Population Of Blue Tits Research Articles

Wild great and blue tits do not avoid chemical cues of predators when selecting cavities for roosting.

Small birds use cavities for roosting to decrease the thermoregulatory costs during the winter nights. The ability of birds to detect and escape from an approaching predator is impaired during roosting and thus the selection of such cavities should take into account the risk that a predator will find the cavity. Previous evidence suggested that birds in captivity are able to detect predator scent and avoid roosting in nest-boxes containing such predator chemical cues. Here, we tested whether birds also show this avoidance response under natural conditions. We performed three studies in three populations of blue and great tits. We added predator scent, a pungency scent or an odourless control to nest-boxes and compared the use of these nest-boxes for roosting. We found no differences between the scent treatments in the use of nest-boxes. Therefore, chemical cues indicating the potential presence of a predator are not enough for birds to avoid roosting in nest-boxes under natural conditions.

Gene flow does not prevent personality and morphological differentiation between two blue tit populations.

Understanding the causes and consequences of population phenotypic divergence is a central goal in ecology and evolution. Phenotypic divergence among populations can result from genetic divergence, phenotypic plasticity or a combination of the two. However, few studies have deciphered these mechanisms for populations geographically close and connected by gene flow, especially in the case of personality traits. In this study, we used a common garden experiment to explore the genetic basis of the phenotypic divergence observed between two blue tit (Cyanistes caeruleus) populations inhabiting contrasting habitats separated by 25km, for two personality traits (exploration speed and handling aggression), one physiological trait (heart rate during restraint) and two morphological traits (tarsus length and body mass). Blue tit nestlings were removed from their population and raised in a common garden for up to 5years. We then compared adult phenotypes between the two populations, as well as trait-specific Qst and Fst . Our results revealed differences between populations similar to those found in the wild, suggesting a genetic divergence for all traits. Qst -Fst comparisons revealed that the trait divergences likely result from dissimilar selection patterns rather than from genetic drift. Our study is one of the first to report a Qst -Fst comparison for personality traits and adds to the growing body of evidence that population genetic divergence is possible at a small scale for a variety of traits including behavioural traits.

Complete brood failure in an altricial bird is almost always associated with the sudden and permanent disappearance of a parent

A central goal in evolutionary ecology is to identify factors that explain variation in reproductive success, i.e. in the number of offspring produced. In altricial birds, a substantial part of this variation is determined by the number of nestlings that die before fledging, but surprisingly little is known about the proximate causes of offspring mortality during the nestling period. We used a uniquely comprehensive dataset of parental nestbox visits from seven breeding seasons to investigate the association between parental behaviour and nestling mortality in a population of blue tits (Cyanistes caeruleus). In almost all nests that suffered complete brood mortality one of the parents had suddenly disappeared during the nestling stage. In contrast, parental disappearance in nests with partial brood mortality was rare and equally common as in nests with no brood loss. With few exceptions, parents that disappeared during the nestling stage were never observed again and never returned to breed. In contrast, parents that remained after their partner disappeared were equally likely to be observed again or return to breed as parents of nests where both parents stayed. Visit rates at nests where a parent would disappear did not differ from those at nests where both parents stayed. Taken together, our results show that - in contrast to partial brood failure - complete brood failure is almost always associated with the sudden and permanent disappearance of one of the parents, probably due to predation. Partial and complete brood mortality should be treated as distinct processes that have different underlying causes.

Patterns of female nest attendance and male feeding throughout the incubation period in Blue Tits Cyanistes caeruleus

Most bird species exhibit biparental care, but the type of care provided by each sex may differ substantially. In particular, during the incubation phase in passerines, females perform most or all of the incubation, while the male cares for the brood indirectly by feeding the female. However, detailed descriptions of this male investment during the incubation period are missing. Here, we quantitatively describe female nest attendance and male incubation feeding throughout the ~ 14‐day incubation period in a population of Eurasian Blue Tits Cyanistes caeruleus breeding in nestboxes. Males and females progressively increased their daily activity at the nest over the incubation period. The amount of day‐time incubation, measured as the proportion of the active day (time interval between first nestbox exit in the morning and last entry in the evening) a female spent inside the nestbox, varied between 52 and 60% with an average of 55% per day. The frequency of male incubation feeding varied between 0 and 74 times per day with an average of 12 feeds per day. Both male feeding rate and female nest attendance were highest in the morning and declined rapidly throughout the day. Females were more likely to be off the nest during the warmest periods (15–21 °C), as expected based on thermal needs of the developing embryos, but also during the coldest periods (2–5 °C), presumably due to the energetic needs of the female. This was despite the fact that males fed their females more often at the nest when ambient temperatures were low. Females that received more feeds incubated more and their off‐nest bouts were shorter after a feed. The observed variation in female incubation and in male feeding rate was not linked to individual age or to variation in measures of reproductive success. However, direct observations showed that in some pairs a substantial amount of feeding by males occurred outside the nestbox. This suggests that the true male investment might have been underestimated, here and in previous studies.

