The effect of old age on the reproduction of Great Tits Parus major and Blue Tits P. caeruleus

The results from two data sets show that in Great Tits Parus major and Blue Tits P. caeruleus reproduction is influenced by age. In both species, laying dates become earlier while clutch- and brood-size increase between the ages of 1 and 2, but there is no change in nesting success or post-fledging juvenile survival. Great Tits aged 5 or older are 'old' in that laying starts later and nesting success, brood-size and post-fledging juvenile survival decrease. Blue Tits become 'old' 1 year earlier than Great Tits: females aged 4 or older lay later, have a lower nesting success and smaller brood-size, and their young show a decreased post-fledging survival. The effect on laying date, in the Blue Tit, becomes apparent only for females aged 6 and older. It is concluded that ageing in small passerines is to be expected more generally, but that no extrapolations can be made as to the timing of the effect from one species to another.     

Habitat and laying date of Great and Blue Tit Parus major and P. caeruleus

Using 19 year's data from nine study areas at Ghent we investigated the effect of habitat on laying date, and found it to be quite different for Great and Blue Tits. In Great Tits we found a clear gradient in laying dates from urban over suburban to rural habitats. Blue Tits laid earliest in a suburban habitat and latest in a rural habitat. All other areas, including urban, suburban and rural ones, formed one intermediate group. The overall average laying date for the Great Tit, 18.9 April, was slightly earlier than that of the Blue Tit, 19.4 April. In urban areas Great Tits laid significantly earlier than Blue Tits, in optimal oak habitat and in one suburban area Blue Tits laid earlier, whereas in the five remaining areas no significant differences between the two species were found.
We argue that the differences in laying dates, although correlated to temperature, are probably caused by differences in the timing of food availability. We suggest that differences in laying dates of Great and Blue Tits are caused by a different response to environmental variations through differences in feeding ecology.     

Similarity of growth among Great tits (Parus major) and Blue tits (P. caeruleus)

Differences in morphology among species are proximately caused by changes in the ontogeny of individuals. It is therefore of importance to analyse possible differences in growth parameters among closely related species in order to understand what parameters are most and least likely, respectively, to change in evolution. In this paper I analyse growth in two closely related sympatric species, namely Great tit, Parus major, and Blue tit, P. caeruleus. The former is considerably larger than the latter in all external traits. The growth rates of the two species were found to be very similar for all traits, thus excluding differences in growth rate as a potential cause of evolutionary size changes. Offset of growth occurred at relatively similar times in the two species, excluding this factor as a major cause of the final size differences. However, size differences at hatching were pronounced and remained so throughout ontogeny, pointing to initial size (egg size or hatching size) as the target of factors promoting change. Bivariate allometric relations of traits vs. body size (mass) were similar between the two species at all ontogenetic stages. There was a high correlation among traits especially at intermediate age stages (5 and 8 days), but these correlations became weaker at older age and approached the low pattern of integration found in adults. All this suggests the operation of a general growth factor affecting all parts of the phenotype simultaneously, which has its major influence at the time of maximal growth. If closely related species in general have highly similar growth patterns, strong evolutionary allometry as found in many avian taxa is to be expected.     

The effect of direct supplementary feeding of nestlings on weight loss in female Great Tits Parus major

Experimentally hand-feeding nestlings of enlarged (+3 nestlings) broods reduced female weight loss during the nestling period in a single-brooded Great Tit Parus major population in Scotland but did not affect nestling size. The result is consistent with the existence of a trade-off in parental care between reproductive costs and benefits.     

Breeding time,food supply and fitness components of Blue Tits Parus caeruleus in Mediterranean habitats

We analysed the relationship between the timing of food availability and within-season variation of both reproductive success and nestling body size of Blue Tits Parus caeruleus in Mediterranean habitats. Synchronization between food supply and reproduction was expected to be positively related to fitness components. We measured deviation from maximum food supply using a parameter that we called “time-lag”, which quantifies the degree of synchronization between the date of maximum food requirements by the nestlings and the date of maximum caterpillar supply in the habitat. This parameter was expected to be related to reproductive success as measured by the number and body-condition of fledglings. The predictions were that time-lag should be negatively correlated with the proportion of nestlings raised to fledging and the size of the fledglings. These predictions have been tested in different types of habitat. The results demonstrate that caterpillar supply during a critical nestling period can have a strong influence on fitness components. As predicted, synchronization with caterpillar supply is positively related to the number and body size of fledglings. Since there is large between-habitat variation in the timing of food supply, the key issue seems to be the adjustment to local patterns of food availability.     

