At the Minnesota Zoo, in Apple Valley, Minn., it’s called the “howdy door”—a mesh divider between a male and female tiger.
“They can see and smell each other, but there’s no way to get a tooth or a paw through it,” said Dr. Tara Harris, the Zoo’s vice president for conservation and coordinator for the Association of Zoos and Aquariums Tiger Species Survival Plan®.
Away from public view, zookeepers at the Minnesota Zoo and a few other AZA-accredited facilities are using various techniques to increase the chances of tiger breeding. Helping these cats reproduce is not a small task. Introductions must be timed and the animals must be receptive to each other.
Howdy doors help. When a female shows signs of estrus, they will place her in an enclosure near the door with a breeding age male on the other side. Estrus isn’t always apparent in a female, but one telltale sign is when she lays down and rolls on her back. Other indicators they’re ready to meet include the animals rubbing their cheeks against the door and “chuffing,” an endearing vocalization that is usually returned by the other tiger.
Introductions last no longer than 15 minutes because breeding traditionally happens quickly or not at all. And Zoo staff members always stand on the sidelines, ready to safely intervene if things go awry.
The Challenges of Felid Reproduction
To say that felid reproduction is as simple as putting a door between two cats and hoping for the best would be grossly inaccurate. This is the method used for some, but the science behind successful breeding can be difficult at best and something straight out of a Jurassic Park spinoff more often than not.
There are a myriad of issues facing felid reproduction. Depending on the species, some females ovulate spontaneously or only during small windows of time. Sperm count in males is not yet fully understood by researchers—some males don’t have issues in this area while others have counts so low that breeding is nearly impossible.
And then there’s the logistics. Movement of cats, large and small, requires a tremendous amount of zoo-to-zoo—sometimes country-to-country—coordination, and is only worth it if the animals are healthy and of breeding age.
Dr. Jason Herrick, director of reproductive sciences at Omaha’s Henry Doorly Zoo and Aquarium, in Omaha, Neb., is one of the AZA’s leading minds in felid reproduction, and works regularly with tigers.
“Lets say there are 150 tigers total and half of them are female, so that’s 75 tigers,” he said. “But then some are too old and some are too young to mate. And some live at zoos that don’t support reproductive research. That number goes down dramatically from 75.”
And that’s just an example from the big cats. Small cats managed by AZA facilities have even thinner numbers, said Dr. Bill Swanson, a longtime felid expert and director of animal research at the Cincinnati Zoo and Botanical Garden in Cincinnati, Ohio.
“We manage roughly 20 different cat species in the AZA and half are small cats,” he said. “Unlike big cats we don’t have 100-200 animals to work with. We might have 30-80 animals total. I’m the coordinator for the Ocelot SSP, which is the largest population at around 100. We also work with black-footed cats, fishing cats, Pallas’s cats and sand cats, all of which average around 50 in our population, which makes it hard to maintain gene diversity, and makes it super important for them to breed.”
Why is the Breeding of Felids so Important?
“Our wild populations are being decimated; I don’t know of a cat species we manage that is increasing,” said Dr. Cheryl Morris, chief conservation officer at Omaha’s Henry Doorly Zoo and Aquarium. “Look at the Amur leopard. There are only 100-150 left on the earth.
“The goal of the AZA SSPs is to make sure each species has enough genetic diversity and population numbers to last for the next 100-200 years. Since a lot of felids haven’t reached population targets, the numbers are going down, making it even more important to focus on reproductive research.”
The good news is that husbandry practices across zoos have improved dramatically in recent years, thereby helping zookeepers manage populations. And some natural breeding practices have worked.
“The clouded leopards are a great example,” said Herrick. “We now know that adults that don’t know each other are likely to become very aggressive when introduced to breed, so we now introduce them at young ages and have found it to help breeding quite well.”
But still, there is pressure. Generally speaking, zoos no longer get animals from the wild, which means that zookeepers must use those in collections to create sustainable populations. And in 100 years, that means hundreds of cats could be related.
“And then we wouldn’t have a lot of genetic diversity left,” he said. “It’s the long-term projections that are really scary.”
Researchers are working on solutions that involve artificial insemination (AI) in cats. While these efforts have been going on for decades—starting back in the early 90s—methods have gotten better over the years. Still, though, the process is far from foolproof, largely because felid research is still in its early stages, especially compared with AI work in domestic animals and livestock.
“The number of AI studies that have resulted in births in tigers, for example, are quite low,” said Herrick. “Overall there have only been four successful AI pregnancies in tigers.”
While AI research continues, Herrick, Morris and the team in Omaha are taking another route: saving as much tiger sperm as possible in a genome resource bank (they dub “the GRB”). The idea: to preserve genetic diversity to use in future AI procedures.
The bank is housed onsite at a research building in Omaha, alongside liquid nitrogen, and under heavy security. If the liquid nitrogen goes down, Herrick and his team get alerted—anytime, day or night. (Cue the Jurassic Park soundtrack.)
The GRB launched in 2017 and is an exciting development in the fight against the ticking time bomb that is felid population sustainability.
“Historically, if we needed more male genes, we’d go to Asia, catch a male tiger and bring him to the zoo,” said Herrick. “We don’t do that anymore for ethical and legal reasons. But with the GRB, we can go to Indonesia or Russia to collect sperm and bring it back.”
Sperm collection is not limited to tigers. Herrick has been working since 2004 with colleagues in South Africa to collect sperm from black-footed cats via a radio collar study.
On a macro level, the collection of sperm for any species is a very big deal. The use of frozen semen is being tested at the moment, and although it is not yet successful at producing offspring, advances in research and science are promising and can help populations of various species remain sustainable across continents. No longer do specific zoos have to shoulder the burden of housing a certain number of animals for sustainability purposes. The hope is that frozen semen could make populations more accessible worldwide.
Natural Habitat Solutions
AI isn’t the only hope AZA-accredited facilities have when it comes to felid reproductive sustainability. Fecal hormone analysis is another way zoos are learning whether females are in estrus or pregnant. Several outsourced labs around the country provide this service to facilities without research departments, including the South-East Zoo Alliance for Reproduction & Conservation (or SEZARC), based in Yulee, Fla.
SEZARC works with 14 AZA facilities, helping onsite teams with breeding for a variety of water, air and land-based species.
“We’ve been working with the team at the Dallas Zoo, monitoring lions to know when females are in estrus and ready to be introduced to males,” said Director Dr. Linda Penfold. “It was really challenging and the Zoo hadn’t had a cub in a long time, but in spring 2017 we helped them produce their first lion cub in decades by providing support, visiting the Zoo and encouraging them to put male with female, all based on fecal hormone analysis.”
Breeding can also require creativity. When a pair of lions at the North Carolina Zoo in Asheboro, N.C., refused to breed because they’d entered the proverbial “friend zone,” Penfold experimented with a little trickery. Her team put the feces from another lion around the female’s crate. The male got jealous, the female thought the male was another lion and—bingo—the pair had their first cub.
“We focus on mimicking what is happening in their natural environment, which can mean tricking them to think other mammals are around,” Penfold said.
Spreading the Love
AZA facilities that house felids can get involved in reproductive research by contacting SSP coordinators. Equally importantly, though, is discussing lessons learned with zookeepers and curators just coming on the scene.
“We have a lot of great data with the Tiger SSP and have put out a Tiger Care Manual, but I think one of the most important things for all zoos to do is to capture the institutional knowledge of some of our retiring experts,” said Minnesota’s Harris. “We want to make sure that knowledge is passed on to help as many animals and species as possible.”
Katie Morell is a writer based in Sausalito, Calif.