Do female great tits (Parus major) assess males by eavesdropping? A field study using interactive song playback

Male singing behaviour correlates with extra-pair success in several passerine birds. Singing interactions during territorial contests provide relative information on the males involved. Such information may be important in female extra-pair behaviour and eavesdropping on singing interactions among males may allow females to make such relative assessments. We used interactive playback to instigate singing contests with male great tits during the peak fertile period of their mate in an attempt to alter females'' assessment of mates'' quality relative to neighbours (potential extra-pair partners). We escalated a contest to one male (by overlapping his songs) and then subsequently de-escalated a contest (by alternating) to a neighbour. Intrusions onto neighbouring territories by females mated to either treatment male were then monitored. Females mated to escalation treatment males were more likely to intrude following playbacks than females mated to de-escalation treatment males. Although the absolute song output of males did not differ between treatments, males produced more song relative to playback in de-escalation treatments and relative song output was positively correlated with female intrusions. Therefore, female great tits eavesdrop on singing interactions and change their visitation rates to neighbouring territories according to their mate''s singing performance relative to neighbours.     

Are colorful males of great tits Parus major better parents? Parental investment is a matter of quality

Given the known influence of parental investment on breeding success of great tits Parus major, females should be expected to use male parental quality as an essential criterion in mate choice. Since parental quality cannot usually be observed directly at the time of pairing, it has been suggested that females rely on male ornaments as indicative of their ability to provide parental care. This hypothesis, called the good parent hypothesis, has been tested repeatedly assessing only parental effort as the number of feedings made by parents. However, in evaluating parental investment, the focus should also be on the quality of prey captured rather than only on its quantity. We analyzed feeding rates and the provisioning of different prey in relation to both male yellow carotenoid-based breast coloration and the size of the black melanin-based stripe in a Mediterranean great tit population. We predicted that more carotenoid ornamented individuals would feed nestlings with a diet consisting of a higher proportion of caterpillars. However, and contrary to predictions, we found that males with higher values of hue in the yellow breast feathers, fed their offspring with a lower proportion of caterpillars and a higher proportion of spiders. In addition, nestlings that received a higher proportion of spiders showed an improved body condition after controlling for tarsus length and other variables. Male feeding rates correlated positively with brood size and tended to correlate negatively with date, although we did not find any effect of male coloration. Our data therefore support the good parent hypothesis, insofar as parental investment is also a matter of quality, and that, at least in the Mediterranean area, caterpillars are not the only key food source.     

Do Great Tit Parus major parents gear their brood defence to the quality of their young?

Parental investment theory suggests that animals should increase their reproductive success by investing more heavily in higher-quality offspring than in lower-quality offspring. Great Tit Parus major nestlings of higher body weight have been shown to enjoy a higher survival rate after fledging. We examine for the first time whether Great Tit parents invest more heavily in heavier nestlings as measured by defence (six variables) against a Pygmy Owl Glaucidium perlatum, similar to G. passerinum, which is a predator of both adult and nestling birds including hole-nesters like the Great Tit. Thirty-two parent Great Tit pairs in a wood- and parkland study area in Essen-Stadtwald did not vary their antipredator behaviour in relation to nestling weight; between-brood variation of weight was similar to that found in different populations and in different years. However, parental defence behaviour varied, as expected, with parent's sex and nestling number, though overall responsivity of parents to many other independent variables appeared lower than found previously.     

Is variation in brood sex ratios adaptive in the great tit (Parus major)?

Life-history theory predicts skewed offspring sex ratios ina range of situations in which the costs and benefits of producingthe two sexes differ. In recent years, many studies have demonstratedbiased sex ratios in a variety of bird species. However, manyof these investigations have been based on small sample sizes,on data from a single year, or both. Using a recently developedpolymerase chain reaction-based molecular DNA technique, 912great tit (Parus major) nestlings from 118 broods in 5 differentyears were sexed. As found in a number of previous studieson the same species, there were significant predictors of offspringsex ratio in individual years. However, there were no consistenttrends across years, and none of the measured variables significantlypredicted sex ratio over all years combined. Furthermore, broodsex ratio of the population did not depart from the expectedbinomial distribution. Although there are theoretical advantagesto manipulating the sex ratio in this and other species, thephysiological mechanism by which it is achieved in birds remainsobscure. We argue that data from several years are needed toconfirm whether facultative sex ratio manipulation is a consistentbreeding strategy used by birds.     

