Great tits (Parus major) reduce caterpillar damage in commercial apple orchards

Alternative ways to control caterpillar pests and reduce the use of pesticides in apple orchards are in the interest of the environment, farmers and the public. Great tits have already been shown to reduce damage under high caterpillar density when breeding in nest boxes in an experimental apple orchard. We tested whether this reduction also occurs under practical conditions of Integrated Pest Management (IPM), as well as Organic Farming (OF), by setting up an area with nest boxes while leaving a comparable area as a control within 12 commercial orchards. We showed that in IPM orchards, but not in OF orchards, in the areas with breeding great tits, apples had 50% of the caterpillar damage of the control areas. Offering nest boxes to attract insectivorous passerines in orchards can thus lead to more limited pesticide use, thereby adding to the natural biological diversity in an agricultural landscape, while also being economically profitable to the fruit growers.     

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.     

Great tits (Parus major) flexibly learn that herbivore‐induced plant volatiles indicate prey location: An experimental evidence with two tree species

1. When searching for food, great tits (Parus major) can use herbivore‐induced plant volatiles (HIPVs) as an indicator of arthropod presence. Their ability to detect HIPVs was shown to be learned, and not innate, yet the flexibility and generalization of learning remain unclear.
2. We studied if, and if so how, naïve and trained great tits (Parus major) discriminate between herbivore‐induced and noninduced saplings of Scotch elm (Ulmus glabra) and cattley guava (Psidium cattleyanum). We chemically analyzed the used plants and showed that their HIPVs differed significantly and overlapped only in a few compounds.
3. Birds trained to discriminate between herbivore‐induced and noninduced saplings preferred the herbivore‐induced saplings of the plant species they were trained to. Naïve birds did not show any preferences. Our results indicate that the attraction of great tits to herbivore‐induced plants is not innate, rather it is a skill that can be acquired through learning, one tree species at a time.
4. We demonstrate that the ability to learn to associate HIPVs with food reward is flexible, expressed to both tested plant species, even if the plant species has not coevolved with the bird species (i.e., guava). Our results imply that the birds are not capable of generalizing HIPVs among tree species but suggest that they either learn to detect individual compounds or associate whole bouquets with food rewards.

     

Great tits provided with ad libitum food lay larger eggs when exposed to colder temperatures

The amount of nutrients deposited into a bird egg varies both between and within clutches of the same female. Larger eggs enhance offspring traits, but as a tradeoff, laying large eggs also infers energetic costs to the female. Income breeders usually lay larger eggs later in the season, when temperatures and food availability are higher. Egg size is thus affected by the daily amount of energy available to produce an egg under cold conditions, but it is less well known in how far temperature exerts direct effects on egg size. We show that great tit females Parus major with access to ad libitum food and breeding in climate‐controlled aviaries varied their egg investments. The size of an individual egg was best predicted by mean temperatures one week pre‐laying, with females laying larger, rather than smaller, eggs under colder conditions. Eggs increased in size over the season, but not significantly over the laying sequence. The degree of daily temperature fluctuation did not influence egg size. In addition to a substantial between‐female variation, sisters were more similar to each other than unrelated females, showing that egg size does also reflect heritable intrinsic female properties. Natural variation in egg size is thus not only determined by energy‐limitation, but also due to females allocating more resources to eggs laid in colder environments, thus increasing early survival of the chicks. That the positive correlation between temperature and egg investments that is found in a natural population is reversed under ad libitum food conditions demonstrates that wild great tits tradeoff own condition with survival prospects of their chicks as a function of available food, not ambient temperature.     

Great tits (Parus major) searching for artificial prey: implications for cryptic coloration and symmetry

It has been suggested that bilateral symmetry may impose a costfor animals relying on camouflage because symmetric color patternsmight increase the risk of detection. We tested the effect ofsymmetry on crypsis, carrying out a predation experiment withgreat tits (Parus major) and black-and-white–patterned,artificial prey items and background. First, we found that detectiontime was significantly longer for a highly cryptic, asymmetricpattern based on a random sample of the background than forits symmetric variants. Second, we were able to arrange theelements of a prey pattern in a way that the resulting asymmetricpattern was highly cryptic and, furthermore, its symmetric variantwas highly cryptic as well. We conclude that symmetry may imposea substantial cost on cryptic patterns, but this cost variesamong patterns. This suggests that for prey, which predatorstypically view from an angle exposing their symmetry, selectionfor pattern asymmetry may be less important and selection fordecreased detectability cost of symmetry may be more importantthan previously thought. This may help to understand the existenceof so many prey with cryptic, symmetric color patterns.     

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.     

Differences in reproductive success and parental qualities between habitats in the Great Tit Parus major

Reproductive success and parental attributes of Great Tits Parus major nesting in good and poor habitats were compared to investigate whether they differed and, if so, whether parental or environmental variation contributed most to the differences.
Monitored over 3 years, clutches in mature woodland were started earlier, were larger and produced larger broods of heavier chicks than those in marginal habitats such as gardens and hedgerows. Fledging success was significantly higher in woodland in 2 of the 3 years although egg weights were lower. Parents nesting in different habitats were very similar in body-size although those in woodland were in better condition. The prey delivered to nestlings in woodland was of significantly higher quality than that delivered in marginal habitats. Furthermore, the heritability of body-size (tarsus-length) was higher in woodland, suggesting that the environment limits nestling growth in poorer habitats. Reproductive success was considerably lower in poor habitats and appears to be constrained primarily by environmental quality, although this may operate partly through its affect on parental body condition.     

