Is the citrus-like plumage odorant of crested auklets (Aethia cristatella) a defense against lice?

Plumage odors may function as chemical defenses against ectoparasites in birds. We tested this hypothesis for crested auklets (Aethia cristatella), a species of colonial seabird that emits a very strong citrus-like odor from its plumage. This odorant contains known chemical repellents. We evaluated evidence for chemical defense in this species using two approaches. First, we exposed pigeon lice to the volatiles emitted by freshly plucked plumage and by whole specimens. Louse survivorship was compared between these treatments and two controls. Second, we compared louse abundance on crested auklets versus a closely related congener that nests in close association. Louse survivorship did not differ between crested auklet treatments and controls. Comparison of ectoparasite loads showed that crested auklets had significantly higher louse abundance than least auklets (A. pusilla), even after controlling for body size. Our results failed to support two expectations for chemical defense. Presence of the crested auklet plumage odorant in our experiments did not reduce louse life span. Presence of the aldehyde odorant in nature did not reduce louse abundance on crested auklets. Hence we conclude that the aldehyde odorant is not immediately lethal to lice at natural concentrations in plumage.     

Size of ornament is negatively correlated with baseline corticosterone in males of a socially monogamous colonial seabird

The Goymann–Wingfield model predicts that glucocorticoid levels in social animals reflect the costs of acquiring and maintaining social status. The crested auklet is one of the few avian colonial species where a mutual ornament in males and females is used in both sexual and aggressive displays. Previous studies of the crested auklet support the notion that the crest ornament is a badge of status in this species. Here, we examined the relationship between the crest ornament size and the adrenocortical function in breeding crested auklets. Crest length was negatively correlated with corticosterone at baseline in males, but not in females. Baseline corticosterone in females (but not in males) was negatively correlated with body condition index. Although male and female crested auklets are monomorphic in their ornamental traits, our results suggest that the socially mediated physiological costs associated with status signaling may differ between the sexes.     

A tangerine-scented social odour in a monogamous seabird

Social odours, conspecific chemical signals, have been demonstrated in every class of vertebrate except birds. The apparent absence is surprising, as every bird examined has a functional olfactory system and many produce odours. The crested auklet (Aethia cristatella), a monogamous seabird, exhibits a distinctive tangerine-like scent closely associated with courtship. Using T-maze experiments, we tested whether auklets preferred conspecific odours and whether they distinguished between different types of scent, two prerequisites of chemical communication. Crested auklets exhibited: (i) an attraction to conspecific feather odour; (ii) a preference for two chemical components of feather scent (cis-4-decenal and octanal), which we identified as seasonally elevated; and (iii) differential responses to odours, as indicated by a preference for auklet odour, an aversion to mammalian musk, but no significant response to banana essence (amyl acetate). Our results suggest that crested auklets detect plumage odour and preferentially orientate towards this stimulus. The striking and well-described courtship display that involves the scented neck region, the 'ruff sniff', provides a conspicuous behavioural mechanism for odour transmission and the potential for scent assessment during sexual selection. Although the importance and full social function of chemical signals are just beginning to be understood in birds, including crested auklets, social odours promise to reveal a largely unexplored and possibly widespread means of avian communication.     

Behavior of crested auklets (<Emphasis Type="Italic">Aethia cristatella</Emphasis>, Charadriiformes,Alcidae) in the breeding season: Visual and acoustic displays

The crested auklet, a highly social planktivorous bird species of the Northern Pacific, is an important component of marine ecosystems. Although visual and acoustic modalities play a major role in the communication of these birds, the available data on the repertoire of their vocal signals and postures are scarce and lack quantitative analysis. This study deals with visual and acoustic displays of crested auklets on their breeding grounds and the occurrence frequencies of certain forms of social behavior in male and female birds. The data were collected on Talan Island (the Sea of Okhotsk) in 1987–1991 and 2008. They show that the rate of contacts between birds is very high and sex-specific: on average, males initiate 1.13 contacts/min, compared to 0.65 contacts/min initiated by females. Directionality of ruff-sniff displays differs depending on the posture of the recipient bird. The duration of the trumpeting display in males depends on their social surroundings. However, the duration of either the trumpeting display or the mutual cackling display during courtship is independent of the behavioral context. Vocalization of crested auklets is characterized by two independent basic frequencies occurring either sequentially or simultaneously. The role of different communicative modalities in the behavior of the crested auklet is discussed.     

