Wildlife fertility control: a mini-review of technologies, efficacy, and welfare impacts.

This review examines the growing challenge of managing overabundant wildlife populations in the context of increasing human-wildlife conflicts. Traditionally, population control has relied on lethal methods such as culling, but these approaches are increasingly restricted due to concerns over environmental harm, non-target effects, human safety, and shifting societal values favouring more humane solutions. Fertility control has emerged as a promising non-lethal alternative, aiming to regulate populations by reducing reproductive success rather than increasing mortality. Its effectiveness depends on species-specific life-history traits: it can rapidly reduce populations of short-lived, highly fecund species, while effects in long-lived animals are delayed. Various fertility control methods are available, including endocrine suppression, immunocontraceptive vaccines, synthetic hormones and non-endocrine approaches such as zona pellucida vaccines. A major limitation to field applications of fertility control is the development of efficient delivery systems, particularly for small or free-ranging species where oral delivery must overcome challenges of palatability, stability, and species-specificity. Animal welfare considerations depend on species, contraceptives and contexts and involve trade-offs between reduced mortality and potential impacts on behaviour, physiology, and reproduction. Nevertheless, fertility control may offer welfare advantages over lethal methods and can reduce the transmission of infectious agents by maintaining social stability. Despite its potential, widespread implementation is constrained by economic and regulatory barriers. Overall, fertility control represents a valuable tool within integrated wildlife management strategies, though continued technological innovation and regulatory adaptation are essential for widespread application in the future.