Evidence for cuckoldry in the Great Tit Parus major

We estimated the frequency of cuckoldry (the proportion of offspring resulting from extra-pair copulations) in Great Tits Parus major using heritability estimates based on the resemblance of offspring tarsus-length to that of their parents. Our results suggest that cuckoldry occurs and may be relatively common in certain years.     

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 .     

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.     

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.     

Characterizing the mammalian hair present in Great Tit (Parus major) nests

Capsule Many birds are known to incorporate mammal hair into their nest lining, but the frequency with which they use hair from different mammals is unknown. We performed one of the first detailed examinations of mammalian hair from 54 Great Tit nests. We identified 5317 hairs belonging to 21 mammal species. Almost all of the examined nests contained hair from Roe Deer (Capreolus capreolus), but hair from Wild Boars (Sus scrofa), European Hares (Lepus europaeus) and Red Foxes (Vulpes vulpes) was also common.     

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.     

Seasonal variation of circulating plasma carotenoids in Mediterranean Great Tit males Parus major

Capsule Mediterranean Great Tits showed a marked increase in levels of circulating carotenoids during moult and autumn.

Aims To study seasonal variation in plasma carotenoid content during a whole annual cycle for Great Tits Parus major inhabiting a Mediterranean woodland.

Methods We used a sample of 71 adult male Great Tits captured in NE Spain during a whole year. Data were organized into four seasons (winter, breeding, moult and autumn). We sampled blood to extract plasma. Carotenoid plasma concentrations were analysed by High-performance liquid chromatography (HPLC).

Results Lutein and zeaxanthin content varied seasonally, with a marked increase in levels during moult and autumn. Within the moulting period, levels increased gradually as the season progressed. This pattern differed significantly from that previously described in northern European populations, where high values appear mainly in the breeding season. Carotenoid concentrations (lutein: 1.2?±?0.25, zeaxanthin: 0.07?±?0.03?µg mL^?1) were also lower than in northern Europe.

Conclusion Mediterranean Great Tits show a very different pattern of circulating carotenoids and lower levels than northern European populations. The increasing pattern of carotenoid availability found within the moulting period raises the need to control for the effect of sampling date when analysing data on carotenoid concentrations at different times of year.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Differential Responsiveness of Great Tit Nestlings,Parus major,to Natural Auditory Stimuli

In one field and two laboratory experiments, wild, wild-captured and partly laboratory-raised 16 to 18-day old great tit nestlings were subjected to repeated presentations of auditory stimuli of varying biological significance. The frequency of occurrence of the stimuli in the study area was censused. — All nestlings showed strong aversive reactions to the ‘seeet’ alarm-call of the species. It is concluded that a selective responsiveness to this call develops independently of previous exposure to it. A functional interpretation of this reaction is derived from its presumed adaptive value. Three hypothetical interpretations are suggested to explain its emergence in the individual nestling; The ‘seeet’-call elicits aversive reactions because of, 1) its novelty, 2) its intensity in terms of relative concentration of energy over its frequency range and 3) its contrasting acoustic structure compared to the nestlings' begging-call which has become strongly associated with approach behavior.