Brain size,head size and behaviour of a passerine bird

A recent increase in comparative studies of the ecological and evolutionary consequences of brain size in birds and primates in particular have suggested that cognitive abilities constitute a central link. Surprisingly, there are hardly any intraspecific studies investigating how individuals differing in brain size behave, how such individuals are distributed and how brain size is related to life history and fitness components. Brain mass of the barn swallow Hirundo rustica was strongly predicted by external head volume, explaining 99.5% of the variance, allowing for repeatable estimates of head volume as a reflection of brain size. Repeatability of head volume within and between years was high, suggesting that measurement errors were small. In a 2 years study of 501 individual adult barn swallows, I showed that head volume differed between sexes and age classes, with yearlings having smaller and more variable heads than older individuals, and females having smaller and more variable heads than males. Large head volume was not a consequence of large body size, which was a poor predictor of head volume. Birds with large heads arrived early from spring migration, independent of sex and age, indicating that migratory performance may have an important cognitive component. Head volume significantly predicted capture date and recapture probability, suggesting that head volume is related to learning ability, although morphological traits such as wing length, aspect ratio and wing area were unimportant predictors. Intensity of defence of offspring increased with head volume in females, but not in males. Barn swallows with large heads aggregated in large colonies, suggesting that individuals with large heads were more common in socially complex environments. These results suggest that brain size is currently under natural and sexual selection, and that micro‐evolutionary processes affecting brain size can be studied under field conditions.     

Context-dependent vocal mimicry in a passerine bird

How do birds select the sounds they mimic, and in what contexts do they use vocal mimicry? Some birds show a preference for mimicking other species' alarm notes, especially in situations when they appear to be alarmed. Yet no study has demonstrated that birds change the call types they mimic with changing contexts. We found that greater racket-tailed drongos (Dicrurus paradiseus) in the rainforest of Sri Lanka mimic the calls of predators and the alarm-associated calls of other species more often than would be expected from the frequency of these sounds in the acoustic environment. Drongos include this alarm-associated mimicry in their own alarm vocalizations, while incorporating other species' songs and contact calls in their own songs. Drongos show an additional level of context specificity by mimicking other species' ground predator-specific call types when mobbing. We suggest that drongos learn other species' calls and their contexts while interacting with these species in mixed flocks. The drongos' behaviour demonstrates that alarm-associated calls can have learned components, and that birds can learn the appropriate usage of calls that encode different types of information.     

Functional infertility in a wild passerine bird

Information about male infertility in free‐living bird populations and its underlying causes are poorly documented in the literature. Here, we assessed sperm quality and infertility among males in a wild population of Blue Tits Cyanistes caeruleus, a socially monogamous passerine with frequent extra‐pair mating. One of 30 males (3.3%) studied across two breeding seasons had morphologically abnormal and nearly immotile spermatozoa in combination with zero annual fertilization success. Demonstration of male functional infertility suggests the possibility that socially monogamous females of the study population could obtain a direct fitness benefit by mating polyandrously to increase fertilization success, which could contribute to selection on extra‐pair mating behaviour.     

Contrasting effects of climate on juvenile body size in a Southern Hemisphere passerine bird

Despite extensive research on the topic, it has been difficult to reach general conclusions as to the effects of climate change on morphology in wild animals: in particular, the effects of warming temperatures have been associated with increases, decreases or stasis in body size in different populations. Here, we use a fine‐scale analysis of associations between weather and offspring body size in a long‐term study of a wild passerine bird, the cooperatively breeding superb fairy‐wren, in south‐eastern Australia to show that such variation in the direction of associations occurs even within a population. Over the past 26 years, our study population has experienced increased temperatures, increased frequency of heatwaves and reduced rainfall – but the mean body mass of chicks has not changed. Despite the apparent stasis, mass was associated with weather across the previous year, but in multiple counteracting ways. Firstly, (i) chick mass was negatively associated with extremely recent heatwaves, but there also positive associations with (ii) higher maximum temperatures and (iii) higher rainfall, both occurring in a period prior to and during the nesting period, and finally (iv) a longer‐term negative association with higher maximum temperatures following the previous breeding season. Our results illustrate how a morphological trait may be affected by both short‐ and long‐term effects of the same weather variable at multiple times of the year and that these effects may act in different directions. We also show that climate within the relevant time windows may not be changing in the same way, such that overall long‐term temporal trends in body size may be minimal. Such complexity means that analytical approaches that search for a single ‘best’ window for one particular weather variable may miss other relevant information, and is also likely to make analyses of phenotypic plasticity and prediction of longer‐term population dynamics difficult.     

