Status signalling in male but not in female Eurasian Tree Sparrows Passer montanus

Male ornaments, such as plumage coloration, frequently serve as signals. The signalling function of similar ornaments in females has, however, received much less attention despite the fact that conspicuousness of their ornaments is often comparable to those of males. In this study we tested the signalling function of a plumage trait present in both sexes in the Eurasian Tree Sparrow Passer montanus. The black throat patch has been repeatedly found to have a signal function in the closely related House Sparrow Passer domesticus, where only males bear the ornamental trait. However, the function of the black throat patch in the females of Passer species that have sexually monomorphic ornament expression has never, to our knowledge, been considered. We investigated the outcomes of aggressive encounters in foraging flocks of free‐living Tree Sparrows, and assessed whether throat patch size and measurements of body size predicted fighting success in these flocks. We found that male throat patch size predicted fighting success against both male and female opponents. However, female throat patch size did not correlate with fighting success against either sex. Among the morphological traits studied, wing length was the best predictor of fighting success in females. Our findings suggest a status signalling function of throat patch size in males but not in females, although further experimental studies are necessary to corroborate these correlative results.     

Assessing the function of house sparrows' bib size using a flexible meta-analysis method

The black throat patch or bib of male house sparrows, Passerdomesticus, is often referred to as a "badge of status" or a"badge" because previous studies have shown bib size to be correlatedwith the social status of males. Yet, little is known abouthow strong and robust this relationship is and how the strengthof this relationship compares with that of other associations.We conducted a meta-analysis for 6 well-studied correlates ofbib size: fighting ability, parental ability (egg incubationand food provisioning), age, body condition, cuckoldry, andreproductive success. We introduce a flexible meta-analysismethod in this study that is better suited in the biologicalsciences than the methods usually employed in popular meta-analysissoftware because our method accounts for a common form of nonindependenceof the data. The relationship between fighting ability and bibsize was found to be strong and robust, and the relationshipbetween age and bib size was moderate and robust. Also, bodycondition was weakly but significantly correlated with badgesize. The other parameters showed nonsignificant small effectsand/or large confidence intervals. Therefore, we conclude thatbib size signals dominance and to a lesser extent age and possiblyreflects body condition in house sparrows. There was weak evidencethat bib size is currently under sexual selection because therewas little association between reproductive success and bibsize. This is surprising as the bib size probably affects theoutcome of male–male competition. Empirical data on sparrowbib size could not be reconciled with sexual selection theory,although there is ample evidence that it is a condition-dependenttrait.     

Sex of opponent influences response to a potential status signal in house sparrows

We evaluated the possible use of a sexually dimorphic plumage trait as a status signal in inter- and intrasexual social interactions in free-living house sparrows, Passer domesticus. Males with larger black throat patches (bibs) tended to be dominant regardless of the opponent's sex. This relationship was maintained after controlling for body size and age in multivariate analyses. However, the nature of social interactions varied according to the sex of the opponent and a male's bib size. Males with larger bibs tended to be less aggressive to male opponents, and received significantly less aggression from those birds, a key predicted benefit of a status signal. However, when the opponent was a female, males with large bibs displayed significantly more aggression than males with small bibs, and this relationship persisted even after controlling for the dominance status of the participants. Females were significantly more aggressive towards male opponents than towards female opponents, and females interacting with two males of known bib size were more aggressive to the one with the larger bib. These results suggest that the bib of male house sparrows may be a signal of status, but that in interactions with females, the bib may also have other functions. Frequent testing by females of the underlying quality being signalled by the bib may be linked to later mate choice, and might be adaptive if the information value of the bib varies among years. Such testing may also contribute to mechanisms for maintaining the bib as a reliable signal of status. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

An investigation of mate choice based on manipulation of multiple ornaments in Kentish plovers

