Male Satin Bowerbirds Research Articles

Bower paint removal leads to reduced female visits, suggesting bower paint functions as a chemical signal

The multifaceted courtship display of male satin bowerbirds, Ptilonorhynchus violaceus, involves several elements that have been studied in detail. However, one of their most unique display elements, bower painting, has received relatively little attention despite males' large investment of time in this behaviour. Male bowerbirds chew plant material and apply the resulting mixture of masticated vegetation and male saliva or ‘bower paint’ to a chest-high band inside their bower walls. Searching females taste this paint, suggesting that paint may be a chemosensory signal. We used both behavioural observations and experimental approaches to examine predictions made by two hypotheses for the function of bower paint. We measured natural variation in paint quantity to investigate whether quantity of paint at bowers is related to other male display traits, male mating success and male physical condition. We also investigated whether males and females are affected by experimental removal of bower paint. Additionally, we assessed male response to paint transplants from other individuals. We found a significant correlation between the amount of paint and a composite estimate of several other measures known to indicate bower and decoration display quality. Also, males whose bowers underwent experimental removal of paint had fewer females return for second courtships and copulations than did control males. This result provides the first experimental evidence that females respond to bower paint. These findings establish that bower paint is a trait that affects mate-searching decisions by females and demonstrates that the quantity of bower paint is important in attracting females.

Male satin bowerbirds use sunlight to illuminate decorations to enhance mating success

Male satin bowerbirds use sunlight to illuminate decorations to enhance mating success

Complex relationship between multiple measures of cognitive ability and male mating success in satin bowerbirds, Ptilonorhynchus violaceus

Many animal species have complex cognitive abilities previously assumed to be limited to humans. Explanations for how these abilities evolved have focused on ways in which cognitive performance may influence survival, such as solving ecological problems or navigating complex social environments. However, sexual selection (differences in the reproductive success of individuals) can also lead to the evolution of complex traits. This could occur, for example, if females prefer males with better cognitive ability. A common assumption of models of female choice for male cognitive ability is that performance scores on different cognitive tasks are intercorrelated. In the present study, we evaluated performance of male satin bowerbirds on six cognitive tasks. Although we found little intercorrelation amongst males’ performance scores of these tasks, males with better scores for two integrative measures of these cognitive tasks had higher mating success, which is a good indicator of reproductive success in this species. In addition, a multiple regression analysis suggested that performance on most cognitive tasks independently predicted mating success. Our results point to an important link between sexual selection and cognitive ability that has not been well appreciated and appears to be quite complex.

Blue, not UV, plumage color is important in satin bowerbird Ptilonorhynchus violaceus display

Several studies have suggested that peak plumage reflectance in birds matches color preferences used in mate choice. We tested this hypothesis in adult satin bowerbird males that have a short‐wavelength saturated blue‐black plumage with a peak reflectance in the UV. We found that the chroma of the blue (405–480 nm), but not the peak reflecting UV (320–400 nm) portion of the male plumage spectrum was significantly correlated with male mating success. A plot of correlation coefficients between male mating success and plumage saturation showed a well‐defined peak in the blue. This suggests that: 1) blue plumage coloration is more important in mate choice than UV or other colors, and 2) that there is a mismatch between the peak reflectance of the plumage of male satin bowerbirds and the range of plumage wavelengths that are correlated with male mating success. This indicates that it is not safe to infer a role of UV or other colors in mate choice simply because of a peak in plumage reflectance.

Experimental blocking of UV reflectance does not influence use of off-body display elements by satin bowerbirds

UV reflectance of plumage display is important in mate choice of many avian species, but its role in off-body display has received little consideration. Male satin bowerbirds (Ptilonorhynchus violaceus) collect objects for use as bower decorations. Here, I test the hypothesis that UV and non-UV colors are important in choice of satin bowerbird bower decorations (colored squares and blue parrot feathers) in an experiment using UV blocking agents at the bowers of 31 males. I found a highly significant preference for blue decorations but no evidence of a preference for UV-reflecting decorations. UV-blocked blue objects were used to the same extent as identical unblocked decorations, and UV-reflecting decorations that were not blue were not attractive. The evolution of off-body decoration displays may have contributed to a reduced role for UV-reflecting decoration displays in satin bowerbirds in 3 ways: 1) use of UV-reflecting display objects that are not made by the bird does not directly signal their owners' condition as would the birds own plumage, 2) because of the relatively low level of ambient UV light available to illuminate decorations displayed on a court the forest floor, UV may be less effective than other wavelengths for these displays, and 3) decorations that are both blue and UV reflective may be too rare under natural conditions to be effective signals of male quality. Off-body displays may provide very different kinds of information from plumage displays, and these differences may have contributed to the evolution of complex multicomponent displays.