Correlates of complete brood failure in blue tits: could extra‐pair mating provide unexplored benefits to females?

Behavioural ecologists have for decades investigated the adaptive value of extra‐pair copulation (EPC) for females of socially monogamous species. Despite extensive effort testing for genetic benefits, there now seems to be a consensus that the so‐called ‘good genes’ effects are at most weak. In parallel the search for direct benefits has mostly focused on the period surrounding egg laying, thus neglecting potential correlates of EPC that might be expressed at later stages in the breeding cycle. Here we used Bayesian methods to analyse data collected over four years in a population of blue tits Cyanistes caeruleus, where no support was previously found for ‘good genes’ effects. We found that broods with mixed paternity experienced less brood failure at the nestling stage than broods with single paternity, and that females having experienced complete brood failure in their previous breeding attempt had higher rates of mixed paternity than either yearling or previously successful females. To better understand these observations we also explored relationships between extra‐pair mating, male and female phenotype, and local breeding density. We found that in almost all cases the sires of extra‐pair offspring were close neighbours, and that within those close neighbourhoods extra‐pair sires were older than other males not siring extra‐pair offspring. Also, females did not display consistent EPC status across years. Taken together our results suggest that multiple mating might be a flexible female behaviour influenced by previous breeding experience, and motivate further experimental tests of causal links between extra‐pair copulation and predation.

Current spring warming as a driver of selection on reproductive timing in a wild passerine.

Evolutionary adaptation as a response to climate change is expected for fitness-related traits affected by climate and exhibiting genetic variance. Although the relationship between warmer spring temperature and earlier timing of reproduction is well documented, quantifications and predictions of the impact of global warming on natural selection acting on phenology in wild populations remain rare. If global warming affects fitness in a similar way across individuals within a population, or if fitness consequences are independent of phenotypic variation in key-adaptive traits, then no evolutionary response is expected for these traits. Here, we quantified the selection pressures acting on laying date during a 24-year monitoring of blue tits in southern Mediterranean France, a hot spot of climate warming. We explored the temporal fluctuation in annual selection gradients and we determined its temperature-related drivers. We first investigated the month-specific warming since 1970 in our study site and tested its influence on selection pressures, using a model averaging approach. Then, we quantified the selection strength associated with temperature anomalies experienced by the blue tit population. We found that natural selection acting on laying date significantly fluctuated both in magnitude and in sign across years. After identifying a significant warming in spring and summer, we showed that warmer daily maximum temperatures in April were significantly associated with stronger selection pressures for reproductive timing. Our results indicated an increase in the strength of selection by 46% for every +1°C anomaly. Our results confirm the general assumption that recent climate change translates into strong selection favouring earlier breeders in passerine birds. Our findings also suggest that differences in fitness among individuals varying in their breeding phenology increase with climate warming. Such climate-driven influence on the strength of directional selection acting on laying date could favour an adaptive response in this trait, since it is heritable.

Colour change in a structural ornament is related to individual quality, parasites and mating patterns in the blue tit.