Many animals have multiple sexual ornaments, a fact variously explained as signalling of multiple attributes, or nonadaptive retention of now redundant, but previously informative, signals. Despite the widespread occurrence of multiple ornaments, and the theoretical interest in how they are maintained by selection, there have been few experimental studies of the phenomenon. We investigated the role of two ornaments, each plausibly signalling different male attributes, in attracting a new mate in the Kentish plover, Charadrius alexandrinus. Previously we have shown that male Kentish plovers vary in how long they take to acquire a new mate, and we hypothesized that this variation may relate to their attractiveness or parental ability. We created single males by removing their mate and clutch, and then manipulated both their badge size (a presumed signal of either their genetic quality or their dominance status and hence defensive abilities) and the length of their flank feathers (a presumed signal of their parental quality in incubation) in a 2×2 factorial design. We found no difference in remating times between manipulated and control males. Furthermore, neither body size nor body condition of males was related to their remating times, although males with enlarged badges spent less time fighting than control males. Taken together, our results suggest that female Kentish plovers do not use either badge size or the length of flank feathers as cues in their mate choice decisions. However, badge size may influence male-male competition.     

Carotenoid and melanin-based ornaments signal similar aspects of male quality in two populations of the common yellowthroat

1.  Female preferences for particular male ornaments may shift between populations as a consequence of ecological differences that change the reliability and detectability of the ornament, but few studies have examined how ornaments function in different populations.
2.  We examined the signalling function of male plumage ornaments in a warbler, the common yellowthroat ( Geothlypis trichas ), breeding in New York (NY) and Wisconsin (WI), USA. Males have two prominent ornaments: a black facial mask pigmented with melanin and a yellow bib pigmented by carotenoids. Previous studies in WI indicate that the size of the mask, and not the bib, is primarily related to female choice and male reproductive success. In NY, however, the pattern is reversed and attributes of the bib (size and colour), and not the mask, are the target of sexual selection.
3.  We found that brightness of the yellow bib was the best signal of humoral immunity (immunoglobulin G) in NY and mask size was the best signal in WI, after controlling for breeding experience and capture date. Thus, similar aspects of male quality appeared to be signalled by different ornaments in different populations.
4.  There was no difference between populations in the level of plasma carotenoids or the prevalence of malarial parasites, which may affect the costs and benefits of choosing males with particular ornaments in each location.
5.  Even though females in different populations prefer different ornaments produced by different types of pigments, these ornaments appear to be signalling similar aspects of male quality. Our results caution against inferring the function of particular ornaments based simply on their type of pigment.     

SEXUAL SELECTION,MULTIPLE MALE ORNAMENTS,AND AGE‐ AND CONDITION‐DEPENDENT SIGNALING IN THE COMMON YELLOWTHROAT

In many animals, sexual selection has resulted in complex signaling systems in which males advertise aspects of their phenotypic or genetic quality through elaborate ornamentation and display behaviors. Different ornaments might convey different information or be directed at different receivers, but they might also be redundant signals of quality that function reliably at different times (ages) or in different contexts. We explored sexual selection and age‐ and condition‐dependent signaling in the common yellowthroat (Geothlypis trichas), a sexually dichromatic warbler with two prominent plumage ornaments—a melanin‐based, black facial “mask” and carotenoid‐based, UV‐yellow “bib.” In a three‐year study, variance among males in the number of social (M_w) and extra‐pair (M_e) mates generated strong sexual selection on mask and bib attributes. Some traits (mask size, bib yellow brightness) were correlated with male age and did not experience selection beyond age‐related increases in M_w and M_e. Other traits showed age‐specific (bib size) or age‐reversed (ultraviolet brightness) patterns of selection that paralleled changes in the information‐content of each ornament. The components of male fitness generating selection in young versus old males were distinct, reflecting different sources of variation in male fertilization success. Age‐ and context‐dependent changes in the strength, direction, and target of selection may help explain the maintenance of multiple ornaments in this and other species.     

