Feather ornaments are dynamic traits in the Great Tit Parus major

In behavioural studies it has been common to quantify plumage colours or ornaments over a range of dates and link them to fitness characteristics without accounting for seasonal changes in these traits. Such changes are likely to be widespread among birds, yet we lack assessments of this variability within individuals. We studied both within‐ and between‐individual temporal changes in Great Tit Parus major ornaments, specifically the melanin‐based black breast stripe and the pigment‐free white cheek patch. During the non‐breeding season both ornaments varied. In juveniles and adult females, the area of the breast stripe first rose and then, from near the end of December, decreased. In adult males there was a linear decrease. In the cheek patch, the irregularity of the cheek borders showed either a linear (adults) or a non‐linear (juveniles) increase as the season progressed. In individuals repeatedly sampled during the same winter, the decrease in the size of the breast stripe was larger for males than females and there was an overall decrease in the regularity of the cheek borders. There was no relationship between the size of the breast stripe and the white cheek patch irregularities or the cheek patch area. These results imply that more attention should be paid to quantification, within individuals, of the components of expression of phenotypic traits. In addition, we suggest that further research should focus on explaining the causes and functions of ornament change.     

Competition and egg-weight in the Great Tit Parus major

The mean weight of eggs in clutches of the Great Tit Parus major varies markedly between clutches. Eggs are lighter in years of high density of breeding pairs than in years of low density, but egg weight is also inversely correlated with the density of breeding Blue Tits Parus caeruleus .     

Parasites as mediators of heterozygosity-fitness correlations in the Great Tit (Parus major)

Positive correlations between heterozygosity and fitness traits are frequently observed, and it has been hypothesized, but rarely tested experimentally, that parasites play a key role in mediating the heterozygosity-fitness association. We evaluated this hypothesis in a wild great tit (Parus major) population by testing the prediction that the heterozygosity-fitness association would appear in broods experimentally infested with a common ectoparasite, but not in parasite-free broods. We simultaneously assessed the effects of parental and offspring heterozygosity on nestling growth and found that body mass of nestlings close to independence, which is a strong predictor of post-fledging survival, increased significantly with nestling levels of heterozygosity in experimentally infested nests, but not in parasite-free nests. Heterozygosity level of the fathers also showed a significant positive correlation with offspring body mass under an experimental parasite load, whereas there was no correlation with the mothers' level of heterozygosity. Thus, our results indicate a key role for parasites as mediators of the heterozygosity-fitness correlations.     

Personality and Nest Defence in the Great Tit (Parus major)

A growing number of studies have shown that individuals differ consistently in a suite of correlated behavioural traits across various contexts and situations. Yet, most work on animal personalities has been performed under laboratory conditions and still little is known about the ecological significance of differences in personality in the wild, and the behavioural mechanisms underlying possible fitness consequences. In this study, we investigated individual differences in personality in relation to nest defence behaviour in wild great tits. Nest defence is an important aspect of parental care and involves a trade‐off between two fitness components (i.e. survival and reproduction). As a measure of personality we used exploratory behaviour in a novel environment as this has been shown to be correlated with several other behavioural traits including risk‐taking and aggression, two important behavioural components of nest defence. We found that the intensity of alarm calling towards a human intruder was positively associated with exploratory behaviour, while there was a negative association between exploration score and number of movements during nest defence. Thus, fast explorers are shown to respond more boldly towards predators in the field. More generally we show that individuals with different personalities vary in their anti‐predator and reproductive investment strategies.     

Isolation and characterization of 16 microsatellite loci in the Great Tit Parus major

Six dinucleotide, three trinucleotide and seven tetranucleotide microsatellite loci developed for the great tit Parus major are presented. Thirty individual birds were screened at each locus. Loci were polymorphic (four to 19 alleles per locus). These markers provide a system to study paternity, genetic diversity in natural populations, gene flow, dispersal and inbreeding.     

The carotenoid‐based red cap of the Middle Spotted Woodpecker Dendrocopos medius reflects individual quality and territory size

Carotenoid‐based plumage ornaments have the potential to signal individual condition and health in many species of birds. However, very little is known about the function of red plumage in woodpeckers. We assessed whether the red cap displayed by both male and female Middle Spotted Woodpeckers reflects individual quality, finding that the size of the cap is sex‐dependent, whereas the brightness of the cap correlates with the body condition of an individual. Furthermore, birds with brighter caps had larger clutches, suggesting that cap coloration may be an honest signal of parental quality in woodpeckers. Interestingly, more colourful individuals also occupied smaller territories, suggesting that territory size and territory quality may be inversely related in the Middle Spotted Woodpecker.     