Do extra‐pair paternities provide genetic benefits for female blue tits Parus caeruleus?

A large body of theories on extra-pair paternity (EPP) in birds has proposed four main "genetic" hypotheses to explain this behaviour: the "good genes" hypothesis, the genetic diversity hypothesis, the genetic compatibility hypothesis and the fertility insurance hypothesis. Empirical tests have been scarce, mainly because high sample sizes are difficult to collect. We have tested these hypotheses in three Mediterranean populations of blue tits Parus caeruleus in which 50–68% of the broods contained extra-pair young. Results showed that the distribution of extra-pair young among broods was not random, and that survival to fledging of extra-pair young was higher than that of their within-pair sibs. These results support the idea of genetic effects benefiting extra-pair young. However, comparison of cuckolded and cuckolding males showed no significant difference in their body size, age, survival or relatedness with their paired females, and offspring morphometrics did not differ between extra-pair and within-pair young. We conclude that none of the genetic hypotheses can explain fully the high level of extra-pair paternity, at least in our populations of Mediterranean blue tits. We suggest that direct ecological benefits of EPP for females should be tested more often in correlative as well as experimental approaches.     

Negotiation over offspring care?--a positive response to partner-provisioning rate in great tits

Game theoretical models of biparental care predict that a changein work rate by one parent should be met by incomplete compensationby its partner. However, in empirical studies on biparentalbirds, there has been some inconsistency in the direction andextent of the response, and the mechanism behind it has so farbeen unclear. Parents could be responding directly to partnerwork rate or indirectly via chick begging. In this study ofgreat tits (Parus major), the work rate of one parent was increasedexperimentally by augmenting the begging of the chicks withplayback of extra begging calls whenever the parent visitedthe nest. The playback had no effect on the chicks' beggingbehavior, so any change in the focal parent's behavior was adirect response to its partner's work rate over a short timescale.An experimental increase in care by either male or female parentled to an increase (to a lesser extent) in the work rate ofits partner, which is counter to the decrease predicted by partialcompensation models. This seemingly paradoxical result may reflectdecisions made exclusively over a short timescale and is inkeeping with new theoretical work, which takes into accountthe information content of partner work rates.     

Do sibling tits (<Emphasis Type="Italic">Parus major,P. caeruleus</Emphasis>) disperse over similar distances and in similar directions?

We studied dispersal movements by sibling pairs of great tits, Parus major, and blue tits, P. caeruleus, in a patchy environment, in order to test whether siblings are more similar in dispersal than expected by chance. Because of possible common environmental effects due to the heterogeneity and finiteness of the study area, we compared the similarity among siblings with the similarity between each sibling and an unrelated bird that fledged in the same patch and year, as close to the siblings nest as possible. Siblings of both species were not more similar in dispersal distance than they were to control birds. However, great tit siblings dispersed in similar directions compared to control birds, and this result was not affected by the degree of matching between sibling and control birds. As a consequence, siblings ended up breeding at closer distances from one another than control birds. Heritability values calculated from parent-offspring regressions were close to zero, suggesting that there is no additive genetic variance for dispersal distance or dispersal direction. We propose that similarity in dispersal direction originates from association of siblings during dispersal or during activities that influence the choice of direction, such as postfledging family movements. Our results show that non-independence in the choice of dispersal direction by siblings may influence small-scale kin structure in this population with high local recruitment.     

Do great tits assess rivals by combining direct experience with information gathered by eavesdropping?

Animals frequently use signals that travel further than the spacing between individuals. For every intended recipient of a given signal there are likely to be many other individuals that receive information. Eavesdropping on signalling interactions between other individuals provides a relatively cost-free method of assessing future opponents or mates. Male great tits (Parus major) extract relative information from such interactions between individuals unknown to them. Here, we show that male great tits can take information gathering a stage further and obtain more information about a previously unencountered intruder, by the hitherto unknown capability of combining information gathered by eavesdropping with that derived from their own direct interaction with an individual. Prior experience with an intruder (A) was achieved by subjecting a focal male to different levels of intrusion simulated using interactive playback. This intruder (A) then took part in a simulated interaction with an unknown male (B) outside the territorial boundary of the focal males. In response to subsequent intrusion by the second male (B), focal males showed low song output in response to males that had lost to a male that the subject was able to beat. Males of known high quality, or those about which information was ambiguous, elicited a high level of song output by focal males. We discuss the implications of this finding for the evolution of communication and social behaviour.     