Within-male melanin-based plumage and bill elaboration in male house sparrows

If there is a cost to producing a dark color patch, the size of a patch may not correspond with its pigment concentration. The plumage of male house sparrows represents a case of dark, melanin-based ornamentation, but also a case of neglecting the composite nature of dark signals in birds. Here, I investigated what kind of associations exist between the brightness, chroma, and hue of dark integumentary patches and the size of a secondary sexual trait, the bib, in male house sparrows. I found that males with a larger bib also had a darker bib and bill, and a more saturated bib, bill, epaulets, head crown, and breast than small-bibbed males. Male bib coloration in terms of brightness and chroma was more strongly related to bib size than the coloration of other integumentary patches. However, with respect to hue, only the hue of the bill and cheeks was related to bib size. My results indicate that size, brightness, and chroma of the bib, but also chroma of other deeply colored patches, convey redundant information about the signaler's quality in male house sparrows.     

Is Territory Defence related to Plumage Ornaments in the King Penguin Aptenodytes patagonicus?

Colourful ornaments in monogamous birds may be directed at potential mates or other conspecifics to signal individual condition, reproductive status or fighting ability, especially in monogamous and territorial species. We investigated whether the size of the orange auricular patch may be an indicator of aggressiveness in the king penguin Aptenodytes patagonicus , a monogamous and territorial seabird. The relationship between auricular patch size and defence behaviour was explored relative to territory location (centre vs. periphery of the colony), period of reproduction (early vs. late), state of reproduction (incubation vs. brooding) and sex. The proportion of time spent in territorial defence and the rate of aggressive behaviours were positively correlated with auricular patch size, mainly because central birds were more aggressive than peripheral birds and also had larger patch sizes. The period of reproduction, state of reproduction and sex did not interact with patch size to affect aggressiveness. Our results suggest that the size of the auricular patch in king penguins may be a reliable signal allowing individuals to evaluate the quality of mates or competitors in terms of aggressiveness. Whether aggressiveness is directly linked to patch size or indirectly through body condition, however, remains to be determined. In any event, birds with larger patches seem to gain central territories in the colony, thereby increasing their reproductive success. Finally, our study adds to the growing evidence that the evolution of sexually monomorphic ornaments may stem from mutual sexual selection.     

Honesty of agonistic signalling and effects of size and motivation asymmetry in contests

Game theoretical models predict that the main function of fighting behaviour is to assess the relative fighting ability of opponents. The sequential assessment game has often been used to investigate contests, while honest signalling theory has received much less attention. With the wolf spider Hygrolycosa rubrofasciata we investigated whether male agonistic signalling can reveal honest information about fighting ability, and how size and motivation asymmetries affect male fighting behaviour. We also determined whether male–male competition affects the courtship behaviour of the males. We found that agonistic drumming activity is an honest indicator of male fighting ability, and that relative size asymmetry and motivation to fight both contribute to the fighting ability. We also found that male–male competition decreases the courtship drumming rate of subdominant males, suggesting that male–male competition limits the opportunities for female choice. We conclude that sequential assessment and honest signalling may both be used in settling contests, and that they may be used simultaneously. Received: 10 December 1998 / Received in revised form: 23 June 1999 / Accepted: 5 July 1999     

Multiple Plumage Ornaments as Signals of Intrasexual Communication in Golden‐Winged Warblers

Avian plumage represents some of the greatest diversity in integument coloration of all animals. Plumage signals are diverse in function, including those that allow for assessing potential mates or the mitigation of agonistic interactions between rivals. Many bird species possess multiple ornamental traits that have the potential to serve as multiple or redundant signals. For example, male golden‐winged warblers (Vermivora chrysoptera) have brilliant carotenoid‐based yellow crowns, melanin‐based black throats, and structurally based white patches on their outer tail feathers. Using a correlative approach, we investigated whether plumage ornaments have the potential to reliably signal ability to acquire higher quality territory, aggressive response to simulated territorial intrusions, and reproductive success. We found that both crown chroma and tail brightness were significantly related to habitat quality and aggression; more ornamented birds held territories with higher quality habitat and were less aggressive toward simulated conspecific stimuli. Older birds sang less threatening songs than younger birds and were more likely to sing their mate attraction song type (type 1) rather than songs typically reserved for agonistic interactions (type 2). Finally, despite our previous research demonstrating that habitat strongly predicts reproductive success in this warbler population, we found no evidence of a direct link between ornamentation and reproductive success. Overall, these data suggest that younger males, and those with lower quality ornaments, compensate with more aggressive behaviors. Additional research is needed to investigate the dynamics between behavioral traits and ornaments to better understand complex signaling and how golden wing signals function in conspecific interactions (male–male interactions and mate‐choice).     