Vocal and Optical Indicators of Individual Quality in a Social Seabird,the Crested Auklet (Aethia cristatella)

Indicators of individual quality in ornamentation or in vocalizations have been reported for different animal species. However, no studies have jointly investigated ornamentation and vocalizations in one species. The crested auklet (Aethia cristatella, Alcidae) is a small colonial seabird of the North Pacific and is unusual for a bird in using optical, vocal, and olfactory signals. We estimated the potential for coding individual quality in vocalizations and plumage ornamentation and the relationship between vocal and optical traits in crested auklets. During the summer seasons of 2008–2009, we recorded 359 trumpet calls from 28 individually marked males and measured indices of body size, condition, and plumage patterns of 58 male and 48 female crested auklets from a breeding colony on Talan Island, Sea of Okhotsk. We found strong interindividual differences in trumpet call characteristics. Furthermore, we found that the maximum fundamental frequency of the loudest notes of the trumpet call is negatively correlated with body condition, and head crest length is positively correlated with body size. However, we found no relationship between vocal and ornamental traits. The results suggest that advertising calls of crested auklets signal caller individuality and quality, but future experimental studies should test whether or not this is indeed case.     

An eye for detail: selective sexual imprinting in zebra finches

To investigate the idea that sexual imprinting creates incipient reproductive isolation between phenotypically diverging populations, I performed experiments to determine whether colony-reared zebra finches would imprint on details of artificial white crests. In the first experiment, adults in one breeding colony wore white crests with a vertical black stripe, while in another colony adults wore crests having a horizontal black stripe; except for their crests, breeders possessed wild-type plumage and conformation. Offspring of both sexes reared in these colonies developed mate preferences for opposite-sexed birds wearing the crest type with which they were reared; neither sex developed a social preference for crested individuals of the same sex. In a second experiment, females reared by crested parents preferred crested males versus males with red leg bands, while control females (reared in a colony of wild-type, uncrested birds) preferred red-banded males in the same test. Results of a third experiment that used sexually dimorphic crest phenotypes indicate that both sexes of offspring imprinted on maternal crest patterns. Results support the hypothesis that sexual imprinting can facilitate isolation both by engendering a preference for population-typical traits and by prioritizing such an imprinting-based preference over species-typical preferences for other traits used in mate choice. Comparison with results of other recent studies indicates that imprinting tendencies of both sexes vary with the characteristics of traits presented as an imprinting stimuli. Tendency to imprint may vary with the perceived information content (e.g., kin, sex, or population indicator) of parental traits, a process dubbed selective sexual imprinting.     

Heterospecific mating preferences for a feather ornament in least auklets

Auklets (Alddae, Aethiini) include five species of small, sociallymonogamous, sexually monomorphic seabirds that display a varietyof feather and bare-part ornaments during the breeding season.Previous experimental work on two auklet species has demonstratedthat some ornaments are likely to be favored by sexual selectionbecause mutual male and female mating preferences benefit individualswith the most elaborate expression of these traits. In thisstudy we experimentally investigated whether naturally crestlessleast auklets Aethia pusilla have a maring preference for foreheadcrests similar to the most prominent ornament of two other species,crested A. cristatella and whiskered auklets A. pygmaea. Ourobjective was to investigate the function of this ornament asa species-recognition mechanism or as a product of one or moreof three proposed sexual selection models that address the originof elaborate traits and preferences. During the experiment,least auklets reacted to realistic models equipped with artificialforehead crests with approximately an order of magnitude morefrequent sexual displays and greater interest, consistent withthe idea that they have a mating preference for crests, eventhough they do not naturally express this ornament This heterospecificpreference also favored large crest size. These results refutethe possibility that least auklet forehead ornamentation alonedetermines species recognition at present Among models of sexualselection considered, the results are consistent with the sensoryexploitation model, although this could not be established unequivocallybecause a viability indicator or Fisherian mechanism could havebeen involved if least auklets had an ancestor with a foreheadcrest.     

