Plumage Brightness Research Articles

Developmental stage-dependent effects of perceived predation risk on nestling tree swallows (Tachycineta bicolor).

The risk of predation directly affects the physiology, behavior, and fitness of wild birds. Strong social connections with conspecifics could help individuals recover from a stressful experience such as a predation event; however, competitive interactions also have the potential to exacerbate stress. Few studies have investigated the interaction between environmental stressors and the social landscape in wild bird populations. In 2 years of field studies, we experimentally simulated predation attempts on breeding female tree swallows (Tachicyneta bicolor). At the same time, we manipulated female breast plumage color, a key social signal. Simulated predation events on tree swallows early in the nestling period reduced young nestlings' mass by approximately 20% and shortened telomere lengths. Ultimately, only 31% of nestlings in the predation group fledged compared with 70% of control nestlings. However, the effects of experimental manipulations were timing dependent: the following year when we swapped the order of the experimental manipulations and simulated predation during incubation, there were no significant effects of predation on nestling condition or fledging success. Contrary to our expectations, manipulation of the social environment did not affect the response of tree swallows to simulated predation. However, manipulating female plumage during the nestling period did reduce nestling skeletal size and mass, although the effects depended on original plumage brightness. Our data demonstrate that transient stressors on female birds can have carry-over effects on their nestlings if they occur during critical periods in the breeding season.

A Note on Status and Breeding Biology of Birds-of-Paradise (Aves: Paradisaeidae)

Based on the extraordinary plumage colours and courtship display, the birds-of-paradise are most significant bird in the world. To know its breeding biology fully, these birds can be study bird to everybody. After reviewing many write-ups, it was possible to mention its status and remarkable breeding biology. Noted, 27 species of these birds were in the order Passeriformes and family Paradisaeidae. Most of the birds were showed polygamous, and only two were (crinkle-collared manucode, Manucodia chalybatus, halmahera paradise-crow/Silky-crow, Lycocorax pyrrhopterus) monogamous. Observation suggested 15 genera of this bird group. Based on the information, 22 species were found least concerned (81.48%), near threatened 4 (14.81%), and vulnerable 1 (3.70%). Habitat loss, limited range, and for bright plumage of male birds, some species are showing their risky life in nature.

Age-Related Change in the Association Choices of Two Species of Juvenile Flamingos.

Flamingos are colonial species commonly kept in zoos, well known for their bright plumage and elaborate courtship displays. This project aimed to determine the differences in flock position and association preferences of juvenile Greater Flamingos (Phoenicopterus roseus) and Caribbean Flamingos (P. ruber) housed in the same zoological collection. Little research has been conducted on the association preferences of juvenile flamingos, especially in captive flocks, and therefore this study collected data using photographs taken throughout 2014 and 2015 to further understand association patterns. Data were collected on the age category of each juvenile flamingo observed, the age of their nearest neighbour and their position within the flock, and the location within an enclosure zone at different times of the day. The results showed that Greater Flamingo juveniles mainly associated with individuals of their own age and were most likely positioned at the periphery of their flock significantly more of the time until approximately 24 months of age. Sub-adult Greater Flamingos spent significantly more time associating with adult flamingos at the centre of the flock. In contrast, data collected on Caribbean Flamingos indicated that juveniles did not segregate themselves from the adults as distinctively. Birds aged 13-24 months were observed significantly more at the centre of the flock and had more associations with adult flamingos, in a similar manner to that observed in Greater Flamingos. Due to population management needs, juvenile Caribbean Flamingos were removed from the flock at the start of 2015 and this may have influenced the association and location preferences of the remaining young flamingos. In conclusion, these results indicated that captive juvenile flamingos were often seen away from adult birds and that sub-adult flamingos returned to the heart of their natal flock to associate significantly more with other adult individuals, potentially preparing for mate selection and breeding. Captive enclosure should therefore be spacious enough to enable young flamingos to remove themselves from adult birds so that behavioural development can be unaffected by artificially high rates of aggression.

