Determinants of male territorial behavior in a Hungarian collared flycatcher population: plumage traits of residents and challengers

In intrasexual conflicts, contestants can rely on relative or absolute size of status badges to mediate aggressive behavior. Most studies focus on the response of focal animals to variation in status badges of their competitors; few have simultaneously considered the traits of both participants under experimental conditions. By simulating territorial intrusions, we tested the importance of two sexual traits [forehead patch size (FPS) and wing patch size (WPS)] in territorial behavior of males in a Hungarian population of the collared flycatcher, Ficedula albicollis. We presented a stimulus male to an unpaired resident male to examine whether the characteristics of the territory owner or those of the challenger were associated with the latency of the first attack of the owner, which is a good predictor of the territorial behavior in general. WPS of the stimulus male was a significant determinant of the latency of the first attack, as males with a larger WPS elicited quicker attacks from the residents than males with a small WPS. From the residents’ perspective, age appeared to influence their territorial behavior, as yearlings had shorter attack latencies than older males. Additionally, latency could be considered an individual-specific attribute because it varied consistently among males, even when the WPS of the stimulus male was controlled, and it was associated with pairing success. Contrary to findings in a Swedish population, FPS seemed to be unimportant in male–male competition in our population, which suggests population differences in the role of the two plumage traits. Our results indicate that in a territorial conflict, the characteristics of both participants are important.     

Contradictory results in sex ratio studies: populations do not necessarily differ

In avian sex ratio studies, results often differ between species and between populations within species. Some researchers argued that positive results were simply statistical artefacts and that sex ratio adjustment did not exist. However, many of the proposed mechanisms of sex ratio adjustment result in costly laying gaps. In these cases, females laying large clutches may restrict the sex manipulation to the first egg of the clutch. Consequently, detectability of sex ratio adjustment on the level of the clutch can be low. Though obvious, this fact is often neglected in the literature. Using simulations, I show that the proportion of undetected sex manipulation can be surprisingly high when the manipulation is restricted to the first egg. If the sample size is 50 broods, there is 47% and 71% chance in 6- and 12-egg clutches, respectively, that sex manipulation is undetected. Even with large samples (n = 100), the figures are 15% and 46%. These data suggest that nonsignificant results for clutch sex ratios do not necessarily mean that sex is not manipulated in a portion of the brood, e.g. in first-laid eggs. Hence, whenever possible, data on laying order-specific sex manipulation should also be collected. Without such data, contradictory results on brood sex ratios should be interpreted cautiously.     

The relationship between maternal ornamentation and feeding rate is explained by intrinsic nestling quality

In altricial birds, parental feeding is essential, and its amount may depend on the quality of both parents. A relationship between parental quality and feeding rate is generally attributed to an active adjustment by parents in order to retain good quality mates or ensure high fitness through raising high-quality offspring. However, the behaviour and need of young may also change with parental quality, and this may affect parental behaviour. A further problem is that most studies have investigated post-hatching parental investment in relation to the secondary sexual signals of males, but not females. In a cross-fostering experiment, we examined the feeding rates of rearing parents in relation to the size and ornamentation of both original and rearing parents in collared flycatchers (Ficedula albicollis). Using this setup, we could examine whether the observed feeding patterns were the results of the decision of the parents based on their own and their partner’s traits or the constraints imposed by the behaviour or need of offspring. When correcting for clutch size and year, we found that feeding rate of both foster parents correlated with the wing patch size of the original female. This implies that original maternal quality had an offspring-mediated indirect effect on investment of foster parents, that is intrinsic nestling quality may constrain parental feeding decisions. This explanation should not be overlooked in future studies on preferential parental investment, and our results also point out that maternal ornaments deserve more attention in such studies.     

Carotenoids in the egg yolks of collared flycatchers (<Emphasis Type="Italic">Ficedula albicollis</Emphasis>) in relation to parental quality,environmental factors and laying order

Birds may influence the fitness of their offspring by transmission of different amounts of carotenoids to their eggs. Carotenoids play crucial roles in antioxidant protection and immune defence mechanisms, but they may be available to females in limiting amounts. Therefore, their allocation to the eggs may be influenced by the female’s condition, age and environmental circumstances. Furthermore, the quality of the male parent, which affects the reproductive value of the offspring, may also influence this investment. In this correlational study, we investigated proximate and ultimate factors that may lead to variation in yolk lutein, zeaxanthin and β-carotene concentrations among and within clutches of a wild passerine, the collared flycatcher (Ficedula albicollis). We found that carotenoid concentration was positively associated with caterpillar supply at the time of egg formation, which suggests a proximate constraint of carotenoid availability on yolk composition. Neither female condition, body size, age, nor male plumage ornamentation, age and body size correlated with carotenoid deposition. Yolk β-carotene concentration was found to be positively linked to yolk testosterone concentration. We suggest that females allocated more β-carotene to their eggs to mitigate the potentially detrimental effects of elevated steroid concentration. We found that concentration of β-carotene increased with laying order. The possible function of this pattern may be to enhance the resistance to oxidative stress and pathogens of the disadvantaged last-hatching nestling, suggesting that collared flycatchers pursue a compensatory, “brood survival” strategy.     

