS ON NORTHERN GOSHAWKS: DO TAILMOUNTS LOWER SURVIVAL OF BREEDING MALES?

Abstract We used the Cormack-Jolly-Seber model to estimate the effects of radiotransmitters on survival of breeding northern goshawks (Accipiter gentilis). We separately compared apparent annual survival of leg-banded goshawks with (1) tailmount- and (2) backpack-style radiotransmitters (hereafter tailmounts and backpacks) to apparent annual survival of breeding adults with legbands only. The best model without radiotransmitter effects, evaluated with Akaikes Information Criterion (AICc), suggested no gender- or year-specific effects on survival. We then added radiotransmitter attachment type (tailmount or backpack) and mass of radiotransmitter as covariates to the base model to estimate the effect of radiotransmitters. Tailmounts on males significantly reduced apparent annual survival from 0.75 (SE = 0.02, 95% CI: 0.71 to 0.78) without radiotransmitters to 0.29 (SE = 0.15, 95% CI: 0.09 to 0.63) with radiotransmitters. Backpacks had no significant effect on survival of adults (0.79, SE = 0.17, 95% CI: 0.33 to 0.97). The strikingly lower survival of goshawks with tailmounts was surprising because tailmounts weighed less (10 g, 1.5% body mass) than backpacks (16–23 g, max = 3.4% body mass) and likely were carried for shorter periods. Due to the small number of goshawks with tailmounts (n = 14) in this study, our results possibly were due to chance. We therefore recommend additional study of the effects of tailmounts on survival of breeding male northern goshawks.

Home range characteristics of male Cooper's Hawks in an urban environment.

Abstract We monitored the movements of nine radio-tagged, adult, male Coopers Hawks (Accipiter cooperii) in adjacent home ranges during the breeding seasons of 1996 or 1997 in Tucson, Arizona, to ascertain the sizes and degree of overlap of home ranges, and to assess habitat selection at two spatial scales. Size of home ranges differed among hawks (13.3–130.6 ha), but the average was small [65.5 ha ± 40.7 (SD)] compared to the size of home ranges reported for Coopers Hawks in the literature. Home range size generally decreased with the number of years that a hawk had lived on its breeding territory. Only one pair of home ranges overlapped each other; overlap of one home range on the other in this pair was 14.2% and 10.6%. Proportions of land-use categories in home ranges varied widely among hawks, and suggested that the hawks did not select their home ranges on the basis of the categories we examined. Patterns of habitat use inside individual home ranges suggested that male hawks hunted primarily in the environments that surrounded their nests. Coopers Hawks in Tucson feed primarily on doves [Mourning Doves (Zenaida macroura), Inca Doves (Columbina inca), and White-winged Doves (Zenaida asiatica)], and we speculate that the abundance of doves throughout Tucson allowed the hawks to hunt successfully in several urban environments. We also speculate that Coopers Hawks in Tucson have relatively small home ranges because they do not need to range far from their nests to find food.

Identifying habitat sinks: a case study of Cooper’s hawks in an urban environment

We studied a population of Cooper’s hawks (Accipiter cooperii) in Tucson, Arizona from 1994 to 2005. High rates of mortality of nestlings from an urban-related disease prompted speculation that the area represented an ecological trap and habitat sink for Cooper’s hawks. In this paper, we used estimates of survival and productivity from 11years of monitoring to develop an estimate of the rate of population change, λ, for Cooper’s hawks in the area. We used a Cormack–Jolly–Seber approach to estimate survival of breeding hawks, and a stochastic, stage-based matrix to estimate λ. Despite the urban-related disease, the estimate of λ indicated that the area does not function as a habitat sink for Cooper’s hawks (

HABITAT ASSOCIATIONS OF SYMPATRIC RED-TAILED HAWKS AND NORTHERN GOSHAWKS ON THE KAIBAB PLATEAU

\widehat\lambda

Supplemental feeding regimes for Egyptian vultures in the Negev Desert, Israel

= 1.11 ± 0.047; P = 0.0073 for the null of λ ≤ 1). Because data required to reliably identify habitat sinks are extensive and difficult to acquire, we suggest that the concept of habitat sinks be applied cautiously until substantiated with reliable empirical evidence.