Diet Preferences of the Salt Marsh Harvest Mouse During a California Drought
Animals residing in estuaries live balanced on the edge between aquatic and terrestrial habitat. Some species, like waterfowl, are clearly adapted for this lifestyle, but others, such as the endangered salt marsh harvest mouse (Reithrodontomys raviventris) are less equipped for a semi-aquatic lifestyle. Nonetheless, these organisms can inhabit similar habitats, and it stands to reason that they consume similar food items. In the Suisun Marsh, a large, relatively intact portion of the San Francisco Bay Estuary, the majority of remaining habitat is privately owned and managed by duck hunting clubs, at no cost to the public. Wetland management practices can promote the growth of plants and invertebrates that ducks prefer to eat. If salt marsh harvest mice prefer the same food items that ducks do it has the potential to expand popular notion of mouse habitat as well as provide additional management techniques to enhance this imperiled species, endemic only to the San Francisco Bay Estuary. I video monitored closed cafeteria trials to investigate the diet preferences of the salt marsh harvest mouse, offering foods known to be preferred by waterfowl and foods presumed to be preferred by mice based on capture locations.
Preliminary results show that across seasons most salt marsh harvest mice preferred watergrass (Echinochloa crusgalli) in cafeteria trials. Watergrass is the third most preferred food item among common waterfowl in the Suisun Marsh. Mice showed strong preferences, often spending more than 80% of the time during the trial feeding on one type of food item. Interestingly, salt marsh harvest mice showed little interest in plants long believed to be their primary food items, such as pickleweed (Salicornia virginica). Many stakeholders in this system believe that management techniques for waterfowl and salt marsh harvest mice are at odds. The results of this study show that despite having quite different lifestyles, salt marsh harvest mice and waterfowl share diet preferences. This opens the door to significant improvements in multispecies management as well as a better overall understanding of this important ecosystem. It also shows that focusing on the biology of endangered species without considering their overall ecology may leave managers lacking tools to conserve biodiversity in increasingly threatened ecosystems worldwide.