Importance of conspicuous colours in warning signals: the great tit’s (Parus major) point of view

Few studies have dealt with the importance of colours per se in warning signalling, with the use of a broader array of different colours. We tested the reactions of great tits (Parus major) to colour modifications (red, orange, yellow, white, blue, violet, and green) of the warning signal of the red firebug (Pyrrhocoris apterus), preserving its typical black pattern. We used the edible Guyana spotted roach (Blaptica dubia) as the prey, each of which carried a paper sticker shield of a particular colour on its back. With such prey, the effects of the other traits of the red firebug (e.g. shape of the legs and antennae or chemical signals) on the birds’ reactions were removed. All of the conspicuous forms of the prey, possessing a black pattern, were protected against great tits better than the non-patterned brown control form. The level of protection decreased from those forms with colours similar to the model and commonly occurring in warning signals in nature (red, orange, yellow), through other conspicuous colours rarely occurring in warning signals in nature (white, violet, blue), to the colour which usually occurs as cryptic in nature (green). In the green form, repeated encounters were necessary to reach avoidance. Avoidance learning came to pass despite the fact that the presented prey was neither inedible nor distasteful.     

Is hissing behaviour of incubating great tits related to reproductive investment in the wild?

Anti-predator behaviour of breeding animals is a complex trait that depends on current reproductive investment as well as individual differences in risk-taking propensities. In response to nest predation, many bird species produce specific sounds, such as the hissing calls in incubating great tits (Parus major), that may provoke an acoustic startle response in the predator. However, it is still unclear whether the propensity of incubating females to produce hissing calls towards nest predators depends on the reproductive investment. With our 3-year study, we show that response type (females that do not hiss versus females giving hissing calls) to a potential nest predator, the woodpecker, is a repeatable trait. We found no differences in the studied reproductive traits between hissing and non-hissing birds. Interestingly, among hissing birds, fast-responding females started egg-laying earlier than slow-responding ones. Among non-hissing birds, heavier birds initiated clutches earlier. We also revealed that hissing birds breed in areas with decreased nest-box occupancy, suggesting either that they potentially select different areas to breed or that territory size is larger as a result of hissing birds being more aggressive. These findings demonstrate that response type is not related to the early reproductive value of the brood across distinct behavioural groups. However, our results do suggest that non-hissing and hissing females differ in terms of individual quality or dominance or personality related aspects.     

Biozid-Belastungen bei weiblichen Kohlmeisen(Parus major) w?hrend der Brutzeit

Summary For investigations about changes of the genital system during breeding 7 female Great Tits were killed. Their carcasses were additionally examined for pesticide residues. The values of pesticides lay at the limit of indication, so that any damage for the population of Great Tits in the Siebengebirge (near Bonn) can be excluded.     

How does an increase in minimum daily temperatures during incubation influence reproduction in the great tit Parus major?

Temperature variation affects all life stages of organisms, especially early development, and considering global warming, it is urgent to understand precisely its consequences. In egg‐laying species, incubation behaviour can buffer embryo developmental temperature variation and influence offspring development. We experimentally investigated the effect of an increase in minimum daily nest temperature during incubation in the great tit Parus major, by placing a hand warming pad under the nest in the evenings. As compared to controls, the experimental treatment increased nest temperature at night by an average of 4°C, and this increase carried over to the following day. We measured the consequences of this mainly nocturnal temperature increase during incubation on 1) parental behaviour (incubation and nestling feeding), 2) parental health (quantified by body condition, immune status, physiological and oxidative stress) and 3) reproductive success (nestling body condition, growth, i.e. mass gain, hatching and fledging success, and nestling immune status, physiological and oxidative stress). This study yielded three major results. First, we found that heating the nest did not change the duration of incubation as compared to controls. Second, increasing nest temperature during incubation decreased nestling feeding behaviour but did not affect parental health in terms of body condition, immune status, physiological and oxidative stress. Third, nestling mass at hatching was greater but nestling mass gain was slower in heated nests than in control nests, resulting in similar fledging mass. The present study demonstrates that increased environmental temperatures during incubation influenced nestling development in the great tit and especially hatchling mass, which might produce long‐term life history consequences.     

