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Biparental incubation pattern of the Black-necked Crane on an alpine plateau

Zhang, Lixun, Shu, Meilin, An, Bei, Zhao, Changming, Suo, Yila, Yang, Xiaojun
Journal of ornithology 2017 v.158 no.3 pp. 697-705
Grus nigricollis, breeding, eggs, environmental factors, fecundity, females, males, models, monitoring, nests, parents, plateaus, predation, water birds, weather, China
The biparental incubation model is an excellent one for investigating how parents resolve sexual conflict and achieve cooperation, especially in cold alpine environments. We used video monitoring of 20 nests 24 h/day to systematically investigate the incubation pattern of the Black-necked Crane (Grus nigricollis), a biparental waterbird with threatened status (International Union for Conservation of Nature vulnerable status), inhabiting the Qinghai-Tibetan Plateau, China. Analysis of 3886 h of video recordings indicated high nest attendance (90.1%) by Black-necked Crane parents across 14 nests, with almost equal female and male nest attendance (45.4 vs. 44.8%). The average length of an incubation bout was 2.06 h, with frequent changeovers (10.87 times/day, lasting on average 5.05 min). Males spent significantly more time returning to the nest than females (5.57 vs. 4.65 min, t ₁₈₀ = −46.61, P < 0.001) after the partner left the nest. Six of 20 monitored nests failed, mainly due to egg predation, egg collection, or adverse weather. We provide the first evidence that, under natural environmental conditions, both males and females respond to reduced partner effort with diverse strategies. On average, full compensation was greater than 100% for the decreased partner effort. In this long-lived species with long-lasting pair bonds and low fecundity, a mate may overly compensate for reduced partner investment to avoid forfeiting the current breeding attempt. Our results indicate that females and males are allocated different tasks with complementary patterns during incubation, enhancing egg care efficiency in an alpine plateau environment with severe threats. Both social and natural environmental factors may shape the incubation pattern of Black-necked Cranes.