Intensity of nest defence is related to offspring sex ratio in the great tit Parus major

Nest-defence behaviour of passerines is a form of parental investment. Parents are selected, therefore, to vary the intensity of their nest defence with respect to the value of their offspring. Great tit, Parus major, males were tested for their defence response to both a nest predator and playback of a great tit chick distress call. The results from the two trials were similar; males gave more alarm calls and made more perch changes if they had larger broods and if they had a greater proportion of sons in their brood. This is the first evidence for a relationship between nest-defence intensity and offspring sex ratio. Paternal quality, size, age and condition, lay date and chick condition did not significantly influence any of the measured nest-defence parameters.     

To breed or not to breed: causes and implications of non-breeding habit in the willow tit Parus montanus

Causes and consequences of non-breeding in willow tits were studied in northern Finland during 1986–1992. The breeding status was sex and age biased; males and yearling birds were in excess among the non-reproducers. Due to sex bias in the population it appeared detrimental for males to lose a mate, especially shortly before breeding. Lack of a mate was a important factor for males not reproducing (37% of non-breeding males) than for females (14%). Most of the non-breeding birds maintained a pair bond which only rarely broke up for the next breeding season (divorce rate 5.5%). This implies that parental incompatibility is not a possible explanation for pairs not reproducing. Males that did not breed tended to survive better than reproducing ones, whereas such a relationship was not found for females. It is possible that this sex-related difference in survival cost is attributable to quality differences among non-breeding individuals. It was especially low-quality yearling females, with low survival prospects, that were responsible for the discrepancy. The proportion of non-breeding females in the population correlated highly with clutch size and subsequent juvenile survival. It is therefore suggested that for most of these females non-breeding is a phenotypic response to low offspring value in the prevailing circumstances (inter-generational tradeoff). However, it is uncertain whether willow tits in a northern population can use breeding density as an indicator of changing survival prospects of their descendants, as suggested by Ekman and Askenmo (1986) for southern Sweden.     

Using priority to food access: fattening strategies in dominance-structured willow tit (Parus montanus) flocks

We studied changes in body mass in response to priority to foodaccess by repeatedly weighing free-living willow tits in dominance-structuredflocks. Priority to food access did not correlate to eitheracquisition rate or net turnover of body reserves, but subordinateswith low food availability had larger body reserves than dominants.Removal experiments suggest a causal relationship between rankand the size of reserves. Body reserves of subordinates decreasedwhen their access to food increased after the dominant was removed.Low variability in body mass of subordinates shows that theydo not maintain large reserves in response to uncertain acquisitionof food. Rather, large reserves of low-rank individuals couldserve as insurance for conditions with increasing requirements.Under such conditions, dominants are more likely to claim theirpriority to food, and subordinates would not be able to increasetheir body reserves by feeding.     

Importance of adult survival, local recruitment and immigration in a declining boreal forest passerine, the willow tit Parus montanus

Population growth rate (λ) and its components (adult survival, local recruitment, immigration and their relative contributions to λ) were studied in the declining willow tit Parus montanus in Northern Finland. Capture–recapture models for open populations were used to estimate the population parameters and their process variation. Adult survival was fairly high with low variation (0.593, CV=0.067). As expected, local recruitment was lower and more variable (0.063, CV=0.610). During the 12-year study, the population growth rate averaged to one (0.988, CV=0.197; calculated as However, if the present processes continue, population projections show that the population is likely to decline. There was considerable temporal variation in the relative contributions of demographic parameters to λ. In all years, adult survival had the highest relative contribution (mean 64%) to the population growth rate and it was the least variable trait. Immigration had a higher relative contribution (22%) to λ than local recruitment (14%). Based on the results for the contributions to λ, the main conservation concern for willow tits is adult survival. Due to low variation, adult survival may be difficult to enhance, but at least it should be prevented from declining. High stochasticity in local recruitment and immigration is probably an inherent characteristic of highly seasonal environments, making these traits difficult to address for conservation practices.     

