Keeper timer setting
T5 UVB: one hour later on, one hour earlier off
ON: 1 hour after the daylight lights come on.
OFF: 1 hour before the daylight lights go off.
October: daylight 11 h 40 m; T5 UVB 9 h 40 m per day.
The T5 runs for two hours less than the total photoperiod. Example: daylight 08:00-20:00 means UVB 09:00-19:00. Keep the monthly UVI strength as listed beneath the tube. Existing care values are preserved.
UVI beneath the optional T5 tube
Working exposure targetOctober target at normal back height
UVI 3directly under the tube when it is on
The retained range remains a provisional captive working target. No new species-specific result was found that clearly requires a numerical change. Retaining it is not certification of an experimentally established optimum.
Your measuring point
Measure at the animal's normal back height directly beneath the brightest accessible part of the T5 strip, positioned toward the middle/back. The animal can enter and leave this area freely.
Keep a lower-UVI gradient and fully covered refuges near UVI 0. This is the optional exposure area, not the average across the cage.
Use a UV Index meter, such as a Solarmeter 6.5/6.5R. Warm the tube for about 30 minutes; keep reflector, guards and mesh in place. Raise or lower the fixture within its manufacturer's minimum-distance guidance, then recheck the reading and every higher accessible surface.
Evidence level: Provisional retention. These are working recommendations, often inferred; exact species optima and seasonal UV dose usually have not been measured. Log lamp-on time and animal behaviour as well as UVI.
Baines et al. (2016), UV-Tool ยท Muryn, Baines and Dishman (2026), Reptile Lighting Guide V10
October management
Selected automatically using the Netherlands date
Dry-down begins
Tropical deciduous/thorn forest, open arid scrub, hollow cactus and dry branches - Balsas-Tepalcatepec region, western Mexico
26-29 CDay ambient
19-22 CNight
38-40 CBasking
3T5 UVI*
11 h 40 mPhotoperiod
9 h 40 mT5 UVB duration
40-55 / 55-70%RH day / night*
Light local spray 1-2x/wkSpray / rain
3-4Food offers*
Annual schedule
Scroll sideways on smaller screens
| Month | Day ambient | Night | Basking | T5 UVI* | Photoperiod | T5 UVB duration | RH day / night* | Spray / rain | Food offers* | Status / breeding |
|---|---|---|---|---|---|---|---|---|---|---|
| January | 24-28 C | 17-20 C | 37-40 C | 3 | 11 h 10 m | 9 h 10 m | 30-45 / 45-60% | Very light local spray 1x/wk | 3-4 | Dry-season conditioning |
| February | 25-29 C | 18-21 C | 38-40 C | 3-4 | 11 h 30 m | 9 h 30 m | 30-45 / 45-60% | Very light local spray 1x/wk | 3-4 | Courtship / mating likely |
| March | 27-31 C | 19-22 C | 39-41 C | 3-4 | 12 h | 10 h | 30-45 / 45-60% | Minimal; water always | 4 | Gravid / nest preparation |
| April | 29-32 C | 20-23 C | 39-41 C | 3-4 | 12 h 30 m | 10 h 30 m | 30-45 / 45-60% | Minimal + moist lay chamber | 4 | Probable oviposition |
| May | 30-33 C | 21-24 C | 40-42 C | 4 | 13 h | 11 h | 35-50 / 50-65% | Light local spray 1-2x/wk | 4 | Late dry season / incubation |
| June | 29-32 C | 21-24 C | 39-41 C | 4 | 13 h 15 m | 11 h 15 m | 50-65 / 65-80% | 2-3 rain/mist events/wk | 4-5 | Hatching early-mid month |
| July | 28-31 C | 21-24 C | 39-41 C | 3-4 | 13 h | 11 h | 55-70 / 70-85% | 2-3 rain/mist events/wk | 4-5 | Short wet season |
| August | 28-31 C | 21-24 C | 39-41 C | 3-4 | 12 h 40 m | 10 h 40 m | 55-70 / 70-85% | 2-3 rain/mist events/wk | 4-5 | Short wet season |
| September | 27-30 C | 20-23 C | 38-40 C | 3 | 12 h 10 m | 10 h 10 m | 50-65 / 65-80% | 2-3 rain/mist events/wk | 4 | Late rains |
| October | 26-29 C | 19-22 C | 38-40 C | 3 | 11 h 40 m | 9 h 40 m | 40-55 / 55-70% | Light local spray 1-2x/wk | 3-4 | Dry-down begins |
| November | 24-28 C | 18-21 C | 37-39 C | 2-3 | 11 h 15 m | 9 h 15 m | 35-50 / 50-65% | Very light local spray 1x/wk | 3 | Dry season |
| December | 23-27 C | 17-20 C | 37-39 C | 2-3 | 11 h | 9 h | 30-45 / 45-60% | Very light local spray 1x/wk | 3 | Dry season / pre-breeding |
Keeper notes
Use measured gradients and animal behaviour, not single thermostat readings
T5 UVI measurement
Measure UVI at normal back height directly beneath the brightest accessible part of the optional T5 strip. Place the strip toward the middle/back with free access to and away from it; preserve a gradient into fully covered refuges near UVI 0. These numbers describe the exposure area, not the whole enclosure or a daily average.
UVI review
The retained range remains a provisional captive working target. No new species-specific result was found that clearly requires a numerical change. Retaining it is not certification of an experimentally established optimum.
Taxonomy
The accepted scientific name is Ctenosaura clarki (Bailey, 1928). The spelling 'clarkii' is a common misspelling.
Habitat
C. clarki is endemic to the Balsas-Tepalcatepec region of western Mexico and lives in tropical deciduous/thorn forest and open arid scrub. It commonly shelters in hollow cactus stems, dry branches, tree cavities and wooden posts.
Thermal management
Although the region is extremely hot, microhabitat studies found animals using moderately shaded sites below about 30 C. Provide local basking but keep a genuine shaded cool refuge; do not heat the entire enclosure into the low 30s.
Humidity and rain
The wild dry season lasts roughly 6-8 months. The short rainy season is mainly June-September. Keep dry-season surfaces mostly dry with minimal localized spray, then increase short rain/mist events during summer while maintaining strong airflow.
Diet
Published ecological summaries list both insectivory and herbivory, and zoo husbandry summaries describe adults as mainly vegetarian with occasional insects. Use a plant-dominant adult diet with periodic invertebrates; juveniles can receive somewhat more insect prey.
Reproduction
Oviparous. Field evidence places hatching in early-mid June. Captive-breeding reviews report roughly 5-7 eggs per clutch and eggs about 33-36 x 19-20 mm. April laying is a historical inference rather than a directly observed fixed date.
Social warning
Detailed social biology is limited. House adult males separately unless conditions are exceptionally large and behavior is closely monitored. Separate for repeated pursuit, biting, refuge exclusion or declining body condition.