Paternal age and offspring growth: separating the intrinsic quality of young from rearing effects

Younger individuals are often less successful in reproduction than older ones. This might be because of improving breeding skills with age or because the genetic quality of young or early maternal effects on them vary with parental age. However, no attempt has been made to experimentally separate these processes in vertebrates. We conducted a cross-fostering experiment in collared flycatchers (Ficedula albicollis) in three breeding seasons to disentangle origin- and rearing-related effects of paternal age on chick growth, while controlling for date-specific environmental conditions as well as differences in clutch and brood size. The age of the male at the nest of origin, but not that of the rearing male, had a year-dependent effect on nestling body mass and tarsus length. In two seasons, young of subadult males grew slower in the early linear phase of growth than young of adult males. There was no compensatory growth in the final asymptotic phase, so both body mass and tarsus length before fledging reflected the differential early development. In the remaining year, the age of the male at the nest of origin had no significant effect on chick growth. The environment-dependent origin effect we detected was unexplained by incubation times, hatching asynchrony, chick masses at swapping or previously described age-dependent egg quality patterns. Our results therefore suggest a genotype × environment interaction on the relative development of offspring sired by subadult and adult males. Our results also raise the possibility that female birds may gain genetic benefits by mating with older males. Further studies should identify general patterns of male age-dependent female mate choice and offspring quality in different environmental conditions.     

Aggressive behavior of the male parent predicts brood sex ratio in a songbird

Brood sex ratio is often affected by parental or environmental quality, presumably in an adaptive manner that is the sex that confers higher fitness benefits to the mother is overproduced. So far, studies on the role of parental quality have focused on parental morphology and attractiveness. However, another aspect, the partner’s behavioral characteristics, may also be expected to play a role in brood sex ratio adjustment. To test this hypothesis, we investigated whether the proportion of sons in the brood is predicted by the level of territorial aggression displayed by the father, in the collared flycatcher (Ficedula albicollis). The proportion of sons in the brood was higher in early broods and increased with paternal tarsus length. When controlling for breeding date and body size, we found a higher proportion of sons in the brood of less aggressive fathers. Male nestlings are more sensitive to the rearing environment, and the behavior of courting males may often be used by females to assess their future parental activity. Therefore, adjusting brood sex ratio to the level of male aggression could be adaptive. Our results indicate that the behavior of the partner could indeed be a significant determinant in brood sex ratio adjustment, which should not be overlooked in future studies.     

Integrated plumage colour variation in relation to body condition, reproductive investment and laying date in the collared flycatcher

The possible integration of different sexual ornaments into a composite system, and especially the information content of such ornament complexes, is poorly investigated. Many bird species display complex plumage coloration, but whether this represents one integrated or several independent sexual traits can be unclear. Collared flycatchers (Ficedula albicollis) display melanised and depigmented plumage areas, and the spectral features (brightness and UV chroma) of these are correlated with each other across the plumage. In a 5-year dataset of male and female plumage reflectance, we examined some of the potential information content of integrated, plumage-level colour attributes by estimating their relationships to previous and current year body condition, laying date and clutch size. Females were in better condition the year before they became darker pigmented, and males in better current year condition were also darker pigmented. Female pigment-based brightness was positively, while male structurally based brightness was negatively related to current laying date. Finally, the overall UV chroma of white plumage areas in males was positively associated with current clutch size. Our results show that higher degree of pigmentation is related to better condition, while the structural colour component is associated with some aspects of reproductive investment. These results highlight the possibility that correlated aspects of a multiple plumage ornamentation system may reflect together some aspects of individual quality, thereby functioning as a composite signal.     

Males are sensitive — sex-dependent effect of rearing conditions on nestling growth

The sex-dependent effect of environmental conditions on nestlings has been extensively studied in size dimorphic birds. Whether males or females are more sensitive to poor conditions is not yet clear; however, the degree of sexual size-dimorphism, brood size and their interactions seem to influence the pattern. Much less is known about sex-dependent environmental sensitivity in size-monomorphic species, even though it may result in biased sex allocation. We altered the rearing conditions by brood size manipulation in the size-monomorphic collared flycatcher and then examined the sex-specific development of the nestlings. In all analyses, we controlled for the effect of paternity, because one may expect extra-pair young to be of better genetic quality and perform better at least under poor conditions. However, this was not the case, because we did not find any difference in growth rate or fledging size between extra- and within-pair young. We found that male nestlings had the potential for faster growth under favourable conditions, but suffered more under poor conditions. We found no sex × environment interaction for fledging size probably because the growth curves level off before fledging, and the disadvantaged nestlings can catch up with their siblings. The larger sensitivity of males does not explain the previously found seasonal shift in brood sex ratios and contradicts previous findings in another size-monomorphic species where females were more sensitive. This suggests that even in size-monomorphic species, no general rule exists, which determines the more sensitive sex.     

Context-dependent effects of nestling growth trajectories on recruitment probability in the collared flycatcher

Nestling growth is known as an important determinant of fitness in altricial birds, but its evolutionary potential has been debated, and little is known about detailed patterns of current selection on growth. Relationships are often reported between nestling growth and attributes of nestlings and parents, but the interpretation of these depends on the advantages a given growth difference confers to the chicks. Increased growth may have positive, negative or context-dependent effects on offspring fitness, but these effects are largely unknown in natural populations. We measured growth trajectories of body mass in fostered broods of collared flycatchers (Ficedula albicollis) in 3 years of contrasting food conditions. We examined the growth of young and their recruitment probability to the breeding population in relation to year quality, hatching rank, sex, paternal age and paternal attractiveness. We also looked at the interactive effects of growth and intrinsic offspring attributes on recruitment probability. The predictors of nestling growth and those of recruitment did not agree. Moreover, the recruitment consequences of a given nestling growth rate were significantly influenced by nestling rank and paternal ornamentation. Differential recruitment effects of nestling growth in relation to parental traits and nestling attributes suggest that using growth as a generally applicable measure of nestling quality may not be justified. These findings also have implications for morphological evolution and the indicator value of sexual signals.     

Ornaments and condition: plumage patch sizes,nutritional reserve state,reserve accumulation,and reserve depletion

Behavioral Ecology and Sociobiology - Cooperation plays a crucial role in primate social life. However, the evolution of large-scale human cooperation from the cognitive fundamentals found in other...