Carry-over effects refer to processes that occur in one season and influence fitness in the following. In birds, two costly activities, namely reproduction and moult, are restricted to a small time window, and sometimes overlap. Thus, colour in newly moulted feathers is likely to be affected by the costs of reproduction. Using models of bird vision we investigated male colour change in a free-living population of blue tits (Cyanistes caeruleus) in three sampling occasions: spring 1, winter and spring 2. We related crown, tail, breast and cheek feather colouration after the moult (winter) to the intensity of infections by blood parasites during reproduction (spring 1). In the following spring (spring 2), we explored mating patterns with respect to changes in feather colour (springs 1 vs. 2). Males that were less intensely infected by the malaria parasite Plasmodium while breeding showed purer white cheek feathers in winter, which may indicate higher feather quality. Increased brightness in the white cheek was associated with better body condition during reproduction. In the following season, males with brighter cheeks paired with females that had noticeably brighter cheek patches compared to the male's previous mate. These results suggest that the conditions experienced during reproduction are likely to affect moult and thus feather colouration, at least in the white patch. High quality individuals may allocate resources efficiently during reproduction increasing future reproductive success through variation in mating patterns. Carry-over effects from reproduction might extend not only to the non-breeding phase, but also to the following breeding season.

Difference in arrival date at the breeding site between former pair members predicts divorce in blue tits

Divorce occurs when both members of a breeding pair survive to the following year but then pair with other individuals instead of reuniting. Divorce is common in birds, but its frequency can vary widely both between and within species, or even between populations across years. Several explanations for divorce have been described, both adaptive and nonadaptive. Many studies have compared the breeding success of faithful and divorced individuals, but fewer have considered the process of divorce, i.e. the events that lead up to divorce. In this study, we used data from eight breeding seasons to investigate divorce in a population of blue tits, Cyanistes caeruleus, in southern Germany. To compare our results to previous work, we first describe the frequency of divorce and compare the breeding success of divorced and faithful pairs. We then use data from an RFID transponder-based system, where all visits of individuals to any nestbox in the study site are automatically recorded throughout the year, to compare the behaviour of pairs in the interbreeding period. We found that the probability of divorce was not affected by breeding success in Year X. However, divorce was predicted by the difference in arrival time to the study site between the members of Year X pairs. Furthermore, during the interbreeding period, compared to their divorced counterparts, members of faithful pairs had more interactions with one another than with other individuals of the opposite sex. In Year X + 1, faithful females started egg laying earlier, had somewhat larger clutches and produced slightly more fledglings, than females that had divorced. We propose that divorce in blue tits is a by-product of separation of the two pair members after the Year X breeding season, leading to asynchrony in the timing of settlement and pair formation in Year X + 1.

Personality‐related differences in response to habitat in Mediterranean blue tits

AbstractHabitat‐specific selection pressures have been widely recognized, but whether selection favours different personality types in different habitats has rarely been evaluated. This study aimed to test whether personality‐related differences in annual reproductive success differed between two populations of blue tits (Cyanistes caeruleus) occupying different Mediterranean habitats (oakwood and pinewood). We measured exploration and parental provisioning behaviours and used a path analysis to ask how the interplay between these two behavioural traits affected reproductive success in each of these two habitats. We found that blue tits breeding in the pinewood were slow‐exploring compared to blue tits breeding in the oakwood, suggesting the occurrence of personality‐related differences in settlement, or behavioural plasticity in response to habitat. Exploration behaviour and feeding rates were positively associated, suggesting that they affect each other or that there is an environmental factor affecting both traits simultaneously. Finally, fast explorers were favoured in the pinewood, while there was no selection acting on exploration behaviour in the oak habitat. These findings emphasize the importance of integrating habitat selection, plasticity and personality in the study of behavioural evolution.

Heterozygosity\u2013fitness correlations in blue tit nestlings (Cyanistis caeruleus) under contrasting rearing conditions

Understanding the relation between genetic variation and fitness remains a key question in evolutionary biology. Although heterozygosity has been reported to correlate with many fitness-related traits, the strength of the heterozygosity–fitness correlations (HFCs) is usually weak and it is still difficult to assess the generality of these associations in natural populations. It has been suggested that HFCs may become meaningful only under particular environmental conditions. Moreover, existing evidence suggests that HFCs may also differ between sexes. The aim of this study was to investigate correlations between heterozygosity in neutral markers (microsatellites) and fitness-related traits in a natural population of blue tits (Cyanistes caeruleus). Additionally, we tested whether sex and environmental conditions may influence the magnitude and direction of HFCs. We found a positive relationship between heterozygosity and body mass of 14 days post-hatching nestlings, but only among females. Our results suggest that the correlation between heterozygosity and nestling body mass observed among female offspring could be attributed to within-brood effects. We failed to find any evidence that environmental conditions as simulated by brood size manipulation affect HFCs.

