Over the past years, or actually rather decades, I have been intensely been involved in field herpetology. I have visited numerous tortoise habitats throughout the Mediterranean region and first just watched the animals living there, but then began to really study their ways of life and behaviour.
Depending on local climatic conditions of the various natural habitats, the first tortoises usually emerge from their winter shelters as early as during the month of February in order to bask in the sun of early spring.
By March at the latest, all animals have become active once more and, weather permitting, do what they normally do during the day.
The only deviations from this pattern are found in populations living at higher altitudes in the hinterland of the coast.
Tortoises in these areas resume their activity only later in the year when temperatures have risen sufficiently. Here, plant growth and the flowering season are shifted more towards the summer months.
Daily activity begins after the first rays of the morning sun have warmed the soil. The tortoises then leave their night shelters and bask extensively.
After they have reached a body temperature that permits their metabolism to function properly they become very active, foraging or exploring their environment.
Increasing heat towards noon sees the animals retreating into thick underbrush, from which they emerge again later during the afternoon hours to become active once more.
Later in the afternoon, while the sun is still out, the tortoises return to their shelters where they bury themselves and spend the night.
European tortoises generally avoid open areas, and young specimens feel visibly uncomfortable in open situations, instinctively realizing their being exposed to predators from above.
Within their natural habitats, every adult animal claims for themselves a relatively small area around a shelter spot. European tortoises do not establish territories and therefore do not display territorial behaviours. In other words, they do not defend their personal space against others, but rather live side by side in an open society that shares a common habitat in which individual home ranges may overlap significantly.
The tortoises prefer to bury themselves beneath thick, often thorny brush, larger clusters of grass, old wood, or large rocks.
Small natural cavities or holes in the ground excavated by other animals are readily adopted as well.
These shelters may be used for resting and even hibernating every year again if their habitat remains unaffected by major changes.
In nature, European tortoises "inhabit" their shelters alone as a matter of principle. Exceptions from this rule are enforced in areas with a chronic shortage of shelters and hiding places. This is commonly the case on sparsely vegetated mountain slopes in Greece, for example.
Individual home ranges are usually only a few square metres in dimension and may overlap neighbouring plots significantly. The home ranges of males are about twice as large as those of females.
Male specimens also become active earlier in the year and remain active longer than their female counterparts.
If a male encounters another during springtime, combats are a regular occurrence. These duels are very similar to a mating ritual and regularly end in favour of the larger and therefore stronger contestant. These ritualised fights have nothing to do with territorial disputes, though.
The question of superiority is often decided already after brief mutual sniffing, which causes the inferior male to hurry away.
The males emerge from hibernation earlier than the females and soon begin to roam within an extended perimeter of their home ranges in search of female conspecifics.
Once a male eventually encounters a female, he will court her right away, with the courtship ritual varying slightly with the species at hand.
Females leave their home ranges only for the purpose of finding a suitable oviposition site or, if necessary, for finding food.
Tortoises are roaming grazers and may forage for food within a wider range than their actual home ranges if the conditions of their individual habitats dictate their doing so.
If two females meet, they will ignore, or just briefly sniff each other and then go separate ways.
Spring rains are common throughout the Mediterranean, subjecting the tortoises to regular showers in the shape of sometimes heavy downpours. They also leave behind puddles from which the animals can drink and replenish their water household after hibernation.
As is widely known, tortoises are able to absorb water also via their cloaca and skin.
These rains also facilitate the growth of grass and herbs as early as in February. By the beginning of April, the tortoise habitats will then have turned into oceans of flowers, and even poor soils may be blanketed with colourful flower carpets.
The air then carries a heady scent of flowers and the spicier aroma of herbs.
During spring, the tortoises feed mainly on flowers and juicy, fresh greens loaded with vitamins.
In nature, the period shortly after hibernation in spring forms the major mating season, followed by another mating period in autumn.
These are the times when the tortoises are particularly active.
A few weeks after spring copulation, the females begin to produce their first clutches. Depending on the species, these may be followed by a second clutch several weeks later and possibly even a third clutch.
European tortoises show a high degree of site fidelity. Their home areas are typically situated in habitats marked by a more or less dense scattering of trees and brush. This type of vegetation does not necessarily facilitate an ideal degree of insolation that would create the relatively high substrate temperatures necessary for the successful incubation of eggs.
Gravid females are therefore often forced to leave their home turfs and venture to more sun-exposed and, especially, moister spots with a low vegetation cover to lay their eggs.
This sometimes necessitates them to wander several kilometres.
In order to protect emerging hatchlings from predators, the nest pit is not excavated in an open area, but habitually in spots that enjoy at least some protection from a small, open bush.
Once she has laid her eggs, the female returns to her home area, which she has no problems finding thanks to her excellent senses of smell and direction.
This ability also enables females to return to the same oviposition spot time and again.
In some regions, there are centralized communal oviposition sites on which all females converge from the wider surroundings.
Everybody of you who is keeping female European tortoises has surely noted this urge to wander at times. The animals typically walk up and down in a show of restlessness and often even try to escape from their enclosure.
Towards the end of May, the rains cease while the heat increases, ending the splendour of flowers quite quickly.
Most plants do not stand a chance in the sweltering heat of summer.
Grass and herbs wilt and turn into hay, and perennial plants fall into some form of aestivation to survive this period.
