Ritualized display of a leaf: A putative agonistic signal in both sexes of a tropical bird.

Birds use many different signaling modalities (e.g. vocalizations, displays) to transmit information about their motivation to defend valuable resources. A handful of taxa use "props", inedible objects scavenged from the environment, in signaling. Several species of motmots (Coraciiformes) hold a leaf in their bill in a display that observational evidence suggests is agonistic. We used a simulated intruder experiment to test this display's agonistic signaling function using data from both members of pairs of russet-crowned motmots (Momotus mexicanus). If the display is agonistic, we expected territory-holding pairs to respond more strongly toward taxidermic mounts displaying a leaf. Our results showed that resident pairs reacted differently to the leaf display depending on the intruder's sex. Display of a leaf by the intruder increased the closeness of the pairs' approach when the model was male, but increased the probability of the territorial defenders displaying a leaf themselves when the model was female. Pairs spent more time responding to male models regardless of leaf display. Our results suggest that the leaf display is an agonistic signal, that territory owners react differently to the leaf display depending on the sex of the intruder performing it, and that the participation of both sexes in territorial defense-which is common among tropical resident birds-extends to this unusual signaling modality.

Seasonal variation in the utility of a status signaling system: Plumage ornament predicts foraging success only during periods of high competition.

Status signals allow competitors to assess each other's resource holding potential and reduce the occurrence of physical fights. Because status signals function to mediate competition over resources, a change in the strength of competition may affect the utility of a status signaling system. Status signals alter competitor behavior during periods of high competition, and thus determine access to resources; however, when competition is reduced, we expect these signals to become disassociated from access to resources. We investigated seasonal changes in status signaling of the male black-crested titmouse (Baeolophus atricristatus), a species that experiences substantial changes in population density and competition for food over the annual cycle. We compared the size of the prominent head-crest to foraging success at community-used feeding stations; we tested this relationship when competition was seasonally high, and when competition was seasonally low. We then experimentally decreased the number of feeders to increase competition (during the season of low-competition), and again tested whether male crest size predicted access to feeders. When competition was seasonally high, males with longer crests had greater access to feeders, but this pattern was not apparent when competition was seasonally low. When competition was experimentally increased, males with longer crests were again more successful at maintaining access to feeders. These findings provide evidence of a context-dependent status signaling system, where the status signal only mediates access to resources during periods of high competition. We discuss possible hypotheses for why the signaling system may not be functional, or detectable, during periods of low competition, including that competitors may interact less frequently and so have reduced opportunity for signaling, or that status signals are disregarded by receivers during periods of low competition because signalers are unlikely to escalate a contest into a fight. In any case, these results indicate that resource availability affects a status signaling system, and that the potential for status signaling persists in this system between seasons, even though such signaling may not be overtly present or detectable during periods of low competition.

Migration and the evolution of sexual dichromatism: evolutionary loss of female coloration with migration among wood-warblers.

The mechanisms underlying evolutionary changes in sexual dimorphism have long been of interest to biologists. A striking gradient in sexual dichromatism exists among songbirds in North America, including the wood-warblers (Parulidae): males are generally more colourful than females at northern latitudes, while the sexes are similarly ornamented at lower latitudes. We use phylogenetically controlled comparative analysis to test three non-mutually exclusive hypotheses for the evolution of sexual dichromatism among wood-warblers. The first two hypotheses focus on the loss of female coloration with the evolution of migration, either owing to the costs imposed by visual predators during migration, or owing to the relaxation of selection for female social signalling at higher latitudes. The third hypothesis focuses on whether sexual dichromatism evolved owing to changes in male ornamentation as the strength of sexual selection increases with breeding latitude. To test these hypotheses, we compared sexual dichromatism to three variables: the presence of migration, migration distance, and breeding latitude. We found that the presence of migration and migration distance were both positively correlated with sexual dichromatism, but models including breeding latitude alone were not strongly supported. Ancestral state reconstruction supports the hypothesis that the ancestral wood-warblers were monochromatic, with both colourful males and females. Combined, these results are consistent with the hypotheses that the evolution of migration is associated with the relaxation of selection for social signalling among females and that there are increased predatory costs along longer migratory routes for colourful females. These results suggest that loss of female ornamentation can be a driver of sexual dichromatism and that social or natural selection may be a stronger contributor to variation in dichromatism than sexual selection.

Blood parasite infection differentially relates to carotenoid-based plumage and bill color in the American goldfinch.

Male and female American goldfinches (Spinus tristis) express condition-dependent carotenoid-based plumage and bill coloration. Plumage color is relatively static, as pigments incorporated into feathers during the spring molt cannot be mobilized thereafter. In contrast, bill color is dynamic, reflecting changes in condition over short time periods. Previous studies have shown that male and female ornaments, though similar in expression, are differentially related to measures of immunocompetence, suggesting that the relationship between ornamentation and parasite infection may differ between the sexes. In this study, we evaluate the relationship between condition-dependent ornamentation (plumage and bill color) and blood parasite infection in male and female American goldfinches. We captured goldfinches after completion of the pre-alternate molt and prior to the onset of nesting and assessed prevalence of Trypanosoma parasites via blood smears. Plumage color strongly predicted trypanosome infection: Birds with more colorful plumage were less likely to present infections. In contrast, we detected no relationship between infection and bill color, which in other studies has been shown to dynamically reflect current condition. Sex did not affect the relationship between infection status and either ornament. Together, these results suggest that physiological pathways linking carotenoid ornamentation and infection may vary even within a single species.

