Lilian T. Manica

Here comes the sun: multimodal displays are associated with sunlight incidence

Conspicuousness of courtship signals in animals likely evolved to maximize mate attraction while minimizing predator detection. It is assumed, though largely unknown, that environmental and luminosity conditions affect the detectability of ornaments and motor displays and could thus strongly influence behavior. We combined visual models and behavioral observations to test whether the multimodal display of the blue-black grassquit (Volatinia jacarina) is influenced by environmental conditions, predicting that males should display more often in moments with high sunlight incidence upon their bodies. By displaying in such a context-dependent fashion, males would be able to maximize conspicuousness of their iridescent blue-black plumage and avoid displaying continuously, since the latter would involve higher energetic investment. We recorded the rates of both complete displays (leap with singing) as well as incomplete ones (singing while perched) for males during repeated 30-min focal observations in varying environmental situations in the field. We found that when bathed directly in sunlight, males increased their rates of displays, tending to exhibit more complete rather than incomplete displays in this condition and suggesting a potential trade-off between display types. Our results suggest that animals may adjust the timing and precise location of signal activity to improve the efficiency or likelihood of detection of some signal elements.

Blood parasites in Brazilian Atlantic Forest birds: effects of fragment size and habitat dependency

Deforestation, fragmentation and habitat disturbance may alter the relationship between pathogens and hosts. We tested, apparently for the first time, whether habitat fragmentation and degree of dependence on forests affect the prevalence of avian blood parasites. We estimated the prevalence of Plasmodium , Haemoproteus and Trypanosoma through the inspection of 925 blood smears from 109 species captured in six pairs of small ( 1,000 ha) Brazilian Atlantic Forest fragments. Prevalence of the three types of parasites did not differ between small and large forest patches. Forest-independent birds were usually more infected with Plasmodium and Haemoproteus than other birds, but forest-dependent birds were more infected with Trypanosoma . Parasite richness on birds was not affected by patch size.

Vocal output predicts territory quality in a Neotropical songbird.

Females who choose highly ornamented mates may gain resources that improve offspring production and survival. Studies have focused on the relationship between male quality and the complexity of sexual ornaments; however, less is known of the communicative content of courtship displays, and whether they indicate the quality of resources males can provide to mates. Here, we used blue-black grassquits (Volatinia jacarina) to test the relationship between male display attributes and territory quality, measured as food availability. Our main hypothesis was that territory quality would be better predicted by dynamic displays than by static ornaments. During four breeding seasons in central Brazil, we quantified display song attributes (output and consistency) and the timing of nuptial molt. We measured territorial seed density, body condition, and ectoparasite infestation. We found a positive relationship between song output and territory seed density, suggesting this attribute provides a reliable indicator of territory quality. However, the timing of molt was unrelated to territory quality. Additionally, no other male attribute was associated with seed density. The link between song output and territory quality might reflect variation in male condition in response to territorial resources, or extra time males on higher quality territories have to invest in territorial defense. This article is part of a Special Issue entitled: Neotropical Behaviour.

Vigor and skill in the acrobatic mating displays of a Neotropical songbird

Animal social behaviors are often mediated by signals that provide information about signaler attributes. Although some signals are structurally simple, others are temporally dynamic and multifaceted. In such cases, exaggeration of some display components is likely to curtail the expression of others. We quantified features of the acrobatic, multimodal “leap display” of blue-black grassquits (Volatinia jacarina), which appears to entail moderate-to-high performance levels in terms of vigor and skill. We video recorded and quantified leap parameters (height, duration, rotation angle, launch velocity, and number of wing beats) and assessed how these parameters covaried with each other and with vocal parameters, display rates, and body mass index. Our analyses revealed correlations among multiple performance variables: leap height, duration, launch velocity, and number of wing beats. Leap height also correlated positively with song duration. By contrast, no leap parameters covaried with rotation angle. Our analyses also revealed a trade-off in vigor and skill-based leap attributes: birds with a lower body mass index showed a negative relationship between leap heights and the proportion of displays that included leaps (vs. perched vocalizations only). Our results identify directions of display evolution subject to mechanical or timing constraints and provide evidence that display attributes that emphasize vigor and skill may limit one another. Our results also support a key expectation of handicap models of display evolution, which is that costs of display execution should be borne disproportionately by signalers of lower quality.

