Species keeper protocol

Iguana iguana - St. Thomas population

St. Thomas Green Iguana - U.S. Virgin Islands
A locality-specific Green Iguana protocol using St. Thomas climate cues. The St. Thomas population has unusual Caribbean genetic affinities, so locality and pedigree records should be preserved.

Day ambient28-31 CWarm year-round; do not create a cold winter

Basking surface37-41 CBroad high-output basking zone with cooler shaded retreats

Humidity72-88 / 85-95%Drier early year, wetter late summer/autumn; good ventilation always

Breeding cuePeak wet phase / condition buildingDry-season courtship/nesting, then rising rainfall for hatch/recovery

Keeper timer setting

T5 UVB: one hour later on, one hour earlier off

During active care — ON: 1 hour after daylight starts.
OFF: 1 hour before daylight ends.

During hibernation / full brumation: T5 UVB OFF (0 hours). In transition months, keep UVB off while dormant and use the active timer only once the animal is warmed and active.

October: daylight 11.8 h; T5 UVB 9 h 48 m.

The active T5 duration is the photoperiod minus two hours. Example: daylight 08:00–20:00 means UVB 09:00–19:00. Follow the monthly UVI strength measured beneath the tube and provide access to shade. This timing rule does not introduce hibernation for species whose schedule has only a mild or active winter rest. If an older combined heat / UV column is present, the new T5 UVB duration column governs UVB timing; existing heat settings are preserved.

UVI beneath the optional T5 tube

Working exposure target

October target at normal back height

UVI 4-6directly 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 · Muryn, Baines and Dishman (2026), Reptile Lighting Guide V10

October management

Selected automatically using the Netherlands date

Peak wet phase / condition building

St. Thomas, USVI; warm Caribbean island climate with a relatively dry early year and wetter late-summer/autumn period

28-31 CDay ambient

24-25 CNight

37-41 CBasking

4-6T5 UVI*

11.8 hPhotoperiod

9 h 48 mT5 UVB duration

72-88 / 85-95%RH day / night*

Frequent rain/mistRain / mist

7Food days/week

Annual schedule

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Month	Day ambient	Night	Basking	T5 UVI*	Photoperiod	T5 UVB duration	RH day / night*	Rain / mist	Food days/week	Seasonal management
January	27-30 C	22-24 C	37-41 C	4-6	11.2 h	9 h 12 m	55-70 / 70-80%	Light AM mist 3-4x/wk	6	Dry-season courtship / mating
February	27-30 C	22-24 C	37-41 C	4-6	11.6 h	9 h 36 m	50-68 / 70-80%	Light AM mist 3-4x/wk	6	Peak mating; watch male aggression
March	28-31 C	23-24 C	38-42 C	4-6	12.1 h	10 h 6 m	50-65 / 68-78%	Dry upper surfaces; humid nest	6	Gravid females / nest preparation
April	28-31 C	23-25 C	38-42 C	4-6	12.6 h	10 h 36 m	55-70 / 70-82%	Light mist; deep moist nest	5-6	Main laying window / recovery
May	28-31 C	24-25 C	38-42 C	4-6	13.0 h	11 h	60-75 / 75-85%	Rain/mist increasing	6-7	Post-lay recovery / incubation
June	29-32 C	24-26 C	38-42 C	4-6	13.2 h	11 h 12 m	65-80 / 78-88%	Daily AM rain/mist	7	Early wet phase; hatch window begins
July	29-32 C	24-26 C	38-42 C	4-6	13.1 h	11 h 6 m	65-80 / 78-88%	Daily AM rain/mist	7	Growth / hatchlings / browse abundant
August	29-32 C	24-26 C	38-42 C	4-6	12.8 h	10 h 48 m	70-85 / 82-92%	Rain/mist 1-2x/day	7	Wet season / recovery
September	29-32 C	24-26 C	38-42 C	4-6	12.3 h	10 h 18 m	70-85 / 82-92%	Rain/mist 1-2x/day	7	Wet season / body condition
October	28-31 C	24-25 C	37-41 C	4-6	11.8 h	9 h 48 m	72-88 / 85-95%	Frequent rain/mist	7	Peak wet phase / condition building
November	28-31 C	23-25 C	37-41 C	4-6	11.3 h	9 h 18 m	70-85 / 82-92%	Frequent rain; good ventilation	6-7	Wet phase easing
December	27-30 C	22-24 C	37-41 C	4-6	11.0 h	9 h	60-75 / 72-82%	Rain reduced; AM mist	6	Drying trend / reproductive conditioning

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

Population identity

St. Thomas iguanas have an unusually complex origin. Published genetic studies found Caribbean haplotypes related to Saba/Montserrat, while the USVI has also experienced historic/recent introductions. Keep this animal labelled Iguana iguana - St. Thomas population unless pedigree or genetic testing supports a different assignment.

Enclosure

Large and strongly arboreal. For one adult use about 200 x 120 x 200 cm or larger; breeding adults benefit from room-scale accommodation. Provide heavy climbing trunks, broad shelves, shade, visual barriers and deep terrestrial nest substrate for females.

Heat and UVB

Use about 27-32 C daytime air, 22-26 C nights and a broad 37-42 C basking surface. A measured UVI around 4-6 at the main basking zone is a practical target, with several retreats below UVI 1.

Humidity and seasonality

No brumation. Use a drier Jan-Apr phase and wetter Aug-Nov phase, reflecting St. Thomas climate. Upper branches should dry between spray events while drinking water, humid retreats and fresh browse remain available.

Diet

Adults should be overwhelmingly herbivorous: diverse calcium-rich greens, safe browse, leaves and flowers daily, fibrous vegetables, and smaller amounts of fruit. Avoid routine animal protein.

Breeding

Green iguanas usually synchronize reproduction with tropical dry/wet seasons. A St. Thomas-style working cycle uses Dec-Feb for courtship/mating, Mar-Apr for gravid females and nesting, with hatch/recovery as rainfall and new plant growth increase.

Nesting and incubation

Provide a secluded 45-60+ cm deep compactable sandy-soil nest before females are visibly gravid. Green iguanas commonly lay about 10-30 eggs, with larger clutches possible. Start incubation around 28.5-30 C with stable moisture and ventilation; roughly 90-120 days is common.

Keeper warning

Adult males can be highly territorial. Watch females for persistent digging, straining or failure to lay. Monitor all adults for rostral trauma, burns, dehydration, obesity and renal/metabolic disease.