Male territorial aggression does not drive conformity to local vocal culture in a passerine bird

In many songbird species, young individuals learn songs from neighbors and then settle nearby, thus creating neighborhoods of conformity to local vocal culture. In some species, individuals appear to postpone song learning until after dispersal, possibly to facilitate conformity to local dialects. Despite decades of study, we still lack a consensus regarding the selective pressures driving this delayed song learning. Two common hypothetical benefits to conformity, and thus delayed song learning, are rooted in territorial interactions; individuals preferentially produce local song either to avoid detection as new arrivals (deceptive mimicry) or to be more effectively recognized as conspecific territory holders. The dickcissel (Spiza americana) is an ideal species in which to study these hypotheses. Males of this species appear to delay song learning until they arrive at their first adult territory, each individual sings a single song type, and conformity to the local song culture is high. Using playback, we contradicted both of the territorial hypotheses described above; male dickcissels did not respond differentially to local vs foreign song playback treatment. We are confident in this lack of difference because dickcissels clearly responded less strongly to a third treatment, neighbor song, than to the other two treatments, demonstrating sufficient power in our experimental design (and providing the first evidence of the dear‐enemy effect in dickcissels). Our results raise the question of why dickcissels respond equally aggressively to both local and foreign songs when other bird species often show reduced aggression toward foreign song. If reduced aggression to foreign song is not ubiquitous in species that achieve conformity through delayed learning, then selection from aggressive territorial interaction seems unlikely to be a general explanation for such delayed learning. Reduced aggression in response to foreign songs in other species may be due to reduced exposure to the stimulus of foreign song or to different cost‐benefit trade‐offs when responding to songs that deviate from the local average.     

Gamma-tubulin complexes: size does matter.

gamma-Tubulin is a conserved component of all microtubule-organizing centres and is required for these organelles to nucleate microtubule polymerization. However, the mechanism of nucleation is not known. In addition to its localization to organizing centres, a large pool of gamma-tubulin exists in the cytoplasm in a complex with other proteins. The size of the gamma-tubulin complex and number of associated proteins vary among organisms, and the functional significance of these differences is unknown. Recently, the nature of these gamma-tubulin complexes has been explored in different organisms, and this has led us closer to a molecular understanding of microtubule nucleation.     

Stopover strategies in passerine bird migration: a simulation study

Long-distance bird migration consists of a series of stopovers (for refuelling) and flights, with flights taking little time compared to stopovers. Therefore, it has been hypothesized that birds minimize the total time taken for migration through efficient stopover behaviour. Current optimality models for stopover include (1) the fixed expectation rule and (2) the global update rule. These rules maximize the speed of migration by determining the optimal departure fuel load for a given fuel deposition rate. We were interested in simple behavioural rules approaching the stopover behaviour of real birds and how these rules compare to the time minimizing models above with respect to the total time taken for migration. The simple strategies were to stay at a site (1) until a fixed fuel load was reached or (2) for a constant number of days. We simulated migration of small nocturnal passerine birds across an environment of continuously distributed but variable fuel deposition rates, and investigated the influence of different stopover strategies on the duration of migration. Staying for a constant number of days at each stopover site, irrespective of the fuel deposition rate, resulted in only slightly longer than minimum values for migration duration. Additionally, the constant stopover duration, e.g. 10 days, may change by a day or two (per stopover) without having a large effect on total migration duration. There is therefore a possibility that real birds may be close to optimal migration speed without the need for very complex behaviour. When assessing the sensitivity of migration duration to factors other than stopover duration, we found that flight costs, search and settling time, mean fuel deposition rate and the accuracy in the choice of flight direction were the factors with the largest influence. Our results suggest that migrating birds can approximate optimal stopover duration relatively easy with a simple rule, and that other factors, e.g. those above, are more relevant for travel time.     