Offspring sex ratio is related to male body size in the great tit (Parus major)

Sex allocation theory predicts that the allocation of resourcesto male and female function should depend on potential fitnessgain realized through investment in either sex. In the greattit (Parus major), a monogamous passerine bird, male resourceholdingpotential (RHP) and fertilization success both depend on malebody size (e.g., tarsus length) and plumage traits (e.g., breaststripe size). It is predicted that the proportion of sons ina brood should increase both with male body size and plumage traits,assuming that these traits show a father—offspring correlation. Thiswas confirmed in our study: the proportion of sons in the brood increasedsignificantly with male tarsus length and also, though not significantly,with the size of the breast stripe. A sex ratio bias in relationto male tarsus length was already present in the eggs because(1) the bias was similar among broods with and without mortalitybefore the nestlings' sex was determined, and (2) the bias remainedsignificant when the proportion of sons in the clutch was conservativelyestimated, assuming that differential mortality before sex determinationcaused the bias. The bias was still present among recruits.The assumption of a father—offspring correlation was confirmedfor tarsus length. Given that both RHP and fertilization successof male great tits depend on body size, and size of father andoffspring is correlated, the sex ratio bias may be adaptive.     

Intraseasonal patterns in shorebird nest survival are related to nest age and defence behaviour

Nest survival may vary throughout the breeding season for many bird species, and the nature of this temporal variation can reveal the links between birds, their predators, and other components of the ecosystem. We used program Mark to model patterns in nest survival within the breeding season for shorebirds nesting on arctic tundra. From 2000 to 2007, we monitored 521 nests of five shorebird species and found strong evidence for variation in nest survival within a nesting season. Daily nest survival was lowest in the mid-season in 5 of 8 years, but the timing and magnitude of the lows varied. We found no evidence that this quadratic time effect was driven by seasonal changes in weather or the abundance of predators. Contrary to our prediction, the risk of predation was not greatest when the number of active shorebird nests was highest. Although nest abundance reached a maximum near the middle of the breeding season, a daily index of shorebird nest activity was not supported as a predictor of nest survival in the models. Predators’ access to other diet items, in addition to shorebird nests, may instead determine the temporal patterns of nest predation. Nest survival also displayed a positive, linear relationship with nest age; however, this effect was most pronounced among species with biparental incubation. Among biparental species, parents defended older nests with greater intensity. We did not detect a similar relationship among uniparental species, and conclude that the stronger relationship between nest age and both nest defence and nest survival for biparental species reflects that their nest defence is more effective.     

Selection on the genetical and environmental components of tarsal growth in juvenile willow tits (Parus montanus)

We studied selection on tarsus length among first year willow tits Parus montanus in relation to environmental and genetical influences on growth. The main environmental influence on growth was a cohort effect. We also found a substantial heritable component of phenotypic variation for tarsus length (h² = 0.61), and crossfostering in one year showed no shared environment effect which could account for parent/offspring resemblance. The deteriorating conditions for growth later in the season did not confound our heritability estimates as the time of laying was not correlated to parent size, and no maternal effects operating through egg size were found. We tested for selection during the summer dispersal phase by comparing tarsus length among fullgrown pulli (age 14 days, controlled by repeated measurements of the same individuals later during breeding and the ensuing winter) and the tarsus length of the first year cohort in autumn composed of a mixture of locally born birds remaining within our study area after the dispersal phase and immigrants born outside the study site. Following a season with poor nestling growth, birds with short tarsi were selected against when underweight, suggesting that growth condition is the target of selection. Such selection on those individuals which show the strongest environmental influence on phenotypic variation will reduce the potential for an evolutionary response to selection.     

Song evolution in the coal tit Parus ater

Since in oscine birds song divergence often leads to premating reproductive isolation, we asked which factors drive the evolution of song in a widespread species, the coal tit Parus ater. Based on an almost taxon‐complete phylogeny we correlated song divergence with morphometric (ecology), genetic (time), and geographic distances (separation). We found eight well‐supported mitochondrial lineages, one of which consists of melanolophus (usually treated as a separate species) and whose relationships remain generally unresolved. Due to intense song variability even sophisticated sonametric analyses failed to separate sub‐specific units. We tested for the role of song in reproductive isolation by playing songs from China and the Himalayas to Central European males. They recognize them as conspecific, but react to their playbacks less aggressively than to local songs. While morphological divergence is correlated with neither time nor separation, song divergence coincides more with geographic than genetic distance. This is mainly driven by differences along longitude and is especially prominent in the southern part of the species’ range, where six lineages persisted during the last glaciation while the north was subsequently re‐occupied by two lineages.     

