Incubation strategies of the Black-necked Crane (Grus nigricollis) in relation to ambient temperature and time of day

摘要

Background: The behavior of cranes reflects many of their survival strategies, but little has been known of the incu-bation strategies of cranes, in which both parents share incubation duties, in response to cold temperatures in alpine environments. The lack of information may restrict the effective conservation of the threatened Black-necked Crane (Grus nigricollis), a biparental bird nesting in high elevation wetlands. Methods: We directly observed and used infrared video cameras from 2014 to 2015 to study the incubation behav-ior and quantitatively measured the frequency and details of egg turning behavior in the Black-necked Crane at the Yanchiwan National Nature Reserve in western Gansu Province, China. Results: At lower ambient temperatures in the morning, crane parents spent more time on the nest with less recess frequency and prolonged on-bout duration, while at higher temperatures around noon, the parents had more frequent recesses from incubation and shorter periods between nest exchanges. They adjusted the amount of time incubating by varying the recess frequency and the length of on-bout duration. Mean nest attendance and egg turn-ing frequency of females were significantly higher than those of the males. The nest attendance and on-bout duration of females showed a significantly negative relationship with those of males. The two parents responded differently to the change of temperature. Females spent more time on the nest at lower morning temperatures, while males increased their time on the nest at higher temperatures after noon. Higher incubation recess frequency and egg turn-ing frequency were observed at noon, probably because parents spent more time foraging, taking advantage of the lower egg cooling rate. Conclusion: Both Black-necked Crane parents in the alpine environment adjusted their behavior in response to the thermal requirements of eggs and the weather conditions experienced. Our findings demonstrate that parents of this species incubated in different but complementary ways and efciently enhanced egg care in a dynamic environment, so as to maximize benefits from the warm portion of the day and the intense solar radiation while minimizing the cost of rewarming eggs and the risks of cooling eggs.