Fecundity selection does not vary along a large geographical cline of trait means in a passerine bird

Local environmental and ecological conditions are commonly expected to result in local adaptation, although there are few examples of variation in phenotypic selection across continent‐wide spatial scales. We collected standardized data on selection with respect to the highly variable plumage coloration of pied flycatcher (Ficedula hypoleuca Pall.) males from 17 populations across the species' breeding range. The observed selection on multiple male coloration traits via the annual number of fledged young was generally relatively weak. The main aim of the present study, however, was to examine whether the current directional selection estimates are associated with distance to the sympatric area with the collared flycatcher (Ficedula albicollis Temminck), a sister species with which the pied flycatcher is showing character displacement. This pattern was expected because plumage traits in male pied flycatchers are changing with the distance to these areas of sympatry. However, we did not find such a pattern in current selection on coloration. There were no associations between current directional selection on ornamentation and latitude or longitude either. Interestingly, current selection on coloration traits was not associated with the observed mean plumage traits of the populations. Thus, there do not appear to be geographical gradients in current directional fecundity selection on male plumage ornamentation. The results of the present study do not support the idea that constant patterns in directional fecundity selection would play a major role in the maintenance of coloration among populations in this species. By contrast, the tendency for relatively weak mosaic‐like variation in selection among populations could reflect just a snapshot of temporally variable, potentially environment‐dependent, selection, as suggested by other studies in this system. Such fine‐grained variable selection coupled with gene flow could maintain extensive phenotypic variation across populations. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 808–827.     

Footedness predicts escape performance in a passerine bird

Behavioral lateralization, which is associated with the functional lateralization of the two brain hemispheres, commonly exists in animals and can provide an individual with benefits such as enhanced cognition and dual tasking. Lateral bias in limb use, as a type of behavioral lateralization, occur in many species, but the reasons for the coexistence of left‐ and right‐biased individuals in a population remain poorly understood. We examined the footedness of male yellow‐bellied tits (Pardaliparus venustulus) when they used feet to clamp mealworms against a perch, and tested its association with other fitness‐related behavioral traits (i.e., feeding efficiency, exploration tendency, and escape performance). We expected differently footed individuals to have respective advantages in these behaviors and thereby coexist (“respective advantage” hypothesis). We found their footedness repeatable, and there was no population‐level bias. While no associations of feeding efficiency and exploration tendency with footedness were detected, the right‐footed individuals were found to be harder to catch than the other individuals. Future studies need to investigate the reasons for the right‐footed individuals' superior escape performance. Moreover, the escape advantage for being right‐footed and the lack of population‐level bias in footedness in male yellow‐bellied tits suggest that the benefits related to left footedness also remain to be explored.     

Heritability of parental effort in a passerine bird

Abstract The study of the evolution of parental care is central to our understanding of social systems, sexual selection, and interindividual conflict, yet we know virtually nothing about the genetic architecture of parental care traits in natural populations. In this paper, we use data from a long term field study of a passerine bird, the long-tailed tit ( Aegithalos caudatus ), to examine the heritability of the rate at which parents feed offspring. This measure of effort is positively related to offspring survival, is repeatable within individuals, and does not appear to be confounded by environmental effects. Using both parent-offspring regression, and an animal model approach, with a pedigree derived from ringing data, we show that our measure of effort has a significant heritable component.     

Invasion success: does size really matter?

The recent paper by Roy et al . (2001) presents a compelling relationship between range limit shifts, climatic fluctuations, and body size for marine bivalves in the fossil record. However, their extension of body size as a correlate for contemporary marine bivalve introductions is problematic and requires further scrutiny. Unlike their analysis of the fossil assemblage, the approach used for contemporary invasions does not adequately control for dispersal mechanism (vector) or source region. First, their analysis included mariculture species, intentionally introduced because of their large size, creating a vector-specific bias. Second, successful invaders from multiple source regions (Northern Hemisphere) were compared with potential invaders from a single source region (north-eastern Pacific), leaving both source and vector as uncontrolled variables. We present an analysis of body size for bivalve introductions from a single vector and source region, indicating no correlation between body size and invasion success when eliminating intentional introduction, source region and transport vector as confounding factors.     