During summer, the tortoises are thus faced with a completely different range of available foods. Aside from some succulent plants, such as various species of stonecrop, evergreen shrubs, and greenbrier that forms vast thickets in some regions and is readily consumed, most of the food still available is meagre and dry. Since the intake of vitamins and essential unsaturated fatty acids remains vital also throughout the summer months, the tortoises resort to consuming seeds, wild fruit and berries of all kinds. These wild-growing fruits and berries are, however, not at all comparable to the sweet and watery fruits and berries meant for human consumption.
Tortoises living in habitats near the coast reduce their activity substantially during the hottest months of summer, i.e., in July and August.
They tend to retreat deeply into the cover provided by brush or remain in their shelters, only emerging briefly in the early morning or late evening hours. Varying with the species and location, they may also aestivate buried in the soil or in cool rocky caves.
In general, tortoises feel most comfortable when day temperatures range between 20 and 35C.
When the rains return in autumn, sometimes as early as in September, the plants likewise return to life and sprout new green. Annual plants will now germinate and continue growing even in winter.
These first autumnal rains are also the signal for the hatchlings to emerge from their nest pits.
Once the hatchlings have exited their nests, they will stay hidden beneath the mat of wilted plant matter that is plentiful at this time of the year. There they will typically spend their first year of life, remaining very close to their nests and thus in the moister habitat of a depression.
Over the years that follow, the young tortoises will then begin to roam in ever widening circles and so migrate out of the breeding depression and into the surrounding hills. By the time they eventually become sexually mature, they will have found themselves their own small parcel of land around a shelter.
Depending on local climatic conditions in the various parts of the range, European tortoises will begin to prepare for hibernation from about October.
This period of dormancy varies greatly with the individual habitats and does not compare at all to the hibernation imposed on tortoises kept in captivity at our latitudes out of pure necessity.
In the wild, hibernation is driven by local temperature conditions and thus varies with the region as to both course and duration.
Mediterranean winters are marked not only by rainy weather, but also by mild to rather warm days, especially in regions near the coast.
In nature, the tortoises instinctively respond to certain climatic stimuli, such as changes in light, temperature and barometric pressure, which herald the cold time of the year. In particular it is the continuous drop of night temperatures that causes them to reduce their food intake. Even though day temperatures may still be very high in the sun, the animals will not let themselves be influenced by them. The high temperatures during the days are very important for the metabolism of the animals, which is still in full swing. The tortoises now absorb the nutrients contained in the pulp filling the gut and do therefore not suffer hunger if they eat less and eventually stop feeding altogether, as we would imagine. The reduced temperatures may now prolong the lingering time of fibre-rich food to as long as four weeks.
During this transition period, the tortoises leave their shelters less and less frequently and for ever briefer periods of time. When the night temperatures eventually drop substantially below 10C for a longer period of time, the tortoises remain unanimated in their shelters. Being poikilothermic animals, they eventually become unable to move about.
However, reptiles are in general able to effect instinctive digging motions in response to changing environmental temperatures even while hibernating and so determine the depth at which they are buried. If the weather turns particularly cold, the tortoises will bury themselves to a depth where the frost cannot reach them. If, on the other hand, the weather turns warmer, they will respond with rising closer to or even above the surface. These default responses keep the tortoises alive in nature as they prevent both freezing to death and poisoning as a result of incomplete metabolic processes. Fluctuating air temperatures, on the other hand, do not affect the animals directly. Here, the soil works as a buffer that allows changes in temperature to be felt deep in the ground only if they persist for some time.
If continuous sunny weather keeps on warming the topsoil for some time, the tortoises may therefore appear on the surface and, attracted by the sunlight, expose themselves to the radiant warmth. To do so is of vital importance for the animals. In European tortoises, metabolic functions begin to set in slowly at a temperature of as low as 8C, even though it takes a body temperature of about 30C to run at full speed. Metabolic waste products are basically toxic, but can be stored away safely in the kidneys for some time. Persistent low temperatures do not permit these to be flushed out, however. This eventually causes the kidneys to fail, resulting in the tortoise to become comatose, which you would not notice owing to its hibernating state, and inevitably die.
These intermissions of winter activity in the wild are temporary and only necessary until the soil temperatures do not decrease to values of less than about 8C anymore. After the animals have warmed up, always in the immediate vicinity of their shelters, they will bury themselves superficially once more and reappear for basking if the next day is equally warm, or bury themselves deeper and resume their dormant state if temperatures decrease.
These brief stints of activity do not require the tortoises to consume food. Owing to the naturally rich fibre content in their diet, the gut is not entirely empty even during the winter months and so conserves the intestinal flora necessary for digestive processes. The animals therefore do not live off fat reserves stored, but rather first consume the remains of their last meals in the intestinal tract. As long as there is some food pulp left in the intestines, they will not suffer hunger either and therefore remain disinterested in food.
This illustration makes it plausible that tortoises kept in human care need to be accommodated, unlike in the wild, at hibernation temperatures that are constantly between 2 and at maximum 7C; in the case of Testudo horsfieldii, temperatures between 2 and 4C are ideal. Tortoises that are overwintered in captivity become uneasy at about 8C and will eventually exit their substrate. There, they will not find a warming sun that would bring their body temperature to a level where metabolism is possible, though. The metabolic functions that are started are incomplete, produce toxins, and sentence the animals to death.
At temperatures around 4C, the tortoises hibernate motionlessly and do also not execute motoric digging motions, which are in any case uncalled for in human care.