Abstract
Variation in grassland vegetation structure influences the habitat selection of insectivorous birds. This variation presents a trade‐off for insectivorous predators: Arthropod abundance increases with vegetation height and heterogeneity, but access to arthropod prey items decreases. In contrast, grazing by large herbivores reduces and homogenizes vegetation, decreasing total arthropod abundance and diversity. However, the presence of livestock dung may help counteract the overall reduction in invertebrates by increasing arthropods associated with dung. It is unclear, however, how the presence of arthropod prey in dung contributes to overall habitat selection for insectivorous birds or how dung‐associated arthropods affect trade‐offs between vegetation structure, arthropod abundance, and access to prey. To explore these relationships, we studied habitat selection of the Black‐necked Crane (Grus nigricollis), a large omnivorous bird that breeds on the Qinghai–Tibet Plateau. We assessed the relationships between habitat selection of cranes and vegetation structure, arthropod abundance, and the presence of yak dung. We found that Black‐necked Cranes disproportionately foraged in grassland patches with short sward height, low sward height heterogeneity, and high numbers of dry yak dung, despite these habitats having lower total arthropod abundance. Although total arthropod abundance is lower, these habitats are supplemented with dry yak dung, which are associated with coleopteran larvae, making dung pats an indicator of food resources for breeding Black‐necked Cranes. Coleopteran adults and larvae in yak dung appear to be an important factor influencing the habitat selection of Black‐necked Cranes and should be considered when assessing grassland foraging trade‐offs of insectivorous birds. This research provides new insights into the role of livestock dung in defining foraging habitats and resources for insectivorous predators.
Highlights
Variation in vegetation structure poses a trade‐off for insectivorous birds between abundance and access to arthropod prey: The abundance and diversity of arthropods in‐ crease with vegetation height and heterogeneity (Dennis et al, 2008; Kruess & Tscharntke, 2002), but at the same time access to these prey items decreases (Butler & Gillings, 2004; Devereux, McKeever, Benton, & Whittingham, 2004)
Previous work has suggested that dung‐associated arthropods may be an important invertebrate resource for insectivorous birds (Atkinson, Buckingham, & Morris, 2004), but the extent to which dung‐associated arthropods contribute to overall habitat selection in insectivorous birds is unclear
By explicitly accounting for livestock dung, we can assess the role of dung in veg‐ etation structure trade‐offs and test whether dung‐associated arthropods might mitigate the impacts of reduced arthropod prey as vegetation height and heterogeneity decrease with increases in grazing
Summary
Variation in vegetation structure poses a trade‐off for insectivorous birds between abundance and access to arthropod prey: The abundance and diversity of arthropods in‐ crease with vegetation height and heterogeneity (Dennis et al, 2008; Kruess & Tscharntke, 2002), but at the same time access to these prey items decreases (Butler & Gillings, 2004; Devereux, McKeever, Benton, & Whittingham, 2004). We test how domesticated livestock impact habitat selection in a large omnivorous bird, the Black‐necked Crane (Grus nigricollis), by assessing the relationships between foraging habitat selection, vegetation structure, livestock dung, and arthropod abundance within the dung itself. By explicitly accounting for livestock dung, we can assess the role of dung in veg‐ etation structure trade‐offs (i.e., abundance of vs access to arthro‐ pod prey items) and test whether dung‐associated arthropods might mitigate the impacts of reduced arthropod prey as vegetation height and heterogeneity decrease with increases in grazing. The intensity of grazing from domesticated livestock varies spatially and temporally across the Qinghai–Tibet Plateau, creat‐ ing a dynamic and heterogeneous grassland landscape These gradients of grazing pressure provide a natural experimental setting to explore the relationships among vegetation structure, arthropod abundance, livestock dung, and habitat selection of Black‐necked Cranes. We quantified foraging habitat selection and diet of Black‐necked Cranes in relation to vegetation structure and arthropod abundance and diversity on the grassland surface and within domestic yak dung
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