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Tucson Audubon Society
IBA Program
Coordinator Meets with Santa Cruz River Landowners—Mesquite Bosque Most
Threatened Habitat Along River
by Scott Wilbor, Arizona IBA
Program Coordinator
Contact info: (520) 628-1730
(This article was first published in the Vermilion Flycatcher, newsletter of the Tucson Audubon Society [October 2004]. To receive the newsletter in the mail, become a Friend of Tucson Audubon.)
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After a summer spent meeting with landowners along the Upper Santa Cruz River from the U.S./Mexico border to Tubac (a proposed Important Bird Area, [IBA]) and touring habitats with these landowners and residents, it is apparent that the once vast mesquite bosque (woodland) is the most threatened habitat along the river. The vegetative structure and composition of this mesquite bosque is composed of many large mesquite (12 inches diameter and greater & 15 feet tall and greater-some much larger in size), mixed with large netleaf hackberry, elderberry in a mostly closed forest canopy, a dense diverse mid-story layer of acacia, smaller mesquite, and desert hackberry, and an under-story layer of graythorn, wolfberry, mulberry, Arizona grape, climbing milkweed, forbs (like morning glories, amaranth, buffalo gourd), and grasses (like vine mesquite grass). Cottonwood-willow habitat also remains under threat from water pumping (from south of the border to north of Rio Rico), and is seriously impacted by grazing throughout the reach (with a few exceptions).
The threat to mesquite bosque is primarily from clearing for housing development, and this could result in permanent loss or degradation of unprotected forest. From north of Tubac (Chavez Siding Rd.) and extending south bordering the cottonwood-willow gallery forest all the way to Rio Rico, the mesquite bosque is being cut, cleared, developed, or is under serious threat from future development. Groundwater pumping has an impact near irrigated pastures as well. Conservation of this very threatened habitat has, to date, been mostly overlooked, even within the newly issued Santa Cruz County Comprehensive Plan (2004).
West of the river (Tubac to Rio Rico), much of this once vast bosque has either been developed into houses or resort facilities, or converted into expansive irrigated pastures. A significant exception is the newly protected land within the expanded boundaries of the Tumacacori National Historical Park. A 300-acre expansion, completed this summer, encompasses high quality mesquite bosque extending for a mile along the Juan Bautista de Anza Trail. Other remaining mesquite bosques include the narrow strip of old growth mesquite from south of Tumacacori to Rancho Santa Cruz (1.3 miles long), and another narrow bosque at the confluence of Peck’s Canyon and the Santa Cruz River (0.9 mile long).
East of the river, substantial bosque still exists east and south of Chavez Siding, extending south to Tubac (1.7 miles). But this bosque is extremely threatened, and a substantial bosque from Josephine Canyon south to opposite Peck’s Canyon confluence (3.6 miles long) is also extremely threatened. Small patches exist at Chivas Wash, south of Tubac State Park, and along the "dry Santa Cruz River" from south of Rio Rico to the border (all less than 0.4 mile long).
What breeding bird populations are most threatened in this reach? The mesquite bosque avian community in southern Arizona includes the Yellow-breasted Chat, Lucy’s Warbler, Bell’s Vireo, Bewick’s Wren, Ladder-backed Woodpecker, Varied Bunting, Ferruginous Pygmy-Owl, and Gray Hawk. The Ferruginous Pygmy-Owl may no longer be present in the upper valley. The Gray Hawk requires extensive mesquite bosque near its cottonwood-willow nesting habitat to forage for lizards (whiptails, Cnemidophorus sp.) and small mammals, and is the most threatened due to its need for a large home range. Yellow-billed Cuckoo may also nest and forage in thick dense mesquite bosque, as well as in cottonwood-willow forest, and could be further limited in its distribution on the Santa Cruz by mesquite habitat loss. Owls, woodpeckers, and Lucy’s Warblers require trees large enough for nesting cavities. Gray Hawk, Varied Bunting, and Yellow-billed Cuckoo are extremely limited in their distribution in southern Arizona, and their historical populations have undoubtedly declined dramatically. We must strive to protect and restore their remaining habitat in order to have healthy riparian wildlife communities along the Santa Cruz River. The stretch from Tubac to Tumacacori remains a stronghold for many of these species in the Upper Santa Cruz. (A small portion of this is now coming under protection at Tumacacori National Historical Park, but it is insufficient by itself to support mesquite bosque-dependent bird populations).
What are we doing? We provided comment to the Santa Cruz Planning and Zoning Commissioners regarding the conservation need for this habitat (a special committee will investigate protection and new zoning for mesquite bosque habitat). Negotiations are nearing completion on a 300-acre conservation easement along the Santa Cruz River, and we continue to meet with key landowners and land management entities to emphasize the importance and rarity of this habitat. We build partnerships for conservation of the riparian corridor, promote landscape conservation strategies, and collaborate with partners to contribute to common conservation efforts. Finally, we continue to map and monitor sensitive avian species & habitat, collaborate with our Mexican partners doing the same, and draft an Audubon IBA Conservation Plan for the Upper Santa Cruz River. We will keep you informed as we strive to protect this and other key IBAs throughout Arizona! Thank you for your support!
Note: To comment on this issue, contact Community Development Planning Director, Mary Dahl, Santa Cruz County Offices, 2150 N. Congress Drive, Nogales, AZ 85621, or email mdahl@co.santa-cruz.az.us.
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This page was updated on 02/21/06