Extrapair paternity in the blue tit (Parus caeruleus) : female choice, male charateristics, and offspring quality

Extrapair paternity is common in many birds, and it is now generallyaccepted that female choice plays an important role. However,die benefits that females obtain from extrapair paternity aremuch less dear. To test the hypothesis that females obtain indirectfitness benefits, we studied paternity in a blue tit populationover 4 years. Extrapair paternity occurred in 31-47% of allnests and accounted for 11-14% of all offspring. Most malesthat fathered extrapair young did not lose paternity themselves,males never "exchanged" paternity, and within nests the extrapairoffspring were usually fathered by a single male. Comparisonsbetween males that did and did not lose paternity and pairwisecomparisons between the extrapair male(s) and the within-pairmale showed that successful males had longer tarsi and sangon average longer strophes during the dawn chorus. Successfulmales weighed less (relative to their size) during the nettlingstage, but nevertheless they survived better. Male age did notinfluence their likelihood of losing paternity, but extrapairmales were usually older than the within-pair male they cuckolded.Within nests with mixed paternity, extrapair young were morelikely to survive than within-pair young in cases of partialbrood mortality. Our data also suggest that extrapair offspringwere more likely to be males. Because extrapair males were usuallyclose neighbors, male quality should be considered relativeto the quality of the neighbors. Despite this, we found consistencyin female choice over years. Our observations provide supportfor the hypothesis that female blue tits engage in extrapaircopulations to obtain good genes for their offspring.     

Promiscuity, paternity and personality in the great tit

Understanding causes of variation in promiscuity within populations remain a major challenge. While most studies have focused on quantifying fitness costs and benefits of promiscuous behaviour, an alternative possibility--that variation in promiscuity within populations is maintained because of linkage with other traits-has received little attention. Here, we examine whether promiscuity in male and female great tits (Parus major)--quantified as extra-pair paternity (EPP) within and between nests--is associated with variation in a well-documented personality trait: exploration behaviour in a novel environment. Exploration behaviour has been shown to correlate with activity levels, risk-taking and boldness, and these are behaviours that may plausibly influence EPP. Exploration behaviour correlated positively with paternity gained outside the social pair among males in our population, but there was also a negative correlation with paternity in the social nest. Hence, while variation in male personality predicted the relative importance of paternity gain within and outside the pair bond, total paternity gained was unrelated to exploration behaviour. We found evidence that males paired with bold females were more likely to sire extra-pair young. Our data thus demonstrate a link between personality and promiscuity, with no net effects on reproductive success, suggesting personality-dependent mating tactics, in contrast with traditional adaptive explanations for promiscuity.     

Dawn chorus and female behaviour in the Willow Tit Parus montanus

We studied the effect of female behaviour on the dawn chorus of Willow Tits Parus montanus. Ten females were temporarily kept in their nest holes in order to delay their dawn emergence. Simultaneously, their mates' singing behaviour was measured. We compared the control dawn behaviour (during which the females emerged when they wanted) with that during the experimental delay. The dawn song by the males lasted longer when the females' emergences were delayed. Our results show that the duration of the dawn chorus is directly related to the female's behaviour. We suggest that at least one function of the dawn song is intrapair signalling, which is often linked to sperm competition.     

High frequency of multiple paternity in broods of a socially monogamous cichlid fish with biparental nest defence

In several animal taxa, genetic analyses have demonstrated that social monogamy and biparental brood care do not preclude polygamous reproduction. Few studies have been conducted in fish, but in fish species without alternative reproductive phenotypes, social monogamy was largely congruent with genetic parentage. In contrast to these findings, we report an exceptionally high level of multiple paternity in a socially monogamous cichlid fish with biparental nest defence ( Variabilichromis moorii ), inferred from microsatellite and mitochondrial data of 10 broods. Whereas all offspring in a nest shared a common mother, each brood was sired by 2 to > 10 males. None of the inferred sires was assigned a large proportion of the brood. Paternity was estimated as the minimum number of sires required to explain multilocus offspring genotypes, and as the maximum-likelihood number of sires given population allele frequencies. Analysis of simulated brood genotypes suggested that, although these two methods tend to under- and overestimate, respectively, the true number of sires, primary sires with many offspring in a brood would have been detected. Hence, the genetic data indicate that the nest tending males suffer substantial cuckoldry and provide alloparental care for a large number of unrelated fry. We have no data on the social status of the cuckolding males, but due to synchronous spawning of pairs and commitment to brood care of paired males, it is possible that most of the parasitic spawners are solitary males.     