Differences in the Breeding Success of Blue TitsCyanistes caeruleusbetween a Forest and an Urban Area: A Long-Term Study

Birds have specific habitat requirements during the breeding period. The Blue Tit Cyanistes caeruleus is a species evolutionarily associated with forest areas that prefers deciduous and mixed forests, whilst its breeding in urban areas is a relatively recent phenomenon. Long-term data (2002–2015) on reproductive performance (number of hatchlings, hatching success, number of fledglings and fledging success (fledging success as the number of fledglings in relation to the number of hatchlings)) were quantified for two Blue Tit populations in two, floristically and structurally contrasting areas (a mature deciduous forest and an urban parkland) in central Poland. The principal aim of this study is to see whether the habitat type, year or the food availability affect the breeding success of Blue Tits. Forest Blue Tits produced significantly more hatchlings (9.82 ± 2.64 (SD) in the forest vs.9.17 ± 2.16 in the parkland) and fledglings (9.18 ± 2.84 in the forest vs. 8.14 ± 2.68 in the parkland) than urban Blue Tits. The number of fledglings was positively correlated with the number of hatchlings in both study areas. Both forest and urban Blue Tits shared a similar hatching success (85.9 % in the parkland and 85.5 % in the forest), while the fledging success was significantly higher in the forest (83.4 % in the parkland and 86.1 % in the forest). The amount of caterpillar frassfall was also studied (caterpillars are the optimal food for nestlings) at both study areas and it suggested that caterpillars were more abundant in the forest than in the parkland (the maximum amount of frassfall, averaged 0.21 ± 0.11 g frass/m2/day in the urban parkland and 0.59 ± 0.50 g frass/m2/day in the forest in 2003–2015). In the forest area, the mean number of fledglings tended to be related to the amount of frassfall but in the parkland, this relation was non-significant. The long-term dynamics of fledging success in our study sites seems to be mutually independent. Thus low fledging success in the forest site does not mean similarly low fledging success in the urban parkland site and vice versa. We suggest that food availability is one of key drivers of differences in the tits breeding success between both studied habitats.

Multiple extreme climatic events strengthen selection for earlier breeding in a wild passerine.

Global climate warming results in an increase in mean temperatures and in the frequency of extreme climatic events (ECEs), which could both strongly impact ecosystems and populations. Most studies assessing the impact of global warming on ecosystems have focused on warming trends while neglecting ECEs. In particular, the effects of multiple ECEs on fitness, and their consequences for selection, are still missing. Here we explored the effects of daily extreme rainfalls, as well as the occurrence of extremely hot and cold days, on clutch size and laying date in a wild blue tit population (Cyanistes caeruleus) monitored over 25 years. During the nestling phase (8-15 days old), the number of fledglings in a brood was negatively correlated with extremely hot days. The presence of extremely hot days between days 8 and 15 was also associated with an increase in the strength of selection acting on laying date, independently of mean temperature trends during the same period: when 10% of broods in the population experienced this type of ECE, selection for earlier breeding increased by 39%. Our results represent a unique quantification of the impact of multiple ECEs on the fitness landscape and emphasize their role as climatic drivers of selection.This article is part of the themed issue 'Behavioural, ecological and evolutionary responses to extreme climatic events'.

Conserved G-matrices of morphological and life-history traits among continental and island blue tit populations.

The genetic variance-covariance matrix (G-matrix) summarizes the genetic architecture of multiple traits. It has a central role in the understanding of phenotypic divergence and the quantification of the evolutionary potential of populations. Laboratory experiments have shown that G-matrices can vary rapidly under divergent selective pressures. However, because of the demanding nature of G-matrix estimation and comparison in wild populations, the extent of its spatial variability remains largely unknown. In this study, we investigate spatial variation in G-matrices for morphological and life-history traits using long-term data sets from one continental and three island populations of blue tit (Cyanistes caeruleus) that have experienced contrasting population history and selective environment. We found no evidence for differences in G-matrices among populations. Interestingly, the phenotypic variance-covariance matrices (P) were divergent across populations, suggesting that using P as a substitute for G may be inadequate. These analyses also provide the first evidence in wild populations for additive genetic variation in the incubation period (that is, the period between last egg laid and hatching) in all four populations. Altogether, our results suggest that G-matrices may be stable across populations inhabiting contrasted environments, therefore challenging the results of previous simulation studies and laboratory experiments.

