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Article Excerpt
The eastern White-winged Dove (Zenaida asiatica asiatica) is a migratory species that historically nested in large, rural colonies during May to August in southern Texas and northeastern Mexico (Cottam and Trefethen 1968). Colonies generally were in continuous nesting habitat varying in size from 5 ha to 1000s of hectares with nest densities ranging from to 10 nests/ha outside of colonies to >500-1,000 nests/ha within colonies (Cottam and Trefethen 1968). The historic breeding range of the eastern White-winged Dove extended from southern Texas to southern Tamaulipas, Mexico with the most productive nesting areas in the Tamaulipan thorn-scrub and semi-deciduous forests (Brown et al. 2007) of the Tamaulipan Biotic Province (Purdy and Tomlinson 1982, George et al. 1994, Schwertner et al. 2002).
Thousands of hectares of native, thorn-scrub vegetation have been lost in northeastern MExico and southern Texas resulting from land-use changes including agricultural practices, timber harvest, urban development, and dam construction. Much of this habitat loss and fragmentation has occurred within historic White-winged Dove nesting areas. Many nesting colonies of the historic complex that once existed have already disappeared, and others are currently at risk. Little knowledge exists regarding the precise sites of these colonies prior to the 1990s because of their remote locations and lack of global positioning systems (GPS) technology. Lack of knowledge of historic and current colony location is of considerable concern because this region once represented the primary breeding range of White-winged Doves. Understanding why some colonies persisted while others failed may provide insight useful in White-winged Dove conservation. Our objectives were to: (1) review all available literature to provide a historical account of White-winged Dove colonies in northeastern Mexico, and (2) document the physical location of historic and current colonies, their status, and possible causes of their disappearance.
METHODS
Study Area.--Our study concentrated in the northeastern Mexican State of Tamaulipas. The climate in Tamaulipas varies from semiarid to subtropical from north to south. Annual precipitation varies from 600 to 1,050 mm (Comision Nacional del Agua 2005). Most rainfall is received during the spring and fall but local, heavy thunderstorms during summer also contribute substantial precipitation in some years. Maximum temperatures usually vary between 35 and 40[degrees]C during summer (Comisi6n Nacional del Agua 2005). Minimum temperatures during winter seldom fall below 2[degrees]C (Almaguer 2005). The current landscape is composed primarily of agricultural fields planted to grain sorghum (Sorghum vulgare) and corn (Zea mays). Other crops such as citrus (Citrus reticulata), cotton (Gossypium hirsutum), and melon (Cucumis spp.) also are prevalent. The most common crops in southern Tamaulipas are sugar cane (Saccharum officinarum) and agave (Agave tequilana). Pasturelands for livestock grazing are common throughout the state. There are remnant patches of native Tamaulipan brushland, mainly in central and southern Tamaulipas, and include the biotic communities of Tamaulipan thorn-scrub and Tamaulipan semideciduous forests (Brown et al. 2007). The native vegetation described by George et al. (1994, 2000) is composed of shrubs and small trees 3-10 m in height such as ebony (Pithecellobium ebano), huisache (Acacia smallii), mesquite (Prosopis glandulosa, P. reptans, and P. juliflora), brasil (Condalia hookeri), coma (Bumelia celasterina), barreta (Helietta parvifolia), guajillo (Acacia berlandieri), granjeno (Celtis pallida), anacahuita (Cordia bossieri), manzanita (Malpighia glabra), and several species of cacti (Cactacea).
Historical Account.--We obtained copies of government (e.g., U.S. Fish and Wildlife Service [USFWS], Texas Parks and Wildlife Department [TPWD], Secretarfa de Agricultura y Recursos Hidraulicos [SARH] [Secretary of Agriculture and Hydraulic Resources] and Secretaria del Medio Ambiente y Recursos Na turales [Secretary of Environment and Natural Resources]) visit reports which contained historical information of nesting colonies (e.g., general location, nesting habitat conditions, water and food availability, number of nesting White-winged Doves) to investigate the historic status of White-winged Dove nesting colonies in northeastern Mexico. We also reviewed published studies related to nesting colonies of White-winged Doves in north-eastern Mexico.
Identification and Location of Colonies.--We conducted personal interviews with biologists who participated in colony visits in northeastern Mexico during the last 20-30 years, and who had significant knowledge of White-winged Dove nesting areas. Biologists included: D. R. Blankinship (USFWS), G. L. Waggerman (TPWD retired), H. Ortega-Melendez (Comision Estatal de Vida Silvestre de Tamaulipas; CEVST), and H. V. Zamora-Trevino (Habitat y Palomas del Noreste A. C.; HPN). We formed an international team to locate historic and current nesting colonies in Tamaulipas. The team consisted of G. L. Waggerman, H. Ortega-MelEndez, and H. V. Zamora-Trevino, S. Benn (TPWD), P. Castillo (CEVST), C. Chavez (SEMARNAT), F. Hernandez (Caesar Kleberg Wildlife Research Institute; CKWRI), and D. G. Hewitt (CKWRI). We conducted site visits to colonies in Tamaulipas, Mrxico during May-August 2004 and 2005. Locations of all current and historic colonies were recorded using a hand-held, real-time differential GPS unit (Trimble[TM] GeoExplorer III, Trimble[TM] Navigation Limited, Sunnyvale, CA, USA). Delineation of entire colonies was not logistically practical and a series of...
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