Conspicuous sexual signals in a socially monogamous passerine: the case of neotropical Blue-black Grassquits

Sexual selection has shaped many traits involving communication, behavior, morphology, and reproductive strategies. Sexual communication in the Blue-black Grassquit Volatinia jacarina involves an iridescent, nuptial plumage and the exhibition of a complex motor and acoustic mating display. Blue-black Grassquits breed in small, aggregated territories, are socially monogamous, but have high rates of extrapair fertilization and intensive paternal care. Here, we discuss the evolution of sexually selected ornaments in this species and review some studies that have evaluated their costs and benefits. Our data suggest that females have an active role in obtaining extrapair fertilizations, but appear to be indiscriminate in their choice of extrapair males. However, it remains necessary to evaluate female choice in natural circumstances, and the effects of such on male reproductive success. This is particularly important because, in the field, we found that the male motor display may provide a useful cue for nest predators, and therefore evolution of female choice may be constrained by the probability of higher nest predation associated with choosing males exhibiting high display rates. Our studies also indicate that small males have an advantage in aggressive interactions with larger males. We hypothesize that small male size may be driven by female choice for male motor performance, including aspects of display agility and acrobatic capacity, leading to better performance by small males in intrasexual interactions involving flight within confined spaces. Alternatively, the food resource may be more valuable to smaller males, resulting in higher aggression to access the food.

Flights of Fancy: Mating Behavior, Displays and Ornamentation in a Neotropical Bird

Studies on sexual selection in birds have focused on female assessment of genetic or non-genetic qualities of potential partners, using cues such as plumage coloration and song. Here, we review published data on breeding, mating systems, and communication in the blue-black grassquit (Volatinia jacarina), a common neotropical passerine with social monogamy and a cryptic polyandrous sexual system. During the breeding season males molt into a structurally colored plumage and execute aerial courtship displays, suggesting sexual selection for extravagant attributes. Overall, studies have shown that plumage and motor display in blue-black grassquits reliably reveal individual quality, and possibly are under conspecific evaluation in different social and sexual contexts. One of the main challenges in understanding sexual selection in blue-black grassquits, especially the role of female choice, is due to the fact that the choice of a social pair by females in this species is not necessarily equivalent to the sexual choice. Females engage in high rates of extra-pair copulations, and thus to evaluate the breeding success of males it is necessary to determine the genetic paternity of offspring. Future studies will incorporate paternity analyses to allow further understanding of the social and sexual mating system in this species, and to determine how and whether motor and acoustic components of male display influence female choice.Abstract Studies on sexual selection in birds have focused on female assessment of genetic or non-genetic qualities of potential partners, using cues such as plumage coloration and song. Here, we review published data on breeding, mating systems, and communication in the blue-black grassquit (Volatinia jacarina), a common neotropical passerine with social monogamy and a cryptic polyandrous sexual system. During the breeding season males molt into a structurally colored plumage and execute aerial courtship displays, suggesting sexual selection for extravagant attributes. Overall, studies have shown that plumage and motor display in blue-black grassquits reliably reveal individual quality, and possibly are under conspecific evaluation in different social and sexual contexts. One of the main challenges in understanding sexual selection in blue-black grassquits, especially the role of female choice, is due to the fact that the choice of a social pair by females in this species is not necessarily equivalent to the sexual choice. Females engage in high rates of extra-pair copulations, and thus to evaluate the breeding success of males it is necessary to determine the genetic paternity of offspring. Future studies will incorporate paternity analyses to allow further understanding of the social and sexual mating system in this species, and to determine how and whether motor and acoustic components of male display influence female choice.

Immune-related effects from predation risk in Neotropical blue-black grassquits (Volatinia jacarina)

Predation is a major force shaping natural history traits of birds because of their vulnerability during nesting and higher visibility during diurnal activities. For most birds in the Neotropics, predation is the major cause of nest failure due to the regions high diversity and abundance of predators. The blue-black grassquit (Volatinia jacarina), similarly to other small passerines in the savanna region of central Brazil, suffers extremely high rates of nest predation. Additionally, males may be particularly vulnerable to predators since they are very conspicuous when executing courtship displays. We assessed some of the non-lethal costs of predation risk on this species by comparing physiological and morphological parameters of birds exposed to predator vocalizations with that of control subjects exposed to non-predator vocalizations. Birds exposed to the predator vocalizations exhibited an immune-related reaction (changes in their H/L ratio), but no changes were observed in other biological parameters measured. This article is part of a Special Issue entitled: Neotropical Behaviour.