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The observations of microorganisms revealed how they swim. As inspired by them, studies on artificial micro-robots with various actuation mechanisms have been thriving. To elucidate the essential concepts in understanding the dynamic behaviors of natural and artificial micro-swimmers—so as to control the latter in future applications, in this paper, we summarize the historical achievements and describe our theoretical perspectives. We first introduce the studies on microorganisms and their propulsion mechanisms. After reviewing the basic principles and the development of the understanding of them, we take the flagellated micro-swimmers as an example to elaborate on the theories of their locomotion. We review the progress in actuation strategies of artificial flagellated micro-swimmers and then propose two possible strategies to realize the turning of a flagellated micro-swimmer—the key step toward steerability through remote fields. Finally, we describe the inadequacies of the investigations on this topic and our perspectives on future developments.

Knowing the diet of endangered wild animals is a prerequisite for species-specific conservation and habitat management. The Sichuan partridge Arborophila rufipectus is a globally endangered Galliformes species endemic to the mountains of southwest China. Existing information on the diet of this species is biased and fragmented owing to traditional observation methods. Little is known about their dietary composition or how they respond to temporal variations in food resources throughout the year. In this study, a dietary analysis was performed on 60 fecal samples using DNA Metabarcoding of invertebrates and plants to determine the primary animal and plant components of the diet across 3 critical periods of adult life history (breeding, postbreeding wandering, and overwintering). Preys from the dipteran order, followed by the lepidopteran and araneaen spp., were the predominant, animal-derived foods. Symplocos, Rubus, Celastrus, Holboellia, and Actinidia spp. supply a large abundance of fruits and seeds for this omnivorous bird. Substantial temporal dietary changes among the 3 periods and a general shift toward lower dietary diversity during the breeding season were observed, suggesting that the Sichuan partridge can adjust their diet according to the availability of food resources and their own needs. Characterizing the composition and seasonal changes in Sichuan partridge diets informs the habitat management of native flora (the plant taxa that can generate berries and seeds, such as Symplocos, Rubus, Celastrus, and Holboellia, which are likely of conservation interest) to achieve full life-cycle conservation.

BackgroundUnderstanding how species diversify is a long-standing question in biology. The allopatric speciation model is a classic hypothesis to explain the speciation process. This model supposes that there is no gene flow during the divergence process of geographically isolated populations. On the contrary, the speciation with gene flow model supposes that gene flow does occur during the speciation process. Whether allopatric species have gene flow during the speciation process is still an open question.MethodsWe used the genetic information from 31 loci of 24 Chinese Bamboo Partridges (Bambusicola thoracicus) and 23 Taiwan Bamboo Partridges (B. sonorivox) to infer the gene flow model of the two species, using the approximate Bayesian computation (ABC) model. The ecological niche model was used to infer the paleo-distribution during the glacial period. We also tested whether the two species had a conserved ecological niche by means of a background similarity test.ResultsThe genetic data suggested that the post-divergence gene flow between the two species was terminated before the mid-Pleistocene. Furthermore, our ecological niche modeling suggested that their ecological niches were highly conserved, and that they shared an overlapping potential distribution range in the last glacial maximum.ConclusionsThe allopatric speciation model cannot explain the speciation process of the two Bamboo Partridges. The results of this study supported a scenario in which speciation with gene flow occurring between the allopatric species and have contributed to our understanding of the speciation process.

In this study, we report an unusual homing behavior of the Sichuan Partridge (Arborophila rufipectus) at the Laojunshan National Nature Reserve, Sichuan Province, China. Hen Sichuan Partridges led the chicks back to the nests where they hatched in the evening and roosted there over night. This behavior lasted 6.7 ± 4.3 nights (range = 1–15; n = 13) after the chicks hatched. At this stage, the hens became very vigilant to predators and human disturbance. If disturbed, they often abandoned the nests immediately and no longer returned thereafter. The ambient temperature at night during the early brooding period of Sichuan Partridge at our study site was ~ 12.4 °C. Our findings suggest that hen Sichuan Partridges may make trade-offs between nest predation risks versus the thermoregulatory needs of their young.

