Time Patterns of Peromyscus Activity and Their Correlations with Weather

The activity of Peromyscus maniculatus in an Ontario forest and Peromyscus truei and Peromyscus californicus in California chaparral was observed directly and monitored electronically. The activity of all three species outside the burrow was pulsed through the night, with different individuals not in tight synchrony and a depression in overall activity in the middle of the night. Activity of P. californicus was similar to that of P. truei, but P. californicus had in addition a pronounced burst of activity before dawn. As summer progressed, the amount of activity of P. maniculatus diminished and was compressed into the early part of the night. Wind and moonlight had no strong effect upon activity within a night. From night to night, P. truei had conspicuous fluctuations in total nightly activity (at a period of about 4 days), the entire population usually being in synchrony. Night-to-night fluctuations in P. californicus activity were in phase with those of P. truei. Night-to-night fluctuations in vole tracks in Quebec (unpublished data from R. Bider) had low correlations with P. maniculatus tracks in the same area. Night-to-night fluctuations in P. truei activity had a positive correlation with barometric pressure and a negative correlation with low pressure weather variables (humidity, temperature). There was no correlation with wind or cloud cover. None of the weather variables had a strong periodicity at 4 days, but P. truei activity was in phase with the 4-day-component of barometric pressure, out of phase with temperature, and leading humidity. The evidence suggested that sundown temperature was the key variable. Fluctuations in tracks of P. maniculatus (Quebec) had similar properties, except they were in-phase with low pressure weather variables. Vole tracks (Microtus pennsylvanicus and Clethrionomys gapperi) showed the same periodicities as weather and were tightly correlated with weather.