Traditional diet studies using bite count and fecal composition analyses offer some useful insight into tortoise food selection; however, their scope can be limited since desert tortoises manage their energy and nutrient budgets over long periods. Furthermore, such research only encompasses part of their foraging season.
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Grass
Desert tortoises need access to sufficient grass in order to acquire enough protein and calcium in order to avoid stunted growth, thin shells, and decreased lifespans.
In 1992, above average precipitation in the western Mojave Desert led to above average plant blooming at Desert Tortoise Research Natural Area (DTRNA), providing desert tortoises with an assortment of food sources during spring foraging season.
However, foraging studies that compare food plant availability with tortoise selection can be misleading if they fail to take account of the hierarchical nature of food selection. For example, if investigators count only plant species encountered along tortoise foraging routes without also measuring selection at these sites, estimates of plant availability will likely be overstated and can lead them to believe tortoises are selecting certain foods when in reality they’re selecting only those of highest quality at each feeding site.
Leafy Greens
Tortoises require an abundance of grasses, weeds and dark leafy greens in their diet – especially grass hay, clover, alfalfa, dichondra dichondra filaree spurge native plants like globe mallow.
Ideal, they should make up around 85% of a foraging diet. Also include dandelion greens and flowers, escarole, endive, mustard greens and watercress as options.
Foods rich in various vitamins and minerals provide essential nutrition. Many also serve as excellent sources of fiber which can help prevent obesity.
Some leafy vegetables should be limited or avoided altogether, particularly those high in sodium such as spinach, kale and collard greens. Oxalic acid present can bind calcium unnecessarily leading to health issues like depressed thyroid function and gout; additionally, cabbage family vegetables provide poor sources of nutrition that could potentially cause digestive distress in tortoises. Occasional use is fine but should form part of a balanced diet plan.
Fruits
As tortoises are grazing animals, their diet should mainly consist of grass/hay and leafy greens; fruit should only form part of their daily food consumption.
If possible, provide your desert tortoise with an abundance of fruits/weeds/vegetables to supplement their diet and provide variety. This will give them the chance to consume something similar to what they might find in nature while adding variety and ensuring an ideal feeding environment.
Be mindful not to feed too many fruits/weeds/vegetables to your tortoise as these items may not contain the appropriate balance of vitamins and nutrients needed. In particular, high sugar contents could increase their susceptibility to intestinal parasites.
Your tortoise should avoid feeding brassica vegetables such as broccoli and other members of the brassica family as these contain goitrogens which will reduce thyroid activity, leading to an enlarged thyroid gland (goiter). Strawberries or slices of melons may be given occasionally but only sparingly; treat these treats like treats!
Seeds
Seeds like alfalfa (pictured on the right), rapeseed, snap peas and sunflower seeds provide protein that makes a valuable supplement to a tortoise diet. But too much protein from seeds could disrupt its calcium/phosphorus ratio and cause bone and shell abnormalities.
Desert tortoises receive their protein through eating plants found in nature. Tortoises are opportunistic eaters and will devour nearly any plant if it smells or tastes appealing – such as loco weed and lupines in my yard that have long been known to be poisonous or painful to tortoises, yet they still enjoy devouring these!
Native grasses, annual wildflowers, nopales (Opuntia cacti pads and fruit), mulberry leaves, common cheese mallow and other mallow varieties, dandelion greens, nasturtium flowers, rose petals and hibiscus flowers all offer excellent sources of nutrition. Avoid spinach and other cruciferous vegetables which contain oxalates that bind with calcium absorption to make these sources unavailable as food sources.
