Do headstart programs work? Survival and body condition in headstarted Mona Island iguanas Cyclura cornuta stejnegeri

Headstarting refers to the raising of hatchlings in captivity and subsequently releasing them into the wild and it is a widely used tool to protect endangered species by increasing survivorship. Evaluating the success of headstart programs is necessary but challenging. We evaluated a headstart program for the endangered Mona Island iguana Cyclura cornuta stejnegeri by analyzing demographic and spatial data and by comparing growth rate, body condition, and external parasitic load of headstarted and wild iguanas. Hatchlings were released at about 3 yr age. Minimum survival rate was 40.3 %, at 7.6 to 48.3 mo after release. Most migrated from the release site back to the rearing facilities about 633 m away. Density around the rearing facility increased from 7.5 to 11.5 iguanas ha super(-1) (25 of 75 captures were headstarted iguanas). Released headstarted iguanas exhibited growth rates similar to the maxima observed in captive and wild mid-sized iguanas. Growth rates decreased immediately prior to release, indicating that husbandry practices ought to be reviewed. There was no evidence for an effect of captivity on susceptibility to external parasites. Increased local density indicates that the program was successful. However, the longer-term success remains unknown, as most headstarted iguanas returned to the headstart facility without establishing territories typical for adult wild Mona iguanas.