In this work, we proposed a bar-joint model based on the corrected resistive force theory (CRFT) for studying artificial flagellated micro-swimmers (AFMSs) propelled by acoustic waves in a two-dimensional (2D) flow field or with a rectangular cross-section. Note that the classical resistive-force theory for 3D cylindrical flagellum leads to over 90% deviation in terminal velocity from those of 2D fluid-structure interaction (FSI) simulations, while the proposed CRFT bar-joint model can reduce the deviation to below 5%; hence, it enables a reliable prediction of the 2D locomotion of an acoustically actuated AFMS with a rectangular cross-section, which is the case in some experiments. Introduced in the CRFT is a single correction factor K determined by comparing the linear terminal velocities under acoustic actuation obtained from the CRFT with those from simulations. After the determination of K, detailed comparisons of trajectories between the CRFT-based bar-joint AFMS model and the FSI simulation were presented, exhibiting an excellent consistency. Finally, a numerical demonstration of the purely acoustic or magneto-acoustic steering of an AFMS based on the CRFT was presented, which can be one of the choices for future AFMS-based precision therapy.

Additional file 1: Table S1. Sample information. Table S2. Primer information. Table S3. Summary of nuclear genes. Table S4. Prior distributions of demographic parameters for all demographic models. Table S5. Command line for each model in the running msABC. Table S6. Records of original occurrencefor the two species. Table S7. Occurrence points used to construct theecological niche models. Table S8. Correlation coefficient of each environmental layer. Table S9. Morphological characteristics of the specimens.

Additional file 2: Figure S1. Study area and occurrences used for constructing the ecological niche of B. thoracicus in the current time. Figure S2. Study area and occurrences used for constructing the ecological niche of B. sonorivox in the current time. Figure S3. Study area and occurrences for constructing the ecological niche of both B. thoracicus and B. sonorivox in the LGM. Figure S4. Potential distribution area of B. thoracicus in the current time. Figure S5. Potential distribution area of B. sonorivox in the current time.

A new sliding-mode triboelectric energy harvester in the form of a cantilever beam with a tip mass that is acted upon by both magnetic and friction forces is modelled and simulated. A numerical scheme based on the trapezoidal rule with the second-order backward difference formula (TR-BDF2) method is introduced to solve the combined non-smooth mechanical and stiff electrical system. This is the first study of the structural dynamics of the sliding-mode triboelectric energy harvesting; additionally, a magnetic field that induces multistability is present. A comparison between the coupled and uncoupled electromechanical models suggests that the electrostatic force between the electrodes can be ignored, which makes the uncoupled model preferable in the dynamical analysis. The influence of the non-conservative force (the friction force) on the multistability of the system is investigated. It is found that the distribution of the multistability on the parametric plane changes even when a small amount of friction is involved, and the areas of bistability and tristability shrink while that of the monostability expands. A comparison among these three types of stability reveals the superiority of invoking bistability as it facilitates broadband energy harvesting. The excitation level plays an important role in inducing the snap-through motion (the interwell oscillation) by enabling the crossing of the energy barriers between wells. The increase in the friction shrinks the frequency band of interwell oscillations from high frequencies down to low frequencies on the discrete frequency sweep. An analysis of the basins of attraction finds that at low frequencies the bistable system can undergo only interwell oscillations, while the tristable system can merely experience intrawell oscillations. The basins can intermingle with each other in both bistable and tristable systems. Finally, an increase in the excitation level can break the basins into discrete pieces and/or points.