Colorful displays signal male quality in a tropical anole lizard.

Parasites influence colorful ornaments and their behavioral display in many animal hosts. Because coloration and display behavior are often critical components of communication, variation in these traits may have important implications for individual fitness, yet it remains unclear whether such traits are signals of quality in many taxa. We investigated the association between ectoparasitic mite load and the color and behavioral use of the throat fan (dewlap) by male Anolis brevirostris lizards. We found that heavily parasitized lizards exhibited lower body condition, duller dewlaps, and less frequent dewlap displays than less parasitized individuals. Our results thus suggest that highly parasitized individuals invest less in both ornamental color and behavioral display of that color. Because the two components of the signal simultaneously provide information on male quality, this study provides novel support for the long-standing hypothesis that colorful traits may function as social or sexual signals in reptiles.

Carotenoid-based ornaments of female and male American goldfinches (Spinus tristis) show sex-specific correlations with immune function and metabolic rate.

Conspicuous ornamentation has been linked to immunological and physiological condition in males of many species. In species where both sexes are ornamented, it is unclear whether the signal content of ornaments differs between males and females. We examined the immunological and physiological correlates of carotenoid-based bill and plumage ornamentation in American goldfinches Spinus tristis, a species in which bright orange bills are sexually monomorphic but yellow plumage is sexually dimorphic during the breeding season. Because bill color is dynamic over short periods while plumage color is static over longer time frames, we tested whether these signals have the potential to provide temporal information about immunity and condition. In both sexes, bill color (but not plumage color) was negatively related to leukocyte differential, a measure of recent stress, while plumage color (but not bill color) was positively related to resting metabolic rate. In females, bill color also positively correlated with immunoglobulin Y, a component of acquired immunity, while plumage color positively predicted natural antibody levels, a component of innate immunity. In males, neither bill color nor plumage color predicted immune function, suggesting that the mechanisms underlying these signals vary with sex. Our results demonstrate that dynamic signals such as bill coloration do not merely reflect the same information provided by static signals but that these two classes of signal provide information about different temporal aspects of phenotypic quality. Furthermore, our results indicate that a signal expressed in both sexes has the potential to provide different information depending on the sex of the bearer.

Male bias in the song control system despite female bias in song rate in streak-backed orioles (Icterus pustulatus).

The song control system is a group of discrete interconnected nuclei found in the brains of all songbirds (suborder Passeri). Previous studies have reported a positive relationship between sex differences in song nucleus volumes and sex differences in song behavior across numerous songbird species, with species exhibiting greater sex differences in behavior also exhibiting greater sex differences in the brain. This body of comparative research, however, has failed to incorporate data from a bird species in which females sing more than males. In this study, we examine song nucleus volumes in both sexes of the streak-backed oriole (Icterus pustulatus), a New World blackbird with a female bias in song rate and similar song complexity between the sexes. Results from this neuroanatomical analysis are contrary to what was to be expected from previous research: despite the female bias in song rate, males have a significantly larger HVC and area X song nucleus volumes. Specifically, male HVC was 75% larger than that of females, and male area X was 64% larger than that of females. There was no significant sex difference in the size of the nucleus robustus arcopallialis. The lack of a positive relationship between song nuclei and singing behavior in these orioles demonstrates that our current understanding of song modulation via the song control system may be overly reliant on basic measures such as total volumes.

Philornis fasciventris (Wulp) (Diptera: Muscidae): description of the male, larva and puparium, with notes on biology and host association

O macho, larva e pupário de Philornis fasciventris (Wulp) são descritos pela primeira vez, assim como os hábitos larvais e associação com o hospedeiro. O material foi coletado em Yucatan, México no ninho de Eumomota superciliosa (Sandbach) (Coraciformes: Momotidae), primeiro hospedeiro registrado para essa espécie. E. superciliosa é também novo registro de hospedeiro para Philornis.

The male, larva and puparium of Philornis fasciventris (Wulp) are described for the first time, as well as the larval habit and host association. The material was collected in Yucatan, Mexico in a nest of the turquoise-browed motmot, Eumomota superciliosa (Sandbach) (Coraciformes: Momotidae), first host record for this species. E. superciliosa is also a new host record for Philornis.

Philornis fasciventris (Wulp) (Diptera: Muscidae): description of the male, larva and puparium, with notes on biology and host association.

The male, larva and puparium of Philornis fasciventris (Wulp) are described for the first time, as well as the larval habit and host association. The material was collected in Yucatan, Mexico in a nest of the turquoise-browed motmot, Eumomota superciliosa (Sandbach) (Coraciformes: Momotidae), first host record for this species. E. superciliosa is also a new host record for Philornis.