Presence of a conspecific renders survival advantages in the migratory redheaded bunting: test through the effects of restricted feeding on circadian response and survivorship.

This study investigated the effects of a conspecific on survival advantages in a challenged feeding environment created through restricted food availability periods. We measured the daily activity-rest pattern as the circadian response indicator, and changes in body mass and mortality as the survivorship indicator. Migratory male redheaded buntings (Emberiza bruniceps) were housed alone (single, Group 1) or with a conspecific (pair, Group 2) in activity cages that continuously recorded the activity-rest pattern. Cages were individually placed within the isolated photoperiodic boxes providing short-day conditions (8 h light: 16 h darkness, LD 8/16; L = 15 lux; D = 0.5 lux at the cage floor level) with food freely available (ad libitum). Beginning from day 11 of the experiment, food availability was restricted for two weeks to only during the 8 h daytime (zeitgeber time [ZT 0-8]; ZT 0 = time of lights-on). Thus, birds were concurrently subjected to a food zeitgeber cycle, PA 8/16, synchronous (in phase) with the LD 8/16. Thereafter, food availability was changed to only during the 16 h of darkness (ZT 8-0; ZT 8 = time of lights-off). Thus, the food cycle, PA 16/8 (16 h food present: 8 h food absent) was in conflict with the LD 8/16; the LD and PA cycles were in antiphase. This was considered for diurnal redheaded buntings as the challenged feeding environment. After four weeks, singles were returned to the ad libitum food condition; those in pairs remained on the nighttime (darkness) food regimen but were separated to confirm the effects of the nighttime food condition on isolates. The results show that the presence of a conspecific within the cage influenced the daily activity-rest pattern, maintained body mass, and reduced mortality. It is suggested that the presence of a conspecific within the same cage improved the circadian performance of the members forming the pair and enhanced their survivorship.