Warmer springs lead to mistimed reproduction in great tits (Parus major)

In seasonal environments, the main selection pressure on the timing of reproduction (the ultimate factor) is synchrony between offspring requirements and food availability. However, reproduction is initiated much earlier than the time of maximum food requirement of the offspring. Individuals should therefore start reproduction in response to cues (the proximate factors), available in the environment of reproductive decision making, which predict the later environment of selection. With increasing spring temperatures over the past decades, vegetation phenology has advanced, with a concomitant advancement in the reproduction of some species at higher trophic levels. However, a mismatch between food abundance and offspring needs may occur if changes in the environment of decision making do not match those in the environment of selection. Date of egg laying in a great tit (Parus major) population has not advanced over a 23-year period, but selection for early laying has intensified. We believe that this is the first documented case of an adaptive response being hampered because a changing abiotic factor affects the environment in which a reproductive decision is made differently from the environment in which selection occurs.     

Natal dispersal and personalities in great tits (Parus major)

Dispersal is a major determinant of the dynamics and genetic structure of populations, and its consequences depend not only on average dispersal rates and distances, but also on the characteristics of dispersing and philopatric individuals. We investigated whether natal dispersal correlated with a predisposed behavioural trait: exploratory behaviour in novel environments. Wild great tits were caught in their natural habitat, tested the following morning in the laboratory using an open field test and released at the capture site. Natal dispersal correlated positively with parental and individual exploratory behaviour, using three independent datasets. First, fast-exploring parents had offspring that dispersed furthest. Second, immigrants were faster explorers than locally born birds. Third, post-fledging movements, comprising a major proportion of the variation in natal dispersal distances, were greater for fast females than for slow females. These findings suggest that parental behaviour influenced offspring natal dispersal either via parental behaviour per se (e.g. via post-fledging care) or by affecting the phenotype of their offspring (e.g. via their genes). Because this personality trait has a genetic basis, our results imply that genotypes differ in their dispersal distances. Therefore, the described patterns have profound consequences for the genetic composition of populations.     

Mixed species flocking of tits (Parus spp.): a field experiment

Summary We tested two general models of flocking behaviour, namely the antipredation model and foraging efficiency model on mixed-species tit flocks (Parus spp.). After food addition the size of mixed-species flocks was significantly less than in the control samples. In the presence of extra food significantly more birds were observed either in monospecific flocks or solitary, than during the control observations. In the presence of a living predator the birds foraged in larger mixed-specifies flocks than during the control observations. In addition, the social behaviour of Great Spotted Woodpecker, Middle Spotted Woodpecker and Nuthatch shifted to mixed-specific flocking. The size of monospecific flocks was independent of both treatments. The density of birds increased significantly after food addition, while in the predator presence the birds tended to leave the forest. These results support the view that both the antipredation model and foraging efficiency model seem to be valid for mixed-species flocking. However, in the case of monospecific flocks, the territory maintenance could be the most important factor.     

Island biogeography and the reproductive ecology of great tits Parus major

Island biogeography theory has contributed greatly to both theoretical and applied studies of conservation biology (e.g., design of nature reserves, minimum viable population sizes, extinction risk) and community composition. However, little theoretical and empirical work has addressed how island isolation and size affect reproductive ecology. We investigated the reproductive ecology of great tits (Parus major) on one offshore and one nearshore island, as well as on the Danish mainland. Tits breeding on the offshore island bred later, laid smaller clutches, and laid larger eggs than those on the nearshore island and mainland. In addition, the level of ectoparasite infestation in nests was highest on the offshore island, intermediate on the nearshore island, and lowest on the mainland. These insular effects may occur due to lower food abundance on islands, to density-dependent effects, or to effects related to low genetic diversity within island populations. Whatever the cause, the results emphasize that future studies of forest fragmentation/population isolation should consider not only gross measures of reproductive success, but also fine-scale measures such as clutch size, timing of breeding, and parasite prevalence. Received: 10 November 1997 / Accepted: 9 March 1998     

Great tits (Parus major) reduce body mass in response to wing area reduction: a field experiment

Flight performance is crucial in determining whether a smallbird will survive an attack by a predator. Given the importanceof body mass in determining flight performance, it has beensuggested that birds should strategically regulate body massas a response to predation risk. However, all experiments upto now have been carried out with captive birds, comparing experimental to control birds. Here we present data from thefirst experiment in the field using a within-individuals experimentaldesign. The wing area of wild great tits, Parus major, wasreduced by reversibly taping primaries five to seven. Thisallowed for the same individual to alternatively act as controlor experimental bird. Great tits reduced body mass (but not pectoral muscle width) during episodes of wing area reduction,lending support to the view that the reduction in body massexperienced by birds during molt is a strategy rather thanthe result of energetic stress. Theoretical models establishingthe different trade-offs that determine optimal body mass should therefore take into account this important life-history episode.     