A triboelectric energy harvester based on a three-degree-of-freedom vibro-impact oscillator is presented. Both the dynamic model of the oscillator and the theoretical model of the oscillator-based triboelectric energy harvester are established. The dynamic response and its effect on the electrical output are considered for various mass ratios and mass spacings. The study leads to the conclusions that the symmetric mass configurations of the oscillator are more beneficial to energy harvesting than the asymmetric cases. The extent of the initial spacing between the masses influences the dynamics of the system and the electrical output by triggering grazing bifurcation. High-order periodicity is found to accompany a reduction in the electrical power. An increase in mass ratio tends to increase the electrical output, and there may exist an optimal mass ratio at which the electrical output is maximized. Chatter and sticking motion can improve the output performance dramatically, while resonance, as usual, corresponds to large amplitude response, but these large amplitudes are not optimal for triboelectric energy harvesting, and thus the maximal output does not appear around resonance. This is different from other types of vibration-based energy harvesters, such as piezoelectric and magnetoelectric energy harvesters which are usually designed to operate at resonance. In addition, chatter is found to occur at low excitation frequencies, which can help harvest energy from low-frequency ambient vibration.

The operations of the triboelectric nanogenerator (TENG) highly rely on the availability of the mechanical motion source depending on the location, time, weather, etc. Thus, it is highly demanded to achieve moveable mechanical sensing and energy harvesting, but it is also challenging considering the system complexity, size, and weight. To this end, an electrostatic robotic system capable of locomotion, energy harvesting, and vibration sensing is proposed in this paper. The main body of the robot is an integration of an electrostatic actuator and a TENG, both of which share the same structure and materials and utilize the mechanical and electrical characteristics of electrostatic effects, respectively. The prototype is lightweight (2.46 g) and compact (3.7 cm in height and 9.1 cm in length), consisting of two conductive films as the main body in a zipper-like form and two flat conductive films as feet. Here we demonstrate the multifunctionality of this prototype by driving the robot crawling on the ground at a speed of 2.2 mm/s at maximum with a mini camera for monitoring, anchoring by electrostatic adhesive feet at the aim location where vibration is strong, sensing the vibration frequency accurately while having an average relative error of 8.7% in measuring the amplitude, and harvesting the energy by TENG. Such a multifunctional robotic system may enable broad potential applications in structural health monitoring, environmental surveillance, rescue, risky intervention, etc.

Background The Emei Shan Liocichla (Liocichla omeiensis) is an endemic bird species to southwestern China with a small geographic range. However, little was known about the genetic status of this threatened species. Methods We applied restriction-site-associated DNA sequencing (RAD-Seq) for rapid mass identification of microsatellite markers of the Emei Shan Liocichla. Results A total of 11,564 microsatellite sequences were obtained, 600 random loci were designed for screening and 24 polymorphic microsatellite loci were selected for further validation. The average allele number, average observed heterozygosity and average expected heterozygosity were relatively low in our samples, which were 6.08, 0.6618 and 0.7048, respectively, indicating that the Emei Shan Liocichla might have lost some genetic diversity. Further analyses suggested that the populations distributed on two mountains (Daxiangling and Xiaoliangshan) showed a modest degree of genetic differentiation. Conclusions These novel microsatellite markers provided valuable preliminary knowledge regarding the genetic status of the Emei Shan Liocichla and can be useful in further studies, as well as in the management and conservation of this species.

This paper focuses on the primary resonance analysis of a dual-rotor system having two rotor unbalance excitations of different rotating speeds and being connected by an inter-shaft ball bearing. Due to the complex excitation condition and the complicated nonlinear bearing forces of the inter-shaft bearing, the general analytical methods, e.g., the multiple scales method or the harmonic balance method, are failed to give the theoretical solutions. Thus, the harmonic balance–alternating frequency/time domain (HB–AFT) method is formulated to deal with this problem. The basic idea of the method is using the inverse discrete Fourier transform and the discrete Fourier transform, instead of the direct analytical relationship between the supposed solutions of the system and the nonlinear forces, to construct the harmonic expressions of the nonlinear forces, which is the so-called alternating frequency/time domain technique. By using the HB–AFT method, therefore, a Newton– Raphson iteration procedure can be performed to demonstrate the approximate solutions of the system. Accordingly, the frequency responses of the system affected by some critical parameters, such as rotating speed ratio, unbalances of both the inner and outer rotors, and clearance of the inter-shaft bearing, are analyzed, respectively. A variety of phenomena including double resonance peaks, biperiodic and quasi-periodic behaviors, and resonance hysteresis phenomenon are obtained, which are discussed in detail through diagrams for separated frequency responses with different frequency components and rotors’ orbits for different combinations of system parameters. Most prominently, for a relatively small unbalance of rotor as well as a relatively large clearance of the inter-shaft bearing, the resonance hysteresis phenomena are more obvious. The results obtained are also compared with the direct numerical simulation results, and the comparisons show good agreements. In addition, the methodology formulated in this paper is a general approach, which can be applied to other engineering systems with multi-frequency excitations.