Genetic variation and bill size dimorphism in a passerine bird, the reed bunting Emberiza schoeniclus

In passerine birds morphological differentiation in bill size within species is not commonly observed. Bill size is usually associated with a trophic niche, and strong differences in it may reflect the process of genetic differentiation and, possibly, speciation. We used both mitochondrial DNA (mtDNA) and nuclear microsatellites to study genetic variation between two subspecies of reed bunting, Emberiza schoeniclus schoeniclus and E.s. intermedia , along their distributional boundary in western Europe. These two subspecies are characterized by a high dimorphism in bill size and, although breeding populations of the two subspecies are found very close to each other in northern Italy, apparently no interbreeding occurs. The observed morphological pattern between the two subspecies may be maintained by geographically varying selective forces or, alternatively, may be the result of a long geographical separation followed by a secondary contact. MtDNA sequences of cytochrome b and ND5 (515 bp) showed little variation and did not discriminate between the two subspecies, indicating a divergence time of less than 500 000 years. The analysis of four microsatellite loci suggested a clear, although weak, degree of genetic differentiation in the large- and small-billed populations, as indicated by F _ST and R _ST values and genetic distances. The correlation between bill size and genetic distance between populations remained significant after accounting for the geographical distances between sampling localities. Altogether, these results indicate a very recent genetic differentiation between the two bill morphs and suggest that a strong selection for large bills in the southern part of the breeding range is probably involved in maintaining the geographical differentiation of this species.     

Incubation temperature influences survival in a small passerine bird

In birds parental incubation behaviour is an important factor shaping the environmental conditions under which the embryos develop, and sub‐optimal incubation temperatures are known to negatively affect early growth and development. It is less well known if variation in incubation temperature can impose life‐long differences in individual performance and survival. In the present study we investigated the effects of incubation temperature on long‐term survival in a small passerine bird. Using our captive population of the zebra finch Taeniopygia guttata we artificially incubated eggs at three biologically relevant temperatures (35.9, 37.0 and 37.9°C) for two‐thirds of the incubation period and then monitored individual lifespan of the hatched chicks for two and a half years. We found that individuals from eggs incubated under the lowest temperature exhibited significantly lower long‐term survival compared to those which had been incubated at the highest temperature. Our results show that incubation temperature in birds, and thus parental incubation behaviour, play an important role in shaping the life‐history trajectories of offspring.     

Historical diversification of migration patterns in a passerine bird

Migratory strategies of birds require complex orientation mechanisms, morphological adaptations, and life-history adjustments. From an evolutionary perspective, it is important to know how fast this complex combination of traits can evolve. We analyzed mitochondrial control-region DNA sequences in 241 blackcaps (Sylvia atricapilla) from 12 populations with different migratory behaviors. The sample included sedentary populations in Europe and Atlantic archipelagos and migratory populations with different distances of migration, from regional to intercontinental migrations, and different heading directions (due to a migratory divide in central Europe). There was no genetic structure between migratory and sedentary populations, or among populations from different biogeographic areas (Atlantic islands, the Iberian Peninsula, or the continent), however we found evidence of a genetic structure when comparing populations located on either side of the migratory divide. These findings support an independent evolution of highly divergent migratory strategies in blackcaps, occurring after a postglacial colonization of the continent along western and eastern routes. Accordingly, mismatch-distribution analyses suggested an expansion of blackcaps from a very small population size, and time estimates dated such an expansion during the last postglacial period. However, the populations in Gibraltar, located in a putative Mediterranean refuge, appeared to be independent of these processes, showing evidence of restricted gene flow with other populations and demonstrating insignificant historical changes in effective population size. Our results show that the interruption of gene flow between migratory and sedentary populations is not necessary for the maintenance of such a polymorphism, and that even the most divergent migratory strategies of a bird species are susceptible to evolution in response to historical environmental changes.     

Antioxidant defenses predict long-term survival in a passerine bird

Background

Normal and pathological processes entail the production of oxidative substances that can damage biological molecules and harm physiological functions. Organisms have evolved complex mechanisms of antioxidant defense, and any imbalance between oxidative challenge and antioxidant protection can depress fitness components and accelerate senescence. While the role of oxidative stress in pathogenesis and aging has been studied intensively in humans and model animal species under laboratory conditions, there is a dearth of knowledge on its role in shaping life-histories of animals under natural selection regimes. Yet, given the pervasive nature and likely fitness consequences of oxidative damage, it can be expected that the need to secure efficient antioxidant protection is powerful in molding the evolutionary ecology of animals. Here, we test whether overall antioxidant defense varies with age and predicts long-term survival, using a wild population of a migratory passerine bird, the barn swallow (Hirundo rustica), as a model.

