Leadbeater's possums (Gymnobelideus leadbeateri) are a critically endangered marsupial found in a restricted area of cold, wet forest in South‐Eastern Australia. The majority of Leadbeater's possums inhabit highland forest, with one outlying lowland population. In 2012, a breeding program was established for the lowland Leadbeater's possums when this genetically distinct population faced imminent extinction. Successful reproduction by highland Leadbeater's possums in the international zoo‐based population between 1970 and 2010 led to the widespread belief that the species bred readily in captivity. Lowland possums have not bred in the 2012–2021 contemporary captive conservation breeding program. This study reviewed the historic captive‐breeding data and found that of the 84% (162/194) that reached reproductive maturity; 37% of males (n = 30) and 39.5% of females (n = 32) bred, and this success was highly skewed towards a subset of highly fecund individuals (14% of females and 15% of males produced 75% and 80% of all offspring). Although lack of reproductive output in the captive lowland animals could be explained if age at mortality was lower than that of highlands possums, comparison of the longevity of highland and lowland animals had no significant difference. Conservation objectives that specify how captive breeding may support in situ recovery of wild populations are integral to the success of captive programs. A lack of reflective analysis of past husbandry records allowed misconceptions of success and approaches implemented in the management of the breeding program, reducing the benefits for the conservation of this high profile threatened species. This case study provides a lesson for the management of conservation breeding programs and illustrates the importance of well‐defined conservation objectives, integration of in situ and ex situ strategies, and the importance of objective, systematic and timely analysis of available evidence to inform management objectives and improve conservation outcomes in real time.