Incubation is an energetically demanding phase of avian reproduction. Single-sex incubators are often faced with a direct conflict between incubation and foraging. We report an unusual incubation behavior of the Sichuan Partridge (Arborophila rufipectus), with long recesses of females and embryonic hypothermia, at Laojunshan National Nature Reserve, southwest China. The Sichuan Partridge is a globally endangered species that inhabits subtropical evergreen and deciduous broadleaf forests at 1100–2250 m a.s.l. Female Sichuan Partridges incubated eggs alone, and typically took one long incubation recess of 4.5 ± 1.2 h (mean ± SD) day−1. They left the nests at 7:36 a.m. (±50 min) and returned at 12:06 p.m. (±70 min). Nest attentiveness was 81.2 ± 5.2% of the entire incubation period. Females prolonged the recess duration and decreased nest attentiveness significantly in response to high disturbance risk and bad weather. Although eggs experienced ~4.2 h below 26 °C (the physiological zero temperature) for each recess, the total hatching rate was 88.4%, suggesting that embryonic hypothermia had minimal negative effect on the hatching rate. For Sichuan Partridge, the ability to withstand embryonic hypothermia may be an adaptation to cold montane environments.

This paper focuses on the nonlinear dynamic and bifurcation characteristics of an aircraft rotor system affected by the maneuvering flight of the aircraft. The equations of motion of the system are formulated with the consideration of the nonlinear supports of Duffing type and the sine maneuver load of a proposed maneuvering flight model. By utilizing the multiple scales method to solve the motion equations analytically, the bifurcation equations are obtained. Accordingly, the response and the bifurcation characteristics of the system are analyzed respectively. Basically, the increase of the maneuver load may increase the formant frequency as well as the primary resonance frequencies. Through numerical simulations, four different types of response characteristics of the system during the maneuvering flight are found, which are compared with the theoretical results, and it shows good qualitative agreements between them. Furthermore, the maneuver load can make an apparent effect on the bifurcation. The results in this paper will provide a better understanding for the effect of aircraft maneuvering flight on the dynamics and bifurcations of the rotor system.

Vibration energy harvesting has been a popular research topic in recent years and is a promising technology in the development of the Internet of Things. Triboelectric energy harvesting, as a relatively new energy harvesting technique, is drawing attention. However, relevant studies from the perspective of structural dynamics are rare, and a study on how the electrical properties of triboelectric energy harvesters (TEHs) affect their vibration is still missing. In this paper, we perform such a study for TEHs that use the two most common working modes—namely the lateral sliding mode and the vertical contact-separation mode. In the first part of the paper, the coupled electromechanical model of a sliding mode TEH—based on a cantilever beam system involving friction—is established. The effects of the tribo-charge surface density and the load resistance on the vibration of the harvester are investigated. It is found that the effects of the tribo-charge surface density on vibrations are similar to those of mechanical damping, while the load resistance can result in an interesting resistive shunt damping phenomenon which is distinct from the one found in piezoelectric energy harvesters. In the second part, the modelling of a vertical contact-separation mode TEH is established based on a single-degree-of-freedom vibro-impact oscillator, and the effects of the same electrical properties on vibrations are studied. The variation of the tribo-charge surface density can result in both vibration amplitude attenuation and resonance frequency shifting, while the change of the load resistance can influence vibrations only in the case of large tribo-charge surface densities. This study further unveils the electromechanical coupling mechanisms in TEHs and sheds some light on achieving desirable dynamic responses of TEHs via tuning their electrical properties.

