Daily body mass regulation in dominance-structured coal tit (Parus ater) flocks in response to variable food access: a laboratory study

In a dominance-structured flock, social status may determinepriority of access to food. Birds of low social status mayperceive present and future access to food as less predictable,and so have a higher risk of starvation, than birds of highsocial rank. Theoretical models predict that subordinate birdsshould carry larger fat reserves and incur higher mass-dependentcosts than dominants. However, empirical tests of the assumptionsof these models are still scarce and controversial. We investigatedthe effect of dominance rank on daily mass gain under conditionsof fluctuating food availability in a laboratory experimentusing four flocks of four coal tits (Parus ater) each. Thesame amount of food was delivered in two treatments, but inone treatment the food was offered at a constant rate betweendays (fixed treatment), while in the other treatment the dailyfood supply varied in an unpredictable sequence between days(variable treatment). All birds showed greater variance inbody mass in the variable treatment than in the fixed treatment.Body mass within birds showed the same variability at dawn thanat dusk in the fixed treatment, but less variability at dawnthan at dusk in the variable treatment. This may be a mechanismto reduce the immediate risk of starvation at the beginningof the day, when fat reserves are at their lowest and the aggressionbetween flock members when feeding highest. Subordinate birdswere excluded from the feeders by dominants more often in theearly morning than in the rest of the day, and they showedmore variability in daily mass gain and body mass at dawn thandominant birds. These results support the hypothesis that subordinatebirds have a reduced probability of surviving when food availabilitychanges unexpectedly compared to dominants.     

Geographic variation of the storing behaviour in the Coal tit Parus ater: role of winter residency and environmental conditions

Foraging and hoarding behaviour of the Coal Tit Parus ater were studied in two widely separated populations, in the Pyrenees and in Norway. The two populations differed in their degree of winter residence and environmental pressures. Location of foraging and hoarding sites were described in the Pyrenees during winter, and during autumn in Norway where no hoarding takes place during winter. Significant differences in the hoarding behaviour of Coal Tits between these areas were observed. In the Pyrenees, birds hoarded on inner and lower parts of the trees, using trunks and thick branches as caching sites, which are the substrates most heavily used in conditions of winter environmental stress. In Norway, birds hoarded items on outer and higher parts of the trees, mainly among needled twigs, which were the substrates used in normal foraging. Animal food was hoarded more frequently by the Norwegian population. Our results show that hoarding behaviour varies among populations and suggest that the differences recorded may be related to differences in competitive pressures and the prevailing environmental conditions. Furthermore, the absence of a safe long-term hoarding niche in the Norwegian population, due to interspecific competition, would make a strong sedentary habit difficult, offering a functional explanation for the differences observed in the degree of winter residence between Norwegian and Pyrenean Coal Tits.     

Polyandry in coal tits Parus ater: fitness consequences of putting eggs into multiple genetic baskets

Females of many species mate with multiple males within a single reproductive cycle. One hypothesis to explain polyandry postulates that females benefit from increasing within-brood genetic diversity. Two mechanisms may render sire genetic diversity beneficial for females, genetic bet-hedging vs. non-bet-hedging. We analysed whether females of the socially monogamous coal tit (Parus ater) benefit via either of these mechanisms when engaging in extra-pair (i.e. polyandrous) mating. To obtain a measure of within-brood genetic diversity as a function of paternal genetic contributions, we calculated a sire diversity index based on the established Shannon-Wiener Index. In 246 broods from two consecutive years, sire genetic diversity had no effect on either the mean or the variance in brood fitness measured as offspring recruitment within 4 years after birth. The hypothesis that benefits of increasing sire diversity contribute to selection for female extra-pair mating behaviour in P. ater was therefore not supported.     

Variation in growth in the blue tit (Parus caeruleus)

The pattern and amount of phenotypic and genetic variation in growth was analysed using the infinite-dimensional model in natural populations of the blue tit (Parus caeruleus). A size-index was used to analyse patterns of variation and covariation across ages (2, 5, 8, 11 and 14 days). Genetic variation was analysed using mother-, father-, and midparent-offspring regressions in the blue tit. Phenotypic variation in growth was limited to a few dimensions only, while heritabilities were close to zero at all ages except at 2 days when a significant mother-offspring relation was found. The phenotypic variance-covariance matrix over ages was found to be singular, which suggests that there are trajectories for which there is no phenotypic variation, and which therefore they cannot evolve. The phenotypic growth trajectory associated with the largest amount of variation basically showed a high to moderately high covariation across ages. These results have macroevolutionary implications in terms of the outcome of selection which generally will be in terms of overall size changes but with a slow rate of change due to low heritabilities; an outcome consistent with macro-evolutionary patterns of morphological variation in birds. A simulation study supported the conclusion that high covariances among traits and ages can impose considerable constraint on a microevolutionary scale.     