Web-sourced photographic methods reveal dietary composition and shifts in resident and migrant Coracias rollers in southern Africa

Closely related species coexisting in the same niche often have dietary overlap and interspecific competition can result in resource partitioning e.g., dietary shifts, migration or phenological changes. Traditional methods to study avian diets are typically costly, difficult, and invasive. Using web-sourced photographs is an emerging, non-invasive method to study avian foraging ecology. We used this approach, along with photographic road surveys, to study prey composition of migratory European Rollers Coracias garrulus and resident Lilac-breasted Rollers Coracias caudatus where they co-occur in southern Africa. These insectivorous sister species are frequently photographed with prey in their bills because of their conspicuous perch-and-wait foraging behaviour and bright plumage coloration. We collated over 250 photographs of rollers holding prey and identified prey items representing 15 animal orders. Lilac-breasted Roller diet contained six unique orders of prey during the Austral summer (when the European Roller is present), and only one during winter (when the European Roller has migrated north). This suggests that Lilac-breasted Rollers may broaden their diet seasonally to alleviate competition with European Rollers during summer. Additionally, Lilac-breasted and European Rollers had an 84% overlap in dietary composition, potentially representing high interspecific competition - even during wet savanna summers when resource abundance is high - that might have originally driven the evolution of migratory behaviour in the European Roller. Our findings expand the current knowledge of roller diets and highlighting the growing role of social media in ecological studies.

Female and male plumage brightness is positively correlated among populations of the dichromatic Variable Seedeater

Abstract Because studies of plumage coloration often focus on highly elaborate and conspicuous males, little is known about the factors driving theevolution of drab plumage in females of dichromatic species. We explored variation in the color properties of drab female plumage across subspecies of the Variable Seedeater (Sporophila corvina) and found a correlation between plumage brightness of male and female plumage patches. This correlation is consistent with the hypothesis that differences in plumage brightness among females result, at least partially, from a genetic correlation or shared developmental pathway with the more conspicuous male plumage traits that are shaped by sexual selection. Furthermore, we modeled the perception of female plumage using the avian visual system and found that most of the variation in color among females is undetectable by birds; therefore, it is unlikely for such variation to have evolved via direct sexual selection as a signal for recognition or assortative mating. Together, these results suggest that variation in S. corvina female color result from non-adaptive processes. However, we found a reduced variation on color of dorsal patches compared with that of ventral patches among females, which could be explained by natural selection on crypsis, reducing the variation on dorsal patches. Finally, we found little differences in plumage color between adult females and juveniles, which suggest selection for juveniles to resemble adult females possibly to reduce aggression from adult males. Additional within-population studies and behavioral experiments are needed to discern the evolutionary factors driving variation on S. corvina female color and its function.

Plumage Balances Camouflage and Thermoregulation in Horned Larks (Eremophila alpestris).

AbstractAnimal coloration serves many biological functions and must therefore balance potentially competing selective pressures. For example, many animals have camouflage in which coloration matches the visual background that predators scan for prey. However, different colors reflect different amounts of solar radiation and may therefore have thermoregulatory implications as well. In this study, we examined geographic variation in dorsal patterning, coloration, and solar reflectance among horned larks (Eremophila alpestris) of the western United States. We found that plumage brightness was positively associated with soil granularity, aridity, and temperature. Plumage redness-both in terms of saturation (i.e., chroma) and hue-was positively associated with soil redness and temperature, while plumage patterning was positively associated with soil granularity. Together, these plumage-environment associations support both background matching and Gloger's rule, a widespread ecogeographic pattern in animal coloration. We also constructed thermoregulatory models that estimated cooling benefits provided by solar reflectance profiles of the dorsal plumage of each specimen based on the collection site. We found increased cooling benefits in hotter, more arid environments. Finally, cooling benefits were positively associated with residual brightness, such that individuals that were brighter than expected based on environmental conditions also had higher cooling benefits, suggesting a trade-off between camouflage and thermoregulation. Together, these data suggest that natural selection has balanced camouflage and thermoregulation in horned larks, and they illustrate how multiple competing evolutionary pressures may interact to shape geographic variation in adaptive phenotypes.

Inter-annual repeatability and age-dependent changes in plasma testosterone levels in a longitudinally monitored free-living passerine bird.

