Circadian adaptation to seasons: effects on activity behavior in subtropical House Sparrow, Passer domesticus

Abstract

Birds use endogenous circadian clocks to regulate the wide array of functions. In the natural environment synchronized with day–night cycle, they exhibit these as daily rhythms in physiology and behavior. It is less understood, however, whether these daily rhythms have a seasonal perspective. We investigated this by measuring circadian clock governed activity behavior in House Sparrows (Passer domesticus) exposed to natural and artificial light–dark (LD) cycles at 27°N (Lucknow, India). Daily activity of Sparrows was recorded under natural daylight and temperature conditions (NDL) for ~11 months, beginning in late March. With more precise onsets than ends, Sparrows had varied daily activity pattern and duration between seasons. Further experiments investigated effect of seasons on circadian rhythm characteristics in Sparrows exposed to constant dim light (<1 lux) at different times of the year. The circadian rhythm period, activity pattern, and duration, but not the sensitivity of endogenous clock as shown by light-induced phase shifts, significantly varied over seasons. Also, resynchronization time (days) did not differ between seasons; although it was significantly longer to delay than to advance 6 h LD zeitgeber shifts. Thus, endogenous clock seems to closely correspond with environmental photoperiod in determining the daily activity behavior in House Sparrows.