The phylogenetic and taxonomic status of galliform birds is difficult to ascertain. This study reviews previous research on molecular techniques and morphological characteristics (e.g., plumage color) of Tragopan , Ithaginis , and Perdix to elucidate the polymorphism and taxonomic criteria of some galliform genera. Taxonomic criteria include genetic and morphologic characteristics (e.g., body color). Plumage color is associated with sexual selection and environmental factors and, therefore, is an important criterion in bird taxonomy. The results of this study reveal the polymorphism of some galliform birds and the difficulty in ascertaining the taxonomic status of these birds.

The Emei Shan Liocichla (Liocichla omeiensis) is a globally vulnerable babbler, endemic to southwestern China. We investigated its nest predators, nest-site selection and nest success at the Laojunshan National Nature Reserve in Sichuan, China in order to identify the precise nesting-habitat requirements of the species, and to test whether the nest-site-selection cues, preferred by the Emei Shan Liocichla, are positively associated with nest success. We used infrared cameras to determine nest predators. We compared the microhabitat attributes between nest and random sites, as well as successful and failed nests. We used Binary Logistic Regression to determine the most important variables affecting nest-site selection of the Emei Shan Liocichla. We used the nest survival analysis in Program MARK to estimate daily nest survival rates (DSR). Nest success was calculated using the Mayfield method. In total 56 nests were found. The DSR for all nests that contained at least one egg was 0.9564 ± 0.0091 (95 % CI 0.9346–0.9711) (n = 40), while the total nest success was 27.5 %. We identified four categories of predators in 10 nest predation events, i.e. squirrels (n = 5), snakes (n = 3), raptors (n = 1) and wasps (n = 1). We found that: (1) nest predation was the primary reason for nest failure of the Emei Shan Liocichla, (2) tree cover, bamboo cover, liana abundance and distance to forest edge or gap were the most important variables affecting nest-site selection of this species, and (3) the nest-site-selection variables we measured appeared not to be positively associated with nest success. Our findings suggest that the Emei Shan Liocichla tended to select nest sites near forest edges or gaps with good concealment and that nest-site selection by this species was nonrandom but not necessarily adaptive. Reducing forest-edge development and protecting bamboo stands should be effective for conservation of this species.

Additional file 1: Table S1. Variables and measurements for nest-site selection by the Emei Shan Liocichla at Laojunshan National Nature Reserve, Sichuan, China.

We studied the breeding ecology of the Emei Shan Liocichla (Liocichla omeiensis) in two nature reserves (Laojunshan and Wawushan) in Sichuan, China from March to August 2009 and April to August 2010. The breeding density (mean ± SE) was between 1.20 ± 0.46 and 1.55 ± 0.56 males/km2, and the breeding season was from late April to mid-August and from mid-May to late August in Laojunshan Nature Reserve in 2009 and 2010, respectively. This species used the edges of or gaps within natural broadleaf forest between elevations of 1,450 and 2,150 m for nesting. Vegetation around nests was mainly bamboo (Chimonobambusa szechuanensis), small shrubs, and lianes with few large trees. Nests were cup-shaped with a mean height of 137.5 ± 4.6 cm above the ground. Nests were mainly in C. szechuanensis. Females laid one egg per day in the morning and the mean (± SE) clutch size was 2.9 ± 0.2 eggs. Incubation started after the last egg was laid. Both males and females were observed participating in incubation, provi...

