大山雀身体大小的性二态及其季节变化

动物中普遍存在雌雄个体身体大小的性二态现象。了解近缘种之间身体大小性二态现象的差异，可为深入探讨身体大小性二态现象的潜在驱动机制提供证据。国外对欧亚大山雀（Parus major）的研究发现，其喙长、跗跖长、翅长等 6 项身体大小指标存在着明显的性二态，且喙长的性二态存在季节间差异。大山雀（P. cinereus）曾被作为欧亚大山雀的一个亚种，其形态和行为与欧亚大山雀存在着诸多相似之处。为探讨大山雀是否也存在身体大小性二态及季节性差异，本研究分析了 2018 至 2020 年间在河南董寨国家级自然保护区捕捉的 226 只（雌性 96 只和雄性 130 只）大山雀的喙长、头喙长、跗跖长、翅长、尾长和体长这 6 项体征指标的两性差异及其季节变化。结果显示，大山雀上述 6 项身体大小指标均存在不同程度的性二态现象，且雄性个体仅喙长与雌性的差异不显著，其余 5 项指标均显著大于雌性。此外，身体大小指标的两性差异不随季节显著变化，但两性的跗跖长在秋季均显著短于冬季和繁殖季，尾长在繁殖季均显著长于秋季和冬季。上述结果表明，大山雀身体大小的性二态及其季节性差异与欧亚大山雀并不完全相似。无论其身体大小存在性二态和季节变化的原因，还是其与欧亚大山雀在身体大小性二态模式上的差别，都有待今后进一步的研究。     

Offspring sex ratio is related to male body size in the great tit (Parus major)

Sex allocation theory predicts that the allocation of resourcesto male and female function should depend on potential fitnessgain realized through investment in either sex. In the greattit (Parus major), a monogamous passerine bird, male resourceholdingpotential (RHP) and fertilization success both depend on malebody size (e.g., tarsus length) and plumage traits (e.g., breaststripe size). It is predicted that the proportion of sons ina brood should increase both with male body size and plumage traits,assuming that these traits show a father—offspring correlation. Thiswas confirmed in our study: the proportion of sons in the brood increasedsignificantly with male tarsus length and also, though not significantly,with the size of the breast stripe. A sex ratio bias in relationto male tarsus length was already present in the eggs because(1) the bias was similar among broods with and without mortalitybefore the nestlings' sex was determined, and (2) the bias remainedsignificant when the proportion of sons in the clutch was conservativelyestimated, assuming that differential mortality before sex determinationcaused the bias. The bias was still present among recruits.The assumption of a father—offspring correlation was confirmedfor tarsus length. Given that both RHP and fertilization successof male great tits depend on body size, and size of father andoffspring is correlated, the sex ratio bias may be adaptive.     

Blue Tit song repertoire size, male quality and interspecific competition

A recent hypothesis suggested that bird song repertoire size is a reliable indication of male quality because the number of songs emitted by an individual and the expression of many traits important for fitness are highly dependent on developmental conditions. To test this hypothesis, we studied the relationship between song repertoire size and a trait known to be strongly affected by developmental conditions: tarsus length of Blue Tits Parus caeruleus . We studied this relationship in three populations presenting differences in density, quantity of food available and relative and absolute densities of Great Tits Parus major . Great Tit density may be an important factor because this species is supposed to be in competition for acoustic space with the Blue Tit. We found a positive correlation between Blue Tit dawn repertoire size and tarsus length in the three study populations which is consistent with the tested hypothesis. However, this correlation was only significant in the population with the lower Great Tit density. We discuss the significance of this variation and propose that interspecific competition may limit the action of sexual selection on song repertoire size.     

Strong but variable associations between social dominance and clutch sex ratio in a colonial corvid

We studied primary sex ratio of clutches in relation to socialdominance for 6 years in a colony of free-living jackdaws, asmall corvid. Social dominance was strongly associated withclutch sex ratio, with the difference in clutch sex ratio betweenthe most and least dominant pairs being 30–40%. To ourknowledge, this is the first demonstration of an associationbetween social dominance and sex allocation in birds. However,the direction of this effect varied between years. Dominantjackdaws produced more sons during the first years of the studybut fewer sons during the last years. Offspring sex was notrelated to laying order within a clutch, and the effect of socialdominance on sex ratio was similar on eggs laid first, middle,or last. We investigated the effect of 2 factors (laying dateand parental condition) that could have mediated the shift inthe effect of social dominance on sex allocation in the courseof the study. Laying date was positively associated with theproportion of males, but this effect was independent of socialdominance. Maternal condition (residual mass over tarsus andegg volume) was related to social dominance but not to clutchsex ratio. Paternal condition (residual mass over tarsus) wasnot related to clutch sex ratio. We discuss how spatial or temporalvariation in effects of variables such as social dominance onsex allocation can contribute to our understanding of the evolutionof sex allocation in species with complex life histories.     