Dominance and anti-predator behaviour of Great Tits Parus major: a field study

During the winter of 1981–82 the hierarchical system of free-living Great Tits Parus major that visited a feeder supplied with sunflower seeds was studied in relation to the appearance of a predator. Without a predator, dominant birds were more successful in feeding and had to wait less before feeding. A significant negative correlation was found between dominance and the sequence of initial arrival.
After a Sparrowhawk Accipiter nisus had flown over the feeder, a correlation was found between the birds' dominance and the sequence of their return to the feeder. This field study supports the results of an analogous investigation on anti-predator behaviour and dominance in captive Blue Tits P. caeruleus.     

The timing of breeding and offspring size in Great Tits Parus major

The relationship between the timing of breeding, offspring weight and offspring recruitment was investigated in two populations of Great Tits Parus major. In two of six seasons a significant negative correlation was found between laying date and fledgling weight, in three seasons the opposite was true and in one season no significant correlation existed between these variables. Offspring recruitment was quantified in five seasons, and late-nesting birds were found to produce significantly fewer recruiting offspring in two of these, the same two seasons when late fledglings had significantly lower weights. No significant correlation existed between the number of recruits and laying date in the three seasons when late fledglings were as heavy as or heavier than early fledglings. The potential detriment to reproductive success of lateness thus was offset when late-nesting parents managed to produce heavy young. Between-year variations in the seasonal pattern of reproductive success has previously been suggested to contribute to the maintenance of variability in the timing of breeding in Great Tits. In this paper we suggest that producing heavy offspring late in the season might be a proximate factor influencing the seasonal patterns of reproductive success. Producing heavy offspring late in the season is probably not a strategy but rather an effect of chance differences between years in the seasonal availability of food or the seasonality of other factors important for the nesting birds.     

Foraging behaviour of Blue Tits Parus caeruleus in a patchy environment under contrasting levels of natural food supply

We analysed the foraging behaviour of free-ranging Blue Tits Parus caeruleus in open holm oak Quercus ilex woodlands of western Spain during winter. Such woodlands are patchy for foraging tits because of the scattered distribution of trees and the patterns of abundance of canopy arthropods within and among trees. Results were compared with those obtained in spring of the same year, when we found that the foraging behaviour and spatial distribution of Blue Tits were largely unaffected by food availability (Pulido and Díaz 1997). Patch (tree) residence time was highly variable both within and among individual birds, and it was uncorrelated with either previous travel time or patch quality. Contrary to a priori expectations, the behaviour of tits did not conform to short-term energy maximizing rules in winter, in spite of a 2.5-fold decrease in food supply from spring to winter and a likely 2-fold increase in bird requirements. Instead, birds tended to fly towards patches that were further away than locally available. Overall, we conclude that energy intake rate was not the fitness-related currency that birds were trying to maximize while foraging.     

Habitat structure influences the song characteristics within a population of Great Tits Parus major

Capsule: The structure of Great Tit Parus major songs is shaped by the acoustic properties of the habitat within the breeding territory of individuals.

Aim: To test whether the structure of the habitat influences song structure within a population of Great Tits P. major.

Methods: We recorded Great Tit songs from 42 territories on two different days and measured the habitat structure in each territory. We also trapped the males and estimated the breeding density around each territory, so were able to control the analysis by date, breeding density and male characteristics.

Results: Song pause length was positively affected by the ground cover, while the song rate and the minimum frequency were negatively affected by the shrub cover. Male size negatively affected the peak frequency of the songs, whereas the age of the males affected the frequency range; older males sang with a broader bandwidth.

Conclusion: This study suggests that Great Tits are capable of adjusting their vocalizations in each territory, presumably to enhance transmission owing to vocal plasticity.     

