PS 47-131 - Foraging preferences of small mammals at the Sevilleta National Wildlife Refuge

Background/Question/Methods

Granivores are important seed consumers in many dryland ecosystems. Creosotebush (Larrea tridentata) is a dominant shrub that has been invading grasslands throughout the Chihuahuan Desert and is predicted to further expand into grassland under climate change. Their large, nutritious seeds could serve as a reliable food source for small mammals in drylands where other seed resources are highly unpredictable. However, secondary compounds in creosotebush seeds may make them unpalatable to desert granivores, reducing their value as a food source. Thus, it is important to determine if the seeds of creosotebush are a constituent of the food web in dryland ecosystems. We investigated the foraging preferences of granivorous small mammals at the Sevilleta National Wildlife Refuge (SNWR). To do so, we established twelve feeding stations along a grassland to creosotebush-shrubland ecotone at the SNWR. At each station, four petri dishes were filled with different grass and forb seeds, including creosotebush, and set out for three nights each trial (n=10 seeds/dish, 12 dishes/trial, 35 trials from June to February). The dishes were picked up to see how many and which species of seeds were taken. Motion sensor cameras at each station captured pictures of rodents interacting with the dishes.

Results/Conclusions

We found that rodents at the SNWR do include creosote seeds in their diets. Out of the seven species of seeds that were included in the trials, the top three preferred seeds were a forb, devil’s claw (Proboscidea parviflora), creosotebush, and a C4 grass, purple three-awn (Aristida purpurea). Devil’s claw seeds were taken 38% of the time, creosotebush seeds 7%, and purple three-awn seeds 5% of the time. Motion sensor cameras captured photos of kangaroo rats (Dipodomys), desert woodrats (Neotoma albigula), and silky pocket mice (Perognathus flavus) interacting with the dishes. Additionally, empty and cracked seed shells were found in the dishes. The preference for creosotebush seeds increased in the winter months compared to the summer trials, with cresotebush seeds being the second most preferred seed in the winter compared to being third in the summer. Overall, despite the potentially harmful secondary compounds found in creosotebush seeds, they are consumed by seed eating rodents, and may even be preferred over other seeds during different times of the year.