six weeks of the year. The milk contains a higher amount of iron than the milk of placental mammals. In Guiler's 1970 study, no females died while rearing their offspring in the pouch. After leaving the pouch, the devils grow by around a month until they are six months old. While most pups will survive to be weaned, Guiler reported that up to three fifths of devils do not reach maturity. As juveniles are more crepuscular than adults, their appearance in the open during summer gives the impression to humans of a population boom. A study into the success of translocated devils that were orphaned and raised in captivity found that young devils who had consistently engaged with new experiences while they were in captivity survived better than young who had not. Conservation status The cause of the devil's disappearance from the mainland is unclear, but their decline seems to coincide with an abrupt change in climate and the expansion across the mainland of indigenous Australians and dingoes. However, whether it was direct hunting by people, competition with dingoes, changes brought about by the increasing human population, who by 3000 years ago were using all habitat types across the continent, or a combination of all three, is unknown; devils had coexisted with dingoes on the mainland for around 3000 years. Brown has also proposed that the El Niño-Southern Oscillation (ENSO) grew stronger during the Holocene, and that the devil, as a scavenger with a short life span, was highly sensitive to this. In dingo-free Tasmania, carnivorous marsupials were still active when Europeans arrived. The extermination of the thylacine after the arrival of the Europeans is well known, but the Tasmanian devil was threatened as well. Habitat disruption can expose dens where mothers raise their young. This increases mortality, as the mother leaves the disturbed den with her pups clinging to her back, making them more vulnerable. Cancer in general is a common cause of death in devils. In 2008, high levels of potentially carcinogenic flame retardant chemicals were found in Tasmanian devils. Preliminary results of tests ordered by the Tasmanian government on chemicals found in fat tissue from 16 devils have revealed high levels of hexabromobiphenyl (BB153) and "reasonably high" levels of decabromodiphenyl ether (BDE209). The Save the Tasmanian Devil Appeal is the official fundraising entity for the Save the Tasmanian Devil Program. The priority is to ensure the survival