Seasonal Variation of Hearing Sensitivity in the Red-eared Slider(Trachemys scripta elegans)

Seasonal variation of hearing sensitivity has been observed in many vertebrate groups with obvious vocal behaviors.Circulating hormones,conspecific calling signals,and temperature are potential factors that drive these plasticity patterns.Turtles have a hearing range that appears to be limited to under 1.5 kHz and are often thought to be non-vocal;thus,they are commonly neglected in vocal communication research.In this study,we aimed to determine whether the auditory phenotype exhibits seasonal variation in sensitivity and to analyze the potential factors driving such variation patterns in turtles.We measured hearing sensitivity and sex hormone levels in female(estradiol)and male(testosterone and dihydrotestosterone)Red-eared sliders(Trachemys scripta elegans)during spring and winter.The results showed that auditory brainstem response(ABR)thresholds were significantly lower in spring than in winter at a frequency range of 0.5-0.9 kHz.The hearing-sensitivity bandwidth was wider,and the ABR latency was significantly shorter in spring than in winter.No significant differences were found in estradiol,testosterone,and dihydrotestosterone levels in T.scripta elegans between spring and winter.This study is the first to reveal the seasonal variation of peripheral hearing sensitivity in turtles,a special animal group with limited hearing range and less vocalization.Temperature variations may be used to explain these seasonal effects,but further research is required to confirm our findings.

Comparison of head size and bite force in two sister species of parrotbills

Background: Brain size is associated with morphological evolution and behavioral flexibility because animals with large brain size tend to utilize new resources and colonize novel environments more successfully.Therefore, animals with larger brain size should possess larger distribution ranges.Brain size is strongly positively correlated with head size in birds, but also with prey size and vocalizations, because individuals with large heads eat large food items and produce high frequency calls.Methods: To test if there exists an association between head morphology and bite performance, we compared head size and bite force in two sympatric sister species of parrotbills, Ashy-throated Parrotbill(Paradoxornis alphonsianus) and Vinous-throated Parrotbill(P.webbianus), which both originated from the Himalayan area, but differ significantly in their distribution ranges.Results: In Guizhou, southwestern China, the Ashy-throated Parrotbill with a restricted distribution range had smaller heads whilst the Vinous-throated Parrotbill with a large distribution range had larger heads.However, there were no differences in head size between Ashy-throated Parrotbills and allopatric populations of Vinous-throated Parrotbills(Jiangxi and Hebei).Furthermore, the tendency of variation in bite force was opposite to that in head size with populations with larger head size having weaker bite force.Conclusions: We showed that there are no differences in head size between the Ashy-throated Parrotbill and allopatric populations of Vinous-throated Parrotbill, which provides evidence for the hypothesis that differences in head size in the Guizhou populations of two sister species are probably the result of local adaptation rather than species-specific.Our study has implications for avian dispersal and adaption related to head size such as diet ecology and vocalizations.

Breeding ecology of two sympatric laughingthrushes(Trochalopteron milnei and Garrulax berthemyi)in southwestern China

Here we documented up-to-date information on breeding ecology of Buffy Laughingthrush(Garrulax berthemyi),an endemic species of China,and a sympatric coordinal Red-tailed Laughingthrush(Trochalopteron milnei),in southwestern China.Furthermore,we compared breeding ecology of these two sympatric species.No significant differences were found in clutch size,egg size,nest size,nest height,nest habitat and predation rate between these two species except nests depth,nests cover and eggs color.The Red-tailed Laughingthrush nestlings differed from those of the Buffy Laughingthrush in gape morphology and the extent of down.Observation of breeding behavior showed that cooperative breeding might exist in the population of Buffy Laughingthrush.

Nest-site fidelity and breeding dispersal by Common Tailorbirds in a tropical forest

Background:Information pertaining to nest-site fidelity and breeding dispersal over successive years can help to better our understanding of how birds respond to nest predation.Methods:By using mist nets and tracking the color banded individuals,we investigated nest-site fidelity and breeding dispersal by Common Tailorbirds(Orthotomus sutorius)throughout a year and between successive years in 2017–2018.Results:The present study showed that Common Tailorbirds could produce up to four clutches per breeding season.When multiple broods were produced within a year,breeding pairs remained together,and the nest rebuilding rate was up to 92.2%,with only four cases(7.8%)in which birds reused their old nests.The dispersal distance between the nests during multiple breeding was found to be 10.0±10.5 m,and nest-site fidelity within the same year was 90.0%.By the second year of breeding,76.2%of individuals remained in the original breeding pairs,while for those that did switch partners,the females remained in the nest from the previous year and paired with new males.The dispersal distance between years was 26.5±41.9 m,and nest-site fidelity between different years was 80.1%.There was no significant difference between within-year and between-year dispersal distances.Moreover,there was no significant difference in the dispersal distance of rebuilt nests between birds that had experienced nest predation and those that had not.Conclusions:Our findings suggest that Common Tailorbirds maintain a high degree of fidelity to mates and nestsites,and nest predation had no significant effect on territorial changes or breeding dispersal distance between each breeding attempt.

