As part of a one-year postdoc project, I studied the reproductive ecology of the Tree Hole Frog - an endemic of the lowland forest of Borneo - for six months (September 2001 - March 2002). Field data on call variability, calling activity and male hole choice were gathered. Also experimental data on male calling strategies and female call frequency preferences were collected. My research was done in collaboration with Sabah Parks (Kinabalu Park zoologist Maklarin bin Lakim).

After the fieldwork phase, data was compiled during a post-doctoral stay at the Field Museum of Natural History in Chicago (April - September 2002), hosted by Harold K. Voris and Robert F. Inger.

The goal is to publish three papers on the reproductive ecology of these frogs: one on male calling strategies (Lardner & Maklarin), one on the male call pitch variation in the population in relation to female call pitch preference (Lardner & Maklarin), and one on what factors (do not) govern the reproductive activity of the male frogs (Lardner, Kitayama, Maklarin, Voris & Inger).

Accidental to the field work on the frogs, I discovered a fascinating and novel anti-predator behaviour in a common colubrid snake at the field site - more on that issue will appear on a web page linked to this after the observations have been published.

Below are some photos of the tree hole frogs and photos from the field work. Keen herpetologists will, in due time, find also my web pages on herptile photos updated with photos of snakes, frogs and lizards encountered during the last six months of Bornean field work.

Above left: A calling male tree hole frog, with the vocal sac inflated. Not all holes allow visual inspections like this; they are often very narrow. And occasionally 10 meters or more above ground! Above right: A female frog inspecting a male in the same hole as in the photo above. Females seem to roam around the forest as they are ready to breed, and may inspect several potential males before deciding where to lay her eggs. One aspect of my research deals with how the hole size affects the call - in particular in an evolutionary sense! - and how this relates to what types of calls females find attractive.

Do you want to hear what a male tree hole frog might sound like? Here is an example!

Female frogs deposit their eggs in the tree hole territory from which the resident male calls. The tadpoles - presumably the first ones ever identified by a biologist; depicted in the photos below - seem to be endotrophic (non-feeding, living from egg yolk). After about a month in their tree hole miniature pond, they metamorphose into ca 5 mm long froglets (sitting on a thumb nail in the photo below right).