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.     

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.     

Predator-induced take-off strategy in great tits (Parus major)

When birds are attacked by predators the initial take-off is crucial for survival. The strategy in the initial phase of predator evasion is probably affected by factors such as body mass and presence of cover and conspecifics, but it may also be a response to the character of the predator''s attack. In choosing an angle of flight, birds face a trade-off between climbing from the ground and accelerating across the ground. This is, to our knowledge, the first study investigating whether the attack trajectory of a raptor affects the take-off strategy of the prey bird. First-year male great tits (Parus major) adjusted take-off angle to a model predator''s angle of attack. Birds attacked from a steep angle took off at a lower angle than birds attacked from a low angle. We also compared take-offs at dawn and dusk but could not find any measurable effect of the diurnal body mass gain (on average 7.9%) in the great tits on either flight velocity or angle of ascent.     

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.     

Interspecific aggression declines seasonally in breeding great tits Parus major

During the breeding season, great tits show aggression to protect their nest from intra‐ and interspecific intruders. Aggression is a labile trait that can be plastically expressed as a result of individual differences (e.g., personality), seasonal gradients in the costs and benefits of aggression, or other environmental components (e.g., number of competitors). Competitors may try to take over great tit nests, because the number of suitable nesting sites is limited, and great tits may guard high quality territories. Taking over a great tit nest may be especially fruitful in early phenological stages (egg laying) when great tits frequent their nests less often. However, great tits may compensate for this vulnerability by being more aggressive toward intruders during early nesting stages, a pattern that has already been established in an intraspecific context. Previous studies have shown that interspecific intruders were most likely to die from great tit aggression during great tit egg laying, suggesting great tits may also be more aggressive during this phase in an interspecific context. Here, I tested this hypothesis with simulated territorial intrusions in great tit territories using taxidermized blue tits Cyanistes caeruleus (hereafter called blue tit models). Great tit aggression (number of calls and approach distance toward blue tit model) was assayed during egg laying, incubation, and chick rearing in the breeding season of 2014. Although sample size was low due to a high fraction of non‐responders (n = 44 out of 89 assays across 26 out of 35 individuals), I found that great tits showed a seasonal decline in aggressiveness, which is congruent with intraspecific results on this study species. I discuss my findings in the context of differential adjustment to climate change between interspecific competitors.     

Behavioral responses to conspecific mobbing calls are predator‐specific in great tits (Parus major)

When facing a predator, animals need to perform an appropriate antipredator behavior such as escaping or mobbing to prevent predation. Many bird species exhibit distinct mobbing behaviors and vocalizations once a predator has been detected. In some species, mobbing calls transmit information about predator type, size, and threat, which can be assessed by conspecifics. We recently found that great tits (Parus major) produce longer D calls with more elements and longer intervals between elements when confronted with a sparrowhawk, a high‐threat predator, in comparison to calls produced in front of a less‐threatening tawny owl. In the present study, we conducted a playback experiment to investigate if these differences in mobbing calls elicit different behavioral responses in adult great tits. We found tits to have a longer latency time and to keep a greater distance to the speaker when sparrowhawk mobbing calls were broadcast. This suggests that tits are capable of decoding information about predator threat in conspecific mobbing calls. We further found a tendency for males to approach faster and closer than females, which indicates that males are willing to take higher risks in a mobbing context than females.     

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.     

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     

Wild‐caught great tits Parus major fail to use tools in a laboratory experiment,despite facilitation

Studies investigating tool use in animals that are not known tool users in the wild are important in helping to understand how and under what circumstances this ability might arise. Tool use appears to be uncommon in great tits (Parus major), with only a single documented observation in which a wild great tit used conifer needles to extract larvae from crevices in trees. In a laboratory‐based experiment, we examined whether wild‐caught great tits could learn to use tools in a similar manner. We presented the birds with two different tool use tasks in which they would need to use either a stick or a hook to extract an otherwise inaccessible meal worm from a transparent plastic tube. First, the birds passed a simpler training criterion (pulling a tool with an attached food reward) that aimed to reduce the difficulty of the task. Nevertheless, none of the individuals learnt to use tools in either of the two tasks. This result stands in stark contrast to the abilities of some corvids and parrots, which can learn to use tools in captivity, even though some of them are not tool users in the wild. We believe that tool use might be difficult for some birds to learn since the skills required for this ability seem not to be part of their natural foraging behaviour.     

The relationship between plumage colouration,problem‐solving and learning performance in great tits Parus major

Recent studies suggest that individuals with better problem‐solving and/or learning performance have greater reproductive success, and that individuals may thus benefit from choosing mates based on these performances. However, directly assessing these performances in candidate mates could be difficult. Instead, the use of indirect cues related to problem‐solving and/or learning performance, such as condition‐dependent phenotypic traits, might be favored. We investigated whether problem‐solving and learning performance on a novel non‐foraging task correlated with sexually selected plumage colouration in a natural population of great tits Parus major. We found that males successful in solving the task had darker blue‐black crowns than non‐solvers, and that males solving the task more rapidly over multiple attempts (i.e. learners) exhibited blue‐black crowns with higher UV chroma and shorter‐wavelength hues than non‐learners. In contrast, we found no link between behavioural performance on the task and the yellow breast colouration in either sex. Our findings suggest that blue‐black crown colouration could serve as a signal of problem‐solving and learning performance in wild great tit males. Further research remains necessary to determine whether different sexually selected traits are used to signal cognitive performance for mate choice, either directly (i.e. cognitive performance influencing individual's health and ornamentation through diet for example) or indirectly (i.e. due to a correlation with a third factor such as individual quality or condition).     

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.     

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.     

