Be thankful you aren’t a crocodile.

Trying to mate could be life-threatening for the rare Philippine crocodiles at the Henry Doorly Zoo & Aquarium. Crocs in zoos that don’t find the right chemistry and have to share space and resources often wind up trying to kill or eat each other.

But the Philippine crocodile is a critically endangered species, and the zoo’s only male, named Phil, has rare genes. It’s imperative for the genetic diversity of the small captive population for Phil to make babies, and he isn’t getting any younger.

So zookeepers are stepping in to play Cupid.

The Omaha zoo prides itself on its ability to breed endangered animals. In the case of the Philippine crocodile, the zoo has spent years researching and developing a new process to make that happen.


It’s taken years to develop a process to breed endangered Philippine crocodiles, like this one at the Omaha zoo in 1999.

In order to understand how human-assisted reproduction works in zoo animals, let’s look at another species that follows a process more people might be familiar with: Southern white rhinos.

Rhinos’ anatomy is similar to that of horses. Breeding racehorses is a lucrative business, so funding for reproduction research in horses is substantially higher for those breeds. Those concepts translate well to rhinos.

The zoo’s youngest female rhino, Marina, hasn’t yet hit it off with the zoo’s only male white rhino. So a veterinarian comes by every week to perform an ultrasound.

A computer screen, a wand and some gel are involved. But that’s where the human experience ends.

Rhinos are too thick and dense to get a good ultrasound reading from the outside. So, just like in horses, vets have to send that wand inside the exit door.

“My arm gets numb after a while,” said Adrienne Atkins, an associate veterinarian who is part of the zoo’s animal health team, which performs ultrasounds on stingrays, lemurs and other species. “I have to take breaks.”

While she’s shoulder-deep in Marina, Atkins studies her reproductive organs on a laptop screen, gathering information that will help staff find the best time to perform an artificial insemination.


With the ultrasound wand inserted, associate veterinarian Adrienne Atkins keeps an eye on the ultrasound feed on the computer held by Mike Benner, a senior hoofstock keeper. 

According to the zoo’s hoofstock supervisor, Jack Hetherington, the process has a success rate of about 50 percent. This spring, rhino specialists at the Cincinnati Zoo and Botanical Garden collaborated with Omaha’s staff to inseminate Marina, but she didn’t become pregnant.

In some cases, when an animal’s genetics are extremely valuable, zoos may choose to relocate animals to try breeding another pair. With large animals such as rhinos, that’s a rare occurrence, and it can be stressful for animals. So zoos try to do the best they can to make it work even if the animals don’t cozy up.

Zookeepers have no plans to take Marina to another zoo or bring in another rhino. With Phil the crocodile, that’s not even an option.

“These animals are critically endangered, and there are probably less than 100 animals left in the wild,” said Jessi Krebs, the zoo’s curator of reptiles and amphibians. “We do not want to remove them from their protected habitats. His genetics represent him alone. He’s unrelated to any other animal in the country.”

Add to that another problem. The rhino team uses breeding techniques developed for horses, but there is little or no scientific research for such techniques in crocodiles.

“We’re the first people in the world to do this,” Krebs said.

Omaha’s zoo had to develop a brand new method for collecting crocodile sperm. The zoo says it’s the only method that doesn’t involve killing or extremely restraining the animal.


To collect a semen sample from a Philippine crocodile at the Henry Doorly Zoo & Aquarium, zookeepers carefully restrain him, lift his tail, extract his reproductive organ and rinse semen out into a container. The sample is then analyzed in the zoo’s labs.

Zoo scientists refined their reproduction techniques by working with less-threatened American alligators more than a decade ago, then moved on to Phil and his four female counterparts.

Phil, the lone male, is twice the size of the females. Because of that, zookeepers won’t introduce him to the females for another 10 years or so, until they grow much larger.

When zookeepers started, Krebs said they didn’t even know how to get Phil’s reproductive organ out of his body for semen collection.

“We even thought about using Viagra,” Krebs said, “but we didn’t have to. We found someone with smaller hands.”

Crocodiles aren’t built like humans. They have one hole, called a cloaca, that handles everything — urine, excrement and reproduction. In order to collect Phil’s semen, a member of the zoo staff has to reach into that hole and, using two fingers, hook his penis and pull it out of the cloaca. Then, another member of the zoo staff uses a solution to rinse his semen into a collection container.

One of those lucky people is Teresa Shepard, the jungle supervisor. Each Wednesday, her team leads Phil into an off-exhibit room and gently slide a door in place so he can’t snap at keepers. Shepard then reaches into Phil’s cloaca and, within just a few moments, has a sample. On the other end, Phil is munching on treats the whole time, unfazed.


Data collected from the Henry Doorly Zoo & Aquarium’s lone male Philippine crocodile is beginning to show ideal times for breeding.

The zoo is in the process of charting male and female reproduction cycles in Philippine crocodiles. Soon, they hope they can use artificial insemination with the fine female crocs of the Desert Dome, named A, B, C and D.

Just as the zoo intervenes when animals won’t get together, it also intervenes when you can’t stop them from trying to breed.

The zoo’s director of reproductive sciences, Jason Herrick, said the zoo gives birth control to a number of species. Lions receive birth-control implants. Gorillas take the same pills humans do.

“For most of the apes,” Herrick said, “the human pill works.”

It may sound like a lot of work to produce one or two babies, but zookeepers, veterinarians and reproduction staff at the zoo all say it’s worth the effort.