Parental investment by males is less common among birds with polygynous mating systems than in monogamous species. Here, we examined the contribution of males in feeding nestlings in the facultatively polygynous European starling, Sturnus vulgaris. 1. In nestbox colonies around Antwerp, Belgium, males and females within monogamous pairs divided the feeding duties about equally, with a slight bias towards the female, and responded similarly to changes in brood size and age of nestlings. 2. The proportion of primary females receiving male assistance in feeding nestlings was significantly smaller than the proportion of monogamous females during each of the three nestling age stages (early, mid and late) we considered. In most primary broods, the strong decrease in male assistance was not due to the male directing part of his feeding effort toward the brood of the secondary female, but was due to the fact that the male's investment in feeding primary nestlings was negatively affected by his polygynous behaviour. As prospecting females were present after hatching of the primary broods (as contrasted to other studied starling populations), most males spent time trying to attract and courting additional females instead of giving parental care to the primary brood. This suggests that males trade off the attraction of additional females against giving parental care to an existing brood. The proportion of secondary females receiving male assistance in feeding was significantly smaller than the proportion of monogamous females during the early- and mid nestling stages. Overall, secondary females received less male assistance than primary females. The amount of male help to primary and secondary broods was not related to the hatching interval between the primary and secondary brood. 3. Primary females did not suffer reduced breeding success compared to monogamous females. In secondary broods, nestling mortality (partial brood loss) was significantly higher than in both primary and monogamous broods, while average nestling weights were significantly lower. These results suggest that secondary females, as contrasted to primary females, are not able to compensate fully for the reduction in male assistance. 4. During the mid-nestling stage, when nestlings grow most rapidly, but not during the early- and late-nestling stages, polygynously mated females feeding young without male assistance significantly increased their per-caput feeding rate compared with aided polygynous females and monogamous females, and made as many feeding visits as did polygynous pairs in which the male assisted, and as monogamous pairs. The higher nestling mortality rates in polygynous broods without male help during the early and mid-nestling stages suggest that unaided females cannot compensate fully (in terms of quantity or quality of food delivered), that male starlings can improve female fledging success by assisting in feeding nestlings, and that the reduced reproductive success of secondary females is directly linked to the strongly reduced male assistance in feeding.
According to the 'fertility-announcement hypothesis', the song of paired males might function partly as a paternity guard strategy and partly to maximize their own extra-pair copulations (EPCs). A major prediction of this hypothesis is that males should sing most when the fertility of their mate reaches a temporal (both seasonal and diurnal) peak. We report some tests of this hypothesis from a study of monogamously paired male European starlings Stumus vulgaris. Mated males sang significantly more during the fertile period of their mate and most males even completely ceased singing after their mate's fertile period. During the ovulatory period mated males sang significantly more in the late morning (0900-1200 hours) following egg-laying, when most females may have reached peak diurnal fertility, than early in the morning (0600-0900 hours). For six females, we were able to determine precise laying times during their ovulatory period and we found that their mates had a significantly higher song rate within the insemination window (the first hour following egg-laying) than before egg-laying. Although male starlings sing most when their mate's fertility reaches a seasonal and diurnal peak, our observations suggest that post-pairing song in monogamous males does not function primarily to deter other males attempting EPCs, or to attract extra-pair mates. Our results rather suggest that post-pairing song in monogamous males is directed mainly towards their own female and functions to stimulate her to solicit copulations. This may be important in the context of sperm competition if frequent pair copulations result in a higher fertilization rate for the male when EPCs have occurred.
In contrast to male bird song, female song complexity, learning and expression have received much less attention. Female European starlings can produce song of a comparable complexity as males and are also capable of adult vocal learning. Here we recorded song during 3 successive years and investigated variation in song traits (song complexity, song duration and song versatility) in relation to age in captive adult female starlings. We looked at whether individual song traits differ among different age classes (cross-sectional analyses) and whether they change over successive years (longitudinal analyses). Further we studied the repertoire turnover throughout the years, female song sharing in the first year of recording and whether different song traits consistently vary among females across the years. Overall, both cross-sectional and longitudinal analyses showed that repertoire size significantly declined with female age, suggesting that some constraints exist in adult females to maintain large repertoires. Song duration and song versatility appeared to be unrelated to age. Female starlings intensely modified their repertoire across the years by adding new/deleting old phrase types, suggesting a high plasticity as reported in males. Females showed a high variation (between 14% and 83%) in sharing their repertoire, with older females having higher song sharing rates. The individual differences in song complexity and performance were repeatable across the years, which may suggest that song in female starlings is a potential quality indicator trait.
Many behavioural studies rely on playback experiments. While it is known that songbirds decrease behavioural responses after short-term repeated stimulation, long-term behavioural changes due to playbacks are unknown. We studied the response to playbacks in a free-living songbird in the long-term, while also studying the repeatability of the behaviour. Locomotor behaviour (a proxy of aggressiveness) decreased one year after first exposure to a single playback. Song response, however, remained consistent, suggesting that these two behaviours may provide different information. Locomotor behaviour was less repeatable than the song response to playback, the latter showing significant between-years repeatability. To the best of our knowledge, our study is the first to report long-term decrease in response to playbacks in a songbird, and that some aspects of the response to playback are repeatable. Similar studies in other species or populations of the great tit are important, to examine the generality of our findings.
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.
We confronted individually-caged male European starlings, Sturnus vulgaris, with conspecifics of both sexes in order to study singing behaviour during intrasexual and intersexual encounters. Males spent more time at the nestbox, sang more songs and more song types during female presentations than during control periods (observation periods with no conspecifics). Males also sang more songs in the nestbox and flew more to the nestbox with green nest material. During male presentations, only the time spent at the nestbox and the carrying of nest material increased significantly. Males spent more time at the nestbox, sang more songs and more song types in response to a female stimulus than to a male stimulus. Males also sang more songs in the nestbox and flew more to the nestbox with nest material during female than during male presentations. These results suggest that the song and song repertoire of male starlings serve primarily an intersexual rather than an intrasexual function. However, in contrast to a previous study, our results suggest that singing also serves as an intrasexual signal to deter rivals at close encounter. We also tested the hypothesis that the 'whistles' and the 'warbling song' have separate intrasexual and intersexual functions, as has been suggested in the literature. We found no evidence for a specialized intrasexual function of the whistles nor for a specialized intersexual function of the warbling song. From this study it also appears that variations in the size of the aviary can modify the behavioural responses of starling males. New information with regard to the use of green nest material by male starlings is given.