Desert tortoise (Gopherus agassizii) is found in both the Tucson and Rincon Mountain District of the Saguaro Park. These species of tortoise have also been called walking saguaros. This is because they normally leave in rocky desert slope. Even though, the desert tortoises in the park are not endangered or threatened, they are normally secured and considered sensitive. Desert tortoises are large herbivorous reptiles (Lockwood, 2006). They are usually active during the day and when most annual plants are available in abundance, especially during early summer and spring. Nevertheless, they are also active after the rain. When it rains at night, the desert tortoises normally emerge from the tunnels to drink the water. They also move from the tunnels at night due to extreme heat. Walking saguaro normally spends the rest of the year in shelters or tunnels in order to avoid extreme weather conditions, which are usually prevalent in the desert (Lockwood, 2006).
Desert Tortoise Food Supply and Its Physical Environment
Desert food supply of a tortoise differs throughout the year. It depends on the availability of seasonal nutrition and plants available (Esque, 2001). Food supply of desert tortoise identified in the Tucson Mountain District of Saguaro National Park used studies of observational bite tallies and scat samples of live tortoise to identify what plants are mostly beneficial to this land-dwelling reptile in this region. Desert tortoise food supply is mainly composed of safe weeds, fruits, leafy greens and grasses. These food supplies should be free from any contamination with herbicides or pesticides. It is able to digest many plants that many other desert animals find hard to digest (Lockwood, 2006).
In the spring, desert tortoise largely feeds on annual legumes like the desert lupine. These plants have low quantities of potassium and ample amounts of water (Lockwood, 2006). During the summer when water is readily available, a typical diet of a desert tortoise is mainly composed of both perennial and annual grasses. These are complemented by prickly pear fruits and the desert vines.
The desert tortoise is complete terrestrial and herbivorous animal. It is brown with a high doomed shell, stout and legs that resemble those of an elephant. There are various species that have been identified by scientists. The desert tortoise belongs to one of the Testudinidae families in the North America. The physical environment of a desert tortoise comprises of a desert ecosystem (Lockwood, 2006). It has got adaptations that make it endure the harsh desert climates that range between extremely hot temperatures and low temperatures during the night. The desert tortoise is able to maintain its body temperatures by use of burrows; these burrows serve as protection against the extreme hot temperature or cold temperature. Such shelters keep the cool for tortoise during the day and protect it from freezing during the night (Einspruch, 2006).
Desert tortoises spend most of their lives in burrows. They only emerge from these burrows in order to find food, as well as to breed or simply to saunter. Another feature that enables the desert tortoise survive in the desert climate is that it feeds on plants containing high amounts of water (Einspruch, 2006).
Place of Study
This particular research will take place at the Tucson Mountain District of Saguaro National Park.
Literature Review on Methods
Desert tortoises are usually called walking saguaros because they are long-lived and are also found in slope of rocky deserts. The desert tortoises are considered to be endangered species, and thus they are protected and considered being sensitive. Numerous studies have been conducted in order to evaluate the conservation status, as well as the natural history of the desert tortoise. A wide range of methods have been used in the study of desert tortoises in their habitats. The number of adult desert tortoises were investigated in the Rincon Mountain District through observational method. The mark and recapture method has also been used in the same region in early 1980’s (Einspruch, 2006). In between 2000 and 2006, distance sampling studies on desert tortoise were conducted in both Tucson and Rincon Mountain Districts. The desert tortoise’s density in the Rincon Mountain District was estimated to range between 34 and 54 of adult tortoises per square kilometer. In Tucson Mountain District, the result of the applied methods was found to be slightly lower. It only had 25 tortoises per square kilometer.
The radio-telemetry method has also been used in the study of the desert tortoise. This method is usually beneficial since it provides required information concerning the movement patterns and seasonal activities of the desert tortoises. This method has revealed that desert tortoise tends to live in one particular habitat (Einspruch, 2006). This means that desert tortoise occupies the same shelter for several winters. However, this method reveals that desert tortoise tends to make occasional long-distance movement within the habitat. Radio-telemetry method is normally effective in monitoring long-distance movements by the tortoises within their habitats (Einspruch, 2006).
In years between 1996 and 1997, mark recapture method was applied in the study of the Sonoran Desert. This technique is used to approximate the density of desert tortoise on the basis of long-term observing plans. Since then, other methods, such as distance sampling transects method, have also been put in practice (Fox, 2004). This method is also used to estimate the density of the desert tortoise. Other methods include the repeated presence-absence survey method that is used to estimate the percentage of the area occupied by the desert tortoise. This method has been widely used by the researcher in different habitats of walking saguaros.
During the past few years, radio tracking has been used to mark the desert tortoise. This has especially been done by the students. This method was essentially crucial since it allowed the students not only to track the desert tortoise but also to collect data on the weather, movement, desert tortoise’s activity and the habitat (Fox, 2004).
Methods of Field Study
Observational method as well as capture methods will be used to observe the desert tortoise in its real environment. This will be essential in studying the physical landscape of the desert tortoise since the method cannot influence its activities within the habitat. This approach will be valuable to use since it is not time-consuming and it reflects the real life behavior of the desert tortoise in the habitat of study (Cornett, 2002).