Experimental evidence for mutual inter- and intrasexual selection favouring a crested auklet ornament

During the breeding season, female and male crested auklets Aethia cristatella (Alcidae), display similar conspicuous crest ornaments composed of elongated forward-curving feathers on their foreheads. Based on quantifications of brief agonistic interactions at a large breeding colony, we found that crest length was strongly correlated with dominance within both sexes. Across the full range of crest length, individuals with longer crests were dominant over shorter-crested individuals in agonistic interactions involving same-sex adults. Within subadults (2-year-olds of unknown sex), there was a similar trend towards longer-crested individuals being dominant. In agonistic interactions involving individuals of different sex and age, adult males were dominant over adult females and adults were dominant over subadults, regardless of crest length. In an experiment in which we manipulated crest length using life-size realistic models, male auklets that responded were less aggressive to male models with longer crests than to models with normal or shorter crests, confirming that crest length by itself signals dominance status. In a related experiment in which we controlled intrasexual competition, both males and females responded to opposite-sex models with more frequent sexual displays when the models had long crests compared with those having short crests, suggesting that crested auklets also have mating preferences that favour long crest ornaments. Taken together, these results support the idea that the crest ornament is favoured by both intra- and intersexual selection. Copyright 1999 The Association for the Study of Animal Behaviour.     

Variation in plasma steroids and reproductive traits in dimorphic males of corkwing wrasse (Symphodus melops L.)

Differences in plasma steroid levels may reflect behavioral, gonadal, or morphological specializations that characterize different male reproductive phenotypes in teleost fishes. In the present study, we investigated whether differences in plasma steroid levels exist between two distinct male morphs shown in the corkwing wrasse Symphodus melops. In addition, we examined differences in male reproductive traits, including gonad mass, sperm motility, and sperm concentration, between the two male types. Possible associations between plasma steroid levels and reproductive traits were also investigated. The results indicated that males with typical male secondary sexual characters (territorial males) had higher plasma levels of 11-ketotestosterone (11kT) compared to smaller males with female secondary sexual characters (female mimics). The female mimics in turn had higher plasma levels of both testosterone (T) and 17beta-estradiol. In addition, female mimics had relatively larger gonads and longer-lived sperm than territorial males. Relative gonad mass covaried significantly with the plasma levels of 11kT and T among the morphs, indicating that the relative gonad size correlates positively with the plasma level of these two steroids. However, there was no significant covariance between sperm traits and plasma steroids for the two male morphs. Hence, our results do not indicate any causal link between sperm quality and hormones.     

Plasma prostaglandin F2 alpha and reproduction in the female Triturus carnifex (Laur.).

Plasma patterns of prostaglandin F2 alpha (PGF2 alpha) and sex hormones (progesterone, androgens and 17 beta-estradiol) have been studied in the female crested newt, Triturus carnifex (Laur.), during the annual sexual cycle. The effects of exogenous PGF2 alpha on sex hormones were determined. In addition, the effects of one week's captivity on plasma PGF2 alpha and sex hormones were reported. PGF2 alpha plasma level peaked in April, was low in summer, and progressively increased during the autumn to peak again in December. The April PGF2 alpha coincided with a 17 beta-estradiol rise, and with a progesterone drop. The autumn PGF2 alpha increase was coupled to a 17 beta-estradiol rise, and therefore it has been tentatively related to ovary and oviduct development. In newts collected in April, moreover, a PGF2 alpha-dependent 17 beta-estradiol synthesis could occur, since PGF2 alpha injection induced a significant 17 beta-estradiol plasma increase. These findings led us to suppose that PGF2 alpha intervenes in spring breeding season termination through the induction of a 17 beta-estradiol synthesis as in other amphibian species. PGF2 alpha injection caused a progesterone decrease, probably by inducing corpora lutea lysis. The patterns of plasma sex hormones were consistent with the results reported for the same newt species.     

