Com­plex so­cial be­hav­iours

Igua­nas have evolved be­hav­iours far be­yond the per­ceived lim­i­ta­tions of the rep­til­ian brain

World of Animals - - All About Iguanas -

His­tor­i­cally, it was thought that ‘com­plex’ so­cial be­hav­iours were con­fined to mam­mals and birds, but re­cent stud­ies have found that so­phis­ti­cated in­ter­ac­tions such as play, parental care and co-op­er­a­tion are found within many rep­tile groups, in­clud­ing the Iguanidae fam­ily.

Green igua­nas have been doc­u­mented prac­tis­ing pair-bond­ing and kin recog­ni­tion, with ju­ve­niles of­ten de­fend­ing their sib­lings. When threat­ened, the green iguana will bob its head, puff up its body and ex­tend its dewlap, which sits be­neath the jaw, to ap­pear more in­tim­i­dat­ing. How­ever, this doesn’t al­ways work. Igua­nas are fre­quently hunted by preda­tory birds, and un­for­tu­nately for the iguana, the sound of a hawk’s whis­tle or scream can make the iguana freeze, ren­der­ing it eas­ier to cap­ture.

Green igua­nas are par­tic­u­larly so­cial dur­ing the breed­ing sea­son, when they adopt a lek­style dis­play as seen in birds of par­adise. Males seek out a plat­form in the trees around which the veg­e­ta­tion is sparse, al­low­ing max­i­mum vis­i­bil­ity to any pass­ing fe­males. Here, they will bob their heads while mov­ing across the plat­form, demon­strat­ing their large dewlap as they go. Any ap­proach­ing males will be chased out of the ter­ri­tory, while as many as eight fe­males can con­gre­gate around the dis­play­ing male. Those who are in­ter­ested will com­pete among them­selves to lay claim to their mate.

Green iguana fe­males can nest in iso­la­tion, while oth­ers have been known to travel great dis­tances in order to nest upon an is­land as part of a colony. In such ex­am­ples, nest­ing is achieved by dig­ging bur­rows that can cross over and in­ter­lock, grow­ing in com­plex­ity with each year that passes. The fe­males will guard their bur­row site in order to pre­vent their eggs be­ing dug up by other nest­ing fe­males be­fore leav­ing the brood to hatch on their own.

Most igua­nas spend their life on land in ar­bo­real habi­tats, and they are known to some as the ‘chicken of the trees’ due to the sim­i­lar­ity of their meat. How­ever, the Iguanidae fam­ily also con­tains the only ex­tant oce­andwelling lizard, the marine iguana, which ex­ists ex­clu­sively on the Galá­pa­gos Is­lands. Marine igua­nas also per­form in leks dur­ing the breed­ing sea­son, but on rocks rather than in trees, and they are known to stay close to their mate fol­low­ing cop­u­la­tion. It’s thought this guard­ing is an at­tempt to pre­vent the fe­male from mat­ing with an­other male, mean­ing com­pe­ti­tion be­tween sperm doesn’t oc­cur.

Male igua­nas are very ter­ri­to­rial and the strong­est will pro­tect their patch from com­pet­ing males. De­spite this, smaller males are still in with a chance as they can sneak past, un­de­tected due to their mor­pho­log­i­cal sim­i­lar­i­ties to a fe­male iguana. Af­ter the fe­male has mated and is ready to lay her eggs, much like the green iguana she will seek out a soft, of­ten sandy area within which to dig a bur­row. De­spite their aquatic na­ture, marine igua­nas must nest on land as their eggs would drown in an un­der­wa­ter bur­row.

“Green igua­nas have been doc­u­mented prac­tis­ing pair­bond­ing and kin recog­ni­tion”

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