Menorca is covered in bushes and trees. Vast swathes of our island are populated by wild olive, mock privet, and mastic trees (Pistacia lentiscus). Within these woodlands there are a lot of clearings for warming oneself in the sun which make the perfect home for a tortoise. The Mediterranean tortoise, or the subspecies Testudo hermanni hermanni to be precise, is rampant here. We have the highest population in the Mediterranean. They’re also found under holm oak and juniper trees and even amongst sand dunes.
Tortoises have a great sense of smell and sight, and are sensitive to vibrations. They have a marvellous sense of direction too: no matter how many times, or how far away our neighbours carry them from their besieged vegetable garden, they make their way straight back. The dedicated couple are now barricading in the veg by sinking nets into the ground so that the homing reptiles can’t dig their way back in.
Despite their camouflage, tortoises are very easy to spot; while most animals don’t like to be found by humans, it seems that these ones couldn’t care less. They crash about in the undergrowth, fight and even mate in close proximity to people out exploring. A rustling noise that doesn’t stop, even when walkers make their presence obvious, is a dead give-away that a tortoise is nearby. They dig holes with their big claws and lay eggs in them. In winter they fast for a few weeks to empty their guts then dig themselves in to hibernate, though they might wake up again during warmer periods.
They’re also delightfully odd-looking, and though they can power away quickly enough if needed, they’re easy to catch (or run over, strim, set fire to, or feed to the dog). Thus, unfortunately, there are many that end up being killed, injured, or taken back home as pets. Populations in Europe are declining quickly for all of the above reasons as well as human activity causing habitat fragmentation. Therefore, the species as a whole is strictly protected under law. They’re listed as endangered on the IUCN Red List of Threatened Species, and it is banned to own one in the Balearics.
Because we have so many here, Menorca is a great place to study tortoises. Biologist, Albert Bertolero has been the researcher in charge of the monitoring programme since 2015. He comes over twice a year for a couple of weeks’ poking about in the scrub. When he catches one, he weighs and measures it, records its approximate age and sex and the exact position it was found. Then he whips out a hacksaw (or a small file if it’s a baby) and carves grooves into the edges of specific plates, (or scutes) on the shell to give it a number. Males have larger tails and concave plastrons, the part of the shell that is on the underside. The scutes above their tails sort of curl under whilst those on the female stick out more.
This is to meet reproductive technicalities. Together with other scientists, Albert has found out some very interesting things over the years:
Eating Habits
They eat all sorts. Their favourite food in Menorca happens to be clematis, followed by dandelions, clover, poisonous Italian arum and buttercups, lords and ladies, and items from the pea and aster families. They don’t really like anything resinous from the juniper or pine trees, nor do they go for aromatic herbs like lavender and rosemary. More rarely, they’ll also eat meat and have been found gorging on dead chicks fallen from nests,
bones, mussels, and even poo.
Ageing
It’s very hard to accurately age a tortoise, though the internet reckons Testudo hermanii hermanii can get to around 75 years old. Scientists can get a rough estimate of how old they are by observing the concentric rings (which are actually expanding squares) on each scute. But a new ring isn’t necessarily formed every year throughout the tortoise’s life, and growth slows down considerable when they’re hibernating. Thus, they use an approximate guide to class tortoises into ‘un-sexed babies’ if under 10cm long; ‘sub-adults’ if the growth rings are all thick and well-defined; ‘young adults’ if the rings are a mix of fat and thin ones; and ‘old’ if the rings are fading and worn. Also, tortoises can only be sexed once their secondary sexual characters have developed, i.e. the concave plastron, wonky bottom and a bigger tail in males.
Genetics
Our population is actually made up of two different genetic lineages; the ones that are larger on average are found in the southeast of Menorca. This genetic group is not related to any known populations outside Menorca. Those living in the northwest have a smaller average body size and their genetic line can be traced back to the Albera mountain range in the eastern Pyrenees, between Spain and France. The two populations don’t mix, and some believe that the main road across the island keeps them apart. It is thought that tortoises were introduced to the island around 3000 years ago.
Toes
And last of all, some of our tortoises have five toes and claws on the front foot and some only have four. These differences have been shown to be genetically determined by taking blood for tests from the coccygeal vein near the base of the tail. Researchers estimate the population size by monitoring our tortoises year on year. They can observe how many there are each year, if the male to female ratio is stable, and predict movement patterns. Yet with such a long-lived species it will take many years to truly understand their dynamics.
Injured Tortoises
Going back to dog attacks and wayward strimmers, injured tortoises get sent to the Wildlife Recovery Centre at Lithica near Ciutadella. Every new individual that comes in gets a health check and a mugshot taken, is weighed, sexed, and then kept in quarantine for a few weeks to avoid it passing on any possible diseases to the others. If it’s healthy after that time it’ll be released back where it was found. This is important as the carers don’t want to contribute to any genetic mixing that wouldn’t have naturally occurred. If the animal is injured with a damaged shell it goes to the vet. There it gets sedated with a general anaesthetic (how cute) and then gets a plaster cast stuck on its back. Drainage holes are left at the base of the shell and then it’s back to the recovery centre to convalesce. Reptiles take a lot longer than humans to heal due to their cold blood and hibernation. In fact, sometimes the staff keep ill tortoises under heat lamps to prevent them from hibernating so that the healing process isn’t interrupted. Despite this, they’ve kept patients at the centre from months to even years. Still, the hope is that one day they too can be released into the wild. Now and then there’ll be something in the media reminding the public that it’s illegal to keep tortoises in captivity – which results in a sudden influx of new tortoises to the centre. I remember many people had them in their flower beds, even on patios in town. One year they received around 2000 individuals.
Unfortunately, and despite their trade being illegal, there’s also a black market for Mediterranean tortoises as pets. A recent report found some Menorcan ones at a street market in Madrid. Thus, another reason the recovery centre ends up with thousands of new ones a year is because they take in captive tortoises the authorities have impounded. These poor guys have to just sit there and be evidence until the culprit is brought to trial. To summarise, the centre, co-managed by both GOB and COFIB, is generally swamped with inmates of all shapes and size and in varying states of disrepair – making it a great place to learn about them and also contribute a much-appreciated donation to their upkeep.
Ref: Seguiment de la Tortuga mediterrania a Menorca en 2016, Albert Bertolero
www.menorcabiosphera.org
Rachael Adams is a freelance environmental journalist. You can read more of her articles on her blog https://rachaeladamsblog.live/
