I studied a population of Cooper's hawks (Accipiter cooperii) nesting in the metropolitan city of Tucson, Arizona, from 1994 to 1997. I identified 51 Cooper's hawk territories distributed across Tucson with pockets of nesting density as great as 1 pair/64.7 ha. Eucalyptus (Eucalyptus spp.) (70.8%), aleppo pine (Pinus halepensis ) (25.0%), and cottonwood trees (Populus fremontii) (4.2%) were used as nesting structures more frequently than expected based on availability. Nest trees were primarily located in residential yards (48.3%) and high-use recreational areas (28.3%). Nest sites had a greater basal area, canopy cover, stem density, and number of trees >10 m tall than random sites. I compared the breeding ecology of urban Cooper's hawks with those in exurban areas. Urban pairs tended to have larger clutches (urban x̄ = 3.64: exurban x̄ = 3.20) (P = 0.085) and more nestlings (urban x̄ = 3.11; exurban x̄ = 2.78) (P = 0.145) than exurban pairs. Nestling mortality, however, was greater among urban nests (51%) than exurban nests (5%). The primary cause of death among urban nestlings was trichomoniasis (80%), a disease caused by the parasitic protozoan Trichomonas gallinae ; the disease was not a mortality factor among exurban nests. Raptors develop the disease by eating infected prey. Doves (Columbidae) are hosts for the protozoan and accounted for 83% and 10% of the diet of urban and exurban Cooper's hawks, respectively. Breeding age Cooper's hawks were 99% free of infection independent of nesting area. Infection rates were greater among urban nestlings than exurban nestlings (P < 0.0001). Breeding urban Cooper's hawks have high probabilities of survival (0.792) and recapture (0.947), but the estimated juvenile survivorship is low (0.199). Age-specific fecundity and survival suggests the urban population is declining by 8% annually, but has the capacity to increase by at least 2% annually. Paradoxically, the population appears to be stable or increasing, probably due to immigration of Cooper's hawks from outside the study area. Population sinks in human altered landscapes have been described as "ecological traps" because animals are attracted to them but suffer from low productivity or high mortality once they are there. My results suggest Tucson may be an ecological trap for Cooper's hawks.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/288705 |
| Date | January 1997 |
| Creators | Boal, Clint William, 1961- |
| Contributors | Mannan, R. William |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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