Overflowing with Avians

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Zoo InternQuest is a career exploration program for high school students. For more information see the Zoo InternQuest blogs. For more photos see the Zoo InternQuest Photo Journal.

A zoo can be a crowded place. Take for example the San Diego Zoo; there are thousands of individual animals living here, each with its own sleeping quarters and enclosure. Effectively feeding and keeping these animals is a monumental task. Keeping the population at a manageable level is therefore a challenge that must be constantly juggled by both the Keepers and the Researchers. But it is not only population levels that need to be managed. In order to ensure the survival of endangered species, there are many other factors that must be balanced in order to ensure that the species is both healthy and continuing to grow in numbers.

Today, we met Dr. Tom Jensen, a Scientist in the Reproductive Physiology Division at the San Diego Zoo Institute for Conservation Research. A PhD holder with a background in stem cell research, Dr. Jensen works with his colleagues in reproductive physiology and with the Avian Propagation Center to solve the unusual problem of gender imbalance in bird species at the San Diego Zoo.

When a zoo enclosure contains more individuals of a single gender than the other, you have a gender imbalance. This gender imbalance is a potential problem in a zoo’s collection, as it may affect breeding levels. For example, if the species with the gender imbalance is supposed to mate in monogamous pairs (one male and one female breeding solely with each other), then a gender imbalance produces fewer breeding pairs. Since most species produce approximately equal numbers of male and female offspring, left on its own a gender imbalance would never fix itself, with the skewed ratio of male to female remaining fixed and unchanging. What Dr. Jensen and his colleagues are able to do is alter the ratio of male to female offspring being born by identifying the gender of the bird before it actually hatches.

When an egg is laid by a species suffering from a gender imbalance, the Zookeepers take the egg to Dr. Jensen’s incubator. Dr. Jensen can then take this egg and very carefully open it. He demonstrated this gentle operation to us when we met, holding the egg lightly against an electric belt sander until a small portion of the shell disappears. With skillful manipulation of small tweezers to remove any stray shell fragments, a window into the shell is opened.

Once the embryo is exposed, the process of gender identification begins. Dr. Jensen draws a small amount of blood from the embryo, which he can then examine using PCR sexing techniques. By examining specific genetic variations in the blood sample, Dr. Jensen can determine the sex of the tiny, developing bird. If it is a gender of the smaller demographic, the egg will be patched back up and returned safely to the incubator at the Zoo to hatch naturally. If the egg is of the surplus gender demographic, Dr. Jensen may decide to humanely cease the incubation of the egg while it is still an embryo. While it may seem a tragic loss of what may be an endangered animal, the future ramifications in fixing the gender imbalance could help the species for generations to come.

The method has been working well for Dr. Jensen and the bird species that he works with. One example of a rare bird that this technique has been useful for is the storm’s stork. These large birds at the San Diego Zoo represent a critically endangered species, so there was great deal of concern over the fact that breeding was proving largely unsuccessful. What Dr. Jensen and his team found was that there was a huge imbalance in genders of the Zoo’s population of storm’s storks. After taking many eggs back to his lab and intentionally incubating only those of the gender that was underrepresented, he is proud to report that the gender imbalance has begun to be corrected since the start of the program. Another endangered species is on the road to recovery, thanks to the tender care of eggs in a scientist’s lab.

Michael, Career Team