Female preferences drive the evolution of mimetic accuracy in male sexual displays

Males in many bird species mimic the vocalizations of other species during sexual displays, but the evolutionary and functional significance of interspecific vocal mimicry is unclear. Here we use spectrographic cross-correlation to compare mimetic calls produced by male satin bowerbirds (Ptilonorhynchus violaceus) in courtship with calls from several model species. We show that the accuracy of vocal mimicry and the number of model species mimicked are both independently related to male mating success. Multivariate analyses revealed that these mimetic traits were better predictors of male mating success than other male display traits previously shown to be important for male mating success. We suggest that preference-driven mimetic accuracy may be a widespread occurrence, and that mimetic accuracy may provide females with important information about male quality. Our findings support an alternative hypothesis to help explain a common element of male sexual displays.

Stealing behavior and the maintenance of a visual display in the satin bowerbird

Honest signals that indicate male quality have been observed in many species and are thought to have evolved to allow males to assess rivals accurately and respond to cheaters. Females could potentially also use the same honest signals as reliable indicators of male quality. In bowerbirds, the numbers of specific bower decorations may serve as an honest signal of male quality: this study investigates whether decoration stealing among male satin bowerbirds at the Bunya Mountains, Australia, may also involve honest signals. In this study, we aimed to determine 1) predictors for the degree to which individual male satin bowerbirds steal, and are stolen from, and 2) predictors for why some male pairs interact by stealing, whereas other pairs do not. We also assessed how experimentally standardizing the number of decorations on bowers would affect the 1) frequency of stealing, 2) specific interactions among males, and 3) distribution of decorations across bowers. Bower decorations were labeled and tracked through one breeding season. Males that were successful stealers, stole from other successful stealers, had many feathers and bottle tops on their bowers and painted their bower walls often. Male pairs were more likely to interact by stealing if their bowers were in close proximity. Most of the stealing observed was of a reciprocal nature. After we standardized the numbers and types of decorations on a small group of males' bowers, the mean number of daily stealing gains and the total number of males interacting by stealing did not change. In addition, no significant novel stealing interactions were initiated after the manipulation. The average number of all bower decorations and the average number of rosella feathers on a given male's bower prior to the manipulation were proportional to the average numbers for the period after the manipulation. Furthermore, males that originally had better collections of decorations tended to stiffer fewer losses due to stealing after the manipulation. Our results sugguest that the total number of decorations, the total number of rosella feathers on a male's bower, and possibly stealing behavior, may form part of the basis of an honest signal indicating male quality and therefore might be correlated with mating success.

Male satin bowerbirds (Ptilonorhynchus violaceus) compensate for sexual signal loss by enhancing multiple display features

Numerous studies have focussed on the relationship between female choice and the multiple exaggerated sexual traits of males. However, little is known about the ability of males to actively enhance specific components of their display in response to the loss of one component. We investigated the capacity of male satin bowerbirds (Ptilonorhynchus violaceus) to respond to the loss of one of their sexual signals by performing an experiment in which we removed decorations at their bowers. We found that males compensated for decoration loss by increasing bower construction behaviour and decreasing their latency to bower painting. These results are novel because they suggest that males can assess the quality of their own display and make decisions about how to augment their displays. We discuss these results in the context of previous studies of mate choice in satin bowerbirds, as both of the supplementary behaviours we observed are known correlates of male mating success.

Theft of bower decorations among male Satin Bowerbirds (Ptilonorhynchus violaceus): why are some decorations more popular than others?