The effects of anthropogenic noise on nest predation with respect to predator species across different habitats and seasons

Noise pollution is a maj or component of sensory pollution that can disrupt the well-being and functioning of living organisms,affect a variety of life history traits in animals,and reduce their reproductive success.In this study,we used artificial nest experiments with noise manipulation to investigate the influence of anthropogenic noise on nest predation during the breeding and non-breeding seasons and in different forest habitats.We found that the noise treatment did not alter the predation rates or survival probabilities of birds in artificial nests.However,the diversity and species composition of nest predators in artificial pine forests varied between breeding and nonbreeding seasons,which may be explained by season-specific adaption of nest predators to bird nests or the unstable ecosystems of artificial forests.The diversity and species composition of nest predators differed between the different forests,probably because of differences in habitat heterogeneity.Predation time varied with treatment,season,and habitat,although most predators were nocturnal mammals.Niche segregation or changes in optimal foraging time may explain this phenomenon.

Chromatic and achromatic differences of melanin-and carotenoid-based plumage coloration in five minivet species(Pericrocotus spp.)under conspecific and predator visual systems

Adaptive mate choice has been accepted as the leading theory to explain the colorful plumage of birds.This theory hypothesizes that conspicuous colors act as signals to advertise the qualities of the owners.However,a dilemma arises in that conspicuous colors may not only attract mates,but also alert predators.The"private channels of communication"hypothesis proposes that some intraspecific signals may not be visible to heterospecific animals because of different visual systems.To better understand the evolution of plumage colors and sexual selection in birds,here we studied the chromatic difference and achromatic differences of melanin-and carotenoid-based plumage coloration in five minivet species(Pericrocotus spp.)under conspecific and predator visual systems.We found that either the chromatic or achromatic difference among male or female minivets’plumage was consistently higher under conspecific vision than under predator vision for all five studied species of minivets.This result indicated that individual differences in plumage colors of minivets were visible to the conspecific receivers and hidden from potential predators as a result of evolution under predation risk and conspecific communication.However,males were under a higher risk of predation because they were more conspicuous than females to the vision of a nocturnal predator.

Seasonal increase in nest defense,but not egg rejection,in a cuckoo host

The interactions between avian brood parasites and their hosts provide an informative and easy-to-handle system for studying coevolution.Avian brood parasitism reduces the reproductive success of hosts,and thus,hosts have evolved anti-parasitic strategies,such as rejecting parasitic eggs and adopting aggressive nest defense strategies,to avoid the cost brought on by brood parasitism.To test whether host anti-parasitic strategies are adjusted with the risk of being parasitized when the breeding seasons of brood parasites and hosts are not synchronous,we conducted a field experiment assessing nest defense and egg recognition behaviors of the Isabelline Shrike(Lanius isabellinus),a host of the Common Cuckoo(Cuculus canorus).In the local area,the host Isabelline Shrike begins to breed in April,whereas the summer migratory Common Cuckoo migrates to the local area in May and begins to lay parasitic eggs.Results showed that nest defense behaviors of the Isabelline Shrike increases significantly after cuckoo arrival,showing higher aggressiveness to cuckoo dummies,with no significant difference in attack rates among cuckoo,sparrowhawk and dove dummies,but their egg rejection did not change significantly.These results imply that Isabelline Shrikes may adjust their nest defense behavior,but not egg rejection behavior,with seasonality.