Plasma prostaglandin F2 alpha in the male Triturus carnifex (Laur.) during the reproductive annual cycle and effects of exogenous prostaglandin on sex hormones

Plasma patterns of prostaglandin F2 alpha (PGF2 alpha) and sex hormones (progesterone, androgens and 17 beta-estradiol) have been studied in the male crested newt, Triturus carnifex (Laur.), during the sexual cycle. The effects of exogenous PGF2 alpha on sex steroids have also been observed. In addition, effects of one week's captivity are reported. The patterns of plasma sex hormones, during the annual cycle, are consistent with the results previously reported for the same newt species. PGF2 alpha plasma level peaks in April, is low in summer, and progressively increases during autumn to peak again in December. The April PGF2 alpha peak coincides with a plasma estradiol increase and with an androgens drop. In April-collected newts, moreover, PGF2 alpha treatment induces a significant estradiol increase. These findings lead us to suppose that at the end of the breeding season (April) a PGF2 alpha-dependent estradiol synthesis occurs which could be implied in reproductive period termination. In several vertebrates, including some amphibian species, in fact, chronic administration of estradiol results in a strong inhibition of testicular endocrine tissue activity. The putative role of PGF2 alpha-dependent estradiol production in the gonadal regulation in amphibia living in temperate zones is discussed. The autumn PGF2 alpha increase has been tentatively related to the recovery gonadal processes and secondary sexual character development.     

A test of the Darwin–Fisher theory for the evolution of male secondary sexual traits in monogamous birds

The Darwin–Fisher theory proposes that the presence of male secondary sexual traits in monogamous birds is selected for by early season breeding of females that are in good condition. These early breeding females have high fecundity because of their good condition, and they select mates based on secondary sex traits. We tested whether this hypothesis may be responsible for the presence of male sexual ornaments in the great frigatebird, a socially and genetically monogamous seabird. Consistent with the Darwin–Fisher theory, we found that reproductive success declined over the season. However, males with more exaggerated ornaments were not chosen as mates earlier in the season than males with less exaggerated ornaments, and selection gradients on these ornaments were not significantly different from zero.     

Inter- and intra-season stability of vocal individual signatures in a social seabird, the crested auklet

Vocal plasticity due to changes of social context is well documented in passerine birds. In other bird species, the impact of social environment changes on the whole vocal structure and on individual specific signatures remains largely unexplored. Here, we assessed inter- and intra-season stability of specific features of individual signatures in advertising calls of crested auklet (Aethia cristatella) males and tested the effects of pair mate and territory changes on the stability of the calls. The crested auklet is a highly social seabird of the North Pacific that breeds in dense colonies, and its individuals switch pair mates and territories with probability of 25–54%. During summer 2008–2010, we recorded 464 trumpet calls from 21 individually marked males and determined their pair mates and positions of their displaying places on a breeding colony of Talan Island, Sea of Okhotsk. We found that strong individual specific features of crested auklet trumpet calls stay stable not only during one season but also from year to year. However, we failed to find any effects of pair mate or territory changes on individual signatures of crested auklet trumpet calls. Our results suggest that crested auklets can potentially use their individually specific trumpet calls to form long-term social bonds both between pair mates and between neighbors; however, future experimental studies should test whether this is indeed the case.     

Covariation among demographic and climate parameters in whiskered auklets Aethia pygmaea

Annual survival rate and other demographic parameters of whiskered auklets Aethia pygmaea , a small planktivorous seabird, were measured at Buldir Island Alaska during 1992–2003 to provide comparative information for auk life history studies and to test for links among climate, age, productivity and survival. Using two 9  m mistnets, we captured and recaptured 384 adult and 193 sub-adult (one year old, a known-age component of our sample) birds as they arrived at the colony after dark during May and June (1,730  capture events). The best fitting model indicated a lower initial survival rate over the first year following marking (0.708±0.036 SE), and subsequent survival (mean 0.835±0.029) covarying with the Aleutian Low Pressure climate Index, with higher auklet survival in years with weak low pressure over the Aleutian Islands. Annual survival rate varied from 0.726±0.127 in 1998–99 to 0.994±0.077 in 1994–95, rates similar to those previously reported for least A. pusilla and crested auklets A. cristatella . A model based only on recaptures of known-age birds indicated a lower local survival estimate over the first year following marking (age one to two years), with no other age-effects on survival. Breeding propensity by age inferred from recaptures of birds with fully-developed brood patches that were originally marked as sub-adults (one year olds) indicated 53% breeding at age two, 94% breeding at age 3, 97% breeding at age 4 and 100% breeding thereafter. The sex ratio of the sampled birds was significantly male biased (60/40), likely due to differences in behaviour between males and females during the incubation stage. Taken together, our data indicate that whiskered auklet survival and productivity covaried with continuous variation in large-scale climatic conditions, the mechanism being either negative effects of stormy North Pacific weather or indirect effects on food supplies.     

