Rianne Pinxten

Male song as a cue for mate choice in the European starling

This study had two aims. First, we looked at individual differences in song characteristics between males of the European starling, and we related song behaviour to factors such as male age, pairing date, polygyny and male breeding success. Second, we experimentally tested whether song has an effect on female mating decisions. 1. During the breeding season, male starlings sing a very long and complex song consisting of a rapid succession of large number of different song types. We observed marked differences between males in average song bout length (a song bout was defined as a period of at least five seconds of song containing no pauses larger than 1.5 seconds) and in song repertoire size. Average song bout lengths ranged from 16 to 35 seconds. The individual repertoire size ranged from 23 to 67 song types. Repertoire size and average song bout length were positively correlated. 2. Both in the field and in captivity, yearling males sang shorter average song bout lengths and had smaller repertoire sizes than older males. 3. Males singing longer average song bouts and having larger repertoire sizes attracted females for pairing before their rivals with shorter average song bouts and smaller repertoire sizes.

Variation of heavy metals within and among feathers of birds of prey: effects of molt and external contamination

In this study we examined the effect of external contamination on the heavy metal (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn) concentration in feathers. We compared the heavy metal content among the 10 primary wing feathers of sparrowhawks (Accipiter nisus), little owls (Athene nocta) and barn owls (Tyto alba) and the variation within the outermost tail feather of sparrowhawks and tawny owls (Strix aluco). The concentration of Hg was significantly higher in feathers molted first, suggesting that levels in feathers reflect levels in the blood during formation. For some other elements (Al, Co, Ni, Pb, Zn) on the other hand, there are strong indications that external contamination may have an important impact on the levels detected in the feathers. This should be taken into account in future monitoring studies.

Seasonal Changes in Courtship Song and the Medial Preoptic Area in Male European Starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.

Experimental evidence of a testosterone-induced shift from paternal to mating behaviour in a facultatively polygynous songbird

Abstract Previous studies have suggested that testosterone (T) profiles of male birds reflect a trade-off between mate attraction behaviours (requiring high T levels) and parental care activities (requiring low T levels). In this study, we experimentally elevated T levels of monogamous males in the facultatively polygynous European starling (Sturnus vulgaris), and compared mate attraction and paternal behaviour of T-treated males with those of controls (C-males). T-males significantly reduced their participation in incubation and fed nestlings significantly less often than C-males. Females paired to T-treated males did not compensate for their mate’s lower paternal effort. The observed reduction in a male’s investment in incubating the eggs was accompanied by an increased investment in typical female-attracting behaviours: T-males spent a significantly higher proportion of their time singing to attract additional females. They also occupied more additional nestboxes than C-males, although the differences just failed to be significant, and carried significantly more green nesting materials into an additional nestbox (a behaviour previously shown to serve a courtship function). T-males also behaved significantly more aggressively than C-males. During the nestling period, the frequency of mate-attracting behaviours by T-treated and control males no longer differed significantly. Despite the reduced paternal effort by T-males and the lack of compensation behaviour by females, hatching and breeding success did not differ significantly between T- and C-pairs.

Shield characteristics are testosterone-dependent in both male and female moorhens.

The immunocompetence handicap hypothesis proposes that the expression of secondary sexual characteristics is positively related to testosterone levels, but that elevated testosterone levels also impose costs from immune suppression. Hence, testosterone-dependent characteristics should accurately reflect male quality because only high-quality males are able to invest in large sexual characteristics without detrimental effects upon their own immune system. Most studies to date have focused on the role of testosterone in the expression of male ornaments and on the possible immunosuppressant effects of androgens in males. In the moorhen (Gallinula chloropus), a sexually monomorphic monogamous bird species showing a partial sex-role reversal, both sexes have a prominent frontal shield. We implanted both sexes with testosterone-filled implants to examine the effects of testosterone on shield characteristics and immune function. Shield size, thickness, and color were significantly increased by an experimental increase in testosterone concentrations in both males and females. Likewise, removal of the implants led to a rapid decrease in shield size and thickness in both males and females, suggesting that both sexes responded quickly to an increase or a decrease in testosterone. Moorhens implanted with testosterone had higher intensities of ectoparasite infestations than control birds, but other indirect measures of immunocompetence did not differ significantly between the two categories of birds.

Sex role reversal in vertebrates: behavioural and endocrinological accounts

Sex-role reversal occurs when females compete more intensely than males for access to mates. In this paper, we survey the occurrence of sex-role reversal in vertebrates: we focus on behavioural aspects of sex-role reversal and we examine possible endocrinological correlates of this phenomenon. The best documented cases among vertebrates of sex-role reversal occur in fish and birds. In nearly all sex-role reversed species or populations, females have higher potential reproductive rates than males. Some species in which females were previously thought to be the predominant competitors for mates (for instance seahorses and a dendrobatid frog), appear not to be sex-role reversed according to recent studies. The endocrinology of sex-role reversal has been studied in only a few species and therefore remains poorly understood. In birds, which probably have been studied the most in this respect, steroid hormones appear to follow the typical ancestral conditions (for instance no reversal of testosterone levels) in sex-role reversed species, whereas prolactin, a principal regulator of the onset and maintenance of incubation, departs from the usual avian pattern in that it is higher in males than in females. The study of sex-role reversed behaviour offers unique opportunities not only to test sexual selection theory, but also to enhance our understanding of the neuroendocrine mechanisms mediating behavioural sex differences.