Paraphyly of the Blue Tit (Parus caeruleus) suggested from cytochrome b sequences

The phylogenetic relationships of the Blue Tit-Azure Tit assemblage (genus Parus; Aves: Passeriformes) were studied using mitochondrial DNA sequences of 24 specimens representing seven subspecies from Eurasia and North Africa. Previous work based on comparative morphological and acoustic data suggested a division of the Blue Tit (Parus caeruleus) into two species. Our analyses clearly indicate that the Blue Tit represents a paraphyletic assemblage, including a European/Middle Asian clade that is the sister group to the Azure Tit (Parus cyanus) and a North African clade. The North African clade (teneriffae subspecies group) is a sister group to the European Blue Tit/Azure Tit clade. We suggest a division of the Blue Tit into two separate species, Eurasian Blue Tit (Parus caeruleus s. str.) and African Blue Tit (Parus teneriffae). However, our data give no support for assigning species rank to Parus cyanus flavipectus, a subspecies of the Azure Tit, as suggested by several authors on morphological grounds.     

Sex ratio and male sexual characters in a population of blue tits, Parus caeruleus

Sex allocation theory proposes that parents should bias thesex ratio of their offspring if the reproductive value of onesex is greater than that of the other. In the monogamous bluetit (Parus caeruleus), males have a greater variance in reproductivesuccess than females, and high-quality males have higher reproductivesuccess than high-quality females due to extrapair paternity.Consequently, females mating with attractive males are expectedto produce broods biased toward sons, as sons benefit more thandaughters from inheriting their father's characteristics. Songand plumage color in birds are secondary sexual characters indicatingmale quality and involved in female choice. We used these malesexual traits in blue tits to investigate adaptive sex ratiomanipulation by females. We did not find any relationship betweenmale color ornamentation and brood sex ratio, contrary to previousstudies. On the other hand, the length of the strophe bout (i.e.,the mean number of strophes per strophe bout) of fathers waspositively related with the proportion of sons in their broods.The length of the strophe bout is supposed to reflect male qualityin terms of neuromuscular performance. We further showed thatsons produced in experimentally enlarged broods had shorterstrophe bouts than sons raised in reduced broods. These resultsare consistent with the hypothesis that females adjust the sexratio of their broods in response to the phenotype of theirmate.     

Breeding upwards when climate is becoming warmer: no bird response in the French Alps

Altitudinal shifts in distribution were investigated in forest breeding birds, along two elevational gradients in the French northern and southern Alps, from counts repeated at exactly the same locations in the 1970s and the 2000s. Significant shifts were reported for eight of 24 species in the northern alpine site (five downwards, three upwards) and for two of the 17 species in the southern site (one downwards, one upwards). Apart from the Crested Tit Parus cristatus , which shifted significantly downwards at both sites, altitudinal shifts were not significantly correlated between sites. Bird communities did not shift their distribution upwards despite a 2.3 °C increase in spring temperatures in the two study areas. These results suggest that bird distributions by altitude have not yet been affected by climatic warming, and that most specific elevational shifts are probably related to site-specific factors.     

Offspring sex ratio in the sequentially polygamous Penduline Tit Remiz pendulinus

Despite the growing literature on facultative sex-ratio adjustment in chromosomal sex-determining vertebrate taxa (birds, mammals), the consistency of results is often low between studies and species. Here, we investigate the primary and secondary offspring sex ratio of a small passerine bird, the Eurasian Penduline Tit (Remiz pendulinus) in three consecutive years. This species has a uniquely diverse breeding system, in which the male (and/or the female) abandons the nest during egg-laying, and starts a new breeding attempt. This allowed us to test (1) whether patterns of parental care, i.e., male-only care, female-only care or biparental desertion, influence offspring sex ratio, and (2) whether the offspring sex ratio is repeatable between successive clutches of males and females. Using molecular markers to sex 497 offspring in 176 broods, we show that (1) offspring sex ratio does not depend on which parent provides care, and (2) the offspring sex ratio is not repeatable between clutches of a given individual. The overall primary and secondary offspring sex ratio at a population level is not different from parity (54 ± 6% males, and 50 ± 3% (mean ± SE), respectively). We suggest that ecological and phenotypic factors, rather than individual traits of parents, may influence offspring’s sex, and conclude that there is currently no evidence for a facultative adjustment of offspring sex ratio in the Penduline Tit.     

