Nest success
Our results indicated that the total nest success of the Emei Shan Liocichla was low (27.5 %). Similarly lower nest successes have been reported in many species of the family Timaliidae in southern China, such as the Fulvous Parrotbill (Paradoxornis fulvifrons) (18.18 %, Hu et al. 2014), the Red-billed Leiothrix (Leiothrix lutea) (22.95 %, Ma et al. 2010) and the Golden Parrotbill (Paradoxornis verreauxi) (38.89 %, Yang et al. 2011). In these cases, nest predation or nest desertion accounted for most nest failures. In our study, nest predation was the main factor affecting nest success of the Emei Shan Liocichla. Besides, human disturbance (mainly by tourists) may be another important factor affecting success, which prompted nest desertion as the Liocichla seemed to prefer nest sites near trails (we are collecting more related evidence).
Our findings also raise an interesting phenomenon regarding the yearly fluctuation (from 14.7 to 35.5 %) of nest success of our species (Table 1). Whether this was associated with changes of predator densities and therefore resulted in population fluctuation in the number of Emei Shan Liocichlas needs further study.
Nest-site selection
For most bird species, nest-site selection is largely based on small-scale vegetation structure (Yang et al. 2000). Vegetation structures may provide escape cover against predators, suitable nesting sites and/or food sources for birds (Feinsinger et al. 1988; Lima 1993). Bamboo would appear to be the key nesting plant for the Emei Shan Liocichla at Laojunshan, given that most nests (~70 %) were found in bamboo (C. szechuanensis). Bamboo cover (i.e. dense bamboo leaves) may be selected by this species as a potential escape cover, which could be safer compared to other types of understory cover (Reid et al. 2004).
Studies have shown that the Emei Shan Liocichla is a typical forest edge or gap bird (Fu et al. 2011, 2013). Our results confirmed this again (Table 2). Generally, there are fewer trees at the forest edge or gap. Lower tree cover is conducive to the growth of bamboo, which may be one important reason why this species prefers habitats close to the forest edge or gap. As well, the Emei Shan Liocichla shows an apparent preference for shrubs, lianas and herbs, which are important characteristic plants of the forest edge or gap in our study site. For this bird, shrubs with dense foliage, such as Eurya sp. and Rubus sp., are its potential nesting plants. As well as providing part of their nest material, the abundant leaves of lianas and herbs may, to a large extent, increase the concealment of their nest sites. The mean concealments above and around their nests were >90 % (Fu et al. 2011). We conclude that the Emei Shan Liocichla tends to select nest sites with good concealment, which agrees with the nest-concealment hypothesis (Martin 1993b).
Successful versus failed nests
A prevalent theory suggests that habitat preferences of animals should be adaptive, such that fitness is more prevalent in preferred habitats than elsewhere (Hildén 1965; Southwood 1977; Martin 1998). If nest-site selection were adaptive, the attributes of successful and failed nests would differ (Cancellieri and Murphy 2014). However, our results were inconsistent with this hypothesis, although it is possible that a larger sample size would be required to test this fully. A number of studies of cup-nesting passerines have also shown a lack of association between nesting success and habitat attributes (Holway 1991; Filliater et al. 1994; Wilson and Cooper 1998). Nest predation has been suggested as one of the most important factors affecting nest success (Ricklefs 1969; Martin 1988). For example, Lack (1954) estimated that 75 % of all eggs and nestlings lost from open cup nests are taken by predators. Filliater et al. (1994) argued that adaptive nest-site selection is impossible when intense predator pressure reduces the probability of success to little more than a stochastic event.
In our study system, nest predation was the main cause of nest failure, with various nest predators. Among them, squirrels and raptors forage mainly by visual cues, while snakes largely use infrared heat-sensing and wasps chemical information. Differences in search strategies among predators may constrain the ability of Dusky Flycatchers (Empidonax oberholseri) to optimize nest-site selection (Liebezeit and George 2002), which may also characterize the Emei Shan Liocichlas.