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.     

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.     

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.     

Genetic evidence for extra-pair fertilizations in a monogamous passerine, the Great Tit Parus major

The incidence of extra-pair paternity in a Great Tit Parus major population at Wytham Wood, Oxford, in 1985–1987 was determined using two polymorphic allozymes. In 831 nestlings from 94 broods, 27 genetic exclusions were detected in 25 (3%) nestlings from 16 broods. Seven (44%) of these broods contained offspring that excluded the putative male parent from being the genetic parent. The distribution of exclusion types indicated that excluded offspring were the result of fertilizations by extra-pair males and not of egg-dumping. The true frequency of extra-pair paternity was estimated as 14% of offspring. These results suggest a mixed reproductive strategy for males in which they breed mo-nogamously whilst simultaneously seeking extra-pair matings with females of other pairs.     

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.     

Two conflicting needs affecting predator mobbing by great tits,Parus major

Predator mobbing by great tits, Parus major, was studied by manipulating two contextual variables: the proximity of danger to the nest hole (close versus far), and breeding condition (non-breeding versus nest building versus care of nestlings). In five experiments pitting these contextual variables against each other, great tits were presented with a multi-species mobbing chorus signalling danger to which they responded by typical predator harassment. Based on the ‘move on’ hypothesis of harassment and on context manipulation, harassment levels specific for each of the five experiments could be predictably ordered; the ensuing rank order of scores reflected, by its nature, a series of four strong inference tests. Whereas two latency measures supported the move on hypothesis, two distance-from-danger measures suggested nest hole concealment to be an opposing need; a fifth measure of harassment, comprising both latency and distance, held an intermediate position, thus tying in with the compromise nature of harassment. Considering the ‘phantom’ nature of the unseen danger stimulus applied, the defence levels observed must be regarded as moderately conservative. There are natural danger stimuli (e.g. cats) that more effectively prevent great tits displaying predator harassment.     

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.     

A recipe for postfledging survival in great tits Parus major: be large and be early (but not too much)

Survival of juveniles during the postfledging period can be markedly low, which may have major consequences on avian population dynamics. Knowing which factors operating during the nesting phase affect postfledging survival is crucial to understand avian breeding strategies. We aimed to obtain a robust set of predictors of postfledging local survival using the great tit (Parus major) as a model species. We used mark–recapture models to analyze the effect of hatching date, temperatures experienced during the nestling period, fledging size and body mass on first‐year postfledging survival probability of great tit juveniles. We used data from 5192 nestlings of first clutches ringed between 1993 and 2010. Mean first‐year postfledging survival probability was 15.2%, and it was lower for smaller individuals, as well as for those born in either very early or late broods. Our results stress the importance of choosing an optimum hatching period, and raising large chicks to increase first‐year local survival probability in the studied population.     

Sexual, seasonal, and environmental variation in plasma carotenoids in great tits, Parus major

In many birds, carotenoids have dual functions as irreversible plumage pigments and as physiologically essential vitamins and antioxidants. They must be obtained through the diet and may therefore be a limiting resource, a constraint that is likely to vary with factors such as sex, habitat, and time of year. In the present study, we investigated signs of carotenoid limitation in great tits, Parus major , in relation to sex, season, year, and within an urban versus a rural habitat. The two main carotenoids, lutein and zeaxanthin, were analysed by high-performance liquid chromatography in the plasma and in the yellow carotenoid-based breast feathers. We found that plasma carotenoid concentrations were significantly influenced by sex, season, and year, but not by urban versus rural habitat. At moult, plasma concentration was positively correlated with feather pigmentation, independent of body condition and sex. During the breeding season, however, circulating carotenoid concentrations were negatively related to the feather pigmentation (i.e. from previous autumn moult). We suggest that great tits are carotenoid deprived before leaf emergence, and that carotenoid utilization and limitations are sex-specific, but that there are neither any obvious honesty-maintaining costs of pigmentation, nor any fitness consequences of the colour variation.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 521–527.     

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.     

Melanin, carotenoid and structural plumage ornaments: information content and role in great tits Parus major

The importance of plumage colour as an indicator of individual quality and the basis of sexual selection has long been recognized. Of the three generally distinguished classes of plumage colours, melanin-based ornaments are traditionally considered to provide less reliable information than carotenoid-based traits. However, the role of structural ornaments in multiple signalling systems has rarely been examined, and no study has compared the information content and role of the three ornament types simultaneously. Here we investigated three plumage ornaments in great tits Parus major : the size of the melanin-based breast stripe, the carotenoid-based colour of the yellow breast and the structurally based reflectance properties of the black crown. We worked on both the mechanistic and the functional levels. First, we assessed the dependence of ornaments on body condition during moult using ptilochronology. Second, we estimated assortative mating for these traits, as a measure of mutual sexual selection. Only the spectral attributes of crown feathers correlated with body condition during moult. However, breast stripe size was related to age, while the brightness of the yellow breast indicated body size. Relative crown ultraviolet reflectance was much higher in males than in females. Assortative mating was strongest for crown ultraviolet reflectance, but composite measures suggest that a system of multiple sexually selected traits with different information content may work in this population. These data support the accumulating evidence that the condition-dependence of melanin and carotenoid coloration is not qualitatively different. They also suggest that more research should target the reflectance properties of dark plumage areas in general, and ultraviolet crown ornamentation in tits in particular.     

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.     

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.