Sex allocation according to multiple sexually dimorphic traits of both parents in the barn swallow (Hirundo rustica)

Parents should differentially invest in sons or daughters depending on the sex‐specific fitness returns from male and female offspring. In species with sexually selected heritable male characters, highly ornamented fathers should overproduce sons, which will be more sexually attractive than sons of less ornamented fathers. Because of genetic correlations between the sexes, females that express traits which are under selection in males should also overproduce sons. However, sex allocation strategies may consist in reaction norms leading to spatiotemporal variation in the association between offspring sex ratio (SR) and parental phenotype. We analysed offspring SR in barn swallows (Hirundo rustica) over 8 years in relation to two sexually dimorphic traits: tail length and melanin‐based ventral plumage coloration. The proportion of sons increased with maternal plumage darkness and paternal tail length, consistently with sexual dimorphism in these traits. The size of the effect of these parental traits on SR was large compared to other studies of offspring SR in birds. Barn swallows thus manipulate offspring SR to overproduce ‘sexy sons’ and potentially to mitigate the costs of intralocus sexually antagonistic selection. Interannual variation in the relationships between offspring SR and parental traits was observed which may suggest phenotypic plasticity in sex allocation and provides a proximate explanation for inconsistent results of studies of sex allocation in relation to sexual ornamentation in birds.     

Do Great Tit Parus major parents gear their brood defence to the quality of their young?

Parental investment theory suggests that animals should increase their reproductive success by investing more heavily in higher-quality offspring than in lower-quality offspring. Great Tit Parus major nestlings of higher body weight have been shown to enjoy a higher survival rate after fledging. We examine for the first time whether Great Tit parents invest more heavily in heavier nestlings as measured by defence (six variables) against a Pygmy Owl Glaucidium perlatum, similar to G. passerinum, which is a predator of both adult and nestling birds including hole-nesters like the Great Tit. Thirty-two parent Great Tit pairs in a wood- and parkland study area in Essen-Stadtwald did not vary their antipredator behaviour in relation to nestling weight; between-brood variation of weight was similar to that found in different populations and in different years. However, parental defence behaviour varied, as expected, with parent's sex and nestling number, though overall responsivity of parents to many other independent variables appeared lower than found previously.     

Lack of Sex-Biased Maternal Investment in spite of a Skewed Birth Sex Ratio in White-Headed Langurs (Trachypithecus leucocephalus)

Numerous hypotheses have been developed to explain sex allocation. In male-dispersing, female cooperatively breeding species, the local resource competition model predicts male-biased birth sex ratio, the local resource enhancement model predicts female-biased birth sex ratio, and the population adjustment model predicts that biased birth sex ratio should not be favored if the two sexes are equally costly to rear. The male quality model predicts that, in polygynous species, females in better physical condition will either produce more sons than daughters or invest more heavily in sons than in daughters. White-headed langurs are a female philopatry and female cooperatively breeding species. During a 11-yr study, a total of 133 births were recorded, among which birth sex ratio (M:F = 73:49) was significantly male-biased. This is consistent with the prediction of the local resource competition model. On the other hand, if mothers balanced their investment between the two sexes, according to Fisher's population adjustment model, males should be the less-costly-to-rear sex. However, we found no sex difference for infant mortality (12.3% in males and 12.2% in females), and sons induced slightly longer interbirth interval (son: 26.4 ± 1.1 mo, daughter: 24.1 ± 0.6 mo) and lactational period (son: 20.9 ± 1.0 mo, daughters: 19.6 ± 0.5 mo) for their mothers. Thus, the population adjustment model was not supported by this study. The local resource enhancement model was not supported because birth sex ratio did not bias to females who provided more reproductive assistance. On the individual level, probit regression showed no relation between birth sex ratio and group size. Because the group size was considered to be negatively related to female physical condition, our study did not support the male-quality model. We suggested several possibilities to explain these results.     

Is variation in brood sex ratios adaptive in the great tit (Parus major)?

Life-history theory predicts skewed offspring sex ratios ina range of situations in which the costs and benefits of producingthe two sexes differ. In recent years, many studies have demonstratedbiased sex ratios in a variety of bird species. However, manyof these investigations have been based on small sample sizes,on data from a single year, or both. Using a recently developedpolymerase chain reaction-based molecular DNA technique, 912great tit (Parus major) nestlings from 118 broods in 5 differentyears were sexed. As found in a number of previous studieson the same species, there were significant predictors of offspringsex ratio in individual years. However, there were no consistenttrends across years, and none of the measured variables significantlypredicted sex ratio over all years combined. Furthermore, broodsex ratio of the population did not depart from the expectedbinomial distribution. Although there are theoretical advantagesto manipulating the sex ratio in this and other species, thephysiological mechanism by which it is achieved in birds remainsobscure. We argue that data from several years are needed toconfirm whether facultative sex ratio manipulation is a consistentbreeding strategy used by birds.     