Seasonal changes in carotenoid- and melanin-based plumage coloration in the Great Tit Parus major

Plumage coloration plays an important role as a signal of individual quality. We studied plumage coloration in two Great Tit Parus major populations to test the hypothesis that coloration changes during the year without moult. As expected, the coloration of 'yellow' and 'dark green' areas in the breast and back changed with time but not the colour characteristics of the 'black' crown. This suggests that colours based on carotenoids could be more exposed to abrasion or fading than melanin-derived colours, although other factors could affect the patterns of change found. Our results show that effects of colour alteration could be important to the understanding of the potential for reliable signalling of different colours. Seasonal changes in plumage colour should be considered in future analysis of intraspecific variation in coloration.     

Clutch Defence in Great Tit (Parus major) Pairs and the Concorde Fallacy

We conducted an experiment to test whether great tits (Parus major) base their decisions of clutch defence on past investment or future benefits. Results were obtained by manipulation of future benefits. Great tit pairs of an experimental group with reduced clutch-size and thus diminished benefits defended their offspring against a live raptor significantly less than a comparable, non-manipulated control group with the same amount of past investment (clutch-size, incubation stage, time of year). While in the females the difference between the two groups was obvious from the beginning of a trial, the difference in the males developed only during the course of a trial, suggesting that the male bases its response on the female's response deficit. A more onerous explanation of the female signaling the male the egg loss by using a language-like symbol is not supported by the data. The experiment thereby permits the conclusion that at least the great tit female avoids committing the Concorde fallacy in the strict sense.     

Parasites and the blackcap's tail: implications for the evolution of feather ornaments

Although parasites may impair the expression of tail ornaments in birds, the importance of parasitism in driving the evolution of the initial stages of tail ornamentation is not well understood. Parasites could have negatively affected the expression of nonexaggerated, functional traits before these evolved ornaments, or they could have played a relevant role only after tails became ornamental and hence too costly to produce. To shed light on this issue, we studied the correlation between the abundance of feather mites (Acari, Proctophyllodidae) and the size, quality, growth rate and symmetry of tail feathers of blackcaps ( Sylvia atricapilla ), a non-ornamented passerine. Tail length was not correlated with mite load, yet blackcaps holding many mites at the moment of feather growth (fledglings) had lighter and more asymmetric feathers that grew at relatively lower rates. In blackcaps whose mite load was measured one year after feather growth (adults), only the negative correlation between mite intensity and feather symmetry remained significant. Changes in mite load since the moult season could have erased the correlation between condition-dependent feather traits and current parasite load in adults. Our results support the idea that different traits of non-ornamental feathers can signal parasite resistance. Therefore, parasitism could have played a central role in the evolution of tail ornamentation ever since its initial stages.  © 2002 The Linnean Society of London. Biological Journal of the Linnean Society , 2002, 76 , 481–492.     

Sex and age differences in reflectance and biochemistry of carotenoid‐based colour variation in the great tit Parus major

The plumage coloration in great tits (Parus major) is the subject of much behavioural and ecophysiological research, yet there is a lack of analyses of the natural colour variation and its mechanisms. We used reflectance spectrometry and high‐performance liquid chromatography to explore individual, sexual and age‐related variation in carotenoid coloration and pigmentation, paramount to the often presumed, but rarely substantiated, costs and ‘honesty’ of carotenoid displays. In adults, we found that sex was the strongest predictor of ‘brightness’ (higher in males) and of ‘hue’ (longer wavelength in females). There was no sex difference in ‘carotenoid chroma’ or carotenoid content of feathers which also was unrelated to adult age (1 or 2+ years) and condition. Similar patterns were revealed for nestlings. Regarding the biochemical ‘signal content’, ‘carotenoid chroma’, but not ‘hue’, was significantly related to the carotenoid content (lutein and zeaxanthin) of feathers. These results refute the previously assumed exaggeration of carotenoid pigmentation in male great tits, and question the condition‐dependence of carotenoid coloration in this species. However, the sexual dimorphism in total reflectance or ‘brightness’, most likely due to melanins rather than carotenoids, may have implications for signalling or other adaptive explanations that need to be explored. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 758–765.     

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.     

The Tradeoff Between Territorial Defense and Foraging in the Great Tit (Parus major)

We analyze territorial behavior in terms of decisions abouttime allocation.Such decisions must be made whenever time investedin territorial defense cannot be devoted to feeding, and viceversa. We describe the ecology and territorial behavior of thegreat tit (Parus major) to show that a tradeoff exists, andthen outline a series of laboratory and field experiments inwhich the value of feeding or defense was experimentally manipulated.Territorialmale great tits began to invest more heavily in territorialvigilance after encountering intruders, but the increase invigilance depended on the rate at which they could feed, aswell as their hunger level. We outline a dynamic analysis thattakes account of the fact that the optimal tradeoff will changeas hunger is reduced. The results of an experimental test ofthis dynamic model are also presented. We briefly review othertechniques whereby territorial tradeoffs have been investigated.     