Absence of protandry in the spring migration of a population of Song Sparrows Melospiza melodia

Early male arrival at breeding sites, or protandry, is thought to have evolved from intrasexual competition among males for access to mates or breeding resources. Males of polygynous species tend to be larger than females and have exaggerated secondary sexual traits. Additionally, such species show a high degree of protandry, suggesting that timing of arrival is sexually selected. Species showing limited sexual dimorphism and showing sexual monochromatism may be expected to show limited early male arrival. However, there are very few studies of migration timing of the sexes in such species because individuals cannot be readily identified to sex in the hand. In this study, we genetically sexed birds and found no evidence for early male arrival, for a population of migratory Song Sparrows Melospiza melodia . For our study population, males and females display limited sexual size dimorphism and are sexually monochromatic which is characteristic of the species. Fat scores for males were inversely associated with timing of arrival, whereas for females, larger-winged birds arrived sooner – suggesting that early migration timing may be selected for in both sexes.     

黄腹山鹪莺稳定的配偶关系限制雄性欺骗者

多数鸟类通过性特征限制在同性竞争和配偶选择中的“欺骗者”存在,与此相反,雀形目扇尾莺科部分物种表现出繁殖季节性特征消退的身体特征变化模式.在广州市南沙区通过“目字笼”对黄腹山鹪莺配偶关系稳定性的限制机制进行研究,发现虽然雌性个体到访原配个体和对照个体的次数几乎相同,但是雌性个体对原配雄性的单次选择时间明显长于对照雄性个体,总计选择时间也明显长于对照雄性个体.选择实验过程中,原配雄性的跳动次数明显高于对照个体雄性,以竖尾扑哧和鸣声恐吓等为代表的威慑行为次数也明显高于对照雄性个体.结果说明,雌性更青睐于原配个体,配对时间越长,忠诚度越高,而且原配雄性比入侵雄性个体表现出更高的活跃度和威慑行为.繁殖季节性特征消退的物种可以通过保持稳定的配偶关系以限制“欺骗者”存在.可以推测繁殖的巨大投入和雌性之间的同性竞争可能是产生这种配偶稳定性的主要原因.     

Sexual selection, stabilizing selection and fluctuating asymmetry in two populations of pupfish (Cyprinodon pecosensis)

Fluctuating asymmetry of morphological traits is thought to reflect the capacity of a genotype to produce an integrated, functional phenotype. I tested three predictions. (1) In a polygynous breeding system, under intense sexual selection on males, breeding males should show greater symmetry in bilaterally symmetrical traits than non-breeding males or females. (2) If these traits are under stabilizing selection, highly symmetrical individuals also should be modal phenotypes, thus near the mean value for that trait, whereas individuals with increased asymmetry should represent marginal phenotypes, near the extremes of the distribution for that trait. (3) Differences in the intensity of sexual selection should be reflected in differences in the degree of fluctuating asymmetry between sexes among populations. I examined the relationship between male breeding status and the degree of fluctuating asymmetry of four bilaterally symmetrical- traits, preorbital and preopercular pores and pectoral and pelvic fin rays, in two populations of Pecos pupfish which differed in the intensity of sexual selection. These traits do not function in male-male competition or female choice, thus are not directly affected by sexual selection. In Mirror Lake breeding males, as a group, were most symmetrical for all four traits, while non-breeding males and females showed higher levels of fluctuating asymmetry. Similarly, symmetrical individuals also represented modal phenotypes for four traits (breeding males), and for three traits (non-breeding males and females). These patterns were not seen in the Lake Francis population, where breeding males were as asymmetrical as non-breeding males and females, and the degree of fluctuating symmetry did not differ between modal and marginal phenotypes for any of the four traits. When ecological conditions favour intense sexual selection, either through female choice, male-male competition, or both, breeding males represent the most fit phenotypes. Thus sexual selection reinforces the effects of stabilizing selection on characters that do not function as secondary sexual traits. However, when sexual selection is relaxed, differences between sexes disappear.     