Weight change and the body reserves of female blue tits, Parus caeruleus, during the breeding season

A female blue tit lays a large clutch that is commonly heavier than her own body weight. Body reserves cannot provide for the entire clutch and little is known of the importance of these reserves during the breeding season. This study reports on weight changes in adult female blue tits during the breeding season, observed by the use of electronic balances. In addition, data from dissecting 67 adult female blue tits, at different stages of the breeding cycle, were used to investigate the changes in body weight. There was a rapid increase in body weight during a period of 4–5 days before the first egg was laid, which was explained mostly by the development of the oviduct and the production of an egg on the final day. Body weight remained constant during the laying period, before decreasing by approximately one gram after clutch completion, owing to the absence of an egg and the absorption of the oviduct. Body reserves increased during the day after clutch completion, were maintained throughout the incubation period and were mobilized during the first five days of the nestling period. Breeding female blue tits appear to deposit small body reserves to act as a short-term buffer against adverse conditions or to support the brooding phase.     

Detection distance influences escape behaviour in two parids, Parus major and P. caeruleus

When birds are attacked by aerial predators they should benefit by adjusting their escape to the prevailing attack situation. One important factor likely to affect escape decisions of prey, to our knowledge not previously studied, is the distance at which the attacking predator is detected. We investigated if great tits Parus major and blue tits P. caeruleus alter their escape behaviour to two different detection distances (2.3 m and 1m) by simulating surprise attacks using a predator model. Both species used the information about detection distance when escaping by increasing the escape angle at the shorter detection distance. In addition, blue tits adjusted to the shorter detection distance by dodging sideways more frequently. Great tits escaped initially steeper and faster than blue tits, whereas blue tits increased escape angle and speed more than great tits along the measured distance after taking wing.     

Sex-specific recombination rates in Parus major and P. caeruleus, an exception to Huxley's rule

Huxley's rule predicts lower recombination rates in the heterogametic sex than in the homogametic one. The genotyping of Parus major and P. caeruleus families at 8 microsatellite and 4 enzyme loci yielded contradicting data. Significant genotypic disequilibrium was observed between esterase-1, esterase-2 and esterase-3 in adults of P. major and between esterase-2/esterase-3 and esterase-2/microsatellite PK-12 in P. caeruleus. Support comes from linkage analyses of nuclear families. In P. major, the recombination rate of esterase-2/esterase -3 in males is significantly lower than in females (theta(male) = 0.076, theta(female) = 0.145). The opposite is found for the recombination rates of esterase-1/esterase-2 and esterase-2/esterase-3 in P. caeruleus (EST-1/EST-2: theta(female) = 0.218, theta(male) = 0.5, EST-2/EST-3: theta(female) = 0.109, theta(male) = 0.194). We conclude that the basis of differences in recombination rates cannot be heterogamety, per se, but must have multiple genetic causes including chromosomal rearrangments that have evolved after the cladogenesis of the two species.     

Prey selection and foraging performance of breeding Great Tits Parus major in relation to food availability

We studied the nestling diet and the foraging performance of Great Tits in relation to prey abundance in the field. Numerous experimental studies present data on foraging decisions in captive Great Tits. Little is, however, known about prey selection in the field in relation to the food available and the consequences this has for the food delivery rate to nestlings. Since the foraging performance of the parents is one of the main determinants of fledging weight and juvenile survival, foraging behaviour is an important part of Great Tit reproduction. During the early breeding season up to 75% of the prey biomass delivered to the nestlings were spiders, which is in contrast with other studies. Only when caterpillars reached a size of 10–12 mg (approximately the average size of the spiders caught at that time) did the Great Tits change their preferences and 80–90% of the delivered prey masses were caterpillars, as reported by other authors. This 'switching' between prey occurred within a few days. It was not related to the changes in abundance but to size of caterpillars. The rate at which caterpillars were delivered to the nestlings (in mg/nestling/h) was strongly correlated with the caterpillar biomass available (in mg/m of branches) and nestling growth rate was significantly influenced by the mass of available caterpillars. The results provide evidence why perfect timing of breeding is so important for the Great Tit, and contribute to the understanding of the causal link between food supply, growth and breeding success.     