Nest decoration:Black feathers prevent Crested Mynas from nest usurpation

Nests are important structures for birds to raise their offspring and for signaling.Many birds incorporate feathers into the nest,since feathers were traditionally thought to serve the function of insulation.Hypotheses in recent years have considered that some birds place feathers in conspicuous locations in the nest for decoration to trigger a fear response in the competitors.In this study,we investigated whether decorative feathers could deter nest usurpation by Crested Mynas(Acridotheres cristatellus)by manipulating nest box contents.The results revealed that Crested Mynas preferred black feathers to white feathers as decorations and occupied nest boxes decorated with black feathers significantly less than those decorated with white feathers,suggesting that black decorative feathers in the nest could be more effective in preventing nest usurpation by Crested Mynas and that white decorative feathers may have other functions.The black feathers in the nest are prominently placed at the edge of the nest to convey the message that“this nest is occupied”or“the owner of this nest has been preyed upon”to visitor Crested Mynas,thus effectively preventing them from usurping the nest at a later stage.

Hawk mimicry does not reduce attacks of cuckoos by highly aggressive hosts

Background: Resemblance to raptors such as hawks(Accipiter spp.) is considered to be an adaptive strategy of cuckoos(Cuculus spp.), which has evolved to protect cuckoos against host attacks. However, the effectiveness of the mimicry remains controversial, and is not yet fully studied for highly aggressive hosts.Methods: We evaluated the effectiveness of sparrowhawk(Accipiter nisus) mimicry by common cuckoos(Cuculus canorus) in oriental reed warblers(Acrocephaus orientalis), which are highly aggressive hosts. Using a both the single and the paired dummy experiment, defense behaviors and attack intensities of oriental reed warblers against common cuckoos, sparrowhawks and oriental turtle doves(Streptopelia orientalis) were assessed.Results: Oriental reed warblers exhibit strong nest defense behaviors, and such behaviors do not change with breeding stage(i.e., egg stage and nestling stage). Furthermore, assistance from conspecific helpers may increase attack intensities. However, they were deterred from mobbing overall by the presence of the hawk.Conclusions: Oriental reed warblers are able to distinguish cuckoos from harmless doves. However, they may be deterred from mobbing by the presence of the predatory hawk, suggesting hawk mimicry may be ineffective and does not reduce attacks of cuckoos by highly aggressive hosts.

High egg rejection rate in a Chinese population of grey-backed thrush(Turdus hortulorum)

Several previous studies have indicated that nest sanitation behavior is a general adaptation in altricial birds,with egg recog nition capacity evolvi ng as a specific response to in terspecific brood parasitism(IBP).However,a rece nt study suggested an alternative hypothesis,con cludi ng that con specific brood parasitism(CBP)selects for egg rejection in thrushes,with IBP as a by-product.In the present study,we used a spectrophotometer to quantify egg coloration and egg mimicry and performed artificial parasitism experiments in the grey?backed thrush(Turdus hortulorum).We showed that individuals of this species rejected 100%of 12 foreign eggs,without IBP or CBP detected.In a review of previous studies,we also discuss possible explanations for the high egg rejection rate in the grey-backed thrush and suggest areas for future study.Altricial birds have evolved advaneed reproductive behavior to in crease the fitn ess of their offspring by buildi ng elaborate structures(i.e.,nests),in which they lay eggs and rear their nestlings(Hansell,2000).Bird nests not only provide a suitable place for nestling development,but also act as a concealed location for safety from predators.Furthermore,bird parents have evolved nest sanitation behavior to clean foreig n objects from their n ests,in eluding feces,eggshells,branches,and leaves,because they induce predation,facilitate microorganism growth,damage eggs,or hurt nestlings during brooding(Guigueno&Sealy,2012).Therefore,nest sanitation has evolved as a general behavior in altricial birds for distinguishing between egg-shaped and non-egg-shaped objects.

Function of note strings in Japanese Tit alarm calls to the Common Cuckoo:a playback experiment

Background: Birds produce alarm calls to convey information about threats. Some Passerine alarm calls consist of several note strings, but few studies have examined their function. Previous studies have shown that Japanese Tits(Parus minor) can alter the calling rate and number and combination of notes in response to predators. We previously found the combinations of note types in Japanese Tit alarm calls to be significantly different in response to the Sparrowhawk(Accipiter nisus) and Common Cuckoo(Cuculus canorus).Methods: Through playback experiments, we tested whether the note strings in Japanese Tit alarm calls to the Common Cuckoo have different functions in conveying information. The note strings of selected alarm calls were divided into the categories of C and D, and different calls were then constructed separately based on the two note string categories. Original alarm calls(C–D), C calls and D calls were played back to male Japanese Tits during the incubation period.Results: Male Japanese Tits had a significantly stronger response to C calls than to C–D calls, and they showed a significantly stronger response to both C and C–D calls than to D calls, suggesting that Japanese Tits discriminated between the C and D calls.Conclusions: Our study demonstrated that the C-and D-category note strings of Japanese Tit alarm calls to the Common Cuckoo have different functions, which supports the previous finding that different note strings in an alarm call can provide different information to receivers. However, the exact meanings of these note strings are not yet known, and further investigation is therefore required.