Forehead Patch Size Predicts the Outcome of Male–Male Competition in the Pied Flycatcher

Males of many animal species express ornaments that affect their reproduction opportunities through male–male competition or female mate choice. Such ornaments can, for example, inform conspecifics about the fighting ability, condition or territory ownership of the bearer. Pied flycatcher (Ficedula hypoleuca) males have a conspicuous white forehead patch that varies greatly in size. We examined whether the white forehead patch is an intrasexually selected trait in a Finnish population. We artificially manipulated forehead patch size to represent two naturally occurring extremes and competed males against each other in the presence of a female. Males with a large forehead patch were more aggressive than males with a small patch, whereas the original patch size of the male had no influence on aggression. Neither manipulated nor original patch size influenced resource dominance (over female or nest box). These results indicate that forehead patch signals fighting ability of the bearer in the pied flycatcher. The next step is to find out what kind of costs may maintain the honesty of this signal.     

The role of testosterone in bib size determination in the male house sparrow Passer domesticus,is age dependent

Secondary sexual signals are thought to indicate individual quality. In order to understand the evolutionary pressures that give rise to such traits it is important to understand the physiological mechanisms underlying their production. The black bib of the house sparrow Passer domesticus is known to function as a badge of social status in males. Past studies have found that the size of the bib in older males is determined, at least partly, by the androgen testosterone. The immunocompetence handicap hypothesis suggests that testosterone has a key role in maintaining honest signalling – it is both involved in the development or expression of sexual signals and is immunosuppressive. In this paper we test experimentally two hypo theses relating to bib size development, whether 1) testosterone is only immunosuppressive in conditions where the natural feedback loop from the testes has been removed, and 2) testosterone is, in addition to influencing the bib size of older males, responsible for the size of the bib in juvenile sparrows. In the first experiment we found that exogenous testosterone administered to intact males during the winter (when LH and FSH levels are very low and were not artificially increased by castration) caused significant immunosuppression, albeit in interaction with the stress hormone corticosterone. Second, we found that exogenous testosterone administration in castrated fledgling male house sparrows had no effect on subsequent post‐juvenile moult bib size relative to controls. Our results suggest that in some circumstances testosterone can be immunosuppressive, but that its role in bib size determination is age‐dependent.     

Does Male Badge Size Signal Status in Small Island Populations of House Sparrows,Passer domesticus?

The relationship between dominance and throat badge size, body size, and body condition was examined in three small island populations of house sparrows, Passer domesticus, on the coast of northern Norway. Individual dominance rank in males was determined by observation of agonistic interactions in an artificial observation cage (one replicate in Dec. and one in Mar. in two populations and one replicate in Mar. in the third population). Previous studies had indicated that badge size signals status in house sparrows. In this study, because of the small population sizes and stability in their membership, we expected that prior information about fighting ability would reduce the importance of badge size for the outcome of conflicts in favour of traits most directly associated with fighting ability. In two of five replicates, significant relationships were found between components of body size and dominance rank, but in opposite directions. The relationship between badge size and dominance rank was consistently positive, but non-significant. In a pooled sample of the three independent replicates, badge size was the best predictor of dominance, and no other variable explained any variance in dominance. However, the coefficient of determination was low and linearity of dominance hierarchies was poor. We therefore suggest that individual recognition may influence the dominance relationships.     