Methodology/Principal Findings

Plasma antioxidant capacity (AOC) of breeding individuals was measured using standard protocols and annual survival was monitored over five years (2006–2010) on a large sample of selection episodes. AOC did not covary with age in longitudinal analyses after discounting the effect of selection. AOC positively predicted annual survival independently of sex. Individuals were highly consistent in their relative levels of AOC, implying the existence of additive genetic variance and/or environmental (including early maternal) components consistently acting through their lives.

Conclusions

Using longitudinal data we showed that high levels of antioxidant protection positively predict long-term survival in a wild animal population. Present results are therefore novel in disclosing a role for antioxidant protection in determining survival under natural conditions, strongly demanding for more longitudinal eco-physiological studies of life-histories in relation to oxidative stress in wild populations.     

Immune challenge mediates vocal communication in a passerine bird: an experiment

Secondary sexual characters may have evolved in part to signalresistance to parasites. Avian song has been hypothesized tobe involved in this process, but the role of parasites in modulatingacoustic communication systems in birds remains largely unknown,owing to lack of experiments. We studied the relationship betweenparasitism, testosterone, song performance, and mating successin male collared flycatchers (Ficedula albicollis) by experimentallychallenging their immune system with a novel antigen. We predictedthat a challenge of the immune system would reduce song performance,and that this reduction would be conditional on the size ofa visual sexual signal, the forehead patch that was previouslyfound to reflect resistance. An antagonistic linkage betweentestosterone and immune function would predict that a challengeof the immune system should suppress testosterone level. Animmunological treatment by sheep red blood cells (SRBCs) triggereda decrease in body mass, testosterone level, and song rate,but other song traits were not significantly affected by theantigen challenge. Initial testosterone level was associatedwith forehead patch size and all song traits except song rate.SRBC injection caused stronger reduction in song rate amongmales with smaller forehead patches, and the change in songrate was also predictable by song features such as strophe complexityand length. We show that song rate and other song characteristicsmay be important cues in male-male competition and female choice.These results suggest that parasite-mediated sexual selectionhas contributed in shaping a complex acoustic communicationsystem in the collared flycatcher, and that testosterone mayplay an important role in this process. Parasitism may drivea multiple signaling mechanism involving acoustic and visualtraits with different signal function.     

Exploring the genetics of aging in a wild passerine bird

Senescence is the decline in survival and reproduction as an organism ages and is known to occur in collared flycatchers Ficedula albicollis. We consider annual fitness (the estimated genetic contribution that an individual makes to next year's gene pool) as a measure of age-specific fitness. We apply a restricted maximum likelihood linear mixed-model approach on 25 years of data on 3,844 male and 4,992 female collared flycatchers. Annual fitness had a significant additive genetic component (h2 of about 4%). Annual fitness declined at later ages in both sexes. Using a random regression animal model, we show that the observed age-related phenotypic changes in annual fitness were not present on the additive genetic level, contrary to predictions of genetic hypotheses of senescence. Our study suggests that patterns of aging in the wild need to be interpreted with caution in terms of underlying genetics because they may be largely determined by environmental processes.     

Experimental evidence for adaptive personalities in a wild passerine bird

Individuals of the same species differ consistently in risky actions. Such ‘animal personality’ variation is intriguing because behavioural flexibility is often assumed to be the norm. Recent theory predicts that between-individual differences in propensity to take risks should evolve if individuals differ in future fitness expectations: individuals with high long-term fitness expectations (i.e. that have much to lose) should behave consistently more cautious than individuals with lower expectations. Consequently, any manipulation of future fitness expectations should result in within-individual changes in risky behaviour in the direction predicted by this adaptive theory. We tested this prediction and confirmed experimentally that individuals indeed adjust their ‘exploration behaviour’, a proxy for risk-taking behaviour, to their future fitness expectations. We show for wild great tits (Parus major) that individuals with experimentally decreased survival probability become faster explorers (i.e. increase risk-taking behaviour) compared to individuals with increased survival probability. We also show, using quantitative genetics approaches, that non-genetic effects (i.e. permanent environment effects) underpin adaptive personality variation in this species. This study thereby confirms a key prediction of adaptive personality theory based on life-history trade-offs, and implies that selection may indeed favour the evolution of personalities in situations where individuals differ in future fitness expectations.