Seasonal changes in the densities of α2‐noradrenergic receptors are inversely related to changes in testosterone and the volumes of song control nuclei in male European starlings

The functions of song and the contextual cues that elicit song change seasonally in parallel with testosterone (T) concentrations in male European starlings. T is high in spring when at least one function of male song is that of immediate mate attraction, and low outside the context of breeding, when starlings primarily use song for dominance or flock maintenance. Several brain nuclei that control song contain high densities of α2‐adrenergic receptors. T can regulate the density of α2‐adrenergic receptors in the avian brain, indicating that the density of α2‐adrenergic receptors within the song system might change seasonally. Although the function of seasonal brain variation is not entirely clear, in many songbirds the volumes of song nuclei are largest when T is high and males sing most. Male starlings, however, sing both when T is high and when T is low. Therefore, exploring seasonal changes in T and the volumes of song nuclei could provide insight into the function of these changes. The present study was performed to explore the relationships among T, the volumes of song nuclei, and the densities of α2‐adrenergic receptors within the song system of male starlings. Song nuclei (the high vocal center [HVc], robust nucleus of the archistriatum [RA], and Area X) were largest, T was highest, and the density of α2‐adrenergic receptors (within HVc and RA) was lowest during the breeding season. The reverse pattern was observed outside of the breeding season. These results suggest that changes in T, volumes of song nuclei, and α2‐receptor densities might regulate seasonal changes in song behavior or the context that will elicit song in male starlings. J. Comp. Neurol. 444:63–74, 2002.

SHORT- AND LONG-TERM EFFECTS OF MALE-LIKE CONCENTRATIONS OF TESTOSTERONE ON FEMALE EUROPEAN STARLINGS (STURNUS VULGARIS)

Abstract European Starlings (Sturnus vulgaris) exhibit marked sex differences in behavior during spring. Song activity, nest-box occupation, the carrying of green nesting materials into a nest hole (typical mate-attraction behaviors), and aggression occur much more frequently in males who also have higher testosterone (T)-levels than females. Here, we examined whether male-like concentrations of T would activate these behaviors in female starlings. We treated females with implants that were either empty (C-females) or packed with T (T-females) during late December. Although elevated T-levels significantly increased song activity in females, the proportion of time spent singing was still much lower than in males. T-treatment in females also failed to induce singing behavior in the nest box, a typical male mate-attraction behavior. Those results suggest both activational and organizational effects of T on singing. Nest-box occupation, carrying of green nesting material into a nest hole, and aggressive behavior were not activated by elevated T-levels, indicating that sex differences in these behaviors are probably based on early organizational effects of steroid hormones. We also evaluated effects of increased T-concentrations on some physiological, morphological, and immunological parameters. T-treatment strongly suppressed tail feather regrowth after experimental plucking, and also delayed onset of molt of wing feathers and slowed its progress. T-implantation caused color of the bill to change from black to yellow, but did not affect body mass. Immune function was determined by using two indirect measures: blood composition (haematocrit and buffy coat values) and indications of infections. Although haematocrit and buffy coat values did not differ between C- and T-females, T-females were significantly more infected with Staphylococcus aureus than C-females at the end of the experiment.

DOES TESTOSTERONE AFFECT THE TRADE-OFF BETWEEN INVESTMENT IN SEXUAL/TERRITORIAL BEHAVIOUR AND PARENTAL CARE IN MALE GREAT TITS?

Breeding testosterone (T) profiles of free-living male birds are hypothesized to reflect a trade-off between investment in competitive behaviour for mates or territories, typically accompanied by high T-levels, and investment in paternal care, typically accompanied by low T-levels. To test this hypothesis we monitored song activity, as a measure of territorial advertisement or mate attraction, and feeding efforts, as a measure of paternal care, in great tit Parus major males that either received T-filled or empty implants in the middle of the feeding phase, a period of high paternal commitment and low T-levels. In support of the trade-off hypothesis, T-implanted males sang significantly more than controls. However, we found no significant effect of the elevated T-levels on male and female feeding behaviour despite the large increase in T following implantation. Also, no short-term effects on male fitness were found. Taken together these results do not support the trade-off hypothesis. We discuss that the low overall responsiveness in our study might be related to a high fitness cost of neglecting offspring in favour of T-enhanced behaviour.

On the function of singing and wing-waving in the European Starling Sturnus vulgaris

Experiments were performed using captive starlings to examine whether Starling song functions primarily in intersexual communication. Male Starlings showed a significant increase in the time spent at the nestbox, as well as in the total time spent singing, after the introduction of a female into the aviary. After the introduction of a male, only the time spent at the nestbox increased significantly. Wing-waving (a visual display associated with singing) and singing in the nest box occurred only after introduction of a female. Our results strongly suggest that Starling song functions largely in male-female interactions. The primary function of wing-waving seems to be mate attraction.