Age,condition and dominance‐related sexual ornament size before and during the breeding season in the black grouse Lyrurus tetrix

Male ornaments function as honest cues of male quality in many species and are subject to intra‐ and intersexual selection. These ornaments are generally studied during peak expression, however their size outside the breeding season may determine ultimate ornament size and costliness, and as such reproductive success. We investigated whether male black grouse Lyrurus tetrix eye comb size was related to age, condition and measures of male dominance before and during the breeding season. Total combined eye comb size began to increase ~70 d before the start of the breeding season. Adult males (aged ≥ 2 yr old) had consistently larger eye combs than younger males (1 yr old) both before and during the breeding season. Heavier and more dominant adult males (attending the lek more frequently and successfully reproducing) had larger eye combs. For younger males, those that were heavier had larger eye combs. Additionally, males that spent more time on the lek showed increased eye comb size as the breeding season approached. Overall we find that ornament size is positively related to dominance and condition before and during the breeding season. Since dominance is accrued through year‐round interactions in many species, the ability to maintain larger signals over prolonged periods, including outside of the breeding season, is likely to be beneficial for adults. For younger males, it is likely that they cannot sustain or are constrained from producing larger eye combs over long periods of time. They therefore prioritise growth of their ornaments later, and according to the amount of time they spend on the lek.     

Social Control and Physiological Cost of Cheating in Status Signalling Male House Sparrows (Passer domesticus)

Flock-forming passerines often use plumage characteristics to signal their social dominance. While the benefits to signal dominance seem obvious, costs associated with status signalling are ambiguous. The social control hypothesis predicts that individuals of high social status – with large badges – are involved in more social interactions with individuals of similar badge size. Cheaters are therefore exposed to increased risk of fighting with high quality individuals and the costs associated with enhanced fights with dominant males are supposed to outweigh the benefits of cheating. We tested the social control hypothesis in male house sparrows ( Passer domesticus ), by observing social interactions in captive flocks and determining dominance relationships. Two low status individuals within each flock had the size of their badge experimentally increased and the interactions involving experimental and control birds were recorded. We also assessed the potential physiological cost of cheating in terms of enhanced levels of the stress hormone, corticosterone. Dominance was significantly positively correlated with badge size, but not with other morphological traits. We found little support for the social control hypothesis. Birds did not have significantly more interactions with individuals of similar badge size, before the manipulation. Similarly, after the experimental increase in badge size, experimental birds did not tend to have more encounters with large-badged males. Experimental birds with enlarged badges won more fights compared with prior to the manipulation, suggesting that badge size is used as a signal of social dominance even in small and stable flocks. Finally, corticosterone levels in the blood did not increase significantly after the manipulation of badge size, suggesting that there is no measurable cost, resulting from stress, in cheaters.     

Is facial structure an honest cue to real-world dominance and fighting ability in men? A pre-registered direct replication of

Masculine facial morphology (e.g., larger jaw, prominent cheekbones) have been linked to a suite of social outcomes—including greater wealth, career progress, romantic desirability, and even greater political success. A leading explanation for these links is that dominant facial structures represent honest cues of physical dominance and fighting ability. T?ebický et al. (2013) published the first study to demonstrate that masculine facial cues (e.g., large nose, deep-set eyes) similarly predict both dominance judgments and real-world fighting success, but no studies have replicated these popular findings that a large and specific assortment of masculine facial structures are implicated in both fighting ability and dominance perception. Thus, we conducted a pre-registered direct replication and extension of T?ebický et al. (2013). Two separate samples of United States MTurk participants rated 516 UFC fighters' facial photographs on perceived aggressiveness (N = 500) and fighting ability (N = 500). Results showed that perceived aggressiveness was associated with masculine facial morphology (e.g., large nose, deep-set eyes) independent of bodily size. There was also some evidence that perceived fighting ability was associated with masculine facial morphology, which disappeared after controlling for bodily size. There was no support for the relation between facial structure and fighting success, and there were often negative relations between perceived aggressiveness and fighting ability on fighting success (i.e., more successful fighters were perceived as less successful and aggressive). We argue that our evolved psychology differentially processes the distinct avenues to victory that constitute overall fighting success (e.g., knockout versus submission wins).     

