A study from the University of California, Davis, describes a new, non-invasive genetic survey technique for the endangered salt marsh harvest mouse, which lives solely within the tidal marshes of the San Francisco Bay Estuary.

In larger mammals, scientists often collect samples from scat, but the poop of small animals can be so small that it is difficult to detect in the wild.

The new technique, published in the Journal of Mammalogy, uses a combination of bait stations and genetics to sample and identify salt marsh harvest mice, or "salties" as researchers affectionately call them. The species has lost more than 90% of its habitat to development and is also threatened by rising sea levels. That's why it is imperative that the remaining populations are identified accurately and efficiently, the authors note.

Dine and dash

The technique is simple: Scientists bait boxes with a snack of seeds, millet and oats, and lay down cotton bedding. The mice are free to come and go. A researcher returns a week later to collect the fecal pellets for genetic sampling at the lab. There, a unique species identification test differentiates salt marsh harvest mice samples from those of other rodents that may have used the bait box.

Contrast that process with the more common and intensive method of live trapping: A team of three to five researchers check traps at sunrise and sunset for several consecutive days. To prevent animal drownings, those traps must be placed above the tideline, ruling out several areas of tidal marsh habitat. But with the new, non-invasive technique, mice can leave at any time, allowing researchers to monitor more marshes and more mice, safely and efficiently.