Besides the general concerns about having enough space or large enough social groupings, the greatest challenge to the keeping of elephants in zoos has been ensuring reliable breeding. In recent years, there's been a tremendous amount of research done on assisted reproduction in elephants. The reason for this isn't that elephants won't reproduce naturally in a zoo - they will, fairly readily. The problem is that breeding requires a male. And a male means musth.
"Musth," from the Hindi for "Madness" is a period of super-sexual aggression among adult male elephants. Even the most placid bulls becomes the pachyderm equivalent of the Incredible Hulk, behaving in a violent, unpredictable manner, thinking only two thoughts - smashing things and female elephants. Wild elephants are known to take out their fury on other species, chasing giraffes or killing rhinoceroses. During musth, the temporal glands of a bull elephant leak a black, tar-like substance, while the penis dribbles constantly. Swelling in the head causes eye pains and toothaches. Testosterone levels increase by as much as 60 times. Strangest of all, no one quite knows why this happens. There is no correlation between when bulls enter musth and when females are reproductively receptive. Bulls in musth are as likely to interact with females that are in estrus as those who are not.
In the logging camps of South Asia, the traditional method of dealing with a bull is musth was simple. Chain hum up, starve him, deprive him of water, and wait for him to come back to his senses. Isolation was also prescribed - no female elephants to tempt him, no male elephants to provoke him. For much of the history of the American zoo, the traditional method was even simpler - don't. Many zoos refrained from breeding due to the need of having a male... or out of fear that their female would give birth to a male. The fears weren't unfounded. Elephants are big, powerful animals who are capable of accidentally injuring or killing a keeper... and with bulls in musth, it wasn't an accident.
The situation has changed considerably in recent years. Most zoos now work their elephants protected contact-instead of free-contact, greatly reducing the risk on injury. As many zoos redevelop their elephant facilities, they are including specialized bull quarters, powerful enough to contain a male in musth. As more zoos are capable of housing these animals - potentially the most dangerous in the zoo - the more successful breeding can take place.
This in turn will help to establish a future for elephants in American zoos - and considering how things in the wild are looking, we can use every elephant birth we can get.