Blue Iguana Recovery Program

Adult Territoriality and Breeding

For most of the year, an adult female Blue Iguana lives a solitary life. She’s a homebody, staying close to her favorite rock hole and defending a small territory which includes places to bask and feed, and an area of soil deep enough to nest in. No other adult female is allowed near: the resident will signal “keep out of my territory!” with vigorous head-bobbing. If that doesn’t work, she will attack the intruder.

The males are less tied to any one place, and often have several alternative sleeping holes scattered around a much larger territory. During the non-breeding season in late summer through the following winter, males live a lazy life, getting up late, eating a lot, basking motionless for hours, and keeping a casual eye on the females within and near their territories.

With the arrival of spring, hormones surge and the pace picks up. Males reassert dominance relationships, testing out who is the biggest and strongest, and expanding their range to try to monopolize as many female territories as possible. Several males will try to control overlapping areas, and so quite often they encounter one another. High speed, long distance chases ensue, with both iguanas hurtling through the shrubland like missiles. The smaller animal almost always flees from the larger, and physical contact is rare unless they two are evenly matched in size. Fights between matched-sized males can be vicious and bloody affairs, with toes, tail tips, crest spines and chunks of skin torn off in some combats.

Throughout March the females keep well out of the way, retreating into their rock holes whenever the males are around. Their eggs are already formed and their abdomens are swollen, but it is not until late April that they become receptive. Most mating is concentrated in the first two weeks of May.

Throughout the breeding season the iguanas take on their most intense blue colour. The males lose weight, feeding little as they devote all their time to dominating other males and breeding. The females also cease feeding as their digestive tract is squeezed by the expanding mass of eggs.

As her receptive period passes, each female abruptly becomes intolerant of all males, and chases them out of her territory. So aggressive does she become, she will successfully run out males much larger than herself! About six weeks after mating, she is ready to lay her eggs, and starts to burrow in the same area where she nests each year.