Male Satin Bowerbirds (Ptilonorhynchus violaceus) build stick structures known as bowers that serve as the focus for courtships and matings. Males decorate their bowers with numerous coloured decorations and are known to steal these decorations from one another. We investigated the stealing of bower decorations among males at the Bunya Mountains in Queensland, Australia. We aimed to (1) determine which classes of decorations were targets for theft in the studied population, and (2) examine whether the frequency at which individual decorations were stolen related to their intrinsic properties. To address our first aim, all decorations on the bowers of 21 adult males were labelled and their movements tracked throughout one mating season. To address our second aim, decorations stolen at least three times during the season were collected and their morphological and reflectance properties compared to those of decorations that were not stolen. In terms of the classes of decorations, tail feathers of Crimson Rosella (Platycercus elegans) were stolen more than any other class of decoration, but blue plastic bottletops were the most popular decorations relative to their availability on bowers. Frequently stolen individual decorations were similar to non-stolen items in their weights and surface areas, but were darker blue in colour than the decorations never stolen. Both bottletops and feathers reflected higher levels of ultraviolet (UV) light than did all other classes of bower decorations tested, thus suggesting that males may be using UV reflectance in sexual signalling. The darker blue, stolen decorations may increase contrast between the decoration collection and the platform, while the UV-reflecting subset of most frequently stolen decorations (bottletops and feathers) may increase contrast within the decoration collection. This in turn may increase the attractiveness of the display to females.

Iridescent plumage in satin bowerbirds: structure, mechanisms and nanostructural predictors of individual variation in colour

Iridescence is produced by coherent scattering of light waves from alternating layers of materials of different refractive indices. In birds, iridescent colours are produced by feather barbules when light is scattered from alternating layers of keratin, melanin and air. The structure and organization of these layers, and hence the appearance of bird species with different types of plumage iridescence, varies extensively. One principal distinction between different types of iridescent colours is whether they are produced by a single pair of layers or by multiple pairs of layers. Multi-layer iridescence, such as that displayed by hummingbirds, has been relatively well characterized, but single-layer iridescence has only recently been modeled successfully. Here we use electron microscopy, spectrometry and thin-film optical modeling to investigate the glossy, ultraviolet-blue iridescent plumage colouration of adult male satin bowerbirds Ptilonorhynchus violaceus minor. The flattened barbules of adult males are composed of a superficial keratin layer overlying a melanin layer that is several granules thick. A thin-film model based on the thickness of the keratin layer and its two associated interfaces (air/keratin and keratin/melanin) generates predicted reflectance spectra that closely match measured spectra. In addition, hues predicted from this model are positively correlated with measured hues. As predicted from our thin-film model, measured hues shifted to shorter wavelengths at increasing angles of incidence and reflectance. Moreover, we found that individual variation in barbule nanostructure can predict measured variation in both hue and UV-chroma. Thus, we have characterized the microstructure of satin bowerbird barbules, uncovered the mechanisms responsible for producing ultraviolet iridescence in these barbules, and provided the first evidence of a nanostructural basis for individual variation in iridescent plumage colour.

Male satin bowerbirds, Ptilonorhynchus violaceus, adjust their display intensity in response to female startling: an experiment with robotic females

Females of many species preferentially mate with males that produce courtship displays at a high intensity or rate; however, males do not always display at their maximum intensity during courtship. Evidence suggests that this behaviour may be adaptive in satin bowerbirds, because overly intense displays can disrupt courtship by startling females. Females signal the display intensity that they will tolerate from a male; males that respond by adjusting their intensity reduce the likelihood of startling females and increase their courtship success. However, even the most responsive males occasionally startle females. When this occurs, males could avoid further threat to females by decreasing the intensity of their subsequent displays. We used robotic female bowerbirds that mimicked female startling to test the hypothesis that males reduce the intensity of their courtship displays after startling females. Supporting this hypothesis, males displayed at significantly lower intensity after robots were startled in experimental treatments than when they were not startled in control treatments. We found no evidence that the degree of male response to startling was related to male courtship success. In spite of evidence that female bowerbirds prefer the most intensely displaying males as mates, we found that males did not always display at maximum intensity, but rather reduced their intensity in response to female startling during courtship. Our results suggest that males adjust the level of expression of their display traits in response to female behaviours during courtship, and by doing so, males may increase their chances for successful courtship.