Lifespan, lifetime reproductive performance and paternity loss of within-pair and extra-pair offspring in the coal tit Periparus ater

The hypothesis that females of socially monogamous species obtain indirect benefits (good or compatible genes) from extra-pair mating behaviour has received enormous attention but much less generally accepted support. Here we ask whether selection for adult survival and fecundity or sexual selection contribute to indirect selection of the extra-pair mating behaviour in socially monogamous coal tits (Periparus ater). We tracked locally recruited individuals with known paternity status through their lives predicting that the extra-pair offspring (EPO) would outperform the within-pair offspring (WPO). No differences between the WPO and EPO recruits were detected in lifespan or age of first reproduction. However, the male WPO had a higher lifetime number of broods and higher lifetime number of social offspring compared with male EPO recruits, while no such differences were evident for female recruits. Male EPO recruits did not compensate for their lower social reproductive success by higher fertilization success within their social pair bonds. Thus, our results do not support the idea that enhanced adult survival, fecundity or within-pair fertilization success are manifestations of the genetic benefits of extra-pair matings. But we emphasize that a crucial fitness component, the extra-pair fertilization success of male recruits, has yet     

Intersexual niche differentiation in the blue tit (Parus caeruleus)

The intersexual niche differentiation hypothesis, according to which sexual size dimorphism (SSD) has evolved to facilitate niche separation between the sexes, has received equivocal support in studies of birds. One explanation for the inconsistency of the results is that other factors crucial for reproductive success, such as variation in food abundance among territories, may obscure food niche differentiation between parents. We studied the effects of SSD, food availability and food demands of broods on niche differentiation in the blue tit ( Parus caeruleus ). Parents attending experimentally enlarged broods delivered the same amount, but more diverse food items, to their offspring than parents attending reduced broods, although this effect was significant in only one of the two study years. The time-lag (deviation from the peak food abundance in habitat in days) and squared time-lag were the most important determinants of the diversity of food items delivered to young and their condition (fitness surrogate). SSD, as measured by principal component scores of morphological traits, did not explain any variation neither in the diversity or amount of food provided, nor in offspring condition. These results suggest that synchronization of breeding with peak food availability is the most important determinant of diversity of food delivered to young and, more importantly, Their condition. No evidence for intersexual food niche differentiation was found; at best, it is likely to constitute only a weak selection pressure on the maintenance or enhancement of SSD in this system.     

Egg quality and parental ornamentation in the blue tit Parus caeruleus

Components of avian egg quality often show remarkable variation between females and yet the causes of variation in this fitness-related trait remain poorly understood. We investigated the egg size and yolk carotenoid investment of blue tit Parus caeruleus females in relation to multiple parental traits. We show that females produce eggs with more colourful yolks when mated to ultraviolet (UV) attractive males. Since yolk carotenoids may enhance offspring fitness, but may be available to females in limiting amounts, the correlation we found suggests adaptive egg quality adjustment in response to mate attractiveness, but an experimental approach is required to rule out alternative explanations. Yolk colour was also correlated with laying date and yolk mass. Though the effect of laying date could not be explained by ambient temperature during egg formation, it suggests a proximate constraint of general carotenoid availability on yolk composition. Egg size was not affected by male attractiveness; however, females with a brighter crown produced larger eggs, suggesting that crown coloration might indicate individual quality in females too.     

Diurnal rhythms of locomotor activity, changes in body mass and fat reserves, standard metabolic rate, and respiratory quotient in the free-living coal tit (Parus ater) in the autumn-winter period

These studies were conducted in 1999–2010 on the territory of the Zvenigorod Biological Station of Moscow State University (western Moscow suburbs, 55°44′ N, 36°51′ E). Birds (Parus ater) were caught by mist-nets. All the birds were banded and weighed, and their fat reserves were determined; then, the birds were released. A total of 85 individuals were caught. The standard metabolic rate and respiratory quotient (by the method of indirect calorimetry) were measured in 46 experiments with 16 birds. Two peaks were distinguished in the daily locomotor activity: a strongly pronounced daily peak (from 6 a.m. to 4 p.m.) and a weak evening peak (from 6 to 10 p.m.). The body mass did not change during the day. However, some trend for an increase in the mean body mass toward the middle and end of the day was noted. The fat reserves drastically changed during the day. The metabolic rate and respiratory quotient had a well-pronounced diurnal rhythm with minimal values at night (from 12 p.m. to 4 a.m.) and maximum values in the afternoon (from 12 a.m. to 4 p.m.). The total energy budget of Parus ater in the autumn-winter period, energy balance, and the maintenance of constant flying weight along with the dynamics of fat reserves are discussed.     

