Understanding Ferguson Zones
Thomas Merckx
The Ferguson Zones were developed in 2010 by Professor Gary Ferguson of the Texas Christian University. Ferguson and his team of herpetologists gathered data of the daily UV exposure of 15 species of reptiles. In the publication that followed, these 15 species were divided into four groups according to their thermoregulatory behaviour (daily sun exposure) and microhabitat preferences: the “Ferguson Zones”. The corresponding UV guidelines were based on the average irradiance of randomly encountered wild specimens: Zone 1 with the least, to Zone 4 with the highest exposure.
The British and Irish Association of Zoos and Aquaria (BIAZA) built on Dr Ferguson’s research to allocate Ferguson Zones to hundreds of species species of reptiles and amphibians. With the help of 14 zoological organisations, specialist reptile keepers and private herpetologists, a total of 254 species were grouped into the 4 Ferguson zones.
A summary of the 4 zones, their corresponding UVI gradient and for each zone a few examples of commonly kept species:
Zone 1 = Crepuscular or shade dweller, thermal conformer
- Average exposure: UVI 0-0.7; maximum recorded: UVI 0.6-1.4
- Animals that avoid direct sunlight e.g. Crested Gecko, Leopard Gecko, Burmese Python, Milk Snake
- Average exposure: UVI 0.7-1.0; maximum recorded: UVI 1.1-3.0
- Occasional basking for short periods of time (Green Anole, Boa Constrictor, Ornate Box Turtle, Australian Water Dragon)
- Average exposure: UVI 1.0-2.6; maximum recorded: UVI 2.9-7.4
- Basking in full sunlight in the morning or early afternoon, or during mid-day when it’s partially clouded (Frilled Lizard, Yemen Chameleon, Standing’s Day Gecko, Leopard Tortoise)
- Average exposure: UVI 2.6-3.5; maximum recorded: UVI 4.5-9.5
- Basking in full sunlight, possibly at any time of the day (Chuckwalla, Uromastyx, Rhinoceros Iguana, Marginated Tortoise)
(Ferguson et al. (2010), Baines et al. (2016))
Based on basking behavior, the 4 Ferguson zones and the species researched, it is possible to provide appropriate UVB lighting for any species inside the terrarium. Appropriate lighting is a combination of fixture choice, bulb choice and basking distance, as all of these elements will influence UVB exposure.
Thomas Merckx
The Green Iguana (Iguana iguana) is considered to be an open or partial sun basker (Ferguson Zone 3) - Exo Terra Honduras expedition.
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