The desert tortoise will be captured and marked in order to enhance the effectiveness of the observational method. Two types of marks will be used in the study; the label and scute notches. The scute notches are normally small V-shaped hollows that are mostly 0.5cm in width and length. These hollows will be permanently filed into marginal scute. Marginal scute will be located on each side of the tortoise. Each marginal scute will then be given a distinctive number within the notching system (Cornett, 2002). Each tortoise will be identified during observation by adding up the distinctive number given to each marginal scute. Radio telemetry will also be used in order to monitor the movement of the desert tortoise, as well as seasonal activities within the habitat. Small and fragile screw transmitter will be attached to the body of the desert tortoise. These transmitters will make it possible to track the movement of the tortoise during the study. However, caution must be exercised when fixing the transmitter to avoid causing injuries and behavioral manipulation to the desert tortoise (Cornett, 2002).
Labels will also be used to identify desert tortoise within the area of study. Labels are crucial since they make it possible to identify walking saguaros while still in its habitat without having to remove it from the shelter. Using labels is also beneficial since it is long-lasting. In addition, transects will also be used in order to monitor and to collect essential data about the activities of the desert tortoise in relation to its habitat. This method will essentially be used to identify the population of the desert tortoise (Bare, 2007). The radio transmitter will also be used in order to approximate the habitat size of the desert tortoise in the area of study. Furthermore, radio transmitter will be important in determination and description of the desert tortoise’s movement and seasonal activity pattern within the habitat.
In order to assess the diet of the desert tortoise, the fecal samples will be taken from the region of study. The fecal pellets will be sorted manually in order to identity the plant fragment that forms the desert tortoise’s diet in that habitat. The grasses and annual plants that are frequently consumed will be identified in the fecal sample collected (Bare, 2007). Since Saguaro National Park, where the study will be conducted, is often prone to fire, a belt transect will be used to survey the entire area that has been under fire in order to assess the distribution of conflagration. This is because earlier study on the region found about five carcasses of desert tortoises, the death of which was attributed to fire. This investigation will also be essential in assessing the desert tortoise pattern within burnt and unburnt areas (Bare, 2007).
While capturing a desert tortoise that is outside its burrow, the approach of capture should be slow. In a situation where the tortoise is fifteen feet away, it should be approached with pauses to contact it in thirty seconds. The person capturing the tortoise will wear a pair of unused, clean rubber or latex gloves. The tortoise should be grasped at its bridge (Fox, 2002). That is at the connection between the plastron and carapace. The grasping should also be done with both hands.
If the tortoise will be moved from its natural habitat, it should be slowly lifted and moved smoothly to the site of study. Additionally, if the tortoises are collected at the sunset or in the evening, and studies are assumed to take longer, reptiles should be held overnight in unused, clean box or an open disinfected plastic container (Fox, 2002). All tortoises captured should be handled with precision and should be assumed to have contagious diseases.
Variables to Be Measured
In this research, data to be recorded include sex, size, and weight. Before taking any variable from the tortoises, permission or authorization from relevant authorities should be obtained (Cornett, 2002). Consequently, the tortoises should be handled in a cautious way in order to avoid transmission of parasites and diseases. The person handling the tortoise is obliged to wear a pair of disposable rubber or latex gloves. If the gloves become torn in the process of handling a desert tortoise, a new pair should be worn immediately (Cornett, 2002).
Measurement will involve measuring the midline carapace length of the desert tortoise from pygal to nuchals scutes. Tools to be used will include calipers. These tools need to be reliable in their measurement. They must provide the most accurate measurement. All measurements in this research will be recorded in millimeters (Bare, 2007).
It will be difficult to determine the sex of a tortoise in case if it has midline carapace with the length less than 180 millimeters. As a result, other features will be used so as to identify the correct sex of the tortoise (Bare, 2007). For example, longer or more curved gulars, thicker toenails, well-developed chin glands and conical tail will identify distinct male tortoise characteristics (Cornett, 2002).
In the process of measurement of the tortoise’s weight, an attention should be paid to avoid any mishandling or injuring the animal. This is because mishandling a tortoise can interfere with the functioning of its bladder. When using a spring balance, the tortoise will be placed inside a harness made of clean and unused cord so as to avoid the spread of pathogens if any are present. It will further prevent contamination of field equipments with defecation and urine from the tortoises. When measuring the weight of the tortoise, it will be immobilized and placed on the digital scale (Esque, 2001). This will enhance taking accurate measurement. Weighing the tortoise will be done immediately after capturing to record accurate results.
Binoculars. This is a pair of field glasses that are mounted side by side. They will be used to observe the desert tortoise from a distance. The binoculars to be used will have a high magnification capacity. They will help in avoiding reactive effects of the tortoise being studied. This will allow for the collection of accurate data or information regarding the behaviors of the tortoise.
Magnifying Glass. It is also called a hand lens. It will be used to magnify things like the food droppings to identify traces of foods that the tortoise feeds.
Microscope Slides and Cover Slips. This is a flat thin piece glass. It approximately measures seventy five by twenty five millimeters. They will be used to examine things like nail cuticles of the desert tortoise under a microscope. The cover slips are much thinner than the slides. They will be used together with the slides.