Effect of parentage and relatedness on the individual contribution to cooperative chick care in carrion crows Corvus corone corone

Carrion crows Corvus corone corone in northern Spain form complex cooperative groups that contain non-dispersing offspring and immigrants. Reproduction is often shared among group members, with polyandry prevalent over joint egg laying. However, due to incest avoidance or sexual immaturity, reproduction is potentially available only to a fraction of group members (potential breeders), while others do not breed (non-breeders). We combined molecular data with video-recorded observations at nests in order to investigate whether potential breeders and non-breeders adjust their individual effort in nestling feeding respectively to their level of parentage and the relatedness with the chicks. Overall, parents of at least one chick in the brood showed the highest feeding rates. Among potential breeders, genetic mothers and fathers fed chicks at significantly higher rates than individuals with no parentage, but they did not adjust their effort according to the proportion of offspring generated. Current direct fitness benefits are therefore important in determining a high provisioning effort, but crows may lack a mechanism to finely assess their share of parentage. Among non-breeders, males contributed more than females to chick feeding, but we found no significant correlation between feeding rate and relatedness to the nestling. We discuss how the latter result can be reconciled with the fact that kin selection has been shown to be important in shaping the crow cooperative society.Communicated by C. Brown     

Female yellowhammers (Emberiza citrinella) prefer yellower males: a laboratory experiment

The importance of male plumage coloration as a signal of male dominance and a cue for female choice in the monogamous yellowhammer, Emberiza citrinella, was tested in two sets of experiments in an indoor aviary. Dominance was tested by introducing two individuals, with no previous experience of each other, in an aviary with food and water. Aggression occurred more often between two males than between a male and a female and more frequently between pairs of males including at least one old male than between two young males. Dominance was not related to male colour in trials between males of the same age class, but it was in trials between an old and a young male, often differing in colour. Thus, age may be a more important determinant of dominance than colour. Female preference for more colourful males was tested by allowing hormone-induced females to choose between a more and a less colourful dummy male. Females spent more time in front of more colourful than drabber males and also more often perched beside colourful males than duller individuals. Although male colour cannot be ruled out as a dominance signal, the results suggest that male colour is primarily used as a signal in mate choice. Female choice may hence be responsible for maintenance of bright plumage in the male yellowhammer.     

Absence of status signalling by structurally based ultraviolet plumage in wintering blue tits (<Emphasis Type="Italic">Cyanistes caeruleus</Emphasis>)

Structurally based ultraviolet (UV)-reflective plumage parts can be important cues in mate choice. However, it remains largely unknown if UV plumage variation can also function as a signal of social status during competitive interactions. In blue tits (Cyanistes caeruleus), the UV-reflective crown plumage functions as a female mate choice cue that probably indicates male quality, as males with higher UV reflectance have been shown to have better chances of over-winter survival. Possibly, the UV crown plumage acts as a status signal in the competition over scarce food sources during winter. To test this idea, we related dominance of individuals at an artificial food source during adverse winter conditions to spectrophotometric measurements of their crown plumage. However, while controlling for the confounding effects of sex, age, and distance from territory, we found no significant effect of crown UV reflectance on dominance. Consistent with this result, we also found no relation between crown UV reflectance and over-winter survival. We conclude that the structurally based UV reflectance of the blue tit crown feathers plays little role in competition between individuals during winter despite its importance as a cue in mate choice.     

Paternal care in the European starling,Sturnus vulgaris: nestling provisioning

The extent to which male birds in polygynous species with biparental care assist in nestling feeding often varies considerably between nests of different mating status. Both how much polygynous males assist and how they divide their effort between nests may have a profound effect on the evolution of mating systems. In this study we investigated how males in the facultatively polygynous European starling Sturnus vulgaris invested in their different nests. The amount of male assistance affected the quality of the offspring. Polygynous males invested as much as monogamous males, but divided their effort asymmetrically between nests, predominantly feeding nestlings of first-mated (primary) females. Although females partly compensated for loss of male assistance, total feeding frequency was lower at primary females’ nests than at monogamous females nests. Secondary females received even less assistance with nestling rearing, and the extent to which males assisted decreased with the length of the interval between the hatching of the primary and secondary clutches. These results are contrasted with those from a Belgian populations of starlings with a much more protracted breeding season and thus greater opportunities for males to attract additional mates during the nestling rearing period. The results show that both the “defence of male parental investment model” and the “asynchronous settlement model” have explanatory power, but that their validity depends on the potential length of the breeding season. Received: 21 July 1995/Accepted after revision: 13 July 1996     

Extra-pair paternity and male characteristics in the pied flycatcher

The pied flycatcher (Ficedula hypoleuca) is sexually dichromatic with extreme variation in male plumage coloration. The benefit for males of having black plumage is controversial, and few studies have found evidence for a sexual selection benefit of being black rather than brown. However, blacker males may be better able to achieve extra-pair fertilizations (EPFs), which may be an important component of sexual selection. We studied the role of EPFs in sexual selection in the pied flycatcher by establishing a set-up where two males with different back coloration (blacker vs browner) bred simultaneously near each other. DNA fingerprinting analysis revealed that 11% of offspring resulted from EPFs, and that 22% of broods included extra-pair young (EPY) among 36 nests containing 223 nestlings. We found no evidence that browner males suffered more often from EPFs than blacker males. There was no correlation of male or female morphology or age with EPF frequency. However, breeding pairs with low genetic similarity had EPY in their nests significantly more often. Thus we argue that females paired with genetically dissimilar males may try to avoid the effects of extreme outbreeding by seeking extra-pair copulations (EPCs). Alternatively, incompatibility between genetically dissimilar mates may simply expose females to more extra-pair copulations.     

