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Effects of permanent water on home ranges and movements of adult male white-tailed deer in southern Texas.

Article Excerpt
Water distribution may have a large impact on ungulates in arid environments if water is scarce. If water distribution is poor, then ungulates may have large home range sizes, or be concentrated near water sources. Because establishing water sources can be expensive (Bone et al. 1992; Broyles 1998; Gunn 1988; Mouton & Lee 1992), it is important to determine the minimum number of watering sources necessary to support animals in an area, so that resources are not wasted establishing water sources.

There are many proponents and critics of wildlife water developments. Proponents of water developments site scarcity of free-standing water as a limiting factor of wildlife populations in arid environments (Roberts 1977). Critics, on the other hand, suggest that addition of new water sources may not return expected benefits (Broyles 1995; Brown 1998). If new water supplies are to yield expected benefits then water must be limiting to begin with, new sources must be distributed adequately in usable habitat, and they must be sources that wildlife are willing to use. The placement of concrete troughs near roads and human disturbances and the influence of cattle may reduce their usefulness to deer and other wildlife species. Prasad & Guthery (1986) found that deer did not use concrete troughs due to higher human and cattle activity. Ponds are often built on ephemeral drainages, which often contain deeper soils and an abundance of vegetation, resulting in higher levels of screening cover. Therefore, deer may water at ponds instead of concrete troughs due to less human influence and their larger size.

In southern Texas, water may be limited for portions of the year or for several consecutive years because of frequent and widespread droughts. The resulting lack of free-standing water may be deleterious to white-tailed deer (Odocoileus virginianus) because intake of water is essential for body condition maintenance (Maghini & Smith 1990), deer eat less and lose body weight when deprived of water, and are not adapted to dehydration (Lautier et al. 1988).

The location and abundance of water has been found to affect distribution and behavior of white-tailed deer. In Arizona, when water became scarce in June, white-tailed deer moved closer to permanent water, but dispersed when summer rains started (Welch 1960). Maghini & Smith (1990) found that deer would move from established diurnal ranges to distant water sources. Visual observations of deer in the Coastal Prairies of Texas found deer movements may have been attributed to the location of bodies of water (Michael 1965). Because Michael's (1965) data were based on visual observations, it appeared deer used areas in association with water, yet water sources were within 686 m of one another. Therefore, deer were never far from water at any time.

Deer are thought to need free-standing water; therefore, water availability in xeric environments probably influences home range size and location (Maghini & Smith 1990). The importance of drinking water in the life of deer was emphasized by the fact that watering sites were frequently centers of deer home ranges and the presence or absence of water noticeably affected their daily activities (Michael 1968). White-tailed deer are sedentary and reluctant to leave an area; however, during dry seasons when surface water becomes scarce, deer may concentrate near remaining sources of water (Michael 1968). Teer (1996) reported white-tailed deer used water sources 2-3 times/day. Therefore, water appears to exert a strong influence on daily activity patterns, movements, and home ranges.

In contrast, when water distribution was adequate to meet needs, mule deer (Odocoileus hemionus) distribution probably was determined by environmental factors other than water (Boroski & Mossman 1996). Webb et al. (2006) found that white-tailed deer visits to permanent water following rainfall events decreased for three weeks indicating that deer obtained water from ephemeral pools or from vegetation. Camera surveys conducted in conjunction with Webb et al. (2006) found no ear-tagged (i.e., of >150 marked) or radio-collared deer (n = 48) using water during two summers of surveys. Thus, in southern Texas, permanent sources of water may not exert as strong an influence on deer as in other arid environments.

If deer need to expand or shift home ranges when water is limiting, then these expansions or shifts will help dictate the scale at which deer management needs to occur. The objectives of this study were to: (1) determine the effect of permanent water sources on annual home range formation of adult, male deer, and (2) determine how seasonal and annual deer movements were affected by permanent sources of water.

STUDY AREA

This study was conducted on the Callaghan Ranch (27[degrees]48'59"N, 99[degrees]18'49"W), from September 2002 through August 2004, in Webb County, Texas, 43.4 km northeast of Laredo, Texas. The ranch had no deer-proof fences and consisted of 34,400 ha of mesquite-(Prosopis glandulosa) dominated shrubland (McCoy et al. 2005). Principle soils of the Callaghan Ranch were Catarina-Maverick-Moglia which are deep to moderately deep, nearly level to gently rolling with saline, clayey, and loamy soils (Sanders & Gabriel 1985). The ranch was continuously stocked with domestic cattle at a rate of 1 animal unit/21 ha and deer density was estimated to be 1...

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