Extrapair paternity in the great tit (Parus major): a test of the "good genes" hypothesis

In 1993 and 1994 we determined the frequency of extrapair paternityin broods of great tits, Parus major using multilocus DNA fingerprinting.We found no instances of intraspecific brood parasitism, but40% of broods (31/78) contained extrapair-fathered young and83% of offspring (58/681) were xtrapair We identified the geneticfathers of 60% of the extrapair nestlings (35/ 58). Males withfull and lost paternity did not differ significantly in traitsthat have been suggested to indicate male quality, nor did thegenetic and social fathers of extrapair offspring. In 1993,cuckolded males sired more offspring that recruited to the subsequentbreeding season than males with full paternity. Moreover, eventhough genetic fathers of extrapair young (EPY) sired more fledglingsthan the males they cuckolded, genetic and social fathers ofEPY did not differ in the number of recruits sired. Also, theEPY of a brood did not survive better than their half sibs.Thus, our results do not supportthe hypothesis that femaleschoose better quality males for extrapair matings ("good genes"hypothesis). Further, the level of extrapair paternity differedmarkedly between the two years. Our data show that females areconstrained in their extrapair activities by the availabilityof extrapair mates. This is at least partly due to yearly differencesin breeding synchrony.     

Egg quality and parental ornamentation in the blue tit Parus caeruleus

Components of avian egg quality often show remarkable variation between females and yet the causes of variation in this fitness-related trait remain poorly understood. We investigated the egg size and yolk carotenoid investment of blue tit Parus caeruleus females in relation to multiple parental traits. We show that females produce eggs with more colourful yolks when mated to ultraviolet (UV) attractive males. Since yolk carotenoids may enhance offspring fitness, but may be available to females in limiting amounts, the correlation we found suggests adaptive egg quality adjustment in response to mate attractiveness, but an experimental approach is required to rule out alternative explanations. Yolk colour was also correlated with laying date and yolk mass. Though the effect of laying date could not be explained by ambient temperature during egg formation, it suggests a proximate constraint of general carotenoid availability on yolk composition. Egg size was not affected by male attractiveness; however, females with a brighter crown produced larger eggs, suggesting that crown coloration might indicate individual quality in females too.     

Realized heritability of personalities in the great tit (Parus major)

Behaviour under conditions of mild stress shows consistent patterns in all vertebrates: exploratory behaviour, boldness, aggressiveness covary in the same way. The existence of highly consistent individual variation in these behavioural strategies, also referred to as personalities or coping styles, allows us to measure the behaviour under standardized conditions on birds bred in captivity, link the standardized measurements to the behaviour under natural conditions and measure natural selection in the field. We have bred the great tit (Parus major), a classical model species for the study of behaviour under natural conditions, in captivity. Here, we report a realized heritability of 54 +/- 5% for early exploratory behaviour, based on four generations of bi-directional artificial selection. In addition to this, we measured hand-reared juveniles and their wild-caught parents in the laboratory. The heritability found in the mid-offspring-mid-parent regression was significantly different from zero. We have thus established the presence of considerable amounts of genetic variation for personality types in a wild bird.     

Inheritance and variation in eggshell patterning in the great tit Parus major

The inheritance of patterns on avian eggshells is central to understanding the evolution of traits such as egg mimicry (e.g. in cuckoos). Yet little is known about the inheritance, or indeed function, of eggshell patterns. It has long been believed that the evolution of eggshell pattern mimicry required that patterns be determined by genes situated on the female-specific W chromosome. However, it has never been demonstrated for any bird that egg pattern traits (rather than ground colour) are female sex linked, or indeed that they are inherited. We studied the inheritance of three measures of egg-pigment patterns in a wild great tit population. Egg patterns were female specific but unrelated to female attributes such as age or condition and showed only weak environmental effects. Eggs of daughters resembled those of both their mothers and maternal grandmothers, but not of their paternal grandmothers. We conclude that this is the first demonstration of female sex-linked inheritance of avian eggshell patterning, so raising the probability that such a system operates in egg mimics and their hosts.