Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

Sunlight and Aggressive Behavior

©2000 Melissa Kaplan

Some iguana keepers report that their iguanas get aggressive when they are taken outside. Some think there is a link between the brighter light or increased levels of ultraviolet light outdoors, compared to what they get indoors.

There is nothing to indicate that ultraviolet light triggers aggression, especially since iguanas experimentally kept under very high output UV lights didn't become aggressive. What's going on is more psychological rather than physiological: iguanas, no matter how tame, are still wild animals who belong out-of-doors. Unfortunately, that can't be accommodated 24 hours a day, 7 days a week, 365 days a year in captivity.

The more outdoor time captive iguanas get throughout the year, the more used to being outside - with all the varied stimuli the out-of-doors presents - they get. Any initial behavioral "aberrations" will dissipate over time until you may find that, though your iguana may not be thrilled about going back inside and may be unhappy about not being able to go outside during the winter, he is perfectly content when outside, unless something comes along to disturb his peace, like a noisy plane, circling raptor or turkey vulture (he doesn't know the vultures aren't predators), or noisy children poking at him. (Or, as happens where I have lived, the Good Year blimp, hot air balloons and gliders going by overhead.)

I have never had a problem with iguanas becoming aggressive outside, probably because going outside is a normal event in the lives of my iguanas. In addition, the quasi-bay window in their room gives them lots of outdoor views and loads of sun streaming in the open window and lots of swooping shadows from birds (and balloons) going by overhead.

Iguanas who have never been outside since they were first grabbed for export may freak out due to initial sensory overload (they see shadows and movement through their parietal 'eye' as well as with their eyes) and so everything is perceived as a threat until they get used to things and start sorting out what they need to worry about and what they don't...