Inheritance and variation in eggshell patterning in the great tit Parus major

The inheritance of patterns on avian eggshells is central to understanding the evolution of traits such as egg mimicry (e.g. in cuckoos). Yet little is known about the inheritance, or indeed function, of eggshell patterns. It has long been believed that the evolution of eggshell pattern mimicry required that patterns be determined by genes situated on the female-specific W chromosome. However, it has never been demonstrated for any bird that egg pattern traits (rather than ground colour) are female sex linked, or indeed that they are inherited. We studied the inheritance of three measures of egg-pigment patterns in a wild great tit population. Egg patterns were female specific but unrelated to female attributes such as age or condition and showed only weak environmental effects. Eggs of daughters resembled those of both their mothers and maternal grandmothers, but not of their paternal grandmothers. We conclude that this is the first demonstration of female sex-linked inheritance of avian eggshell patterning, so raising the probability that such a system operates in egg mimics and their hosts.     

Realized heritability of personalities in the great tit (Parus major)

Behaviour under conditions of mild stress shows consistent patterns in all vertebrates: exploratory behaviour, boldness, aggressiveness covary in the same way. The existence of highly consistent individual variation in these behavioural strategies, also referred to as personalities or coping styles, allows us to measure the behaviour under standardized conditions on birds bred in captivity, link the standardized measurements to the behaviour under natural conditions and measure natural selection in the field. We have bred the great tit (Parus major), a classical model species for the study of behaviour under natural conditions, in captivity. Here, we report a realized heritability of 54 +/- 5% for early exploratory behaviour, based on four generations of bi-directional artificial selection. In addition to this, we measured hand-reared juveniles and their wild-caught parents in the laboratory. The heritability found in the mid-offspring-mid-parent regression was significantly different from zero. We have thus established the presence of considerable amounts of genetic variation for personality types in a wild bird.     

Foraging behaviour of individual coal tits,Parus ater,in relation to their age,sex and morphology

The aim of this study was to reveal the causes and consequences of individual differences in foraging behaviour of coal tits, Parus ater, on the island of Gotland in the Baltic. On Gotland the willow tit, P. montanus, and the crested tit, P. cristatus, are absent, while these larger species are abundant competitors on the mainland. The Gotland population of coal tits exploited parts of the foraging niches of their absent competitors. Gotland coal tits are bigger than those on the mainland; they have thus evolved towards the size of the missing competitors. Individual differences in niche use were related to their morphology. Large birds more often used the inner parts of trees whereas small individuals foraged more on needles in the outer parts of the trees. Also, individuals with wing shapes more suitable for hovering and slow flight foraged more on needles. It is argued that morphology affects the profitability of different foraging sites. However, for foraging site selection, age was more important than morphology. Older, and probably more dominant, individuals occupied the most profitable foraging sites.     

Speckled eggs: water-loss and incubation behaviour in the great tit Parus major

Many small passerine birds worldwide lay white eggs speckled with red, brown and black protoporphyrin pigment spots (maculation). Unlike some patterns of avian eggshell pigmentation which clearly serve a crypsis or signalling function, the ubiquity of maculation among passerines suggests that its origins lie in another function, not specific to any particular ecological or behavioural group. Elsewhere, we have presented evidence that protoporphyrin pigments serve a structural function related to eggshell thickness and calcium availability: eggshell maculation in the great tit Parus major increases with decreasing soil calcium levels, pigments demarcate thinner areas of shell, and both the pigment intensity and distribution are related to shell thickness. Here we show that maculation also affects the rate of water loss from the egg during incubation (≈ Mass Loss per Day or MLD, which is critical to egg viability), but not that of unincubated eggs. We also demonstrate, both by observation and experiment, that the effect of female incubation behaviour on MLD compensates in some way for variation in egg characteristics, and that differences between females in the degree of such compensation are related to differences in clutch maculation. Our results suggest that, while a principal function of maculation in this species may be to strengthen the eggshell, it may also reduce eggshell permeability when large amounts of pigment are used, and that this necessitates a behavioural adjustment from the female during incubation. We discuss these findings and make further testable predictions from our model.     

