Grazing pressure affects offspring sex ratio in a socially monogamous passerine on the Tibet Plateau

Abstract

Livestock grazing can affect habitat structure and availability of arthropod prey for grassland birds, and ultimately determines habitat quality. The habitat quality may affect breeding strategies (e.g. sex ratio adjustment) in bird species, but studies investigating grazing intensity on offspring sex ratio are still rare. In this paper, we examined the effect of grazing intensity by livestock on the secondary sex ratio of an alpine‐steppe passerine, the isabelline wheatear Oenanthe isabellina, on the Tibet Plateau. Offspring sex ratio of isabelline wheatears significantly correlated with a quadratic term – (grazing intensity)2. The wheatears nesting in areas grazed at low intensity by mixed livestocks produced significantly more sons than those in ungrazed area (0.41 vs 0.58, Z = –2.836, p = 0.005), while brood sex ratios from other treatments (ungrazing vs intensive grazing and low‐intensity grazing vs intensive grazing) did not differ significantly. Variation in offspring sex ratio was not related to other factors such as maternal condition, paternal condition and other two‐way interactions. These results suggest that breeding birds of grasslands are sensitive to variation in habitat conditions, and provide additional evidence that grazing intensity affects avian reproduction in cryptic ways that are rarely studied. Our findings suggest that flexible management including timely rotational grazing is needed to optimize bird species reproduction and maintain ecosystem health.

Life-History and Ecological Correlates of Egg and Clutch Mass Variation in Sympatric Bird Species at High Altitude

“…The average annual temperature recorded in this area was −1.0 • C with a total annual rainfall of 350 mm based on data collected from 1990 to 2010. Around 30 bird species nest in this area, and further details on the research site are available in Li et al [29].…”

“…The confounding effect-number of yearly broods, which is hard to control for species in low-land studies, can be easily reduced at high altitudes. Besides, the habitat at high altitudes tends to be more homogenous [29][30][31], while diverse habitat at low land might confound the final results. Species of different low-land regions experiences rather different biotic and abiotic environment (e.g., climate, vegetation and predator density) which might confound the final results [14].…”

Nest concealment is associated with reproductive traits across sympatric bird species

“…When a nest was located, we recorded the date and nest status (presence of parents, eggs, nestlings) with nests then checked every 2–4 days. Open‐cup nests were checked directly while cavity nests were checked either by a pole‐mounted miniature camera or through a hole dug at the side of the nest chamber (previous studies showed no obvious adverse effects from these methods; Li, Shi, et al., 2018 ). For cavity nests, we recorded the entrance location (on ground or on cliff bank) and measured the burrow length from entrance to the burrow chamber with a measuring tape to 0.1 cm.…”

“…Mammals (e.g., Siberian Weasel M. sibirica and Wild Cat Felis silvestris) are predominant predators in our study site Li S's unpublished data). Details on the study site are available in Li, Shi, et al (2018). Current study (Continues) during the incubation or nestling periods.…”

Phylogenetic relationship and characterization of the complete chloroplast genome of the alpine leaf-warbler in Qinghai-Tibet Plateau

“…An embryo (id alw_001) of this species was sampled in an unhatched egg from an abandoned nest, on June 21th 2017 at bush habitat of Tianjun County (37°18′N, 99° 01′E; 3416 m altitude), northeastern of Tibet Plateau (details of the habitat are available in Li et al. 2018 ). The sample was immediately stored in alcohol.…”