Ferguson Zones

You have probably seen on our various care sheets that we use the term ‘Ferguson Zone’, and you may have wondered what on earth this means. 

The Ferguson Zones are named after Dr Gary Ferguson who, in 2010, proposed a system that would describe how much UV light different species needed based on their behaviour and habitat. It doesn’t just cover the amount of UV light, but also how it is delivered; the two methods are the shade method and the sunbeam method.

The zones cover all reptiles and are split into four: zone 1 for crepuscular/nocturnal reptiles, zone 2 for partial sun/occasional basker, zone 3 for open or partial sun basker, and zone 4 for midday sun basker – the real sun worshippers. 

• Zone 1 – UVI 0.7 -1.4
• Zone 2 – UVI 1.1 – 3.0
• Zone 3 – UVI 2.9 – 7.4
• Zone 4 – UVI 4.5 – 8.0

Lighting and heating should always be planned together; when creating a thermal gradient it must include UVB, and the whole of the animal’s body must be able to be covered by the upper temperature of their preferred temperature range. Always consider your pet’s habitat as a whole, and provide them with the conditions they need to be able to self-regulate their exposure to heat, UVB, and humidity.

The shade method.

The Shade Method provides low-level background UV over a large proportion of the animal’s enclosure, using the “average exposure” figures as a guide, with a gradient to zero in the shade. This would normally be the method of choice for shade-dwelling reptiles and those that rarely bask (i.e., those in Zones 1 and 2).

This is easily achieved using a low level T5 kit, like the Arcadia ‘shade dweller’ units or the Reptile Systems Zone 1 and Zone 2 units. Always make sure that your pet does not have to choose between feeling safe and getting their daily UV dose; plenty of cover to allow them to self regulate their exposure is the way to go. Crepuscular and nocturnal reptiles will often only expose a small part of themselves – a leg or tail tip – to the provided UV light, and this can be enough to allow them to more efficiently metabolise calcium into the all important vitamin D3.

Don’t forget to make sure that the temperatures are in the correct range, and that you are offering species specific calcium and multivitamin supplementation as well.

The sunbeam method.

The Sunbeam Method is designed to provide a higher level of UV for species known to bask in direct sunlight. This higher level must be restricted to the basking zone (“like a sunbeam”) with a gradient to zero in the shade. This method is appropriate for reptiles in Zones 3 and 4, and for some reptiles in Zone 2 when a distinct basking zone is to be provided.

The aim is to provide UV levels in the basking area that are similar to those experienced by a wild animal in direct sunlight in its natural habitat during a typical early to mid-morning basking period. Some metal halide and high output T5 lamps are capable of producing very high levels of UVB light, almost equivalent to natural sunlight. These lamps should be positioned within the vivarium in order to provide a very brightly lit area for the animal to bask in; a suitable heat lamp should also be placed alongside the UV lamp so that the brightest, hottest area within the vivarium has the highest level of UV.

This enables the vivarium inhabitant to choose their levels of UV and heat within their enclosure. It is vitally important to measure your temperatures with a digital thermometer, and that you are offering species specific calcium and multivitamin supplementation as well.

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