While seasonal trends in testosterone levels are known from cross-cohort studies, data on testosterone inter-annual individual repeatability in wild birds are rare. Also, our understanding of hormonal age-dependent changes in testosterone levels is limited. We assessed plasma testosterone levels in 105 samples originating from 49 repeatedly captured free-living great tits (Parus major) sampled during the nesting to investigate their relative long-term repeatability and within-individual changes. Furthermore, we examined the inter-annual repeatability of condition-related traits (carotenoid- and melanin-based plumage ornamentation, ptilochronological feather growth rate, body mass, and haematological heterophil/lymphocyte ratio) and their relationships to testosterone levels. We show that testosterone levels are inter-annually repeatable in females, with a non-significant pattern in males, both in absolute values and individual ranks (indicating the maintenance of relative status in a population). In males, we found a quadratic dependence of testosterone levels on age, with a peak in midlife. In contrast, female testosterone levels showed no age-dependent trends. The inter-annual repeatability of condition-related traits ranged from zero to moderate and was mostly unrelated to plasma testosterone concentrations. However, males with elevated testosterone had significantly higher carotenoid-pigmented yellow plumage brightness, a trait presumably involved in mating. Showing inter-annual repeatability in testosterone levels, this research opens the way to further understanding the causes of variation in condition-related traits. Based on a longitudinal dataset, this study demonstrates that male plasma testosterone undergoes age-related changes that may regulate resource allocation. Our results thus suggest that, unlike females, male birds undergo hormonal senescence similar to mammals.

Elevational plumage divergence in the Rufous‐capped Babbler (Cyanoderma ruficeps) on a mountainous island

Environment plays an important role in the evolution of plumage coloration in birds and may also lead to sexual dichromatism if males and females face different selection pressures. Mountains exhibit varying ecological conditions along their elevation gradient that may impose divergent selection on elevationally widespread species, causing intraspecific plumage divergence. For example, UV light environments often vary between montane and lowland habitats, which could potentially cause differences in plumage UV reflection between birds occurring in the two types of habitats. However, few studies have examined the effects of elevation on plumage evolution. In this study, we quantified the plumage coloration of the Rufous‐capped Babbler Cyanoderma ruficeps from montane and lowland habitats on a mountainous island, Taiwan. We aimed to examine whether their plumage showed differences associated with changing ecological environments across the elevational gradient. The results supported that the plumage of babblers occupying montane habitats had higher UV‐reflectance and brightness than that of lowland birds, corresponding to the higher UV intensity in montane than lowland background light environments. The elevational differences were mainly found across the ventral parts of babblers that had relatively higher levels of UV reflectance compared with their dorsal parts. Alternatively, the brighter plumage, with higher UV‐reflectance in montane than lowland birds, might be mediated by physiological adaptation to other ecological factors, such as parasite pressures. The elevational differences in plumage UV‐reflectance and brightness were more dramatic in males than in females. However, we found significant sexual dichromatism in different body parts between montane and lowland babblers in which females had brighter or stronger UV‐associated coloration than males, suggesting that sexual selection has little impact on babbler plumage. Our study suggests the importance of elevational divergent selection associated with UV light or other ecological environments on avian plumage evolution.

High Contrast Allows the Retina to Compute More Than Just Contrast.

The goal of sensory processing is to represent the environment of an animal. All sensory systems share a similar constraint: they need to encode a wide range of stimulus magnitudes within their narrow neuronal response range. The most efficient way, exploited by even the simplest nervous systems, is to encode relative changes in stimulus magnitude rather than the absolute magnitudes. For instance, the retina encodes contrast, which are the variations of light intensity occurring in time and in space. From this perspective, it is easy to understand why the bright plumage of a moving bird gains a lot of attention, while an octopus remains motionless and mimics its surroundings for concealment. Stronger contrasts simply cause stronger visual signals. However, the gains in retinal performance associated with higher contrast are far more than what can be attributed to just a trivial linear increase in signal strength. Here we discuss how this improvement in performance is reflected throughout different parts of the neural circuitry, within its neural code and how high contrast activates many non-linear mechanisms to unlock several sophisticated retinal computations that are virtually impossible in low contrast conditions.

