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Agonistic conflict is ubiquitous throughout taxa, although the intensity of aggression observed is often highly variable across contexts. For socially monogamous species, a coordinated effort by both pair members can improve the chances of successfully warding off challengers and reinforce pair bonds. However, the intensity of aggression exerted by any one pair member may vary with respect to contextual factors, including the intensity of their mate's aggression. Thus, experimentally exploring how individuals respond to potential rivals via multiple assays with varying social contexts can advance our basic understanding of how aggression varies in socially monogamous systems. We used simulated territorial intrusion and mirror image simulation assays to explore this issue in white-shouldered fairywrens (Malurus alboscapulatus moretoni) of Papua New Guinea. While males tended to be more responsive than females during simulated territorial intrusions, females were more aggressive towards their mirrored reflection than males. Further, individual females that were most aggressive in mirror image simulations were the least aggressive during simulated territorial intrusions, whereas males were inconsistent. These results suggest that female behavioral phenotypes appear to be flexible, relative to context. We discuss how multiple commonly used measurements of aggression might in fact measure different types of responses., Competing Interests: Declaration of Competing Interest We do not have any conflicts of interest to disclose., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Many urban areas have elevated soil lead concentrations due to prior large-scale use of lead in products such as paint and automobile gasoline. This presents a potential problem for the growing numbers of wildlife living in urbanized areas as lead exposure is known to affect multiple physiological systems, including the nervous system, in vertebrate species. In humans and laboratory animals, low-level lead exposure is associated with neurological impairment, but less is known about how lead may affect the behavior of urban wildlife. We focused on the Northern Mockingbird Mimus polyglottos, a common, omnivorous North American songbird, to gain insights into how lead may affect the physiology and behavior of urban wildlife. We predicted that birds living in neighborhoods with high soil lead concentrations would (a) exhibit elevated lead concentrations in their blood and feathers, (b) exhibit lower body condition, (c) exhibit less diverse and consistent vocal repertoires, and (d) behave more aggressively during simulated conspecific territorial intrusions compared to birds living in neighborhoods with lower soil lead concentrations. Controlling for other habitat differences, we found that birds from areas of high soil lead had elevated lead concentrations in blood and feathers, but found no differences in body condition or vocal repertoires. However, birds from high lead areas responded more aggressively during simulated intrusions. These findings indicate that sub-lethal lead exposure may be common among wildlife living in urban areas, and that this exposure is associated with increased aggression. Better understanding of the extent of the relationship between lead exposure and aggression and the consequences this could have for survival and reproduction of wild animals are clear priorities for future work in this and other urban ecosystems., (Copyright © 2018. Published by Elsevier B.V.)

Although conflict is often adaptive and necessary to secure limited resources, it is also frequently a costly endeavor. Signals that reliably communicate competitive ability are commonly employed by animals to reduce conflict costs. Both male and female signals have the capacity to serve as honest indicators of competitive ability, but the extent to which this occurs in females has received relatively limited attention. We studied how natural feather coloration and experimentally manipulated plumage ornamentation in female white-shouldered fairywrens (Malurus alboscapulatus moretoni) relates to their aggressive behavior. These fairywrens are a useful study system in that female, but not male coloration varies throughout New Guinea. We tested behavioral responses to simulated rivals both prior to and after plumage manipulation via two distinct behavioral assays: simulated territorial intrusions (where both sexes jointly respond to rival intruders) and mirror image simulation (where females are isolated from their mate). Plumage manipulation treatments had no measurable impact on female aggression during mirror image simulation tests, though aggression did decrease over the course of multiple assays. Similarly, using simulated territorial intrusion assays, we found no difference in female aggression with respect to both natural coloration and manipulation treatment. Finally, our correlative analysis of natural feather color also revealed no detectable relationship. These findings suggest that female white scapular coloration is unlikely to function as a signal of competitive ability in this tropical species with derived female ornamentation and we discuss possible alternative explanations. Significance statement: Like their showy male counterparts, female animals may use plumage-based signals to mediate aggressive encounters. Determining if and how signals used in female-female competition may mitigate the costs of agonistic encounters is particularly important, as it is thought to be a key driver of female signal evolution. We used a repeated-measures design and two distinct behavioral assays to explore how both manipulated and natural feather coloration relate to aggression in female white-shouldered fairywrens of Papua New Guinea – a species with female, but not male, plumage polymorphisms. We were unable to detect any differences in aggression with respect to female plumage coloration despite two distinct behavioral assays that mimic distinct social contexts, suggesting that female plumage coloration may function in other contexts or lack a modern signaling function altogether in this system. [ABSTRACT FROM AUTHOR]

We know little of the proximate mechanisms underlying the expression of signaling traits in female vertebrates. Across males, the expression of sexual and competitive traits, including ornamentation and aggressive behavior, is often mediated by testosterone. In the white-shouldered fairywren (Malurus alboscapulatus) of New Guinea, females of different subspecies differ in the presence or absence of white shoulder patches and melanic plumage, whereas males are uniformly ornamented. Previous work has shown that ornamented females circulate more testosterone and exhibit more territorial aggression than do unornamented females. We investigated the degree to which testosterone regulates the expression of ornamental plumage and territorial behavior by implanting free-living unornamented females with testosterone. Every testosterone-treated female produced a male-like cloacal protuberance, and 15 of 20 replaced experimentally plucked brown with white shoulder patch feathers but did not typically produce melanic plumage characteristic of ornamented females. Testosterone treatment did not elevate territorial behavior prior to the production of the plumage ornament or during the active life of the implant. However, females with experimentally induced ornamentation, but exhausted implants, increased the vocal components of territory defense relative to the pretreatment period and also to testosterone-implanted females that did not produce ornamentation. Our results suggest that testosterone induces partial acquisition of the ornamental female plumage phenotype and that ornament expression, rather than testosterone alone, results in elevations of some territorial behaviors. [ABSTRACT FROM AUTHOR]