Male-biased sex ratio among unhatched eggs in great tit Parus major, blue tit P. caeruleus and collared flycatcher Ficedula albicollis

An increasing number of studies have demonstrated that brood sex ratios are frequently unequal, but the proximate mechanisms underlying this deviation are largely unknown. In the current study we analysed deviation from expected 1:1 sex ratio among dead embryos from unhatched eggs collected from partially unhatched clutches of three passerine bird species. We showed that male embryos were significantly overrepresented among unhatched eggs of great tit Parus major , blue tit P. caeruleus and collared flycatcher Ficedula albicollis . Moreover, the bias in sex ratio differed among species and tended to differ among study years. We discuss several hypotheses to explain the observed male bias among unhatched eggs. We conclude that sex specific embryo mortality may contribute to explain the observed variation in sex ratios in several species of wild birds and that sexing unhatched eggs is important in studies of sex ratio allocation.     

DIFFERENTIATION OF FORAGING NICHE AMONG TITS, PARUS SPP., IN NORWAY DURING WINTER

The winter foraging behaviour of Willow Tit Parus montanuss, Coal Tit P. ater and Crested Tit P. cristatus was studied in several spruce-dominated, coniferous forest areas in which either Willow Tit alone, Willow Tit and Coal Tit, or all three species together were present. In the areas where Crested Tits were absent, Willow Tits foraged significantly more often in the outermost parts of spruce branches and less frequently on the parts of branches closer to the trunk, than in the area in which Crested Tits were present. In the area in which all three species were present, the same change in foraging pattern of Willow Tits was found in mixed flocks in which Crested Tits were lacking. The foraging pattern of Coal Tits was unaffected by the presence of members of either or both the other two tit species. It is suggested that the expansion of the feeding niche of Willow Tit in the absence of Crested Tit is a result of ecological release, due to a reduction in the degree of interspecific competition.     

Pair bond and breeding success in Blue Tits Parus caeruleus and Great Tits Parus major

Data from 939 nests of the Blue Tit Parus caeruleus and 1008 nests of the Great Tit P. major from nestboxes provided in superabundance in mixed forest study sites between 1976 and 2001 were analysed to examine the effects of mate retention on breeding success and the relationship between mate fidelity and site fidelity. Most birds retained their former partner (76% in Great Tits and 65% in Blue Tits). The probability of a pair divorcing was affected by male age in Great Tits, divorce being more likely in pairs with first‐year males. Great Tit pairs breeding together for a second season bred earlier, but had no higher breeding success than pairs breeding together for the first time. In Blue Tits laying date and start of incubation tended to be earlier in pairs breeding together for a second season, but hatching and fledging dates were not earlier than in other pairs. Great Tit pairs breeding together for two consecutive seasons bred earlier in the second season than in the first, but breeding success did not differ significantly between years. In both species, breeding performance did not differ between pairs that divorced after a season and pairs that stayed together. Thus breeding success did not determine whether a pair divorced or bred together again. Neither Blue Tits nor Great Tits improved their breeding performance through divorce. Blue Tit females even had fewer fledglings in the year after divorce than in the year before. Mate retention affected breeding site fidelity. Blue Tit females had greater breeding dispersal distances between consecutive years when re‐mating than when breeding again with the same mate. In Great Tits both males and females dispersed more when re‐mating than when retaining the former partner, suggesting that mate retention increased the chance of retaining the breeding site. In both species, breeding dispersal distances did not differ between pairs that divorced and pairs in which one mate disappeared. Because no major advantage of mate retention was evident, we suggest that mate retention evolved under different conditions than those found in study sites with high breeding densities and a superabundance of artificial nesting sites.     

Primary sex ratio adjustment to experimentally reduced male UV attractiveness in blue tits

The study of primary sex ratio adjustment in birds is notoriousfor inconsistency of results among studies. To develop our understandingof avian sex ratio variation, experiments that test a prioripredictions and the replication of previous studies are essential.We tested if female blue tits Parus caeruleus adjust the sexratio of their offspring to the sexual attractiveness of theirmates, as was suggested by a previous benchmark study on thesame species. In 2 years, we reduced the ultraviolet (UV) reflectanceof the crown feathers of males in the period before egg layingto decrease their attractiveness. In contrast to the simpleprediction from sex allocation theory, we found that the overallproportion of male offspring did not differ between broods ofUV-reduced and control-treated males. However, in 1 year, theUV treatment influenced offspring sex ratio depending on thenatural crown UV reflectance of males before the treatment.The last result confirms the pattern found in the previous bluetit study, which suggests that these complex patterns of primarysex ratio variation are repeatable in this bird species, warrantingfurther research into the adaptive value of blue tit sex ratioadjustment to male UV coloration.     

