Cost of mobbing call to breeding pied flycatcher, Ficedula hypoleuca

Mobbing signals advertise the location of a stalking predatorto all prey in an area and recruit them into the inspectionaggregation. Such behavior usually causes the predator to moveto another area. However, mobbing calls could be eavesdroppedby other predators. Because the predation cost of mobbing callsis poorly known, we investigated whether the vocalizations ofthe mobbing pied flycatcher, Ficedula hypoleuca, a small holenesting passerine, increase the risk of nest predation. We usedmobbing calls of pied flycatchers to examine if they could lurepredators such as the marten, Martes martes. This predator usuallyhunts by night and may locate its mobbing prey while restingnearby during the day. Within each of 56 experimental plots,from the top of one nest-box we played back mobbing sounds ofpied flycatchers, whereas blank tapes were played from the topof another nest-box. The trials with mobbing calls were carriedout before sunset. We put pieces of recently abandoned nestsof pied flycatchers and a quail, Coturnix coturnix, egg intoeach of the nest-boxes. Nest-boxes with playbacks of mobbingcalls were depredated by martens significantly more than werenest-boxes with blank tapes. The results of the present studyindicate that repeated conspicuous mobbing calls may carry asignificant cost for birds during the breeding season.     

Experimentally reduced male attractiveness increases parental care in the pied flycatcher Ficedula hypoleuca

This study reports effects of experimental manipulations ofreproductive effort and the size of the male's white foreheadpatch (a secondary sexual trait), on provisioning rates, reproductivesuccess, and parental breeding dispersal distance in the piedflycatcher, Ficedula hypoleuca. Parents caring for enlargedbroods resulting from manipulated clutches provisioned nestsat higher rates than parents with reduced broods. Males with a reduced forehead patch fed their nestlings more in relationto males with an unmanipulated forehead patch, and their youngfledging with a longer tarsi. This suggests that males witha reduced attractiveness may perceive their own attractivenessand they devote more time available for parental effort given their poorer prospects in male contest competition and/or femaleattraction for extra-pair copulations. However, their femalesdid not alter their provisioning effort and this runs counterto both the differential allocation and the partner-compensationhypotheses. An artificial decrease in a male secondary sexualtrait led to a wider breeding dispersal distance between successiveyears.     

Descriptive and experimental evidence for timing-mediated polygyny risk in a pied flycatcher Ficedula hypoleuca population

In polygynous species with biparental care, mates are often acquired in succession. Most research has focussed on the cost of polygyny in secondary females, but primary females may also suffer from reduced paternal care. The likelihood of sharing a male may be higher for early laying females, which could counteract the fitness benefits of breeding early. In this study, we use 12 years of data on pied flycatchers Ficedula hypoleuca, to show that the likelihood of becoming a primary female of a polygynous male declines over the season. Moreover, we provide experimental evidence that early breeding elevates polygyny risk, through an experimental manipulation that introduced early breeding females to a population with later breeding phenology. We found that, independently of breeding date, primary females slightly more often experienced complete brood failures than monogamous females, but did not differ in number of fledged offspring among successful broods or number of locally returning recruits. However, apparent survival in subsequent years was substantially lower in primary females, indicating that they may compensate for reduced male care at the expense of future reproduction. Our study reveals that polygyny risk indeed increases with early breeding and entails a local survival cost for primary females. However, this cost is likely largely outweighed by fitness benefits of early breeding in most years. Hence it is unlikely that the increased polygyny risk of early breeding counteracts the fitness benefits, but it may reduce selection for breeding extremely early.     

Handicapped males and extrapair paternity in pied flycatchers: a study using microsatellite markers

We report an attempt to induce extrapair copulations and fertilizations in a species with a low intensity of sperm competition, the pied flycatcher Ficedula hypoleuca. Shortly after pair formation males were made less attractive to females by removing certain wing and tail feathers. Earlier research has shown that this manipulation reduces a male's pairing success. The idea was to test whether females mated to such males (N= 9) were more likely to obtain extrapair fertilizations than females mated to unmanipulated controls (N= 9). Paternity testing was carried out on all 98 young in the 18 broods, using a set of six microsatellite markers isolated from the species. Extrapair fertilizations were revealed in only three (17%) broods; two broods of handicapped males and one of a control male. A total of seven (7%) offspring were not genetically related to their putative father, a level which agrees well with results of other studies of this and other populations. We conclude that there was no evidence to suggest that the fertilization pattern was altered by the experimental manipulation. One reason for the lack of response could be that female mate choice in this species is based on male phenotypic, and not genotypic, quality.     