The Relationship between Shell Morphology and Crevice Size Affecting Retreat Selection of the Keeled Box Turtle(Cuora mouhotii)

Rock crevices are important retreat sites for many reptiles.Unlike lizards and snakes,crevicedwelling turtles have rigid shells which severely limit the size and shape of crevices they are able to use.Few studies have addressed the relationship between turtle's shell morphology,behavior,and crevice size.Here,we investigate the relationship between morphology and crevice size selection in the Keeled box turtle(Cuora mouhotii).We radio tracked turtles in the field to document crevice dimensions and turtle behavior associated with crevices,and we conducted a controlled experiment in the lab to understand how a turtle's morphology influences its decision to select crevices with different dimensions.Both laboratory and field experiments demonstrate that turtles select deep and moderately wide crevices that are low enough to barely accommodate the carapace.Crevices used by turtles tend to be about 2 times as wide,1.2 times as high,and 3 times longer than the turtle's shell.Moreover,turtles tended to prefer crevices with horizontal openings in the field and position themselves head first in the crevice.We conclude that morphology,especially carapace height,influences the Keeled box turtles' decision to select specific sizes of crevice.We argue that the tendency for turtles to select crevices that come into contact with their carapace contributes to successful defense against predators,as it would be more difficult for a predator to remove a turtle when the crevice is nearly touching the turtles shell.

Egg laying behavior of common cuckoos(Cuculus canorus): Data based on field video-recordings

DEAR EDITOR,The egg laying behavior of brood parasites is at the heart of studies on host co-evolution.Therefore,research on egg laying behavior can improve our understanding of brood parasitism and associated processes.Over a seven year study period,we monitored 455 oriental reed warbler(Acrocephalus orientalis)nests during the egg laying period,250 of which were parasitized by common cuckoos(Cuculus canorus).We collected 53 clear videos of common cuckoo parasitism,analyzed all recorded parasitic behavior in detail.

Egg recognition abilities of tit species in the Paridae family:do Indomalayan tits exhibit higher recognition than Palearctic tits?

DEAR EDITOR,Recent studies have shown that the closely related cinereous tit(Parus cinereus)and green-backed tit(P.monticolus)in China display strong egg recognition ability in contrast to tit species in Europe,which lack such ability.However,egg recognition in other populations of cinereous and greenbacked tits and additional Paridae species still requires further research.

Breeding biology of the Green-backed Tit(Parus monticolus)in southwest China

Studies on breeding biology enable us to broaden our understanding of the evolution of life history strategies.We studied the breeding biology of the Green-backed Tit(Parus monticolus)to provide comprehensive data on nest and egg characteristics,parental behavior throughout egg laying and nestling periods,and reproductive outcome.Our study reveals adaptive behavioral patterns and reproductive strategies for P.monticolus.

Responses of cuckoo hosts to alarm signals of different nest intruders in non-nesting areas

DEAR EDITOR,The“call for help”hypothesis proposes that alarm calls produced by a bird can transmit warning information to both conspecific and interspecific neighbors.Neighbors who are attracted by social transmission might benefit from knowing about the presence of danger or by gaining information about the presence of predators or brood parasites nearby.Brood parasite hosts can distinguish threats from different intruders and exhibit varied responses correspondingly.

A new snake species of the genus Gonyosoma Wagler,1828(Serpentes:Colubridae)from Hainan Island,China

A new species of the genus Gonyosoma Wagler,1828 is described herein based on six specimens from the Diaoluoshan Mountains,Hainan Island,Hainan Province,China.The new species,Gonyosoma hainanense sp.nov.,is most similar to its continental sister species,Gonyosoma boulengeri(Mocquard,1897).Both taxa have a scaled protrusion on the anterior portion of the rostrum,distinct from other congeners.However,Gonyosoma hainanense sp.nov.can be distinguished from G.boulengeri by two significant morphological characters:(1)black orbital stripe absent in adults(vs.present in G.boulengeri);and(2)two loreals(vs.one loreal in G.boulengeri).The new species is also genetically divergent and forms a unique clade from its sister species and all other congeners based on sequences of the mitochondrial gene cytochrome b(cyt b).