Selection on parental performance opposes selection for larger body mass in a wild population of blue tits.

There is abundant evidence in many taxa for positive directional selection on body size, and yet little evidence for microevolutionary change. In many species, variation in body size is partly determined by the actions of parents, so a proposed explanation for stasis is the presence of a negative genetic correlation between direct and parental effects. Consequently, selecting genes for increased body size would result in a correlated decline in parental effects, reducing body size in the following generation. We show that these arguments implicitly assume that parental care is cost free, and that including a cost alters the predicted genetic architectures needed to explain stasis. Using a large cross-fostered population of blue tits, we estimate direct selection on parental effects for body mass, and show it is negative. Negative selection is consistent with a cost to parental care, mainly acting through a reduction in current fecundity rather than survival. Under these conditions, evolutionary stasis is possible for moderately negative genetic correlations between direct and parental effects. This is in contrast to the implausibly extreme correlations needed when care is assumed to be cost-free. Thus, we highlight the importance of accounting correctly for complete selection acting on traits across generations.

Environmental heterogeneity and population differences in blue tits personality traits.

Environmental heterogeneity can result in spatial variation in selection pressures that can produce local adaptations. The pace-of-life syndrome hypothesis predicts that habitat-specific selective pressures will favor the coevolution of personality, physiological, and life-history phenotypes. Few studies so far have compared these traits simultaneously across different ecological conditions. In this study, we compared 3 personality traits (handling aggression, exploration speed in a novel environment, and nest defense behavior) and 1 physiological trait (heart rate during manual restraint) across 3 Corsican blue tit (Cyanistes caeruleus) populations. These populations are located in contrasting habitats (evergreen vs. deciduous) and are situated in 2 different valleys 25 km apart. Birds from these populations are known to differ in life-history characteristics, with birds from the evergreen habitat displaying a slow pace-of-life, and birds from the deciduous habitat a comparatively faster pace-of-life. We expected personality to differ across populations, in line with the differences in pace-of-life documented for life-history traits. As expected, we found behavioral differences among populations. Despite considerable temporal variation, birds exhibited lower handling aggression in the evergreen populations. Exploration speed and male heart rate also differed across populations, although our results for exploration speed were more consistent with a phenotypic difference between the 2 valleys than between habitats. There were no clear differences in nest defense intensity among populations. Our study emphasizes the role of environmental heterogeneity in shaping population divergence in personality traits at a small spatial scale.

Hatching asynchrony vs. foraging efficiency: the response to food availability in specialist vs. generalist tit species.

Breeding mistiming is increasingly frequent in several ecosystems in the face of current climate change. Species belonging to higher trophic levels must employ mechanisms to reduce it. One of these mechanisms is hatching asynchrony, with the eggs in a clutch hatching over a period of several days. Some authors have suggested it to be adaptive when food is unpredictable. However, these birds can also suffer associated costs. We tested whether a species with higher foraging efficiency avoid hatching asynchrony compared to its sister species. We studied hatching asynchrony and nestling provisioning in relation to food availability in sympatric populations of blue and great tits. For the first time, we show that sister species respond to food availability with different strategies. Blue tit feeding rates readily responded to the abundance of their main prey, and also reduced the impact of nestling size hierarchy on mean nestling weight, consequently increasing fledging rate. Our results suggest that levels of hatching asynchrony seem to be influenced by species-specific life history traits, as generalist foragers rely less on it. They also highlight the importance of multi-species approaches when studying the response of organisms to environmental unpredictability.

The strength of the association between heterozygosity and probability of interannual local recruitment increases with environmental harshness in blue tits.