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.     

Delayed plumage maturation in Lazuli buntings: tests of the female mimicry and status signalling hypotheses

The evolutionary importance of delayed plumage maturation (DPM) in passerines, the condition when more than 1 year is required to achieve adult-like coloration, remains highly contentious. Adaptive hypotheses propose that aggression from after 2nd-year (ASY) males or predation favors DPM in 2nd-year (SY) males, thereby increasing SY male survivorship or reproductive success. However, each hypothesis suggests a distinct selective mechanism explaining “how” this is accomplished. Alternatively, DPM may be a consequence of a nonadaptive molt constraint. We tested the female mimicry and status signalling hypotheses in territorial ASY male lazuli buntings (Passerinaamoena) using three sets of model presentation experiments. The female mimicry hypothesis proposes that dull SY male plumage deceptively mimics female plumage, and predicts that ASY males can not distinguish SY male from female plumage. The status signalling hypothesis proposes that dull SY male plumage honestly signals low competitive threat, and predicts that ASY males respond less aggressively to dull versus bright, ASY-like plumage. Contrary to the female mimicry hypothesis, ASY males distinguished between SY male and female plumage, as they were aggressive to SY male models exclusively and attempted to copulate with female models. Supporting the status signalling hypothesis, ASY males were significantly less aggressive to SY versus ASY male plumage. While DPM may result from a physiological constraint on bright SY male plumage, our results support the idea that dull plumage in an SY male's first breeding season may be maintained by selection to reduce aggression from ASY males, serving as a signal of competitive status. Received: 21 February 1997 / Accepted after revision: 16 June 1997     

The structural significance of a vocalization that stimulates gaping in black-capped chickadees

In a variety of avian species, vocalizations used to stimulate gaping in nestlings during feeding share similar features such as broad frequency range, multiple spectral components, and sudden onset. It is currently not understood what functional significance, if any, these acoustic features have for close-range communication. One example of such a vocalization is the “squawk” of the black-capped chickadees (Parus atricapillus). The present study analyzes the significant features of the squawk by observing the response of chickadee nestlings to field playbacks of natural and computer-modified squawks. Of the features tested, frequency range appears most critical, but responses to frequency ranges change with age, such that low frequencies are most stimulating around the time of hatching but cease to elicit gaping after 5 days posthatch. Aperiodic stimuli and computer-modified squawks with gradual onsets tend to be less stimulating than natural squawks at some ages, but these differences are not significant at any age. The functional significance of the broad frequency range of the squawk is discussed, including the possible role of accommodating shifting frequency preferences related to ontogenetic changes in auditory sensitivity and elaboration of the vocal repertoire. Received: 16 January 1996 / Accepted after revision: 28 December 1996     

测定水中氰化物影响条件的实验研究

异烟酸—吡唑啉酮分光光度法在实际应用中稳定性较差,通过对显色反应条件的试验,以及对其他影响因素的分析,探索测定了反应的最佳条件。     

Maternal energy expenditure does not change with flight costs or food availability in the pied flycatcher (Ficedula hypoleuca): costs and benefits for nestlings

We manipulated parental work load without changing brood size in a population of pied flycatchers Ficedula hypoleuca by removing two primaries (7 and 9) from each wing of females, thus reducing wing area and increasing flight costs. At other nests, we offered supplementary food in the form of live mealworms (10–20 g daily from hatching) to reduce brood demand and thus parental foraging costs. Other nests were left as controls. The daily energy expenditure of females feeding 12-day-old nestlings was measured with doubly labelled water D₂ ¹⁸O. Females in both treatments expended the same amount of energy, fed at the same rate and had similar body masses to birds in the control group. No effect of treatment on male mass and feeding effort was detected. More nestlings, however, died in nests of handicapped females. Nestlings of handicapped females had significantly lower body mass and haematocrit values than nestlings in food-supplemented nests, with nestlings in control nests occupying an intermediate position. The effects of both treatments on nestling mass, haematocrit values and mortality rates were only noticeable in nests infested with mites. Maternal energy expenditure is apparently constrained and offspring pay the costs imposed by reduced provisioning rate or increased demand caused by ectoparasites, while receiving benefits when food supply improves. The presumption that avian reproductive costs derive from changes in a flexible energy output may not be met in many cases. Received: 24 October 1998 / Received in revised form: 15 March 1999 / Accepted: 26 April 1999