Extra-pair paternity and antiparasitic defence

BackgroundExtra-pair paternity (EPP) in birds provides benefits in terms of more offspring, and characteristics for maintenance of this behaviour have been the subject of investigation. Microorganisms are known to be transmitted during mating, especially when mating with multiple partners, and factors reducing this cost of multiple mating are expected. Further, plumage brightness and colour intensity have been shown to be important traits to benefits from multiple mating as predicted by sexual selection. The aim of this study was to investigate the relationship between the rate of extra-pair paternity and the relative size of the uropygial gland at the interspecific level, as the uropygial gland is an exocrine gland hypothesized to produce antiparasitic substances and further identified to affect plumage brightness. Because of the expected benefits of large uropygial gland in scenarios of sexual selection, we predicted a positive correlation with EPP.MethodsWe collected information from the literature of uropygial gland size and frequency of extra-pair paternity of 60 avian species of different families and explored the predicted positive correlation between them. We did so with means of comparative analyses that considered phylogenetic relationship as random factor and included body mass as covariate. We used Markov chain Monte Carlo generalized linear mixed models that were weighted by number of nests used to estimate extra-pair paternity.ResultsWe detected a positive relationship between level of extra-pair paternity and uropygial gland size at an interspecific level. This finding is consistent with the prediction.ConclusionsWe discuss the importance of this result in scenarios of sexual selection and argue that the detected relationship may have arisen by utilizing antiparasitic secretions through secondary sexual characters indicating parasite resistance.

Examining the link between relaxed predation and bird coloration on islands.

Insular ecosystems share analogous ecological conditions, leading to patterns of convergent evolution that are collectively termed as the 'island syndrome'. In birds, part of this syndrome is a tendency for a duller plumage, possibly as a result of relaxed sexual selection. Despite this global pattern, some insular species display a more colourful plumage than their mainland relatives, but why this occurs has remained unexplained. Here, we examine the hypothesis that these cases of increased plumage coloration on islands could arise through a relaxation of predation pressure. We used comparative analyses to investigate whether average insular richness of raptors of suitable mass influences the plumage colourfulness and brightness across 110 pairs of insular endemic species and their closest mainland relatives. As predicted, we find a likely negative relationship between insular coloration and insular predation while controlling for mainland predation and coloration, suggesting that species were more likely to become more colourful as the number of insular predators decreased. By contrast, plumage brightness was not influenced by predation pressure. Relaxation from predation, together with drift, might thus be a key mechanism of species phenotypic responses to insularity.

Does experimentally altered plumage brightness influence extra-pair mating success in female Tree Swallows (Tachycineta bicolor)?

Recent empirical evidence suggests that ornamental traits displayed by female birds may reflect aspects of their quality, and function during competitive interactions and (or) social mate attraction; however, less is known about how such traits influence extra-pair paternity. In Tree Swallows (Tachycineta bicolor (Vieillot, 1808)), plumage brightness of females signals their quality and may be related to extra-pair paternity if it enables them to invade the territories of other females to seek extra-pair copulations and (or) if potential extra-pair mates perceive their plumage brightness as attractive. Therefore, to examine whether the plumage brightness displayed by females influence rates of extra-pair paternity and the number of sires per brood, we experimentally enhanced and reduced the plumage brightness of females relative to controls. Our results showed that plumage brightness treatment of the female did not influence the number of extra-pair offspring in nests or the likelihood of a brood containing extra-pair offspring. Additionally, the number of extra-pair males siring offspring within the broods of females did not differ by plumage brightness treatment. Although extra-pair paternity has been shown to be beneficial for female Tree Swallows, our results suggest that plumage brightness of females does not influence their ability to engage in extra-pair mating.

Genome-wide variation in DNA methylation is associated with stress resilience and plumage brightness in a wild bird.

Individuals often differ in their ability to cope with challenging environmental and social conditions. Evidence from model systems suggests that patterns of DNA methylation are associated with variation in coping ability. These associations could arise directly if methylation plays a role in controlling the physiological response to stressors by, among other things, regulating the release of glucocorticoids in response to challenges. Alternatively, the association could arise indirectly if methylation and resilience have a common cause, such as early-life conditions. In either case, methylation might act as a biomarker for coping ability. At present, however, relatively little is known about whether variation in methylation is associated with organismal performance and resilience under natural conditions. We studied genome-wide patterns of DNA methylation in free-living female tree swallows (Tachycineta bicolor) using methylated DNA immunoprecipitation (MeDIP) and a tree swallow genome that was assembled for this study. We identified areas of the genome that were differentially methylated with respect to social signal expression (breast brightness) and physiological traits (ability to terminate the glucocorticoid stress response through negative feedback). We also asked whether methylation predicted resilience to a subsequent experimentally imposed challenge. Individuals with brighter breast plumage and higher stress resilience had lower methylation at differentially methylated regions across the genome. Thus, widespread differences in methylation predicted both social signal expression and the response to future challenges under natural conditions. These results have implications for predicting individual differences in resilience, and for understanding the mechanistic basis of resilience and its environmental and social mediators.