Adaptive coloration in pied flycatchers (Ficedula hypoleuca)—The devil is in the detail

Understanding the origin and persistence of phenotypic variation within and among populations is a major goal in evolutionary biology. However, the eagerness to find unadulterated explanatory models in combination with difficulties in publishing replicated studies may lead to severe underestimations of the complexity of selection patterns acting in nature. One striking example is variation in plumage coloration in birds, where the default adaptive explanation often is that brightly colored individuals signal superior quality across environmental conditions and therefore always should be favored by directional mate choice. Here, we review studies on the proximate determination and adaptive function of coloration traits in male pied flycatchers (Ficedula hypoleuca). From numerous studies, we can conclude that the dark male color phenotype is adapted to a typical northern climate and functions as a dominance signal in male–male competition over nesting sites, and that the browner phenotypes are favored by relaxed intraspecific competition with more dominant male collared flycatchers (Ficedula albicollis) in areas where the two species co‐occur. However, the role of avoidance of hybridization in driving character displacement in plumage between these two species may not be as important as initially thought. The direction of female choice on male coloration in pied flycatchers is not simply as opposite in direction in sympatry and allopatry as traditionally expected, but varies also in relation to additional contexts such as climate variation. While some of the heterogeneity in the observed relationships between coloration and fitness probably indicate type 1 errors, we strongly argue that environmental heterogeneity and context‐dependent selection play important roles in explaining plumage color variation in this species, which probably also is the case in many other species studied in less detail.     

Do female pied flycatchers seek extrapair copulations with familiar males? A test of the incomplete knowledge hypothesis

In birds with biparental care, great variation exists in thefrequency of extrapair paternity. Several hypotheses have beenproposed to account for this variation. We tested the incompleteknowledge hypothesis, which states that females are constrainedin their knowledge of male quality and that this influencestheir willingness to engage in extrapair copulations (EPC).By selective removal and release of female pied flycatchersFicedula hypoleuca, we created a situation where females finallysettled with a social mate close to the site where a formersocial mate was breeding. According to the incomplete knowledgehypothesis, this would lower the threshold for females to seekextrapair copulations in cases where their former social matewas of higher quality than the one finally chosen. The hypothesiswas not supported because manipulation of female settlementdid not increase frequency of extrapair paternity, not evenin cases where the female nested close to the previous mateand the current mate apparently was of lower quality becausehe was younger and more dull colored. However, we found that when extrapair paternity did occur, the cuckolder tended tobe a familiar male (i.e., the female's initial social mate).     

Properties of food loads delivered to nestlings in the pied flycatcher: effects of clutch size manipulation, year, and sex

Experimental manipulation of the number of altricial offspring is supposed to modify parental expenditure in birds. In addition to the observed increase in parental feeding rate, it is also possible that the choice of prey or the size of load may change with the changing demand for food. Sexual differences in the provisioning response are also expected, on the basis of earlier studies. We examined the effect of brood size manipulation on choice of prey brought to nestlings and load size in the pied flycatcher. The composition and size of loads differed between years, possibly depending on varying availability of different prey types. Males responded to brood size enlargement by gathering heavier loads, whereas females showed no response. The alteration of load size in males was not explained by a larger number of prey items or mean prey size, but was a combination of these components. It is likely that males also increased their work rate in response to increased food demand at the nest. The absence of response in females might be because they are unable to increase work rate any further, or because food delivery rate in females can not be optimized by changing load properties. Received: 18 December 1997 / Accepted: 1 March 1998     

No evidence for Z‐chromosome rearrangements between the pied flycatcher and the collared flycatcher as judged by gene‐based comparative genetic maps

Revealing the genetic basis of reproductive isolation is fundamental for understanding the speciation process. Chromosome speciation models propose a role for chromosomal rearrangements in promoting the build up of reproductive isolation between diverging populations and empirical data from several animal and plant taxa support these models. The pied flycatcher and the collared flycatcher are two closely related species that probably evolved reproductive isolation during geographical separation in Pleistocene glaciation refugia. Despite the short divergence time and current hybridization, these two species demonstrate a high degree of intrinsic post‐zygotic isolation and previous studies have shown that traits involved in mate choice and hybrid viability map to the Z‐chromosome. Could rearrangements of the Z‐chromosome between the species explain their reproductive isolation? We developed high coverage Z‐chromosome linkage maps for both species, using gene‐based markers and large‐scale SNP genotyping. Best order maps contained 57–62 gene markers with an estimated average density of one every 1–1.5 Mb. We estimated the recombination rates in flycatcher Z‐chromosomes to 1.1–1.3 cM/Mb. A comparison of the maps of the two species revealed extensive co‐linearity with no strong evidence for chromosomal rearrangements. This study does therefore not provide support the idea that sex chromosome rearrangements have caused the relatively strong post‐zygotic reproductive isolation between these two Ficedula species.     

Development of the auditory sensitivity and formation of the acoustically guided defensive behavior in nestlings of the pied flycatcher Ficedula hypoleuca

Age dynamics of generation of the evoked potentials (EP) in the field L of caudal nidopallium (the higher integrative center of the avian auditory system) and development of the auditory-guided defensive behavior were studied in control and visually deprived pied flycatcher Ficedula hypoleuca nestlings. It was shown that the rhythmically organized monofrequency signals with sound frequency 3.5 kHz and higher produced the defensive behavior as the auditory sensitivity to these frequencies matured. After 9 days, the species-specific alarm signal produced more effectively the defensive behavior than the tonal signals. The rhythmically organized sound with filling frequency 0.5 kHz, occupying the less low-frequency diapason than the feeding signal, produced the effect opposite to the alarm signal to increase the nestling mobility. At the initial stage of the defensive behavior development the auditory threshold fell markedly in the frequency diapason corresponding to the frequency diapason of the alarm signal (5–6 kHz), which seemed to facilitate involvement of this diapason signals in the defensive integration. The auditory EP generation thresholds in the whole studied diapason were lower in the visually deprived nestlings than in the normally developing one; however, the ability of the acoustic signals to suppress alimentary reactions fell significantly.     

