“Nocturnal activity in the terrestrial tortoises is practically nonexistent. Although some hot desert species like the spurred tortoise (Centrochelys sulcata) may be crepuscular before they estivate in midsummer”. So say the reference books (Nocturnal Animals, Clive Roots, 2006).
Testudo graeca graeca active after midnight.
We also recall, many years ago, a fascinating lecture by the great M. R. K. Lambert on the ecology of sulcata in Mali, where he described seeing this species graze by moonlight! There is a further report of nocturnal activity in Astrochelys radiata, in Madagascar (Leuteritz, 2003). There is another report of nocturnal activity in Bolson tortoises (Gopherus flavomarginatus) because of elevated ambient burrow and soil temperatures and in response to overnight precipitation (Adest, et. al, 1988). There is also a single published report of nocturnal nesting in Testudo hermanni (Swingland and Stubbs, 1985).
Until now, this has been pretty much the extent of our knowledge of nocturnal activity in arid habitat tortoises. Questions to such sites as Quora elicit responses that they might be active at dawn or dusk, but are not in any way nocturnal, which is defined as 'being active at night rather than during the day'. Our extensive observations here, however, challenge this. Consistent activity after dusk and indeed well into the early hours of the morning has now been recorded in Testudo graeca graeca in Almeria and Murcia, Southern Spain. Our first report of this, back in 2012 is believed to be the very first confirmation of such activity in this species. We have since regularly observed after-dusk activity during late June, and into July. Tortoises can be active for several hours after the sun goes down. This appears to be related to excessively high daytime temperatures. This could fit into the category of crepuscular activity, rather than fully nocturnal, however. So what about TRUE nocturnal activity? Well, yes... that too. At certain times of year, especially in summer, they will remain entirely inactive during the day, but may well emerge in full darkness, or by moonlight, as Mike Lambert observed with the African Spurred tortoises in Mali.
A tortoise emerges from aestivation to drink in late August at 3.00 am in the morning
One factor which stimulates this activity greatly is the occurrence of over-night thunderstorms. During, and immediately after these, tortoises may emerge to drink, and feed. We have observed this at 1.00am and even 3.00 am, in pouring rain. At the same time, they take advantage of the sudden availability of the water to flush urates from the bladder, and to feed upon what would normally be excessively dry food, such as fallen seed pods. Evidence of this activity can be seen the following morning.
This is an exciting and fascinating extension to our knowledge of the behaviour of wild Mediterranean tortoises and demonstrates that even now, completely new insights into their behaviour and ecology can be achieved by sufficiently intensive field studies.
We have now observed this many times since that first observation in 2012, and can confidently say that this is far more common than most people would expect. We strongly suspect that the only reason it has not been more widely reported is that hardly anyone has bothered to look for it. It very likely occurs in many species of terrestrial tortoises under certain conditions.
References:
Adest, G. A., M. A. Recht, G. Aguirre and D. J. Morafka (1988) Nocturnal activity in the bolson tortoise (Gopherus flavomarginatus) Herpetological Review 19 (4): 75-76
Leuteritz, T. E. J. (2003). GEOCHELONE RADIATA (Radiated Tortoise). NOCTURNAL ACTIVITY. Hepetological Review 34(3): 240.
Swingland and Stubbs 1985. The ecology of a Mediterranean tortoise. (Testudo hermanni) J. Zool., Lond. 205:595-610
Text and images copyright (c) 2012-2024 A. C. Highiefield/Tortoise Trust
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