Geographical variation in egg size of the Great Tit Parus major: a new perspective

A recent study on geographical variation in egg size of Great Tits Parus major concluded that: (1) mean egg size tended to increase with increasing latitude; and (2) mean egg size was positively correlated with mean clutch size. Including new data on both egg and clutch size, we reanalysed the relationships between egg size, clutch size and latitude, and investigated the possible effects of habitat type, female body size and egg shape on these relationships. We found that (1) egg volume showed minimum values around 51°N, increasing both north and southwards; (2) female body size increased linearly with increasing latitude; (3) female body size was positively correlated with egg breadth, but not with egg length or egg volume; (4) the sphericity index of the eggs (breadth to length ratio) was largest at medium latitudes, and eggs were more elongated towards the north and the south; (5) the relationship between clutch size and latitude was curvilinear, with the largest clutch sizes at intermediate latitudes; (6) egg size was not correlated with clutch size when the complete latitudinal range was considered, but egg size was negatively correlated with clutch size between 40 and 51°N; and (7) egg size did not differ among habitat types. We suggest that female body size (which probably limits egg breadth), and the pressure for producing large eggs (which in turn increases the reproductive success) are the main determinants of geographical variation in egg size and shape. Populations of small-bodied Great Tits seem to escape from the limits of their size, producing relatively elongated eggs, so that from a certain latitude southwards, egg volume does not decrease in spite of a decrease in female body size. Moreover, the negative relationship between egg and clutch size at low latitudes suggests that energetic trade-offs may also contribute to determine egg size in the south.     

False Alarm Calls as a Means of Resource Usurpation in the Great Tit Parus major

Great tits Parus major regularly gave alarm calls in winter without the presence of actual or potential predators. Such false alarm calls were given to deceive both conspecifics and heterospecifics. False calls were given when flock-feeding sparrows Passer spp. monopolized a concentrated food source; if the food resource was dispersed false alarm calls were not used, independently of the presence of sparrows. Dominant great tits used alarm calls deceptively if a dominant conspecific was present on a concentrated food source but not if a subdominant individual was present; subdominant great tits were displaced by means of threat displays. Subdominant individuals gave false alarm calls both if dominant or subdominant conspecifics were present. False alarm calls were especially used when food was scarce or when great tits were feeding at a high rate, i.e. during snow storms and in the morning and the afternoon.     

Habitat structure and prey composition generate contrasting effects on carotenoid‐based coloration of great tit Parus major nestlings

Carotenoid‐based coloration of nestling plumage is generally considered a reliable signal of quality and has consistently been related to habitat structure. The main hypothesis proposed to explain this correlation is that high quality habitats contain high quality food, which in return affects the expression of carotenoid‐based plumage. It therefore assumes that, at the population level, the link between habitat structure and food composition is consistent and more relevant than inter‐individual differences in foraging ability or parental investment. In addition, it is assumed by default that food and habitat produce concordant effects on nestling coloration. In this work we evaluated habitat structure and prey composition in addition to several measures of parental investment. We investigated their relative effect on carotenoid‐based plumage coloration (lightness, chroma and hue) of great tit Parus major nestlings. We found a low correlation between carotenoid‐based coloration of nestlings and that of their parents. Nestling coloration, especially lightness and chroma, increased with the intake of more spiders. The time of breeding was positively correlated with lightness and chroma and negatively correlated with hue. Finally, the maturity of oak trees surrounding nest‐boxes correlated negatively with lightness, and the size of all tree species surrounding nest‐boxes correlated positively with hue of chick plumage. Our findings support the view that habitat structure and prey composition may produce divergent effects on feather pigmentation, and that prey proportions and variables related to parental investment should be assessed when considering carotenoid‐based coloration of chicks. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 547–555.     

Measurement of plumage badges: an evaluation of methods used in the Great Tit Parus major

There is an increasing interest in the variation in plumage coloration and a number of theories have been proposed to explain its evolution (Butcher & Rohwer 1989, Savalli 1995). Birds haye been considered to signal through plumage their dominance status, ability to evade predators, parasite resistance or for example their parental care abilities (reviewed in Butcher & Rohwer 1989, Anderson 1994, Savalli 1995, Johnstone 1997). However, the measuremcnt of plumage badges and its accuracy have received little attention (Savalli 1995). In the case of the Great Tit Parus major, for instance, several studies have analysed the importance of the breast stripe size as an indicator of dominance status in winter flocks (Jarvi & Bakken 1984, Piiysa 1988, Lemel 1989, Wilson 1992) and its importance in mate choice (Norris 1990, 1993), but the badgc has been estimated using very different indices, even in studies performed by the same authors (Norris 1990, 1993). We compare the performance of differvnt indices in estimating Great Tit stripe size, by comparing them with badge surface area obtained from image analysis of digital photographs. We propose that digital photography provides a reliable and inexpensive method to measure plumage badges in birds and we demonstrate its performance in the Great Tit.