The complete mitochondrial genome of the green-backed tit Parus monticolus was assembled from Illumina sequencing reads. The genome is 16 771 bp long, and harbors 22 transfer RNAs (tRNAs), 13 protein-coding genes (PCGs), two ribosomal RNAs (rRNAs), and one control region. All PCGs are initiated with the ATG codon except for COX1 with GTG as its start codon. Five distinct types of stop codons are inferred, i.e. AGA (ND1 and ND5), AGG (COX1), TAA (ATP6, ATP8, COX2, ND3 and ND4L), TAG (ND6), and the incomplete codon T/TA (COX3, CYTB, ND2 and ND4). The 22 tRNAs range in size from 66 to 75 bp. The 12S and 16S rRNAs are 982 and 1601 bp long, respectively, and are separated by tRNA-Val gene. The putative control region is located between tRNA-Glu and tRNA-Phe with a length of 1187 bp. Phylogenetic analysis indicated that this species is closely related to its congener P. major.

The complete mitochondrial genome of the fulvous parrotbill (Paradoxornis fulvifrons) has been determined from Illumina sequencing data. The circular genome is 17 059 bp long, comprising 37 genes (13 protein-coding genes/PCGs, 22 tRNA genes and two rRNA genes) and a putative control region. Except for COX1 with GTG as its start codon, all PCGs are initiated with the ATR (ATA/ATG) codons. One PCG (COX1) is terminated with AGG, three PCGs (COX3, ND2 and ND4) with the incomplete stop codon T--/TA-, while all the others with TAA. The 22 tRNAs range in size from 64 bp (tRNA-Ser) to 75 bp (tRNA-Leu). The two rRNAs are 982 bp (12S rRNA) and 1600 bp (16S rRNA) long, respectively. The putative control region is located between tRNA-Thr and tRNA-Pro genes with a length of 1235 bp. The base composition is biased (29.06% A, 31.10% C, 14.97% G and 24.87% T) with an overall A + T content of 53.93% ("light strand"). Phylogenetic analysis indicated that P. fulvifrons is closely related to the congeneric vinous-throated parrotbill (P. webbianus).

The complete mitochondrial genome of the white-browed laughingthrush Garrulax sannio was assembled using next-generation sequencing (NGS) technology. The double-stranded circular genome is 17 848 bp in length, including 22 transfer RNAs (tRNAs), 13 protein-coding genes (PCGs), two ribosomal RNAs (rRNAs), and 2 putative control region. All PCGs are initiated with the ATG codon except for COX1 with GTG as its start codon. Five distinct types of stop codons are present, i.e., AGA (ND5), AGG (COX1 and ND1), TAA (ATP6, ATP8, COX2, CYTB, and ND4L), TAG (ND6), and the incomplete codon T/TA (COX3, ND2, ND3, and ND4). The nucleotide composition is moderately asymmetric (28.94% A, 32.82% C, 15.00% G, and 23.24% T) with an overall GC content of 47.82% ("light strand"). Phylogenetic analysis indicated a close genetic relationship between this species and its congeners G. perspicillatus, G. cineraceus, and G. canorus.

Temperature data loggers (TDL) are mostly used to monitor avian incubation behavior in bird studies. In this paper we demonstrate how TDL can also be used to determine different breeding stages and nest success of the vulnerable Emei Shan Liocichla (Liocichla omeiensis). All nests that contained at least one egg were divided into two groups. Group I included six nests monitored traditionally by the observers' visits, while Group II included eight nests monitored by TDL. Group I and Group II were visited every 1-4 days and 7 days, respectively, to check nest contents and status (e.g., active vs. inactive, and the breeding process) until fledging or nest failure. The time of each observation was recorded to verify the interpretation of TDL. The data recorded by TDL were converted into line graphs of temperature against time and assessed visually. The results indicated that TDL can reliably identify different breeding stages and estimate daily nest survival rates (DSR) and total nest success. The nest success of Group II (0.3015) was higher than that of Group I (0.2387), suggesting that deployment of TDL did not negatively influence nest survival rate of Emei Shan Liocichla. In contrast to traditional nest visits, TDL minimized disturbance by observers and provided a more precise estimate of nest survival. We suggest that TDL should be used more widely in studies of the breeding ecology of rare and endangered birds.