The diet in the great outdoors
Tortuga Mora, the black turtle in Spain
European tortoises are herbivores. In their primary habitat, the primeval macchia, the turtles find a rich supply of plant seedlings, leaves, stems, buds, flowers, wild fruits, seeds including their capsules and pods as well as bark between and under the bushes and in the many interspersed clearings , Roots and dried up plants.
In general, the turtles eat everything that is of vegetable origin and can be reached by them. However, the European tortoises have different feeding habits, some of which are also adapted to the different habitats. Basically, the wide-brimmed turtle (Testudo marginata) is not demanding at all and grazes on all edible plants including most grasses. The Moorish tortoise (Testudo graeca) and the eastern subspecies of the Greek tortoise (Testudo hermanni boettgeri) are already much more picky and eat almost no grass, in exceptional cases sometimes various sweet grasses (Gramineae). The western subspecies of the Greek tortoise (T. hermanni hermanni) and also the Dalamtinian tortoise (T. h. Hercegovinensis) are true gourmets. Both are extremely demanding when it comes to plant selection and disdain any kind of grass. If a blade of grass is accidentally eaten, it is literally choked out and pulled out of the mouth with the front feet.
Turtles are grazers, which means that the animals are constantly on the move while they are eating, eat a leaf here and continue to chew on to the next plant.
The plants and the parts of the plants that are preferred to be eaten are also very different from year to year.
Basically, the plants growing in the primary habitats differ not only in their growth but also in the richness of species from the plants growing in cultivated areas. The rocky structure and the strong sunshine ensure a significantly higher base temperature in the heat islands of the habitats. As a result, only tiny plants grow on the stony, shallow, nutrient-poor and lime-rich soils that have a shorter vegetation period and therefore flower and fruit much faster.
Due to the lack of grazing, the plants in the primeval macchia can still develop undisturbed and preserve the diversity of species. Even in dune habitats, the soil is barren, extremely rich in lime and almost free of humus, so that the plants there have the same dwarf growth.
On grazed macchia areas, the plant species quickly become impoverished, which is why the turtles no longer have access to the natural variety of plants. Especially when it comes to nutrition, only the really original primary habitat and not any area that has already been modified and cultivated by humans can be used as a "model of nature".
In spring and again in autumn the turtles need a lot of energy. For this reason, they initially eat almost exclusively freshly sprouted shoots and thus absorb rich protein compounds. The saturated and unsaturated fatty acids have a positive effect on many metabolic processes and strengthen the immune system. In contrast to cultivated plants, wild plants have a higher calcium, mineral, vitamin and crude fiber content with a relatively reduced water content. Most wild plants also contain many health-promoting substances, such as essential oils, bitter substances, flavonoids, tannins, saponins and mucilage and are therefore still used in herbal medicine today.
The essential oils and bitter substances in particular have a positive effect on digestion and help to keep the gastrointestinal tract healthy in the long term. Other ingredients bind poisons, have an antiseptic and blood-purifying effect. All these effects known from folk medicine have only been proven for us humans and mammals, but it can be assumed that these ingredients, like the minerals and vitamins, are equally effective in reptiles.
The spring
A special predilection for certain plants cannot be observed in the spring. The animals graze practically everything that germinates. Also seedlings and fresh shoots of plants, bushes and trees that they usually spurn in the fully grown stage, such as most species of sage ( Salvia sp. ) Or the leaves of the rock roses ( Cistus sp. ). Because of this diversity, the turtles have a varied and balanced diet. The various plants contain all the important basic nutrients, which is why deficiency symptoms in the primeval maquis are excluded.
In the following growing season, European tortoises show a preference for all dandelion-like rosette plants that contain milky sap. Usually these are daisy flowers (Asteraceae). Many spicy-tasting cruciferous vegetables (Brassicaceae), legumes (Leguminosae), most species of clover (Anthyllis, Dorycnium, Lotus, Medicago, Trifolium) with the exception of the oxalic acid-containing bitter clover species (Oxalis) and many other butterflies and labiates are also eaten with preference Lamiaceae) and carnation family (Caryophyllaceae).
The summer
In early summer, the turtles prefer to eat flower buds and flowers, especially those of red and yellow flowering plants and in the further course all kinds of wild fruits, the still green seed pods and pods and finally the various seeds themselves. However, wild fruits are in no way associated with the watery ones grown for human consumption to compare sweet, sugary fruits. They are predominantly dry, taste bland and contain little fructose. In midsummer the animals eat almost exclusively only dry plant components and leaves from various trees and bushes. The turtles also gnaw very persistently on bark and roots, some of which are downright dug up.
In this barren time, the turtles perform the most daring climbing skills to get to leaves, wild fruits and seed pods. In this time, when there is a shortage of forage crops, the energy-rich seeds, due to their high proportion of vegetable oils with valuable saturated and unsaturated fatty acids and protein compounds, are important for a healthy diet and consequently also for successful reproduction.