Juvenile infection and male display: testing the bright male hypothesis across individual life histories

Current tests of the bright male hypothesis focus on assays of adult disease resistance and their relation to male trait development and female choice. We suggest that if parasites have significant harmful effects on juvenile stages of a host, then females selecting males that effectively signal juvenile parasite resistance may gain a significant “good genes” benefit. Currently, there is no information on juvenile and adult infection or resistance in the same male and whether adult male displays signal juvenile parasite resistance. In the present study, we measure infection of the ectoparasitic louse, Myrsidea ptilonorhynchi, in individual male satin bowerbirds (Ptilonorhynchus violaceus) both as juveniles and nine or more years later as adults. We test hypotheses that examine the role of juvenile parasite infection in mediating sexual selection. We found that (1) juvenile infection is higher than adult infection in the same individuals, (2) adult males able to hold display sites have lower juvenile infection, and (3) juvenile and adult infection in the same individuals are not significantly correlated. In addition, comparisons among a larger set of individuals from a single year show that blood and ectoparasite infections are highly correlated, and both decrease with male age and are inversely related to male courtship success. These results, combined with the evidence that females mate exclusively with bower-holding males support the hypothesis that females use adult male display traits to identify males with a high level of juvenile disease resistance. We suggest that effective tests of the bright male hypothesis should include (1) assessment of infection resistance in both subadult and adult life history stages, (2) tests of whether differences in age-specific resistance are indicated in adult male displays, and (3) tests to determine if females attend to these traits in mate choice. Although these requirements increase the difficulty of testing the bright male hypothesis, they are necessary for a more accurate assessment of the effects of parasites on male display and female choice.

Home-range sizes and bower visitation patterns of immature male Satin Bowerbirds (Ptilonorhynchus violaceus)

Adult male Satin Bowerbirds build and decorate stick bowers to which they attract females for matings; females choose among males based on these complex bowers, decorations placed at these bowers, and displays consisting of vocalisations and posturing. Male Satin Bowerbirds undergo an extended period of delayed morphological maturation during which they retain female-like plumage and are assumed to learn adult male behavioural traits. Little is known, however, of how immature males acquire the ability to display and build and decorate bowers, except that they observe the displays of adult males at adults’ bowers, and practise their own displays at both adults’ and ‘practice’ bowers. We present data on the home ranges and movement patterns of six immature males, acquired through radio-tracking at the Bunya Mountains in south-east Queensland. Home-range size averaged 13.67 ± 3.38 ha and immature males visited only some of the bowers located in their home ranges. On average, they visited 2.33 ± 0.52 adults’ bowers and 4.00 ± 2.00 practice bowers.

Structural plumage colour and parasites in satin bowerbirdsPtilonorhynchus violaceus: implications for sexual selection

We investigated whether variation in structural plumage coloration in satin bowerbirds,Ptilonorhynchus violaceus, could reveal the intensity of infection from parasites, as predicted from models of parasite‐mediated sexual selection (PMSS). To do this, we captured adult male, female, and juvenile male satin bowerbirds in Queensland, Australia, and objectively measured individual plumage reflectance from four body regions using a spectrometer. We quantified both ectoparasite load and the intensity of infection from blood parasites. In iridescent blue adult males, plumage reflectance is unimodal, with a single peak in the ultraviolet, while in greenish females and juveniles, plumage reflectance is bimodal, with peaks in both the ultraviolet and green portions of the spectrum. In adult males, the intensity of infection from blood parasites was best predicted by plumage brightness (total reflectance), with brighter males having fewer parasites. Similarly, juvenile males exhibiting greater UV chroma (proportion of reflectance in the UV) had fewer blood parasites. Our findings support a key prediction of PMSS models and provide the first evidence that a structural colour ornament can signal the intensity of infection from blood parasites.

Multiple sexual ornaments in satin bowerbirds: ultraviolet plumage and bowers signal different aspects of male quality

Much attention has been devoted to understanding the evolution of elaborate male ornaments and how they may signal male quality. However, the evolution of multicomponent sexual signals remains poorly understood, and past research on this type of signaling has been largely theoretical. Satin bowerbirds, Ptilonorhynchus violaceus, are polygynous, are sexually dichromatic, and construct sexually selected display structures (bowers): a model system for investigating the evolution and signal function of multiple sexual signals. We studied the interrelationship between bower features, plumage coloration, and indicators of male quality in this species. To do this, we located the bowers of male satin bowerbirds in rainforest in Queensland, Australia, and quantified bower quality. We captured the male bower owners and used reflectance spectrometry to objectively measure the plumage coloration of several body regions. We measured various indicators of male health and condition, including the intensity of infection from ectoparasites and blood parasites. Bower quality and male ultraviolet plumage coloration were significantly correlated. By using multiple regression analyses, we show that bower quality predicts ectoparasite load and body size, whereas ultraviolet plumage coloration predicts the intensity of infection from blood parasites, feather growth rate, and body size. Our findings support the multiple messages hypothesis of multicomponent signals: Female satin bowerbirds should assess both male and bower features to choose the highest quality mates.