Sex ratio of Parus major and P. caeruleus broods depends on parental condition and habitat quality

Brood sex ratio was studied in 88 families of Parus caeruleus (blue tit) and 95 families of P. major (great tit) in deciduous and mixed forest habitats differing in food availability. As a food specialist, the blue tit is expected to be more sensitive to the nutritional differences between the habitats than a food generalist such as the great tit. A shift of brood sex ratio towards males was detected for great tits in the high quality habitat, but there was no significant impact of parental condition or the number of nestlings. In contrast, brood sex ratio of blue tits was not affected by habitat quality. In blue tits, male condition correlated positively with a male-biased sex ratio. Habitat quality, however, affected the body mass differences of male and female blue tit siblings, and nestlings developed differently. The low quality habitat had a negative effect on the sexual dimorphism of siblings in male-biased broods, and the condition of offspring was bad. Nevertheless, sexual dimorphism cannot explain the differences between great and blue tits with respect to the correlation of sex ratio and individual condition.     

Intraspecific Variation and Interspecific Differences in the Bacterial and Fungal Assemblages of Blue Tit (Cyanistes caeruleus) and Great Tit (Parus major) Nests

Although interest in the relationship between birds and microorganisms is increasing, few studies have compared nest microbial assemblages in wild passerines to determine variation within and between species. Culturing microorganisms from blue tit (Cyanistes caeruleus) and great tit (Parus major) nests from the same study site demonstrated diverse microbial communities with 32 bacterial and 13 fungal species being isolated. Dominant bacteria were Pseudomonas fluorescens, Pseudomonas putida, and Staphylococcus hyicus. Also common in the nests were the keratinolytic bacteria Pseudomonas stutzeri and Bacillus subtilis. Dominant fungi were Cladosporium herbarum and Epicoccum purpurascens. Aspergillus flavous, Microsporum gallinae, and Candida albicans (causative agents of avian aspergillosis, favus, and candidiasis, respectively) were present in 30%, 25%, and 10% of nests, respectively. Although there were no differences in nest mass or materials, bacterial (but not fungal) loads were significantly higher in blue tit nests. Microbial species also differed interspecifically. As regards potential pathogens, the prevalence of Enterobacter cloacae was higher in blue tit nests, while Pseudomonas aeruginosa—present in 30% of blue tit nests—was absent from great tit nests. The allergenic fungus Cladosporium cladosporioides was both more prevalent and abundant in great tit nests. Using discriminant function analysis (DFA), nests were classified to avian species with 100% accuracy using the complete microbial community. Partial DFA models were created using a reduced number of variables and compared using Akaike’s information criterion on the basis of model fit and parsimony. The best models classified unknown nests with 72.5–95% accuracy using a small subset of microbes (n = 1–8), which always included Pseudomonas agarici. This suggests that despite substantial intraspecific variation in nest microflora, there are significant interspecific differences—both in terms of individual microbes and the overall microbial community—even when host species are closely related, ecologically similar, sympatric, and construct very similar nests.     

Leafing phenology and timing of egg laying in great tits Parus major and blue tits P. caeruleus

To evaluate the importance of tree leafing for the start of laying and clutch size of birds, we compared the breeding phenology of great tits Parus major and blue tits P. caeruleus between one coastal and two inland sites in the same geographical region. Because of the cooling influence of the sea, trees at the coastal site were known to initiate budburst about a week later than at the inland sites. During 5 years, breeding by the tits and the leaf phenology of birch Betula pendula , and oak Quercus robur were monitored. The leaf phenology of birch and oak explained a significant part of the between-year variation in the start of egg laying in blue and great tits, respectively. The tits started laying earlier at the sites with an early budburst, i.e. normally inland. However, leaf phenology was not an absolute cue to the start of laying, since blue tits laid earlier relative to leafing at the inland site than at the coastal site, and both tit species laid eggs earlier relative to leafing during late springs. In neither species was clutch size affected by leafing phenology. However, great tit females at the coastal site consistently produced fewer eggs than did those at the inland site. No such difference was found in the blue tits. Although leafing phenology may predict the start of laying in tits, other factors also influence its timing. These factors might include other cues, or differing life-history trade-offs depending on site or general climatic factors during the spring.     

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.