Similar patterns of age‐specific reproduction in an island and mainland population of great tits Parus major

The process of ageing was long thought to be too infrequent to affect life‐histories in natural populations. Long‐term studies have, however, recently demonstrated ageing to be ubiquitous even in the wild, although confounding factors, such as emigration instead of mortality, or inter‐population variation in rates of ageing have seldom been addressed. Here, we present analyses of female age‐specific reproductive performance in a Dutch island population of great tits Parus major. For this population with limited connectivity to surrounding areas, we show that, between individuals, reproductive lifespan positively co‐varies with recruit production, while within individuals performance improves up to 3 years of age, after which it gradually declines. We also show these patterns to be strikingly similar to those recently found in a less isolated British mainland population of great tits, characterised by different environmental conditions and life‐history strategies, in particular the frequency of multiple breeding. Our results therefore suggest patterns of age‐specific reproductive performance to be robust to both environmental and life‐history variation.     

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.     

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.     

Chick development in free-living great tits Parus major in relation to calcium availability and egg composition

Evidence from a number of avian studies suggests that limitation of exogenous calcium (Ca) may reduce egg quality and retard nestling growth. However, it is poorly understood whether reduction in chick growth in Ca-poor areas is due to insufficient intake of dietary Ca or caused by maternal Ca limitation mediated through subtle changes in composition of eggs. In this study, we provide new evidence that Ca availability during egg formation may indeed affect egg composition and influence chick development of the great tit Parus major at early developmental stages. Ca-supplemented birds breeding in base-poor pine forests produced eggs with elevated yolk Ca concentration compared with controls, while no such effect of supplementation was detected in case of eggshell thickness. Nestling tarsus length in the first half of the nestling period was positively influenced by both yolk dry mass and yolk Ca concentration. The effect of supplementary Ca did not persist throughout the nestling period; initial effects of egg components disappeared as nestlings aged. We conclude that apparently normal eggs may harbor poor nutrient and mineral conditions for chick growth. Such subtle changes in composition of eggs can depress chick growth, especially in harsh years.     

No evidence for long‐term effects of reproductive effort on parasite prevalence in great tits Parus major

Allocation of resources between the life history traits reproduction and parasite defence are expected because both are energetically costly. Experimental evidence for such allocation has been found in short‐term effects of reproduction on parasite prevalence or immune function. However, there is increasing evidence for long‐term negative effects of reproductive effort on individuals. This study investigates whether long‐term effects of reproductive effort on parasite prevalence exist. Brood sizes of great tits Parus major were experimentally altered in one breeding season and in the subsequent breeding season the prevalence of three parasites types (blood parasites, ticks and fleas) on the surviving parents were investigated. We detected no long‐term effects of brood size manipulation on the prevalence of parasites in the next year and therefore provide no evidence for inter‐seasonal effects of reproductive effort on parasite prevalence. The post hoc level of statistical power was reasonable for effects on blood parasite and flea prevalence, but low for effects on tick prevalence.     

Responses of great tits Parus major to small tortoiseshells Aglais urticae in feeding trials; evidence of aposematism

Abstract.  1. The small tortoiseshell Aglais urticae (Lepidoptera, Nymphalidae) is one of several red-coloured butterflies and moths that are active in early spring in Norway. It has been suggested that tortoiseshells may be warningly coloured and unpalatable to birds, however no experiments have been carried out to test this hypothesis.
2. The reactions of wild-caught great tits Parus major (Paridae) when offered dead specimens of the tortoiseshell and four palatable control species were studied. Two experiments were carried out. In expt 1, only intact prey was presented to the birds. In expt 2, the birds were offered only experimentally de-winged prey. Hence, in expt 2, it was possible to explore to what extent the birds' reaction to the prey offered to them in expt 1 could be explained as a reaction to visual stimuli from the wings of the prey.
3. In both experiments, tortoiseshells were attacked hesitantly, eaten slowly, and rejected often compared with controls, providing evidence that tortoiseshells are mildly distasteful to great tits. Moreover, all birds were more hesitant to attack intact than de-winged tortoiseshells, while there was no such effect for control prey, indicating a warning effect associated with the butterfly wings. There were also indications of avoidance learning in the birds to the presented tortoiseshells. These results are consistent with the idea of aposematism.     

Habitat quality, nestling diet, and provisioning behaviour in great tits Parus major

Variation in early nutrition is often a strong predictor of offspring condition and fitness. In the case of woodland passerine birds, nestling diet is determined by the spatiotemporal distribution of prey items such as caterpillars during the nestling period, and is usually quantified as differences in provisioning behaviour between habitats. However, the habitat level does not account for variation between individual territories, the level at which competition and selection are assumed to operate. Here we use nestbox cameras and Radio Frequency Identification technology (RFID) to simultaneously assess variation in both nestling diet (components) and provisioning rates (quantity) among a sample (n=22) of different quality great tit Parus major territories selected from a larger breeding population (n=310 fledged broods) in a single year. Caterpillars were by far the most numerous item provisioned to nestlings (mean=75% of prey items), as expected given the known importance of this food source for this species. Broods raised close to an oak tree, or far from the woodland edge, were provisioned the highest proportion of caterpillars. Provisioning rates declined seasonally and there was a weak association between low provisioning rates and caterpillar rich diets. During the first week of the nestling stage, nestling condition was unrelated to the proportion of caterpillars in the diet, provisioning rates and oak proximity. Condition at fledging was slightly improved in broods fed a higher proportion of caterpillars in the diet and in broods raised close to an oak tree. However, in our data early breeding was the only predictor of recruitment success, although power was low for this test. Analyses of long‐term data (41 years) from the same population confirmed a relationship between oak proximity and fledgling mass, but not recruitment success. Our results suggest that territory level environmental variation can affect offspring condition, probably through observed changes in nestling diet, but that such variation does not necessarily produce discernable effects on offspring fitness.     

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.