基于形态特征判定五种鹬类性别的可靠性

快速准确地鉴定两性同型鸟类个体性别在鸟类生态学研究中具有重要意义。本文选择2008年春季迁徙期在崇明东滩停歇的大滨鹬(Calidris tenuirostris)、红腹滨鹬(C.canutus)、红颈滨鹬(C.ruficollis)、尖尾滨鹬(C.acuminata)及翘嘴鹬(Xenus cinereus)5种两性同型的鹬类,用分子生物学方法进行性别鉴定,并基于个体的形态特征(体重、翅长、喙长、头喙长及跗跖长)采用判别分析方法对性别进行判定。结果表明,尖尾滨鹬雄性各形态特征均显著大于雌性,其他4种鹬类则相反。5种鹬类形态特征的性别差异指数在0.5%~25.3%之间,重叠度在29.4%~98.6%之间。5种鹬类判别分析判定性别的准确率在(0.69±0.06)~(0.96±0.01)之间,其中,尖尾滨鹬判别准确率(0.96)最高,翘嘴鹬判别准确率(0.69)最低。形态特征在两性间的差异程度影响性别的判别准确率。另外,两性性比对性别判别的准确率也有影响:性比偏雄性鸟类的雄性判别准确率高于雌性,而性比偏雌性鸟类的雌性判别准确率高于雄性。采用判别分析估测的性比与分子生物学鉴定结果相似,表明判别分析在判定种群的性比方面具有较高的可靠性。     

Prey distribution,foliage structure,and foraging behavior of insectivorous birds in two oak species (<Emphasis Type="Italic">Quercus serrata</Emphasis> and <Emphasis Type="Italic">Q. variabilis</Emphasis>)

We examined foraging behaviors of four insectivorous bird species (Great Tit Parus major, Varied Tit P. varius, Long-tailed Tit Aegithalos caudatus and Japanese White-eye Zosterops japonica) on the two oak species (Q. serrata and Q. variabilis) in relation to fine-scale foliage structures, abundance, and distribution of folivorous insects and physical and chemical characteristics of leaves. There was no difference in the mean number of insects for each oak species, but there was a significant difference in the mean biomass. The distance from twigs or branches to leaf tips or blade-petiole junctions showed that leaves of Q. variabilis were more dispersed than those of Q. serrata. The different size distribution of insects influenced insect sizes selected and foraging maneuvers used by each bird species. Parus major and P. varius fed on beetles (low energy gain) with perch-gleaning (the most energy-saving maneuver) from the upper side of leaves on Q. variabilis, whereas they fed on large lepidopteran larvae (high energy gain) from the lower side of leaves on Q. serrata using a variety of maneuvers (including energy-consuming ones). Both A. caudatus and Z. japonica fed on insects from the lower side of leaves by hang-gleaning and reach-gleaning, respectively. These species appeared to be morphologically adapted to the energy-consuming but more effective maneuvers used to take preys from the undersides of leaves. We hypothesize that differences in foliage structures between closely related species of trees have evolved as a balance between defense against folivorous insects and attraction of insectivorous birds.     

Mothers under stress? Hatching sex ratio in relation to maternal baseline corticosterone in the common tern (Sterna hirundo)

Sex ratio of progeny should be balanced if costs and benefits of rearing sons and daughters are equal. However, shifts in sex ratio have been demonstrated across bird species and it was suggested that females are able to adjust the primary sex ratio. One possible mechanism is the glucocorticoid corticosterone which rises under stressful conditions and can be deposited into egg yolk by mothers. We analysed primary sex ratio of common terns Sterna hirundo from 2006 to 2008 and related it to maternal baseline corticosterone level, laying date and year. Therefore, we took 101 blood samples of 71 breeding females via blood sucking bugs, a method with negligible stress for the birds. Sex ratio did not differ from parity in any of the analysed years, which were characterized by poor food availability and breeding success. Only within 1 year there was a tendency for more females in the last hatched chick. Neither corticosterone level nor laying date or year showed an influence on hatching sex ratio. The negative result concerning primary sex ratio and maternal baseline corticosterone level might suggest conditions to be good enough for mothers to prevent them from depositing high levels of corticosterone into eggs.