Social environment affects juvenile dispersal in great tits (Parus major)

1.?Habitat selection can affect individual fitness, and therefore, individuals are expected to assess habitat quality of potential breeding sites before settlement. 2.?We investigated the role of social environment on juvenile dispersal behaviour in the great tit (Parus major). Two main contradictory hypotheses can be formulated regarding social effects on juvenile dispersal as follows: (i) High fledgling density and sex ratio may enhance the intensity of local (kin) competition and, therefore, reduce individual survival chance, enhance emigration and reduce settlement ('repulsion' hypothesis) (ii) Alternatively, high fledgling density and sex ratio may signal high-quality habitat or lead to aggregation and thus increase individual survival chance, reduce emigration and enhance settlement ('attraction' hypothesis). 3.?To disentangle positive from negative effects of high density and male-biased sex ratio on dispersal, we manipulated the social composition of the fledgling population in 12 semi-isolated nest-box areas (plots) via a change of fledgling density (low/high) as well as fledgling sex ratio (female-biased/balanced/male-biased) across 3?years. We then tested whether experimental variation in male and female fledgling densities affected variation in local survival, emigration and settlement of juveniles, and whether social effects on survival and dispersal support the 'repulsion' or 'attraction' hypothesis. 4.?We found no experimental effects on local survival and emigration probabilities. However, consistent with the 'attraction' hypothesis, settlement was significantly and positively affected by local experimental sex ratio in each of the study years: both male and female juveniles avoided female-biased plots and settled more in plots that were balanced and male-biased the previous year. 5.?Our study provides unprecedented experimental evidence that local sex ratio plays a causal role in habitat selection. We suggest that settlers avoid female-biased plots because a high proportion of females may reflect the absence or the low quality of local resources in the habitat. Alternatively, male territory acquisition may be facilitated by a high local density of 'candidate' males, and therefore, juveniles were less successful in settling in female-biased plots.     

Female genetic heterogeneity affects the reproduction of great tits (Parus major L., 1758) in low-quality woodlands

Genetic heterogeneity is considered an important parameter for individual fitness and reproductive success. In 1999 and 2000, we studied the population genetics of great tit ( Parus major L., 1758) in southwestern Germany from two different forest types (deciduous and mixed-coniferous), which may significantly differ in prey diversity and/or food supply. Adults of 99 families were genotyped at four enzyme and eight microsatellite loci, in order to estimate individual heterozygosity. In the mixed-coniferous forest, a significant positive correlation between the genetic heterogeneity of females and early egg-laying date and clutch size was detected. Early egg-laying date and increased clutch size are conditions that positively affect the number of fledglings. This effect of individual heterozygosity was not observed in the deciduous woodland. Maternal genetic heterogeneity, however, did not correlate with fledgling condition, and individual heterozygosity of fathers had no impact on breeding success in either habitat. The positive effect of female genetic heterogeneity on brood size of great tits in mixed-coniferous forests is attributed to early egg-laying date, i.e. a maternal effect, rather than to a specific mating strategy that optimizes fitness through an increased brood size and the quality of offspring.     

Carotenoid diet and nestling provisioning in urban and rural great tits Parus major

Considering the importance of dietary constraints for the widely held view of carotenoid pigmentation as an honest quality indicator, there is surprisingly little data on carotenoid availability in different natural diets or along environmental gradients. Here we investigate the carotenoid availability in the main diet of breeding great tits Parus major , living in urban and rural environments with known differences in carotenoid pigmentation. Carotenoid availability for nestling great tits was investigated in two respects: (1) quantity and quality of diet (i.e., caterpillar abundance and their carotenoid concentration), and (2) parental feeding frequency. First, caterpillars were generally more abundant in the urban environment and the four common Lepidoptera (i.e., caterpillars) genera studied were also heavier here. Second, as determined by HPLC analysis of the caterpillar genera, carotenoid concentration was significantly lower in the urban caterpillars. Furthermore, all except one of the caterpillar genera had higher lutein/zeaxanthin ratio in urban areas, which is in accordance with earlier studies of carotenoid composition in great tit yolk. Third, parental feeding frequency was about twice as high to urban broods compared to rural broods. This result may simply reflect the higher caterpillar abundance (shorter search time) in the urban environment. Poor food quality (low carotenoid concentration) seems therefore to be compensated by quantity in the urban environment. As a consequence the carotenoid availability seems to be similar for nestlings in the two environments.     

