How we do our Research


In the past people have often asked us how we can be sure that we are correct in the advice we give and in our assessment as to whether a particular plant is suitable to feed to tortoises.  This is a good question, as there is notoriously little scientific research into the diets of tortoises in the wild or their adaptability to eat plants which are available in a country that is not their native habitat, and there is a lot of conflicting information in books and on the internet.  We've decided therefore to set out the various ways in which we do our research in preparation for writing entries for the TTT database, and we hope that this will shed a little light on how we work.

Where does our information come from?

The amount of research we do varies, depending on the particular plant species or genus:  sometimes it is easy to find the answers, whereas other times we just reach a dead end.  It is important to keep in mind that very little research has been done on particular plants and their benefits or dangers to tortoises.  In order to discover this you really need observational studies done on tortoises in the wild, and although there are a few of them, there aren’t many.  Andy Highfield of the Tortoise Trust has recently been carrying out observations of tortoises in Spain and has made some interesting and valuable discoveries, but other than that there are only a handful of scholarly articles of which we are aware (some of which are referenced in the Resources section of the website).

So this is what we do.

We consult a wide variety of sources, some of which are:

  • Reference books – particularly those on wild flowers and on garden plants.
  • Reference websites on the Internet, from Wikipedia to professional gardening sites (like Dave’s Garden), to reference sites on edibility and use, like the Plants for a Future database.
  • Published scholarly articles on the chemical constituents of particular plants and the effects on animals in laboratory experiments.
  • Other websites, particularly those related to pets (there are lists of plants toxic to cats, dogs, rabbits, birds, etc. on various pet websites and places like the ASPCA.
  • Online forums and websites devoted to tortoises and turtles, like the Tortoise Trust, African Tortoise, and Russian Tortoise websites (the discussions on forums are often interesting but sometimes have to be taken with a pinch of salt, as comments are often hearsay – or just plain wrong).
  • Horticultural and botanical experts – we regularly write for plant IDs to Dave’s Garden, and have also written to seed producers like Sutton’s seeds (who were particularly informative on which plants can be labelled as Cress under European standards), recognised experts at the Royal Botanic Gardens at Kew, Oxford Botanic Gardens, the Royal Horticultural Society’s Garden at Hyde Hall, and several others.
  • Other sources – there are many, but those listed above are the main ones.

How long does it take to write a plant entry for the database?

It can take a couple of hours to several weeks or months to produce an entry (depending on how difficult it is to find information, or if there is conflicting information).  There are two of us who carry out the research and write up the entries, and a third person who double checks our research and then uploads the entries to the website.  

Most of the published material (either in books or on the internet) is based on knowledge of specific plants and their effects on humans, livestock, and a few pets like cats and dogs, sometimes rabbits, birds and fish – and very occasionally on other reptiles.  As the digestive system of the tortoise is very different from those of humans and other mammals, some of these findings aren’t relevant:  for example, many plants are said to cause contact dermatitis (skin problems) in humans, but as the skin of a tortoise is very different, this is unlikely to be a problem.  Also, it is well known that tortoises from areas with scarce vegetation (this applies to some Mediterranean species, and Horsfields in particular) have developed digestive systems which can cope with plants that are toxic to mammals and other animals, and it is thought that this has evolved to avoid competition in an area where food is in short supply.

We also have to keep in mind that some plants that are fine for humans, other mammals or other pets to eat would not be suitable for tortoises.  For example, some plants contain oxalates which bind up the calcium in food and prevent a tortoise from absorbing and using it, and whereas this isn’t too great a problem for most animals it could be a problem for tortoises, as they need so much calcium to produce all that shell and bone.

Evaluation and the 'Traffic Light' system

Given that much of the material we come across does not deal with a particular plant in relation to tortoises, how do we extrapolate from our research material to make an evaluation and a recommendation?  Often we can find information on toxicity, but not specifically in relation to tortoises, and in these cases we tend to err on the side of caution: where there is evidence of harmful properties, or in the absence of evidence that a plant is harmless, we advise not to feed and give the plant a red (do not feed) or perhaps amber (feed sparingly) 'traffic light'.  This is especially important for tortoises in captivity, as in the wild tortoises will have hundreds of plants to graze on, so that any one plant will form only a small part of its overall diet (even though that plant might form a large part of a wild tortoise’s diet for a short time of the year, when it is growing or in bloom).  In captivity, however, we tend to feed maybe only five to fifteen different plants, so that each plant forms a larger percentage of the diet, and any ill effects will be magnified.  If we find no evidence of toxicity or harmful properties we give it a green 'traffic light' (feed freely) – especially if we know that this plant is often eaten by tortoises in the wild or in captivity with no known ill effects.  

Plants with a red 'traffic light'

People occasionally contact us to say that one of our plants (for the sake of argument, let's say Buttercup) has a red 'traffic' light on the TTT website, but their tortoise has been eating it for years with no ill effects.  The red traffic light means 'should generally not be fed', which indicates that it could be toxic -- in which case we will say so in the entry -- or just that has properties that are potentially not good for your tortoise.  So our entry for Buttercup reads: 
As a lawn invader this plant is mildly toxic.  Many tortoises nibble it occasionally with no ill effects, but try and remove as much as possible as it contains the mild toxin protoanemonine and there is a reference to a tortoise dying after ingesting large quantities of Buttercup.
On the website, the word 'reference' in the last sentence is a live link to the published article containing the information about the tortoise that quite possibly died from eating large quantities of Buttercup.  We have used this example to illustrate that we try to give as much information as possible in our entries, but we do always err on the side of caution.

Why don't we list the nutritional content of plants in the database?

With regards to the nutritional value of particular plants, we spend less time researching this area.  The reason for this is that the nutritional value of any particular plant can vary enormously depending on the soil in which it is grown, the climate, and the general growing conditions, so it is pointless to make a blanket statement.  This also applies to some harmful properties: for example, some plants are very adept at taking up nitrates from the soil.  Nitrates are potentially harmful to tortoises, but if there are low levels of nitrates in the soil this isn’t a problem – so with plants like that we say that it can take up nitrates from the soil so make sure the plant is growing in poor, unfertilised soil (as that will have a lower nitrate content).  And if we find other relevant information (like the calcium to phosphorous ratio of a particular plant – although this too can vary if there is more or less calcium in the soil), then we will mention it.  With most plants what we are looking for is just to find out if it is harmful or safe for tortoises.  As mentioned earlier, there is a great deal of conflicting information out there, and we often have long debates on the merits of individual plants (these sometimes last weeks or months) until we reach what we feel is a satisfactory conclusion.  

The thought that is always uppermost in our minds is that we are ultimately dealing with the lives of people’s precious tortoises, and we want to ensure that if a plant is dangerous to feed or could be harmful in any way, then people are made aware of this.

An evolving database

Finally, it is important to point out that even though an entry is published on the website, it doesn’t mean that it is fixed in stone.  At the time of writing (October 2012) we have over 700 entries in the Plant Database.  Our research, however,  is ongoing, and we are constantly adding new entries to the database, as well as revising existing entries in the light of new evidence that is published.  For example, the Tortoise Trust has recently pointed us towards some new research carried out on plants with oxalates in the diets of some populations of tortoises in the wild, and when all the findings are in that might well cause us to revise our advice on intake of oxalates (but at the moment we need more evidence).

In conclusion

We hope that this has gone some way towards explaining how we arrive at the entries we produce.  

If you have any knowledge about specific plants in the tortoise diet we welcome your input.  If you have questions about whether a plant is safe or want a plant identified, please contact us -- if we don't already have an entry for that plant we will do the research and get back to you as quickly as possible.