The food iguanas eat, being obligate folivors, also includes munching a bit on fallen fruit and picking ripe figs, and also they eat certain flowers that are way up in tees. We know that because some resorts in Costa Rica are built right next to the forest trees, and tourists have written to say they have seen iguanas come out during rains to eat flowers. But 90% of their diet is leaves.
I think it may be true that they come out during rains to be less vulnerable to hawks.
So I assume you are supplementing thiamin. Don't over-do it.