New study shows adult survivorship of captive elephants significantly improving

[ZooElephantMan]

An exciting new scientific study was just completed, which indicated that Adult survivorship of Asian & African Elephants in North American & European zoos has significantly improved between 1910 & today. According to the study, survivorship of zoo populations is currently even higher than some non-zoo populations but lower than others. The article also addresses previous statistics which indicated that captive elephants lived shorter lives than their wild counterparts.

You can read the full article here: https://onlinelibrary.wiley.com/doi/full/10.1002/zoo.21733

I've also provided the abstract / summary:

In the discussion about zoo elephant husbandry, the report of Clubb et al. (2008, Science 322: 1649) that zoo elephants had a “compromised survivorship” compared to certain non-zoo populations is a grave argument, and was possibly one of the triggers of a large variety of investigations into zoo elephant welfare, and changes in zoo elephant management. A side observation of that report was that whereas survivorship in African elephants (Loxodonta africana) improved since 1960, this was not the case in Asian elephants (Elephas maximus). We used historical data (based on the Species360 database) to revisit this aspect, including recent developments since 2008. Assessing the North American and European populations from 1910 until today, there were significant improvements of adult (≥10 years) survivorship in both species. For the period from 1960 until today, survivorship improvement was significant for African elephants and close to a significant improvement in Asian elephants; Asian elephants generally had a higher survivorship than Africans. Juvenile (<10 years) survivorship did not change significantly since 1960 and was higher in African elephants, most likely due to the effect of elephant herpes virus on Asian elephants. Current zoo elephant survivorship is higher than some, and lower than some other non-zoo populations. We discuss that in our view, the shape of the survivorship curve, and its change over time, are more relevant than comparisons with specific populations. Zoo elephant survivorship should be monitored continuously, and the expectation of a continuous trend towards improvement should be met.

 

[Jurek7]

It is a nice conclusion, but some thoughts.

This and the previous studies, especially Clubb et al. (2008), suffer from many methodological shortcomings. Consultations of people familiar with medical statistics and e.g. biases in reporting effects of new treatments on humans or epidemiology would be good.

These studies might describe mostly so-called selection bias.

First, comparing zoo population against selected "benchmark populations" in the wild and in Asian captivity is spurious, because the benchmark populations were openly cherry-picked. This is partially because of the bias in selecting study sites by elephant researchers. Wild populations suffering from natural dangers (droughts, diseases) and unnatural dangers (poaching, persecution by farmers) are not selecterd, as are low density elephant populations in sub optimal and marginal habitats. The benchmark Asian captive centres contain mostly selected healthy and young elephants which live in better conditions than an average domestic elephant in these countries.

The bias of benchmark studies becomes obvious, when benchmark studies indicate demographically growing population and high survival, while total population of wild and domestic elephants in Africa and Asia is falling and has low survival.

Second, reported survivorship of newborn elephants in benchmark populations can be artificially raised by strong selection of mothers to be in optimum age and good health (because other elephants die in the wild or are not kept in the selected Asian institutions).

Third, elephants arriving in zoos are selected with bias, too. African elephant calves caught in the wild were not captured randomly – it is a textbook biology knowledge that weaker and sicker individuals are preferentially captured. Most Asian elephants traditionally arrived second-hand from the Asian captivity and circuses. These elephants were given away because they could no longer work or the original institutions had poor conditions. Therefore elephants arriving in zoos have been strongly selected to be in poor health.

Lower survival of African Elephants may be checked for the possibility of naturally lower life expectancy of this genus.

Interesting would be to check impact of changes of husbandry in Western zoos, which have been taking place for at least two decades. Is occurrence of foot problems falling? Is keeping large herds related to increased lifespan – or more trauma and stress-related deaths? Are newer exhibits, soft surface and more space associated with better survival – or simply receive younger elephants, with older elephants remaining in substandard places? Are herpes deaths becoming more common over the years, or simply more reported?