Hissing calls improve survival in incubating female great tits (Parus major)

Nest predation is among the most important selective pressure shaping nest-site selection and nest defense behavior in many avian species. In this study, we tested whether the production of one such nest defense behavior—hissing calls—may improve survival of incubating female great tits (Parus major). We found that 72.5 % of incubating females gave hissing calls when they were exposed to a stuffed woodpecker in their nest boxes. The repeatability of the number of hissing calls given was high, as was the latency to give the call. Additionally, natural nest predators attacked hissing and nonhissing females equally often. However, hissing females survived better than silent females. We tested responses of feral cats to playbacks of hissing call during their attacks of nest boxes and found that hissing calls prevented the predator attacks. Taken together, our findings indicate that hissing calls can deter predator attacks and potentially increase survival rates of nesting great tits or their offspring, or both. The propensity to give hissing calls may be related to personality type of incubating female great tits, which needs to be tested experimentally.     

Offspring quality and tick infestation load in brood rearing great tits Parus major

Although the impact of nest-dwelling ectoparasites on nestlings in altricial birds is relatively well documented, little information is available on the fitness consequences of bird–ectoparasite systems with limited ectoparasite transmission between parents and their offspring. In this particular context we tested the hypothesis that parental infestation by a haematophageous field ectoparasite, the sheep tick Ixodes ricinus , in a hole-breeding passerine bird, the great tit Parus major , ultimately leads to the reduction of nestling quality. Observational data of a long-term study show that 15 days after hatching, nestlings' body condition (body mass corrected for body size) was negatively associated with the tick load of the mother, while no association was found with tick load of the father. A field experiment was conducted to test if adult infestation by ticks leads to a reduction in offspring quality. The field experiment consisted of a two by two factorial design: neither, one or both parents were infested with a high tick load (12 nymphs) when nestlings were eight days old. Four days after manipulation of the parents, the effect of the treatment on nestlings' health was assessed by measuring haematological and biochemical parameters. Body condition of nestlings was monitored from three days after hatching, until seven days after tick manipulation of the parents. Although parental tick manipulation resulted in successful tick feeding, nestlings' health parameters were not affected. We therefore suggest that the negative association between nestling condition and parental tick load does not reflect a causal effect of parasites, but either reflects a common environmental factor affecting parental infestation levels and offspring condition, or reflects parental quality. We propose different explanations why this association is expressed in female parents only.     

Fat soluble antioxidants in brood-rearing great tits Parus major: relations to health and appearance

The concept of parasite-mediated sexual selection assumes that females may improve offspring fitness by selecting mates on the basis of sexual ornaments that honestly reveal the health state of a partner. Expression of such signals may be particularly sensitive to oxidative damage caused by excess production of oxidative metabolites and free radicals. To control and neutralise free radicals, animals rely heavily on dietary fat-soluble antioxidants such as vitamin E and A, and carotenoids. However, the organism's need for free radical scavenging may interfere with the opposite need to generate oxidative stress for fighting parasitic infections. We investigated plasma concentrations of carotenoids and vitamin A and E in brood-rearing great tits Parus major in relation to carotenoid-based plumage coloration, sex, habitat, leukocyte hemoconcentrations and infection status with Haemoproteus blood parasites. Rural great tits differed from urban ones and males from females with respect to the hue of the yellow ventral feathers. However, plasma antioxidant concentrations were not related to sex, habitat or plumage coloration. Plasma carotenoid concentration correlated positively with indices of immune system activation as measured by blood counts of lymphocytes and eosinophils. Birds with gametocytes of Haemoproteus in their blood had higher plasma concentrations of carotenoids and vitamin E than unparasitized individuals. These results are consistent with the idea that maintenance of high blood antioxidant levels might conflict with individual needs to rely on oxidative stress for fighting infections.     

Heating nest-boxes reveals an energetic contraint on incubation behaviour in great tits,Parus major

According to the ''energetic-bottleneck'' hypothesis, incubation in birds is constrained by the availability of energy. Hence, uniparental incubators are predicted to respond to a change in energy supply by adjusting, positively or negatively, the time spent warming the clutch. Energetic constraints on incubation in the great tit (Parus major) were demonstrated by heating nests, so that the night-time thermostatic component of daily energy expenditure in females was reduced by comparison with a control group. Birds in heated nests increased the time allocated to incubation during the day by 55 minutes, consistent with the predictions of the energetic-bottleneck hypothesis. Daily energy expenditure of all birds was inversely related to night-time ambient temperature, and did not differ between warmed and control birds on mild nights. When temperatures were low, however, escalation of daily costs was less for birds in heated nests. It is suggested that the balance of the energy budget may effect a proximate control on the constancy of incubation, with likely implications for reproductive success.     

