When it's a marsupial baby! So far you have read about smelly koalas and loud koalas (see Jen's previous blogs: Smelly Koalas and Motorcycles and Koalas) and you have enjoyed learning about koalas in the wild (see Bill Ellis' most recent blog, Koalas by Day, Koalas, by Night) but did you know how a koala starts it life?

Koalas are marsupials and they have a unique reproduction system. Koala joeys are born after about a 35-day gestation and are not fully developed. They are born hairless and are about the size of a jelly bean! The most pronounced physical features they have are a mouth and front limbs, which allow them to crawl to their mother's pouch and latch onto one of her nipples. The pouch is where the joey will stay and finish developing.

Part of our ongoing research with the koala colony at the San Diego Zoo has included examining all the data the keepers have collected on koala joey development. At what age do they first emerge from the pouch? When do they eat leaves? Do the female and male joeys differ? What we have found, from 18 years of data, is that both males and females emerge from the pouch, eat leaves, and wean from their mothers at approximately the same times. Koala joeys stay with their moms until they are about one year old and don't fully emerge from their mother's pouches until they are about six months old, at which time they also start eating leaves.

Koalas are not the only marsupials living at the San Diego Zoo. Another marsupial that you will see by the koalas is a Buerger's tree kangaroo (pictured). And you should catch a glimpse of their newest addition, a joey that is about 9 months old at this time. Since little is known about the development and behavior of tree kangaroo joeys, Chris Hamlin-Andrus (lead koala keeper) and I are working with a volunteer who is currently collecting behavior data on this joey. She is keeping track of the joey's behaviors throughout the day and has witnessed the emergence of the joey from the pouch. Some of the behaviors that we want to look at are how long the joey stays out of the pouch, how often it nurses, and what activities it engages in while out of the pouch. Our volunteer will continue to closely watch this joey over the next few weeks, so if you happen to see her, say hello and she can tell you all her latest news about the tree kangaroo joey.

Jennifer Tobey is a Research Fellow in the Behavioral Biology Division of CRES. She is giving a talk titled " Koala Chatter" at the Zoo on September 13.

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