Fat reserves and perceived predation risk in the great tit, Parus major

The fat reserves of small birds are built up daily as insurance against starvation. They are believed to reflect a trade-off between the risks of starvation and predation such that in situations of high predation risk birds are expected either to reduce their fat reserves in response to mass-dependent predation risk or to increase them in response to foraging interruptions. We assessed the effect on fat reserves of experimentally altering the perceived (but not the actual) risk of predation of wild great tits at a winter feeding site. The perceived predation risk was alternated between 'safe' and 'risky'. Increasing the perceived risk of predation involved 'swooping' a model sparrowhawk over the feeder at four unpredictable times each day using a remote mechanism We produce evidence that the experiment was suceessfull in altering the perceived risk of predation. As predicted from the hypothesis of mass-dependent predation risk, great tits (Parus major) carried significantly reduced fat reserves during the 'risky' treatment. Furthermore, dominant individuals were able to reduce their reserves more than subordinates. As birds returned to feeders within seconds after a predator 'attack', the reduction in fat reserves cannot be attributed to an interruption in feeding.     

Alarmlaute der Tannenmeise(Parus ater)

Ohne Zusammenfassung     

Paternal leakage of mitochondrial DNA in the great tit (Parus major)

Animal mitochondrial DNA is normally inherited clonally from a mother to all her offspring. Mitochondrial heteroplasmy, the occurrence of more than one mitochondrial haplotype within an individual, can be generated by relatively common somatic mutations within an individual, by heteroplasmy of the oocytes, or by paternal leakage of mitochondria during fertilization of an egg. This biparental inheritance has so far been reported only in mice, mussels, Drosophila, and humans. Here we present evidence that paternal leakage occurs in a bird, the great tit Parus major. The major and minor subspecies groups of the great tit mix in the middle Amur Valley in far-eastern Siberia, where we found a bird that possessed the very distinct haplotypes of the two groups. To our knowledge this is the first report of paternal leakage in birds.     

Glacial history and colonization of Europe by the blue tit Parus caeruleus

Mitochondrial control region sequences from European populations of the blue tit Parus caeruleus were used to reveal the Pleistocene history and the post-glacial recolonization of Europe by the species. The southern subspecies, P. c. ogliastrae was found to represent a stable population with isolation-by-distance structure harboring a lot of genetic variation, and the northern subspecies P. c. caeruleus a recently bottlenecked and expanded population. We suggest that after the last Ice Ages, the subspecies have colonized Europe from two different southern refuges following previously proposed general recolonization routes from the Balkans to northern and Central Europe, and from the Iberian Peninsula north- and eastwards. The two subspecies form a wide secondary contact zone extending from southern Spain to southern France.     

Environmental factors shape cloacal bacterial assemblages in great tit Parus major and blue tit P. caeruleus nestlings

Despite their potential ecological and evolutionary importance, factors shaping the composition of bacterial communities in wild vertebrate populations remain poorly understood. The goal of this study was to examine the relative contributions of environmental factors and genetic factors (e.g. species and common origin) to the variation of cloacal bacterial assemblages in wild bird nestlings. We conducted a partial cross-fostering experiment with two passerine species, the great tit Parus major and the blue tit P. caeruleus, sharing similar habitats and breeding biology. Nestlings of the two species were exchanged four days after hatching and cloacal bacteria were sampled nine days later. The structure of cloacal bacterial communities was determined by Ribosomal Intergenic Spacer Analysis. Our results showed that each nestling displayed a unique bacterial community. Furthermore, nestlings raised in the same nest shared significantly similar bacterial communities. The similarity of bacterial community was higher among heterospecific siblings raised within the same nest than between biological siblings raised in separate nests. Effects of common origin between species could not be detected and, if present, were dominated by nest-based short-term environmental effects. Our results show that growth conditions within nests and individually based endogenous factors have significant effects on cloacal bacteria assemblages and could affect post-fledging condition.     

Local specialization and maladaptation in the Mediterranean blue tit (Parus caeruleus)

Although the evolutionary interplay between gene flow and local adaptation of organisms in heterogeneous environments has been widely discussed from a theoretical point of view, few empirical studies have been designed to test predictions on the consequences of habitat patchiness on the evolution of life history traits. Using blue tits in Mediterranean habitat mosaics as a model, we defined two nested levels of habitat heterogeneity: an inter-regional level which compares two isolated landscapes (mainland, southern France vs the island of Corsica), and an intra-regional level which compares two habitat types within each landscape (deciduous vs evergreen trees). Deciduous habitats are more common than evergreen habitats on the mainland whereas the opposite is true on the island. Results suggest that: (1) on a regional scale, each population is specialized to the more common habitat, i.e. life history traits have evolved in such a way that breeding success is high; (2) in the less common habitats within each landscape, birds are clearly mistimed because they mismatch the best period of food availability, and hence their breeding success is lower; and (3) the density of the populations and the morphometry of the birds support the model of ideal despotic distribution. These results, which are supported by preliminary data on the genetic variation and gene flow of populations in the mainland landscape, are consistent with a source-sink model of population structure within each landscape. They are discussed in the framework of metapopulation theory and habitat selection models.