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.     

The costs of egg production and incubation in great tits (Parus major).

The costs of egg production and incubation may have a crucial effect on avian reproductive decisions, such as clutch size and the timing of reproduction. We carried out a brood-size enlargement experiment on the great tit (Parus major), in which the birds had to lay and incubate extra eggs (full costs), only incubate extra eggs (free eggs) or did not pay any extra cost (free chicks) in obtaining a larger brood. We used female fitness (half the recruits produced plus female survival) as a fitness measure because it is the female which pays the costs of egg production and incubation, and because clutch size is under female control. Female fitness decreased with increasing costs (fitness of free chicks females is higher than that of free eggs females which is higher than that of full costs females). These fitness differences were due to differences in female survival rather than in the number of recruits produced. This is the first time that the costs of egg production and incubation have been estimated using such a complete fitness measure, including, as our measure does, the local survival to the following year of both the female and her offspring. Our results emphasize that reproductive decisions cannot be understood without taking egg production and incubation costs into account.     

Egg yolk antioxidant deposition as a function of parental ornamentation,age, and environment in great tits Parus major

Females can modify phenotype of their offspring through the deposition of biologically active compounds into eggs, including carotenoids, vitamins and other antioxidants. Understanding patterns of deposition is critical for better insight into the significance of maternal effects. Here we investigated how egg yolk antioxidants (lutein, zeaxanthin, β‐carotene, vitamin A and E) related to environmental conditions and parental characteristics in great tits Parus major using data from three breeding seasons. Male and female traits included condition, age and multiple feather ornaments, both carotenoid‐ and melanin‐based (carotenoid and UV chroma of yellow breast feathers, area of black breast band, white cheek immaculateness). Yolk mass increased with ambient temperature during laying, laying date, and the area of male black breast band. Lutein, zeaxanthin, and vitamin E increased with laying date. Total antioxidants increased with female age, immaculateness of female white cheek patch, and UV chroma of carotenoid‐based yellow breast feathers of the social mate. These patterns were thus consistent with 1) environmental effects on yolk mass and composition, 2) higher quality females depositing more antioxidants, and 3) differential allocation of resources in females in relation to male ornamentation. Overall, environmental factors, female traits, and male traits all had an influence on egg yolk characteristics in this socially monogamous songbird.     

No evidence for survival selection on carotenoid-based nestling coloration in great tits (Parus major)

In several vertebrate species evidence supports the hypothesis that carotenoid-based coloration of adults has evolved due to sexual selection. However, in some birds already the nestlings display carotenoid-based coloration. Because the nestling's body plumage is typically moulted before the first reproductive event, sexual selection cannot explain the evolution of these carotenoid-based traits. This suggests that natural selection might be the reason for its evolution. Here we test whether the carotenoid-based nestling coloration of great tits (Parus major) predicts survival after fledging. Contrary to our expectation, the carotenoid-based plumage coloration was not related to short- nor to long-term survival in the studied population. Additionally, no prefledging selection was detectable in an earlier study. This indicates that the carotenoid-based coloration of nestling great tits is currently not under natural selection and it suggests that past selection pressures or selection acting on correlated traits may have led to its evolution.     

Ultraviolet-blue reflectance of some nestling plumage patches mediates parental favouritism in great tits Parus major

The colouration exhibited by nestling birds is generally cryptic, but in some species it has a conspicuous appearance. The adaptive function of these nestling displays is poorly known, especially in altricial species. We performed an experimental study in which the ultraviolet-blue reflectance of the carotenoid-based plumage of great tit Parus major nestlings was reduced in order to find possible evidence of parental favouritism. Tarsus length increment in a three-day period was significantly lower in manipulated nestlings than in their control siblings. As tarsus length may be a good predictor of survival, the parents may increase their fitness return by investing more in those nestlings reflecting more in the UV-blue spectral region. Interestingly, this effect was only found in a yellow patch located at the nape of nestlings that has been previously overlooked, as all the studies on plumage colouration in this species have focused on the breast plumage. Some quality indicators are proposed for the colour of nestling plumage, though the possibility exists that selection may operate through aspects of signal efficacy instead of aspects of signal content.