Experimental triggering of reproduction in a natural population of Microtus montanus.

A nonbreeding winter population of Microtus montanus was given limited supplements of fresh green wheatgrass over a 2-week period. The population was sampled at the end of the feeding period and compared to an adjacent population receiving no grass supplements. All of the experimental females were pregnant, while animals from the control area remained in nonbreeding condition. Replication of the experiment during the next winter produced similar results. The data suggest that Microtus montanus cues reproductive effort from chemical signals in the plant food resources.