Molting and Seasonal Bill-Plate Shedding in the Whiskered Auklet (Aethia pygmaea)

Feather molting and bill-late shedding were studied because of the unique features of the whiskered auklet biology; i.e., they continue to visit the colony after departure of their young. Like other auklets, the whiskered auklets begin to molt during breeding and do not lose their capacity for flight. The molt pattern of different wing feathers is adaptive and allows new feathers to be protected (when they are soft and could be easily injured) by old or full-grown new feathers during flight or feeding (diving) due to the different timing of the molt of primary feathers and their coverts. The possibility of combining breeding with molt appears to be related to the feeding features of the species. The species that feed on abundant and highly aggregated plankton are able to molt during breeding. The pattern of bill-plate shedding in the whiskered auklet is similar to that in the crested auklet.     

Plasma prostaglandin F2α in the male triturus carnifex (Laur.) during the reproductive annual cycle and effects of exogenous prostaglandin on sex hormones

Plasma patterns of prostaglandin F2α (PGF2α) and sex hormones (progesterone, androgens and 17ß-estradiol) have been studied in the male crested newt, Triturus carnifex (Laur.), during the sexual cycle. The effects of exogenous PGF2α on sex steroids have also been observed. In addition, effects of one week's captivity are reported. The patterns of plasma sex hormones, during the annual cycle, are consistent with the results previously reported for the same newt species. PGF2α plasma level peaks in April, is low in summer, and progressively increases during autumn to peak again in December. The April PGF2α peak coincides with a plasma estradiol increase and with an adrogens drop. In April-collected newts, moreover, PGF2α treatment induces a significant estradiol increase. These findings lead us to suppose that at the end of the breeding season (April) a PGF2α-dependent estradiol synthesis occurs which could be implied in reproductive peroid termination. In several vertebrates, including some amphibian species, in fact, chronic administration of estradiol results in a strong inhibition of testicular endocrine tissue activity. The putative role of PGF2α-dependent estradiol production in the gonadal regulation in amphibia living in temperate zones is discussed. The autumn PGF2α increase has been tentatively related to the recovery gonadal processes and secondary sexual character development.     

Sexual selection resulting from extrapair paternity in collared flycatchers

Extrapair paternity has been suggested to represent a potentially important source of sexual selection on male secondary sexual characters, particularly in birds with predominantly socially monogamous mating systems. However, relatively few studies have demonstrated sexual selection within single species by this mechanism, and there have been few attempts to assess the importance of extrapair paternity in relation to other mechanisms of sexual selection. We report estimates of sexual selection gradients on male secondary sexual plumage characters resulting from extrapair paternity in the collared flycatcher Ficedula albicollis, and compare the importance of this form of sexual selection with that resulting from variation in mate fecundity. Microsatellite genotyping revealed that 15% of nestlings, distributed nonrandomly among 33% of broods (N=79), were the result of extrapair copulations. Multivariate selection analyses revealed significant positive directional sexual selection on two uncorrelated secondary sexual characters in males (forehead and wing patch size) when fledgling number was used as the measure of fitness. When number of offspring recruiting to the breeding population was used as the measure of male fitness, selection on these traits appeared to be directional and stabilizing, respectively. Pairwise comparisons of cuckolded and cuckolding males revealed that males that sired young through extrapair copulations had wider forehead patches, and were paired to females that bred earlier, than the males that they cuckolded. Path analysis was used to partition selection on these traits into pathways via mate fecundity and sperm competition, and suggested that the sperm competition pathway accounted for between 64 and 90% of the total sexual selection via the two paths. The selection revealed in these analyses is relatively weak in comparison with many other measures of selection in natural populations. We offer some explanations for the relatively weak selection detected. Copyright 1999 The Association for the Study of Animal Behaviour.