Individual color variation and male quality in pied flycatchers (Ficedula hypoleuca): a role of ultraviolet reflectance

Bright coloration of males in many animal species has inspiredresearchers for more than a century. In this field study, weinvestigated whether color variation between individuals isrelated to individual quality in pied flycatcher (Ficedulahypoleuca) males in terms of arrival time at the breeding sites.In addition to traditional visual color scoring, plumage color was measured using spectroradiometric measurements between 320and 700 nm. This range includes the near-ultraviolet wavebandfrom 320 to 400 nm. Males that arrived earlier at breedingsites had higher proportional UV reflectance in the crown andmantle. The proportional UV reflectance in the crown and mantlewas not related to traditionally scored general brownness inmales. However, adult males had a higher proportion of ultravioletin the plumage than yearling males or females. These resultssuggest that in pied flycatcher males, the UV reflectance ofplumage may be positively correlated with individual quality.     

Corticosterone metabolites in blue tit and pied flycatcher droppings: effects of brood size, ectoparasites and temperature

The hypothalamic-pituitary-adrenal (HPA) axis of birds induces the secretion of corticosterone (CORT) as a response to different ecological variables. In this study we tested experimentally if manipulations of brood size or ectoparasitism led to subsequent differences in the concentration of excreted CORT metabolites of adult and nestling blue tits (Cyanistes caeruleus). No significant effect of the manipulation of brood size was detected in adults or nestlings. No significant effect of ectoparasitism was detected in males or nestlings, although females from uninfested nests showed lower concentrations of excreted CORT metabolites. In addition, we analysed if weather conditions had an influence on the concentration of excreted CORT metabolites of blue tits and pied flycatchers (Ficedula hypoleuca) breeding in the same forest. We detected no effect of weather conditions on adults, but nestlings of both species showed a negative correlation between their excreted CORT metabolites and the average mean temperatures they were subjected to during their growth. This effect was not found in blue tits in a colder year, suggesting that the sensitivity of the HPA axis to ambient temperature may be subjected to interannual variation. Moreover, we found a positive effect of the maximum temperature on the day of sampling on the concentration of CORT metabolites of blue tit nestlings in one of the years. These results suggest that weather conditions may act as environmental stressors to which the HPA axis of blue tit and pied flycatcher nestlings may be sensitive.     

Certainty of paternity and paternal effort in the collared flycatcher

Models of optimal parental investment predict that variationin certainty of paternity can affect the optimal level of paternalinvestment when a male's expected paternity in different nestingattempts is not fixed throughout his lifetime. Several attemptsto test this prediction experimentally in monogamous birds havefailed to induce a reduction in care by males. This may be becausethe method used, detaining males, is a poor model for what happenswhen a male's certainly of paternity is naturally reduced. Wecaught and detained female collared flycatchers Ficedula albicollisfor 1 h immediately after laying on one or two occasions inan attempt to induce variation in certainty of paternity forthe males they were mated to. By capturing females immediatelyafter laying we hoped to exploit the existence of an "inseminationwindow" since males should be very sensitive to female absenceduring this period. The general effect of the experimental manipulationwas consistent with reduced certainty of paternity: males respondedby reducing their level of paternal care to nestlings, and malesmated to females that had been caught on one morning fed nestlingssignificantly less often and made a smaller share of feedingvisits than males mated to control females. The effects of theexperiment were generally weak, however, and we argue that certaintyof paternity may be fixed well before egg laying, in which caseexperimental manipulations are unlikely to have large effects.It is difficult to predict die effects of natural variationin certainty of paternity on levels of male paternal care becausedifferential allocation by females mated to attractive malesmay act in the opposite direction     

Black-and-white plumage in male pied flycatchers (Ficedula hypoleuca) reduces the risk of predation from sparrowhawks (Accipiter nisus) during the breeding season

Bright colors in birds might signal that they are undesirableas prey (aposematic), an idea that has been difficult to test.When stuffed pied flycatchers Ficedula hypoleuca are exposedto migrating sparrowhawks Accipiter nisus in spring or in autumn,the hawks attack cryptic females more often than bright males.To achieve better statistical control and to assess whethermale plumage also reduces predation risk in the breeding seasonand in the nesting habitat of the pied flycatcher, I placedpairs of male and female flycatcher mounts in similar positionsnear 22 nests of sparrowhawks. The hawks attacked mainly femalemounts, verifying that the preference is real. The sparrowhawkscaught at least 19 live pied flycatchers; 12 young, 5 adultmales, 1 adult female, and 1 female or young. Hawks that caughtan adult male seemed to prefer attacking female mounts. I discussthree interpretations of these results, suggesting that black-and-whitemale flycatchers may benefit from being a novel and aberrantprey, at least early in the breeding season.