Prediction of individual differences in non-iridescent structural plumage colour from nanostructural periodicity and regularity.

Non-iridescent structural plumage reflectance is a sexually selected indicator of individual quality in several bird species. However, the structural basis of individual differences remains unclear. In particular, the dominant periodicity of the quasi-ordered feather barb nanostructure is of key importance in colour generation, but no study has successfully traced back reflectance parameters, and particularly hue, to nanostructural periodicity, although this would be key to deciphering the information content of individual variation. We used matrix small-angle X-ray scattering measurements of intact, stacked feather samples from the blue tit crown to estimate the sex-dependence and individual variation of nanostructure and its effects on light reflectance. Measures of nanostructural periodicity successfully predicted brightness, ultraviolet chroma and also hue, with statistically similar effects in the two sexes. However, we also observed a lack of overall effect of the nanostructural inhomogeneity estimate on reflectance chromaticity, sex-dependent accuracy in hue prediction and strong sex-dependence in position estimation error. We suggest that reflectance attributes are modified by other feather structures in a sex-specific manner, and that within-individual variation in nanostructural parameters exists within or among feathers and this confounds the interpretation of structure-reflectance relationships at the plumage area level.

Responses in the breeding parameters of the collared flycatcher to the changing climate.

Global climate change involves various aspects of climate, including precipitation changes and declining surface wind speeds, but studies investigating biological responses have often focused on the impacts of rising temperatures. Additionally, related long-term studies on bird reproduction tend to concentrate on breeding onset, even though other aspects of breeding could also be sensitive to the diverse weather aspects. This study aimed to explore how multiple aspects of breeding (breeding onset, hatching delay, breeding season length, clutch size, fledgling number) were associated with different weather components. We used an almost four-decade-long dataset to investigate the various aspects of breeding parameters of a collared flycatcher (Ficedula albicollis) population in the Carpathian Basin. Analyses revealed some considerable associations, for example, breeding seasons lengthened with the amount of daily precipitation, and clutch size increased with the number of cool days. Parallel and opposing changes in the correlated pairs of breeding and weather parameters were also observed. The phenological mismatch between prey availability and breeding time slightly increased, and fledgling number strongly decreased with increasing mistiming. Our results highlighted the intricate interplay between climate change and the reproductive patterns of migratory birds, emphasizing the need for a holistic approach. The results also underscored the potential threats posed by climate change to bird populations and the importance of adaptive responses to changing environmental conditions.

Plumage color degradation indicates reproductive effort: an experiment.

Plumage color has traditionally been regarded as a static ornamental trait, but evidence is accumulating for significant color changes without molt that typically reduce the conspicuousness of ornamentation. In some species, the social partner seems to increase its reproductive investment if the color trait is experimentally enhanced, suggesting that color change could act as a signal. However, the information content of this signal is so far unclear. For example, birds in poor condition or making greater effort may deteriorate more severely. We used brood size manipulations to alter the reproductive effort of male and female collared flycatchers Ficedula albicollis. Both sexes showed less severe decline in some reflectance attribute of their white breast when their brood was experimentally reduced. In each sex, greater deterioration of the reflectance trait affected by the manipulation was accompanied by increased feeding rate by the partner. These feeding patterns do not prove, but are consistent with, a compensatory response by the partner to induced degradation. The manipulation effects on color change we detected confirm for the first time that plumage color deterioration can indicate current reproductive effort, thereby providing a potential fitness advantage to social partners that react to such deterioration.

Are brood sex ratios adaptive?-The effect of experimentally altered brood sex ratio on nestling growth, mortality and recruitment.

Brood sex ratios (BSRs) have often been found to be nonrandom in respect of parental and environmental quality, and many hypotheses suggest that nonrandom sex ratios can be adaptive. To specifically test the adaptive value of biased BSRs, it is crucial to disentangle the consequences of BSR and maternal effects. In multiparous species, this requires cross-fostering experiments where foster parents rear offspring originating from multiple broods, and where the interactive effect of original and manipulated BSR on fitness components is tested. To our knowledge, our study on collared flycatchers (Ficedula albicollis) is the first that meets these requirements. In this species, where BSRs had previously been shown to be related to parental characteristics, we altered the original BSR of the parents shortly after hatching by cross-fostering nestlings among trios of broods and examined the effects on growth, mortality and recruitment of the nestlings. We found that original and experimental BSR, as well as the interaction of the two, were unrelated to the fitness components considered. Nestling growth was related only to background variables, namely brood size and hatching rank. Nestling mortality was related only to hatching asynchrony. Our results therefore do not support that the observed BSRs are adaptive in our study population. However, we cannot exclude the possibility of direct effects of experimentally altered BSRs on parental fitness, which should be evaluated in the future. In addition, studies similar to ours are required on various species to get a clearer picture of the adaptive value of nonrandom BSRs.

Triparental care in the collared flycatcher (Ficedula albicollis): Cooperation of two females with a cuckolded male in rearing a brood.

Certain predominant forms of mating and parental care systems are assumed in several model species among birds, but the opportunistic and apparently infrequent variations of "family structures" may often remain hidden due to methodological limitations with regard to genetic or behavioral observations. One of the intensively studied model species, the collared flycatcher (Ficedula albicollis), is usually characterized by social monogamy with polyterritorial, facultative social polygyny, and frequent extrapair mating and extrapair paternity. During a brood-size manipulation experiment, we observed two females and a male delivering food at an enlarged brood. A combination of breeding phenology data (egg laying and hatching date), behavioral data (feeding rates) from video recordings at 10 days of nestling age, and microsatellite genotyping for maternity and paternity suggests a situation of an unrelated female helping a pair in chick rearing. Such observations highlight the relevance of using traditional techniques and genetic analyses together to assess the parental roles within a population, which becomes more important where individuals may dynamically switch from their main and presupposed roles according to the actual environmental conditions.