Why hoard? The economics of food storing in tits, Parus spp.

We present two models of food storage by small birds such astits (Parus spp): a simple, energy-maximizing model and a morecomplex dynamic programming model. The results show that hoardingis advantageous when (1) the metabolic costs of carrying reservesare high, (2) food supply is variable, (3) the mean rate ofintake is low, and (4) overnight expenditure of energy is high.The dynamic programming model predicts daily routines of storingand retrieval as well as changes in body mass. The predictedroutine (storage in the early part of the day, retrieval neardusk) has been observed in some species that store food. Wepredict differences in the pattern of change of body mass throughthe day between storers and nonstorers, but data to test thisprediction are not yet available.     

The function of extrapair paternity in blue tits and great tits: good genes or fertility insurance?

DNA fingerprinting of an island population of blue tits andgreat tits in southeast Norway revealed that extrapair paternityaccounted for 36% (17/47) and 27% (15/55) of broods and for7% (31/466) and 8% (33/408) of young in the two species, respectively.Cuckolded males did not differ from noncuckolded males withrespect to morphology, age, or survival. There was no seasonalpattern in the frequency of extrapair paternity, and males showedno individual consistency in paternity loss over multiple broods.Extrapair offspring did not grow faster, they did not fledgewith a higher body mass, and they did not show a higher localsurvival rate than their half siblings. Hence, there was noevidence of any association between extrapair paternity andmale phenotypic or genotypic quality. Extrapair offspring wererandomly distributed among broods, with the only exceptionsof one blue tit and two great tit broods in which all young(six to nine) were sired by an extrapair male. This patternis best explained by a small proportion of males (2%–4%)being infertile and by most females performing a few extrapaircopulations as insurance against laying infertile eggs. We concludethat the results suggest a role for fertility insurance butthat alternative functional explanations to extrapair paternityin these populations cannot yet be ruled out.     

Should congruence between intra- and interspecific ecomorphological relationships be expected? A case study with the great tit,Parus major

We studied the relationship between leg morphology and posture while feeding in a population of great tits (Parus major) under controlled conditions to investigate to what extent morphology and ecology are linked at the individual level. From predictions generated at the interspecific level within the genus Parus (Moreno and Carrascal 1993), we tested whether intra- and interspecific ecomorphological relationships are consistent. Within our population, neither leg bone lengths nor leg muscle morphology were related to the feeding posture of individuals. However, differences in body weight were correlated with inter-individual differences in time spent hanging. These results demonstrate that the association between intra- and interspecific ecomorphological relationships is not uniform. We argue that, at the intraspecific level, body weight overrides the significance of other traits that have a functional meaning at the interspecific level (i.e. leg segment lengths, muscular morphology), due to isometric variation of morphological traits (muscular and skeletal) with body mass. Thus, the discrepancy between the ecomorphological associations at intra- and interspecific levels is the result of a problem of scale (morphological changes in evolutionary time and isometric variation of morphological traits with body mass in ecological time).     

Untersuchungen zu Brutaktivit?ten der Kohlmeise(Parus major) in der Zeit der Eiablage

Ohne Zusammenfassung     

Are avian blood parasites pathogenic in the wild? A medication experiment in blue tits (Parus caeruleus).

The Hamilton and Zuk hypothesis on haemoparasite-mediated sexual selection and certain studies of reproductive costs are based on the assumption that avian blood parasite infections are detrimental to their hosts. However, there is no experimental evidence demonstrating harmful effects of blood parasites on fitness in wild populations, it even having been suggested that they may be non-pathogenic. Only an experimental manipulation of natural blood parasite loads may reveal their harmful effects. In this field experiment we reduced through medication the intensity of infection by Haemoproteus majoris and the prevalence of infection by Leucocytoazoon majoris in blue tits (Parus caeruleus), and demonstrated detrimental effects of natural levels of infection by these common parasite species on host reproductive success and condition. The fact that some of the costs of infection were paid by offspring indicates that blood parasites reduce parental working capacity while feeding nestlings. Medicated females may be able to devote more resources to parental care through being released from the drain imposed upon them by parasites and/or through a reduced allocation to an immune response. Therefore, this work adds support to previous findings relating hosts' life-history traits and haematozoan infections.