The extent of inbreeding depression and the magnitude of heterozygosity–fitness correlations (HFC) have been suggested to depend on the environmental context in which they are assayed, but little evidence is available for wild populations. We combine extensive molecular and capture–mark–recapture data from a blue tit (Cyanistes caeruleus) population to (1) analyze the relationship between heterozygosity and probability of interannual adult local recruitment and (2) test whether environmental stress imposed by physiologically suboptimal temperatures and rainfall influence the magnitude of HFC. To address these questions, we used two different arrays of microsatellite markers: 14 loci classified as neutral and 12 loci classified as putatively functional. We found significant relationships between heterozygosity and probability of interannual local recruitment that were most likely explained by variation in genomewide heterozygosity. The strength of the association between heterozygosity and probability of interannual local recruitment was positively associated with annual accumulated precipitation. Annual mean heterozygosity increased over time, which may have resulted from an overall positive selection on heterozygosity over the course of the study period. Finally, neutral and putatively functional loci showed similar trends, but the former had stronger effect sizes and seemed to better reflect genomewide heterozygosity. Overall, our results show that HFC can be context dependent, emphasizing the need to consider the role of environmental heterogeneity as a key factor when exploring the consequences of individual genetic diversity on fitness in natural populations.

Energy Reserves, Information Need and a Pinch of Personality Determine Decision-Making on Route in Partially Migratory Blue Tits

In facultative partial migrants some individuals in a population are migratory and others are resident and individuals decide each year anew which strategy to choose. While the proportion of birds migrating is in part determined by environmental conditions and competitive abilities, the timing of individual departure and behaviours on route are little understood. Individuals encounter different environmental conditions when migrating earlier or later. Based on cost/ benefit considerations we tested whether behaviours on route were affected by time constraints, personality and/or age in a partially migrating population of Blue tits (Cyanistes caeruleus). We captured female Blue tits on migration at the Southern tip of Sweden during early, peak and late migration and measured latency to feed in an unfamiliar environment, exploration of a novel object and hesitation to feed beside a novel object (neophobia). Lean birds and birds with long wings started feeding earlier when released into the cage indicating that foraging decisions were mainly determined by energetic needs (lean and large birds). However, juveniles commenced feeding later with progression of the migratory season in concordance with predictions about personality effects. Furthermore, lean birds started to explore earlier than birds with larger fat reserves again indicating an effect of maintaining threshold energy reserves. Moreover, late migrating juveniles, started to explore earlier than early migrating juveniles possibly due to time constraints to find high-quality foraging patches or a suitable winter home. Finally, neophobia did not change over the migratory season indicating that this behaviour is not compromised by time constraints. The results overall indicate that decisions on route are mainly governed by energetic requirements and current needs to learn about the environment and only to a small extent by differences in personality.

Courtship Calls in Blue TitsCyanistes caeruleus: Daily and Seasonal Occurrence and Link to Paternity

Many bird species use specific vocalizations in the context of courtship or (attempted) copulations. These vocalizations can be used to gain information about the courtship behaviour of individuals, even when courtship or copulation behaviour itself is difficult to observe. We recorded courtship vocalizations of Blue Tits Cyanistes caeruleus during three breeding seasons. In 2014, we recorded courtship calls at 14 locations spread out over a 40 ha forest containing a nestbox-breeding population of Blue Tits. Courtship calls occurred throughout the breeding season, but were most common in the period just before and during egg-laying. The rate of courtship calling showed a clear daily peak around dawn. In 2012 and 2013, we recorded courtship calls during the fertile period of the male's social mate. We monitored the presence of the female inside the nestbox and describe the occurrence of courtship calls that are apparently not directed to the social mate. The rate of these potential extrapair courtships correlated positively with a male's extra-pair paternity gain in 2012, but not in 2013. Extra-pair courtship call rate did not relate to paternity loss in the male's own brood.

Relationship between Blood Haemoglobin and Glucose Concentrations in Adult Great Tits (Parus Major) and Blue Tits (Cyanistes Caeruleus)

Haematological and blood chemistry variables are widely used in ecophysiological research as physiological indices of body condition in various vertebrate taxa. In this study, we analysed relationships between blood glucose and blood haemoglobin concentrations of adult birds in wild populations of Blue Tits ( Cyanistes caeruleus) and Great Tits ( Parus major) during the breeding season in central Poland. We found that blood glucose and blood haemoglobin concentrations are negatively correlated. We also show that individual Blue Tits have higher mean haemoglobin levels adjusted for the common value of glucose concentration than individual Great Tits and that females of both species have higher mean haemoglobin concentrations than males. Our results suggest that haematological as well as biochemical variables may be used in tune as complementary indices of body condition in wild bird populations.