Testosterone Might Not Be Necessary To Support Female Aggression In Incubating Northern Cardinals

Testosterone\u27s (T) influence on male aggression has been well established in many vertebrate species, but the impact of T on female aggressive behaviour is poorly understood. Among birds, a link between T and female aggression is plausible, as females of many species exhibit a seasonal peak in T concentrations at the onset of breeding when social instability is greatest and they may have circulating T through much of the breeding season. However, investigations examining the relationship between T and female aggression are few and have yielded conflicting results, with experimentally or endogenously elevated T supporting aggressive behaviour in females of some species but not others, and T elevating with aggression at some points of the reproductive cycle but not others. We examined the relationship between endogenous levels of T and female aggression in the northern cardinal, Cardinalis cardinalis, a resident temperate species in which pairs exhibit prolonged territoriality and females have measurable levels of T year-round, including all stages of reproduction (incubation, nestling feeding, etc.). Using simulated nest intrusions, we assessed aggressive responses of incubating females to intrasexual \u27intruders\u27 at the nest and quantified T levels after each aggressive encounter. Displays of aggression towards \u27intruders\u27 varied among females; yet, individuals showing greater levels of aggression did not demonstrate higher levels of T. These results imply that T might not support maternal aggression in this species

Multidimensional signals and analytic flexibility: Estimating degrees of freedom in human speech analyses

Recent empirical studies have highlighted the large degree of analytic flexibility in data analysis which can lead to substantially different conclusions based on the same data set. Thus, researchers have expressed their concerns that these researcher degrees of freedom might facilitate bias and can lead to claims that do not stand the test of time. Even greater flexibility is to be expected in fields in which the primary data lend themselves to a variety of possible operationalizations. The multidimensional, temporally extended nature of speech constitutes an ideal testing ground for assessing the variability in analytic approaches, which derives not only from aspects of statistical modeling, but also from decisions regarding the quantification of the measured behavior. In the present study, we gave the same speech production data set to 46 teams of researchers and asked them to answer the same research question, resulting insubstantial variability in reported effect sizes and their interpretation. Using Bayesian meta-analytic tools, we further find little to no evidence that the observed variability can be explained by analysts’ prior beliefs, expertise or the perceived quality of their analyses. In light of this idiosyncratic variability, we recommend that researchers more transparently share details of their analysis, strengthen the link between theoretical construct and quantitative system and calibrate their (un)certainty in their conclusions

Melanin Ornament Brightness and Aggression at the Nest in Female Northern Cardinals (\u3ci\u3eCardinalis cardinalis\u3c/i\u3e)

Research is increasingly addressing the evolution and use of sexually selected traits in females. One strong area of interest is the display of intrasexual aggression and how female ornaments are used in intrasexual competition. One particular type of ornament focused on for its use in intrasexual aggression in both sexes is the melanin pigmented ornaments. Over the course of 2 breeding seasons in a southeastern Mississippi population of cardinals, we assessed brightness of the melanin face mask plumage ornament in female Northern Cardinals (Cardinalis cardinalis) and compared it to behavioral responses during intraspecific simulated nest intrusions (SNIs). All females responded to the SNI, but face mask brightness did not co-vary with the level of aggression shown. Our findings do not support earlier work suggesting that the face mask in female Northern Cardinals is an indicator of aggression at the nest. Potentially, differences in behavior and environmental variables between populations of cardinals could be factors in this difference and deserve further assessment. Future research should investigate other populations of cardinals to fully assess the communicative malleability of this ornament type and different selective pressures on female ornamentation and behavior

Female Performance of Male Courtship Display In Northern Cardinals

Courtship behaviors in birds are often considered male-specific, as males compete for mates through displays that exhibit individual quality. Several courtship displays have been described for male Northern Cardinals including the complex song-dance display. We observed female cardinals performing the song-dance display on two separate occasions in south Mississippi within pre-breeding and breeding periods. Female performance of the display was very similar as reported for males. Given the behavioral attributes of cardinal mating pairs, it is plausible that bi-directional mate choice exists for this species and females are demonstrating aspects of individual quality to males through the song-dance display. Additional monitoring of courtship behavior is needed to determine the function of female performance display that was previously thought to be male specific

Similarities In Expression of Territorial Aggression In Breeding Pairs of Northern Cardinals, \u3ci\u3eCardinalis cardinalis\u3c/i\u3e

Avian pairs that defend resources year-round may demonstrate similar territorial behavior. We examined male and female responses of northern cardinal pairs to male simulated territorial intrusions. Pair members demonstrated comparable responses towards a male ‘intruder’, as latency to respond and proximity scores were very similar between pair members in the majority of pairs examined. Similarity in territorial behavior could be important in cardinal pairs for maintaining year-round resources

Testosterone Elevation and Response to Gonadotropin-Releasing Hormone Challenge by Male Northern Cardinals (\u3ci\u3eCardinalis cardinalis\u3c/i\u3e) Following Aggressive Behavior

There is much discrepancy about the relationship between testosterone (T) and male aggressive behavior. For example, in birds, males of many species significantly elevate T levels during inter-male conflict. However, this is not universal, and in species where males typically do not elevate T during aggressive interactions, concentrations of the hormone are often assumed to be circulating at maximum levels. We examined if male northern cardinals (Cardinalis cardinalis) significantly elevated T during simulated territorial intrusions (STIs). We also examined if individuals had the capacity to further elevate T levels in response to gonadotropin-releasing hormone (GnRH) injections immediately after an aggressive encounter. Our results indicate that male cardinals do not significantly elevate T levels in response to STIs, but have the physiological capacity to significantly elevate T in response to GnRH injections following aggressive interactions. This implies that T levels of individuals captured during STIs were not at maximum concentrations. However, additional findings in this study also suggest the possibility that prolonged social instability could elicit significant elevations in T in males of this species, warranting further investigation

Non-Breeding Gonadal Testosterone Production of Male and Female Northern Cardinals (\u3ci\u3eCardinalis cardinalis\u3c/i\u3e) Following GnRH Challenge

Yearly, testosterone (T) levels fluctuate as many vertebrates cycle through reproductive and non-reproductive periods. Among many temperate birds, it is well established that levels of T peak as gonads recrudesce for breeding and then fall as gonads regress prior to the non-breeding season. While the tissues producing breeding season T are well studied, the tissues responsible for non-breeding T have received less investigative attention. We examined the ability of male and female Northern Cardinals (Cardinalis cardinalis) to elevate gonadal T following standardized injections of gonadotropin-releasing hormone (GnRH) across three non-breeding seasons. Males and females were capable of significantly elevating gonadal T production following GnRH injections during periods of reproductive quiescence. The magnitude of T elevation varied across the non-breeding season, but not between sexes. To our knowledge, this is the first report of a significant increase in gonadal T production following GnRH injections administered in the non-breeding season

Female Performance of Male Courtship Display in Northern Cardinals

Courtship behaviors in birds are often considered male-specific, as males compete for mates through displays that exhibit individual quality. Several courtship displays have been described for male Northern Cardinals including the complex song-dance display. We observed female cardinals performing the song-dance display on two separate occasions in south Mississippi within pre-breeding and breeding periods. Female performance of the display was very similar as reported for males. Given the behavioral attributes of cardinal mating pairs, it is plausible that bi-directional mate choice exists for this species and females are demonstrating aspects of individual quality to males through the song-dance display. Additional monitoring of courtship behavior is needed to determine the function of female performance display that was previously thought to be male specific