Function of the uropygial gland in eiders (Somateria mollissima)

BackgroundThe uropygial gland is an exocrine gland located above the tail of birds that produces a diverse range of biochemicals. It has been hypothesized to be involved in chemical protection, water-proofing and maintenance of plumage brightness. Although these not necessarily mutually exclusive functions have received some empirical support, there has been little empirical research on the function of water-proofing.MethodsHere we analyzed data for 229 individual eiders (Somateria mollissima) collected by Danish hunters during 2016‒2018.ResultsThe Eider is a sea-duck that spends almost its entire life in sea water emphasizing water-proofing of the plumage. The size of the uropygial gland increased with body mass in males, but not in females, and it increased with age. The size of the uropygial gland decreased during winter. Eiders with small uropygial glands grew their feathers at a fast rate. Eiders with large wing areas had large uropygial glands.ConclusionsThese findings are consistent with large uropygial glands playing a role in water-proofing during molt and foraging, but also that uropygial glands may play a role in chemical defense.

Sex differences in song and plumage color do not evolve through sexual selection alone: new insights from recent research

Recent studies show that traits long recognized as sexually selected ornaments, such as the bright plumage colors and melodious vocal displays of songbirds, have evolved in surprising ways. Male plumage colors are generally more elaborate and diverse than female colors, and in many species only males sing, so both of these dimorphisms are widely presumed to have evolved through sexual selection on males. Yet, in multiple widely divergent songbird clades, sexual differences in colors and songs have evolved through losses in females rather than gains in males. Indeed, changes in female phenotypes may be the principle driving factor affecting such sexual dimorphisms in most songbirds. Sexual dichromatism and song dimorphism also tend to be associated with life history traits other than mating system, such as seasonal migration or territorial behaviors. Altogether, these recent findings support the view that sexual dimorphism is an evolutionary byproduct of multiple, different selection pressures acting on each sex rather than just sexual selection on males. Researchers should therefore be cautious to avoid assuming that dimorphism itself is a character solely reflecting levels of sexual selection in species.

Fifty shades of brown: Macroevolution of plumage brightness in the Furnariida, a large clade of drab Neotropical passerines.

Both natural and sexual selection are thought to affect the evolution of bird color. Most studies of the topic have focused on sexually dichromatic taxa and showy plumages, which are expected to be more influenced by social selection and usually result in increased conspicuousness. However, many bird clades display dull brown or gray plumages that vary greatly in brightness (lightness), but little in hue (shade). Here, we examine the macroevolution of brightness in one such clade, the Furnariida. We make comparisons across light environments, body parts, monochromatic lineages, and each sex of dichromatic lineages. We found that support for models including light environments is greater for the dorsum than for the venter, and that brightness evolution is more constrained in the former than in the latter. Plumages in this clade have evolved to be darker in darker habitats, consistent with natural selection for increased crypsis. Finally, the features of brightness macroevolution are broadly similar across the sexes of the dichromatic clade, challenging the view that sexual dichromatism is driven by different evolutionary processes acting in each sex. We conclude that, in the Furnariida, light environments and dorsal-ventral variation are more important than sex as axes of color evolution.

Does experimentally altered plumage ornamentation of female passerines influence nestling quality? A test in female tree swallows

AbstractIt is widely recognized that female animals in a variety of taxa display ornamental traits, such as elaborate plumage, but elucidating whether such traits evolve by selection or genetic correlation remains a challenge because more ornamented females are often found to produce low‐quality offspring. While resource trade‐offs between the production of ornaments and offspring may underlie this negative relationship, it is not an adequate explanation for species where the timing of production of ornaments and offspring does not overlap. Instead, costs associated with engaging in agonistic interactions with conspecifics, which maintains the honesty of signals of quality, may also reduce resources available to invest in offspring. In this study, we enhanced and reduced the plumage brightness of female tree swallows (Tachycineta bicolor) relative to controls to test whether social costs associated with displaying bright plumage is a potential mechanism underlying the observation that more ornamented females produce low‐quality nestlings. Our results showed that nestlings reared by females in the enhanced plumage brightness treatment were structurally smaller, having shorter lengths of the combined head and bill than nestlings in the reduced plumage brightness treatment, and tended to grow their head and bills more slowly than nestlings in the reduced and control plumage brightness treatments. Nestlings in the enhanced plumage brightness treatment also tended to gain mass more slowly than nestlings in control treatment. Overall, that females with enhanced plumage brightness produced structurally smaller nestlings provides evidence that social costs paid by females may lead to the production of low‐quality offspring and should be considered in future studies.