Until well into the hot summer, forage plants are still green and bloom extremely profusely. Cardiac plants such as the scabiosa (Scabiosa), the chicory (Cichorium intybus), the little meadow button (Sanguisorba minor) are most represented here. and various convolvulaceae and thistle species.
The autumn
In autumn, when the macchia awakens to its "second spring" after the first autumn rains, the circle closes again with the germinating young plants, which are now also available to the hatchlings as the first energy and nutrient-rich source of food.
General
Rough, dry parts of plants, like the older leaves of most trees and bushes, are only eaten by the turtles when the fresh green plants have dried up in midsummer and the trees and bushes no longer have any young shoots.
Resinous plants such as the Aleppo pine (Pinus halepensis), the star pine (Pinus pinaster), the tamarisk (Tamarix), the wild juniper (Juniperus oxycedrus) and shrubs that are very common in some habitats are not or only really eaten in an extreme emergency of the Phoenician juniper (Juniperus phoenicea). However, I have often found the ripe juniper berry cones, 8 to 14 millimeters in size, in turtle droppings in late summer. Especially in the summer months, excrement soaked in water gives a good insight into the nutrition of the turtles. Many hard-leaved leaves such as those of the strawberry tree (Arbutus unedo) and hard, hard-to-digest fruits such as the 10 to 30 millimeter large, bright orange-brown fruits of the dwarf palm (Chamaerops humilis) can be found next to snail shells and small limestone of various sizes.
Obviously none of the species of milkweed family (Euphorbia) and herbs containing various essential oils such as rosemary (Rosmarinum officinalis), lavender (Lavandula sp.), Marjoram (Origanum sp.) Or the karst mountain mint (Satureja montana) are not eaten at all.
Toxic plants
European tortoises also value plants with substances that are toxic to humans and mammals. Above all, various buttercups (Ranunculaceae) and predatory plants such as the various types of adder's head (Echium) that occur in abundance in the habitats and are part of the turtle's staple diet. But also highly poisonous species such as the sea onion (Urginea maritima), which was previously used as a rat poison, arum plants such as the Italian arum (Arum italicum), the crook (Arisarum vulgare) or the common serpent (Dracunculus vulgaris) and the common wreath that covers entire bushes (Tamus communis), are preferred to eat. The butterfly flowers of the many types of gorse, such as the gorse (Ulex euro-paeus), the broom (Cytisus scoparius) or the hairy thorn (Calicotome villosa) and the prickly thorn (Calicotome spinosa) are just as popular. Gorse, especially in its leaves and seeds, contains alkaloids that are highly toxic to mammals. In Sicily I have often seen turtles feasting on fallen poisonous oleander flowers (Nerium oleander).
The sedum species, which are often very abundant and which are also classified as poisonous due to their oxalic acid content, which disrupts calcium metabolism, are also preferred.
The difference between medicinal substance and poison, however, is only a matter of dosage. Even the most important doctor and natural philosopher Paracelsus had the following insight: "All things are poison and nothing is without poison, only the dose makes that a thing is not poison."
The need for lime
The plants grown on calcareous soils contain enough calcium to adequately supply adult turtles. The increased calcium requirement that females need to shell their eggs and young animals for building bones and the bone shell is something that the turtles get in very different ways. Even the hatchlings are still eating their own egg shells in the egg pits and are later specifically looking for small white limestone stones. Wild turtles only eat the stones to absorb minerals and trace elements and not to drive out intestinal parasites or to aid digestion like birds do.
I have often seen young and old turtles eating from empty houses of the bush, tower and snail snails lying around. The bones of dead animals lying around in the maquis are also used by the turtles as a source of lime. The turtles gnaw at the bones with infinite persistence as we otherwise only know it from dogs. Sepia shells are sometimes found in large numbers on the beaches in spring and are carried far into the country by the wind and also by the seagulls. Eggshells, which lie in abundance in the abandoned ground nests of pheasant, partridge, stone fowl and quail, are also used as a source of lime.
Extra food
The droppings of herbivores such as rabbits, deer, sheep and goats are also very popular with turtles. I have also seen turtles feeding on wild boar droppings. Eating feces is innate in turtles. Hatchlings eat the excrement of older conspecifics in order to vaccinate their intestinal flora as quickly as possible with specialized bacteria and protozoa. Without this intestinal flora, fermentation of the feed and thus the removal of nutrients from the feed pulp would only be incompletely possible. Herbivore faeces regularly contain concentrated undigested nutrients and a whole range of excess vitamins and minerals that the turtles use in addition.
Animal food in the form of snails or small insects is more likely to be eaten by turtles in the wild. However, according to reports, turtles do not stop at carrion. In many conversations with locals myself, I have not yet met anyone who has made similar observations. Although I occasionally found dead animal carcasses in habitats near active turtles, I have never seen a turtle feeding on them myself. I think these are negligible individual observations outside of primary habitats.
You can find detailed information about nutrition and a selection of well over 300 forage plants in my book Forage Plants