Dual functions of a melanin-based ornament in the common yellowthroat

Melanin-based ornaments often function as signals in male-male competition, whereas carotenoid-based ornaments appear to be important in female mate choice. This difference in function is thought to occur because carotenoid pigments are more costly to produce than melanins and are thus more reliable indicators of male quality. We examined the role of melanin- and carotenoid-based ornaments in male-male competition and female choice in the common yellowthroat Geothlypis trichas, a sexually dichromatic passerine. Males display a black facial mask produced by melanin pigmentation and a bright yellow bib (throat, breast and belly) produced by carotenoid pigmentation. In controlled aviary experiments, mask size was the best predictor of both male-male competition and female mate choice, and, therefore, mask size may be regarded as an ornament of dual function. These dual functions may help to maintain the reliability of mask size as an indicator of male quality, despite the potentially low cost of production. The size of the bib was unrelated to male-male competition or female choice, but there was a tendency for females to prefer males with more colourful bibs. We propose that the black mask is important in competition for territories with other males and for attracting females. Our results highlight the need for more studies of the mechanisms of sexual selection in species with ornaments composed of different pigment types.     

Multiple Ornaments in Male Northern Cardinals, Cardinalis cardinalis, as Indicators of Condition

Investigations of male ornaments in the context of sexual selection have tended to focus on single ornaments, although many species of birds possess multiple ornaments. Understanding the evolution of multiple ornaments requires knowledge of correlations among ornaments in the same individual and the extent to which ornament expression reflects individual condition and behavior. Variation in four male ornaments in socially monogamous, biparental northern cardinals (Cardinalis cardinalis) was related to body size, indices of condition, level of paternal care, and reproductive success. Redness of breast plumage positively predicted body size and negatively predicted nestling feeding rate. Bill color predicted current body condition, with birds with redder bills in better condition. Birds with smaller black face masks had greater reproductive success. These results are consistent with the hypothesis that different ornaments in male cardinals provide information on different aspects of condition and behavior.     

Territory Defence in Black Redstarts,Phoenicurus ochruros: Effects of Intruder and Owner Age?

European black redstarts, Phoenicurus ochruros, vigorously defend all-purpose territories and exhibit delayed plumage maturation, most subadult males looking exactly female-like in their first breeding season. We tested the hypotheses that such dull subadult male plumages are beneficial in order to reduce aggression of adult males either by deception or by honest signalling of subordinance status, and that, in turn, conspicuous (adult) plumage colorations are able to intimidate contenders because they act as a signal of fighting ability and aggressive motivation. Adult and dull yearling black redstart territory owners were confronted with intruders mimicked by stuffed mounts of either a conspicuous adult or a dull subadult male. Our results do not support the hypotheses tested: dull plumages of young intruders did not reduce aggression from adult territory owners and aggressiveness towards intruders was significantly higher in yearling territory owners as compared with adult owners. Conspicuous intruders did not deter dull territory owners and we found no indications that conspicuous male coloration is a signal of fighting ability or aggressive motivation in this species. Instead, the amount of aggressive response to intruders showed considerable individual variance within age classes regardless of the plumage of the intruder and the status of the owner.     

Cutaneous antipredatory secretions and pheromones in anurans and urodeles

The article analyses the main chemical signals used by anurans and urodeles for social interactions such as defence and reproduction. Some emblematic examples have been selected from the most significative reports. The antipredatory arsenal of many frogs and toads includes secretions of cutaneous glands, randomly distributed on the body or localised in “critical” skin regions. These substances act as repellent, alarm or venom, with specific toxicity and pharmacological actions. Other chemical cues facilitate social interactions. These “pheromones” allow animals to recognize conspecifics and to identify their sex, reproductive condition and social status. In many cases courtship pheromones play a crucial role in increasing male success. Evidence such as that suggests that selective pressures from environmental and social constraints produced the high incidence of chemical signalling typical of the amphibia, a view confirmed by the similarity of chemical cues across different taxa.