Achromatic plumage brightness predicts stress resilience and social interactions in tree swallows (Tachycineta bicolor)

AbstractTheory suggests that signal honesty may be maintained by differential costs for high and low quality individuals. For signals that mediate social interactions, costs can arise from the way that a signal changes the subsequent social environment via receiver responses. These receiver-dependent costs may be linked with individual quality through variation in resilience to environmental and social stress. Here, we imposed stressful conditions on female tree swallows (Tachycineta bicolor) by attaching groups of feathers during incubation to decrease flight efficiency and maneuverability. We simultaneously monitored social interactions using an RFID network that allowed us to track the identity of every individual that visited each nest for the entire season. Before treatments, plumage coloration was correlated with baseline and stress-induced corticosterone. Relative to controls, experimentally challenged females were more likely to abandon their nest during incubation. Overall, females with brighter white breasts were less likely to abandon, but this pattern was only significant under stressful conditions. In addition to being more resilient, brighter females received more unique visitors at their nest-box and tended to make more visits to other active nests. In contrast, dorsal coloration did not reliably predict abandonment or social interactions. Taken together, our results suggest that females differ in their resilience to stress and that these differences are signaled by plumage brightness, which is in turn correlated with the frequency of social interactions. While we do not document direct costs of social interaction, our results are consistent with models of signal honesty based on receiver-dependent costs.

Why do birds matter to us-a perspective from Kashmir valley, India in light of declaration of 2018 as the year of birds?

The year 2018 has been declared as the Year of Birds with the aim of celebrating and protecting them. Birds are mysterious, cheerful and a marvellous creation with some unique and peculiar features. They are ecologically crucial in maintaining the balance of many ecosystems by sustaining various food chains and energy cycles. With their colourful bright plumage they enrich the natural scenic beauty of earth. Their migration, foraging, singing, breeding and nesting behaviour is quite astonishing. Birds make a variety of calls, sounds and songs with a language as complex as any spoken words that have many meanings, purposes and uses. Birds are the indicators of climatic conditions, natural calamities and bio-indicators of potential human impact and environmental degradation. Birds are facing continuous natural and anthropogenic threats due to multiple problems in the environment. The unregulated and unsustainable tourism and poaching threatens the habitat of so many game birds. Climate change, chemical use, loss of food source, overharvesting are the other impacts on bird loss. Awareness about stopping of habitat destruction, indiscriminate poaching birds, and regulated bird watching is the need of the time. We need to use more resources and put more sincere efforts for their management and conservation in view of the changing environment. Climate change has already altered the biological life on this planet, it would be interesting to know how climate change threatens bird’s life and survival. That will enable us in true sense to fulfil the objectives of the year of birds.

Experimentally altered plumage brightness of female Tree Swallows (Tachycineta bicolor) influences nest site retention and reproductive success

That ornamental traits of females can act as signals of quality has gained empirical support, but whether and how such ornaments of females mediate social interactions with conspecifics remains less clear. Female Tree Swallows (Tachycineta bicolor (Vieillot, 1808)) aggressively compete for and defend nest sites, and as such, nest site intrusions by conspecific females challenging ownership of a nest may prevent territory-owning females from dishonestly displaying ornamented plumage. We tested whether plumage brightness of female Tree Swallows influences nest site retention and reproductive success by experimentally enhancing or reducing their plumage brightness relative to controls prior to breeding. Females with reduced brightness were more likely to retain their nests sites and breed relative to control females and females with experimentally enhanced brightness. Females displaying enhanced brightness also tended to initiate clutches later than females with control and reduced brightness. Overall, lower nest site retention and reproductive success for females with enhanced brightness is consistent with social costs imposed on individuals dishonestly signalling high quality. Future studies in female birds should consider whether costs of losing a nest site to intruding conspecific females, especially in species where nest sites are limited, is a mechanism that maintains the honesty of signals of quality.