Egg laying and incubation rhythm of the Chinese Grouse (Tetrastes sewerzowi) at Lianhuashan, Gansu, China

Incubating birds must balance the conflict between thermal needs of the developing embryos and their self-maintenance needs for energy. The Chinese Grouse (Tetrastes sewerzowi) lives in high mountain conifer forests and faces energy stress, cold environment, and predation pressure. Females might adjust incubation rhythm to adapt to these constraints.

Two methods were used to investigate egg laying and incubation pattern of the Chinese Grouse; 25 nests were monitored by data loggers and 12 nests by infrared video cameras.

Female Chinese Grouses usually laid an egg every 2 days. The incubation period was 28-31 days. Overall incubation constancy for Chinese Grouse was 93%. The females took 5.0 recesses per day and 34% of all 1696 recesses were taken in the crepuscular period. The average recess duration was 20.3 min. Females took more and shorter recesses in the latter part of incubation. The females who allocated more time to foraging had a higher reproductive success.

Probably due to its high egg/body mass ratio, the Chinese Grouse has a long laying interval of 49 h. We suggest that, due to energy stress, females have relatively more recesses and they increase the number of recesses as incubation progresses. To compensate for the embryos' thermal needs, they extend the incubation period and shorten the recess duration in this cold environment.