Development and behavior of Plaintive Cuckoo(Cacomantis merulinus) nestlings and their Common Tailorbird(Orthotomus sutorius) hosts

Background:Our knowledge of avian brood parasitism is primarily based on studies of a few selected species.Recently,researchers have targeted a wider range of host–parasite systems,which has allowed further evaluation of hypotheses derived from well-known study systems but also disclosed adaptations that were previously unknown.Here we present developmental and behavioral data on the previously undescribed Plaintive Cuckoo(Cacomantis merulinus) nestling and one of its hosts,the Common Tailorbird(Orthotomus sutorius).Methods:We discovered more than 80 Common Tailorbird nests within an area of 25 km2,and we recorded nestling characteristics,body mass,tarsus length and begging display every 3 days for both species.Results:Plaintive Cuckoo nestlings followed a developmental pathway that was relatively similar to that of their well-studied relative,the Common Cuckoo(Cuculus canorus).Tailorbird foster siblings were evicted from the nest rim.The cuckoo nestlings gained weight faster than host nestlings,and required 3–9 days longer time to fledge than host nestlings.Predation was high during the early stages of development,but the nestlings acquired a warning display around 11 days in the nest,after which none of the studied cuckoo nestlings were depredated.The cuckoos' begging display,which appeared more intense than that of host nestlings,was initially vocally similar with that of the host nestlings but began to diverge from the host sound output after day 9.Conclusions:The developmental data on Plaintive Cuckoo nestlings and their tailorbird host builds an important foundation for future work on the co-evolutionary interactions in this parasite–host system.

Determining the level of extra-pair paternity in yellow-bellied prinias,a socially monogamous passerine

DEAR EDITOR,Previous work based on molecular evidence has shown that most socially monogamous birds follow a genetic polyandrous mating system.However,our knowledge about avian mating systems is heavily biased toward the north temperate zone,with data on tropical birds remaining relatively scarce.This uneven distribution of both phylogenetic and spatial sampling has hampered our understanding and interpretation of results.In this study,we investigated the frequency of extra-pair paternity(EPP)in a tropical population of yellow-bellied prinias(Prinia flaviventris)in Guangxi,southern China.A total of 129 individuals belonging to 24 nests were sampled,among which 12 out of 83 chicks(14.46%)in seven nests were found to be EPP offspring.In nests in which all nestlings were sampled,only five out of 56 chicks were EPP offspring,accounting for an unbiased EPP rate of 8.93%.This rate is below the average rate of EPP in the family Sylviidae.The possible causes of EPP in prinias and the occurrence of EPP in birds with high resource investment and intensive parental care are discussed.This study highlights the value of genome-wide markers in determining relatedness in a wild bird species without a reference genome.

Effect of Morphology and Age on the Closure Ability of Asian Box Turtles(Cuora)

The ability of box turtles to close their shell as an antipredation adaptation and the potential impact of the anterior and posterior lobes of the plastron on the closing force and closing time remain relatively unexplored.Here,keeled(Cuora mouhotii)and flowerback(C.galbinifrons)box turtles,whose shell cannot and can be completely closed,respectively,were studied.Anterior and posterior closing forces were measured using a force transducer,and the closing time was recorded.The anterior closing force in both turtle species was substantially greater than the posterior closing force,reaching approximately 4-fold in adults.Moreover,the anterior closing time in adults was significantly longer than the posterior closing time.This closing force difference can be attributed to the substantially smaller anterior plastron lobe than the posterior lobe in the two species.Additionally,the anterior and posterior closing forces in both species positively correlated with body weight and showed no relationship with the length of the bridge and hinge.Interspecies comparison showed that the anterior and posterior closing forces were significantly greater(approximately 2–4-fold)in flowerback box turtle than in keeled box turtles,regardless of age,and the closure time was significantly longer in adult flowerback box turtles than in adult keeled box turtles.Although the closing forces in both species showed negative allometry,the increase rate was significantly higher in flowerback box turtle than in keeled box turtle.The closing forces in both species were observed to be approximately 4-fold stronger in adults than in juveniles.No sexual dimorphism concerning the anterior and posterior closing forces was observed in either species.In summary,this is the first study to comparatively evaluate the anterior and posterior closing ability of box turtles,demonstrating that age,weight,plastron shape,and the degree of shell closure are important factors affecting closing ability.