Reacción a "The ageing of animals jeopardises the conservation objectives of zoos"

Zoos must act as key players in conservation efforts. However, the ageing of the animals that inhabit them is a problem that hinders this work. Many zoos act as reservoirs for species that are threatened in the wild, as well as being key to numerous research and educational tasks. In this sense, the article is part of the current debate on the role of zoos as providers of a public conservation service, beyond their recreational function. However, because animals in captivity tend to live longer than those in the wild, due to the success of animal care, the high number of animals in zoos is beginning to jeopardise their ability to accommodate new ones. For this reason, population control is sometimes carried out through reproductive measures such as castration or sex segregation, leading to an inverted pyramid where older individuals predominate, to the detriment of younger ones. The study shows that this strategy, although understandable from a logistical and individual welfare point of view, is problematic in the long term from a conservationist perspective.

This study provides strong evidence based on data from a total of 361 and 413 mammal populations in North America and Europe, respectively, over 53 years (1970 to 2023), with the aim of studying their demographic trends. This lends great robustness to the study, as monitoring of this calibre is rare in demographic studies. The use of an internationally standardised database (Species360) and consistent analysis of multiple taxonomic groups reinforce the validity of the patterns observed. It is noted that as time progresses, the population pyramid takes on a diamond shape, with an increase in the average age of the population over time. Furthermore, this change occurs regardless of the conservation status of the species or the conservation strategy. This is also accelerated in North America, probably due to the smaller size of zoos in that area, although a pyramid shape is observed in years when conservation strategies have been implemented. However, the authors' predictions are based on theoretical scenarios and do not take into account causes of mortality, genetic information or the actual capacity of each zoo.

The authors do not merely expose the problem, but also provide a broad discussion of future management. They observe a decline in reproduction, leading to the disappearance of various populations studied. In addition, historical trends indicate that zoos have not managed species according to their priority based on their conservation status. As a result, ageing populations lose their capacity for renewal and resilience, calling into question their role as self-sustaining populations within ex situ conservation programmes.

The authors point out how harmful it is to prevent births without taking into account the need for reproductive replacement. For zoos to play a key role in species conservation, the promotion of reproduction and the management of older animals must be taken into account. This brings with it the need to broaden the debate about the strategies that should be implemented to achieve conservation objectives, even when these strategies may be controversial. Keeping animals in captivity requires a purpose that transcends mere exhibition, based on clear conservation and population sustainability objectives.