Bower location and orientation in Satin Bowerbirds: optimising the conspicuousness of male display?

Male Satin Bowerbirds, Ptilonorhynchus violaceus, have been reported to construct their bowers with the decorated portion of the bower platform oriented northward. Given the regularity of this orientation, it has been suggested that the intensity and quality of incoming solar radiation may enhance male displays. However, previous reports of bower orientation originate from studies conducted in open-canopy, sclerophyll forest, where diel variation in the intensity of light striking the bower is mostly influenced by the altitude and azimuth of the sun. We studied 12 Satin Bowerbird bowers in the mountainous rainforest of the Atherton Tablelands, Australia, and found no significant tendency for bower platforms to face north. Instead, bowers were invariably constructed near canopy gaps, and there was a significant tendency for bowers to face away from these gaps. We suggest that this pattern of orientation allows displaying males to be illuminated predominantly from the front when viewed by females from within the bower avenue. There was also a significant positive association between bower orientation and the orientation of the slope of the hill on which the bower was constructed, such that bowers were oriented upslope, further enhancing frontal illumination. We suggest that Satin Bowerbirds may use a variety of means, including bower orientation, to achieve this objective.

Male displays adjusted to female's response.

Models of sexual selection generally assume that behavioural courtship displays reflect intrinsic male qualities such as condition, and that males display with maximum intensity to attract females to mate. Here we use robotic females in a field experiment to demonstrate that male satin bowerbirds (Ptilonorhynchus violaceus) do not always display at maximum intensity - rather, successful males modulate their displays in response to signals from females. Our results indicate that sexual selection may favour those males that can produce intense displays but which know how to modify these according to the female response.

The Value of Objects to Satin Bowerbirds Ptilonorhynchus violaceus

SummaryThe mating success of male Satin Bowerbirds Ptilonorhynchus violaceus is known to correlate with the numbers of decoration objects present at their bowers. It was expected that the value of an object, in terms of fitness payoffs to males, would be less in an area where the average number of objects at bowers was high than in an area where the average numbers of objects at bowers was low. We found (a) rates of visiting bowers by adult females and immature individuals were correlated with the number of marked objects at those bowers within but not between areas, (b) the rate of stealing objects was higher in the area at which the average number of objects at bowers was lowest and (c) bower destruction increased relative to stealing in the area where the average number of objects was highest. These findings suggest that the relative importance of behaviour associated with competition and sexual display in male Satin Bowerbirds is subject to variation in response to environmental conditions.

Age-Related Effects of Testosterone, Plumage, and Experience on Aggression and Social Dominance in Juvenile Male Satin Bowerbirds (Ptilonorhynchus violaceus)

Age-Related Effects of Testosterone, Plumage, and Experience on Aggression and Social Dominance in Juvenile Male Satin Bowerbirds (Ptilonorhynchus violaceus)

Female choice for parasite-free male satin bowerbirds and the evolution of bright male plumage

Hamilton and Zuk proposed that bright male plumage may have evolved in males of polygynous species as a result of female preferences for males that are able to demonstrate their resistance to disease. They predicted an inverse correlation between female mating preferences and the level of parasitic infection of males. We found such a correlation between the level of infection by a common ectoparasite (Myrsidea ptilonorhynchi: Menoponidae) and mating success of male satin bowerbirds (Ptilonorhynchus violaceus). In addition, we tested and were able to confirm three other predictions derived from their model: that (1) older males had fewer parasites than their younger counterparts, (2) levels of individual parasitic infection are highly correlated between years, and (3) that individuals resighted in successive years are less parasitized than those that fail to return. These results support the bright male model, but they are also consistent with two other hypotheses that may explain plumage dimorphism based on the level of parasitic infection. The correlated infection model suggests that females choose males with few ectoparasites because of a correlation between the level of ectoparasitic infection and heritable resistance to internal infections. In the parasite avoidance model, females favor parasitefree males because it lowers their own prospects for parasitic infection. Our data did not show the predicted relationship between parasite numbers with plumage quality that is needed to support the bright male hypothesis, nor did it show the inverse correlation between male condition and parasite numbers that is predicted by both the bright male and correlated infection hypotheses. Our results are most consistent with the parasite avoidance hypothesis.