Kangaroo Rats Tracked
As part of our research on small mammals we use track tubes. They are a great tool for monitoring small mammal populations without actually having to capture the animals in live traps. This technique is not new. The USGS has been using track tubes to monitor Pacific pocket mice for years. The equipment is quite simple yet effective. The concept is to use a narrow tube which small mammals can walk through. These have a stamp pad at each entrance and a piece of white card in the middle that can record their inky footprints. The stamp pads are infused with non-toxic black ink which only stays on their feet for a brief amount of time. Once they walk on the normal substrate the ink rubs off quite quickly. We use a tube of PVC pipe and bait the center of the card with sterilized millet seeds. This entices the small mammals into the tube and we are able to tell which species walked through from their distinctive footprints. Each type of small mammal has recognizable foot prints. For example deer mice from the genus Peromyscus have round evenly spaced toes versus rodents from the heteromyid family which have narrower more triangular shaped paw prints.
So far, track tubes have only been used on quadrupedal small mammals, the ones that walk around on all four feet. But we wanted to try and use them with the endangered San Bernardino kangaroo rat, which are bipedal and hop around on their two back legs. San Bernardino kangaroo rats were once common in floodplains of San Bernardino, Menifee and San Jacinto Valleys. But starting in the 1940s their habitat in these areas decreased due to development and changing land use. At this point 96% of their previously occupied habitat has been developed into agricultural and urban areas and is unavailable for San Bernardino kangaroo rats. At this time, San Bernardino kangaroo rats are only found in small areas of four waterways; the Santa Ana River, Cajon and Lytle creeks and the San Jacinto River. If we can track them with the tubes it will make studying their ecology and behavior easier for us and less invasive for them. With track tubes they don’t waste some of their night stuck in a trap. Rather they are free to forage and go about their business. They are a small species of kangaroo rat and are known to be able to pass through small tubes so we thought they might be able to use a track tube.
In order to test this out we made some slightly larger track tubes than the ones we use with Pacific Pocket mice. We set them out in habitat that is known to have San Bernardino kangaroo rats along with camera traps to take photos and video so that we could check if they were using them. We set up several of these track tubes and cameras and left them out in the field for a few days. When we returned we came back to find the tubes covered in foot prints and the SD cards full of photos. When we excitedly checked the cards we were ecstatic to find San Bernardino kangaroo rats in the photos. They visited the track tubes and left their foot prints. They looked different than any of the other small mammal foot prints that we had seen before. We know that kangaroo rats have large furry back feet and we could see imprints of the hairs. Their front paws have smaller toes and we saw some of those too, which means they must sometimes crawl through the tube on all four feet. The test was successful and it turns out that they have very distinctive prints from other small mammals. You can tell which tubes have been visited by San Bernardino kangaroo rats because of their distinctive large furry back toes and wide front paws. Also sometimes their tail gets a little ink on it and leaves a mark.