Sex-Specific Associations Between Nest Defence, Exploration and Breathing Rate in Breeding Pied Flycatchers

Are animal personality, body condition, physiology and structural size integrated? A comparison of species, populations and sexes, and the value of study replication

A major question in behavioural ecology is why behaviour, physiology and morphology are often integrated into syndromes. In great tits, Parus major, for example, explorative males are larger (vs. smaller) and leaner (vs. heavier) compared to less explorative individuals. Unfortunately, considerable debate exists on whether patterns found in specific studies are replicable. This debate calls for study replication among species, populations and sexes. We measured behavioural (exploration), physiological (breathing rate) and morphological traits (body mass, tarsus length, wing length, bill length) in two species (great vs. blue tits Cyanistes caeruleus), two populations (Forstenrieder Park vs. Starnberg) and two sexes (males vs. females). We then tested whether the same pattern of integration characterized all unique combinations of these three biological categories (hereafter called datasets). We used a multi-year repeated measures set-up to estimate among-individual trait correlation matrices for each dataset. We then used structural equation modelling to test for size-dependent behaviour and physiology, size-corrected (i.e. size-independent) behaviour-physiology correlations and size-corrected body mass-dependent behaviour and physiology. Finally, we used meta-analyses to test which structural paths were generally (vs. conditionally) supported (vs. unsupported). We found general and consistent support for size-dependent physiology and size-corrected body mass-dependent physiology across datasets: faster breathers were smaller but heavier for their size. Unexpectedly, condition-dependent behaviour was not supported: explorative birds were neither leaner, nor was this relationship heterogeneous across datasets. All other hypothesized patterns were dataset-specific: the covariance between size and behaviour, and between behaviour and physiology differed in sign between datasets, and both were, on average, not supported. This heterogeneity was not explained by any of our moderators: species, population or sex. The specific pattern of size- and condition-dependent physiology reported for a unique combination of species, population, and sex, thus generally predicted those in others. Patterns of size- or condition-dependent behaviour (i.e. 'personality'), or behaviour-physiology syndromes reported in specific datasets, by contrast, did not. These findings call for studies revealing the ecological background of this variation and highlight the value of study replication to help understand whether patterns of phenotypic integration reported in one study can be generalized.

When aggressiveness could be too risky: linking personality traits and predator response in superb fairy-wrens

Personality syndromes in animals may have adaptive benefits for survival. For example, while engaging in predator deterrence, reactive individuals tend to prioritise their own survival, while proactive individuals engage in riskier behaviours. Studies linking animal personality measured in captivity with individual fitness or behaviours in the wild are sparse, which is a gap in knowledge this study aims to address. We used playback experiments in superb fairy-wrens (Malurus cyaneus), a common Australian songbird with a cooperative breeding system, to assess whether three personality traits measured during short-term captivity correlated with behavioural responses in the wild to a perceived nest and adult predator, the grey currawong (Strepera versicolor). We used three standard measures of personality in birds: struggle responses to human handling (boldness), exploration during a novel environment test, and aggressiveness during a mirror presentation. Superb fairy-wrens showed a significantly stronger response to the predator playback than to the control (willie wagtail, Rhipidura leucophrys) playback, suggesting that they recognised the predator playback as a threat without any accompanying visual stimulus. Birds that attacked their mirror image during the mirror presentation and those that spent a moderate amount of time close to the mirror responded more strongly to predator playback (by approaching the speaker faster and closer, spending more time near the speaker, and being more likely to alarm call) compared to those with low aggressiveness or those that spent very short or long durations close to the mirror. Neither boldness nor exploration in the novel environment test predicted playback response. Our results align with a growing number of studies across species showing the importance of animal personalities as factors for fitness and survival.

Are behaviour and stress-related phenotypes in urban birds adaptive?

Urbanisation is a world-wide phenomenon converting natural habitats into new artificial ones. Environmental conditions associated with urbanisation represent great challenges for wildlife. Behaviour and stress tolerance are considered of major importance in the adaptation to novel urban habitats and numerous studies already reported behavioural and stress response phenotypes associated with urbanisation, often suggesting they represented adaptations, while rarely demonstrating it. The main goal of this study was to test the adaptive nature of urban shifts in behavioural and stress-related traits, and by adaptive we mean phenotypic change favouring traits in the same direction as selection. Using 7 years of monitoring of urban and forest great tits, we first tested for differences in exploratory behaviour, aggressiveness and breath rate, between both habitats. Second, we performed habitat-specific analyses of selection on the three former traits using (a) reproductive success and (b) survival estimated via capture-mark-recapture models, as fitness estimates, to determine whether shifts in these behavioural and stress-related traits were aligned with patterns of ongoing selection. We found that urban birds displayed higher exploratory behaviour and aggressiveness, and higher breath rate, compared to forest birds. Selection analyses overall revealed that these shifts were not adaptive and could even be maladaptive. In particular, higher handling aggression and higher breath rate in urban birds was associated with lower fitness. Higher exploration scores were correlated with lower survival in both habitats, but higher reproductive success only in forest males. Overall, differences in patterns of selection between habitats were not consistent with the phenotypic divergence observed. Taken together, these results highlight that phenotypic shifts observed in cities do not necessarily result from new selection pressures and could be maladaptive. We hypothesise that divergences in behavioural traits for urban birds could result from the filtering of individuals settling in cities. We thus encourage urban evolutionary scientists to further explore the adaptive potential of behavioural traits measured in urban habitats (a) by replicating this type of study in multiple cities and species, (b) by implementing studies focusing on immigrant phenotypes and (c) by measuring selection at multiple life stages.

A meta-analysis of sex differences in animal personality: no evidence for the greater male variability hypothesis

The notion that men are more variable than women has become embedded into scientific thinking. For mental traits like personality, greater male variability has been partly attributed to biology, underpinned by claims that there is generally greater variation among males than females in non-human animals due to stronger sexual selection on males. However, evidence for greater male variability is limited to morphological traits, and there is little information regarding sex differences in personality-like behaviours for non-human animals. Here, we meta-analysed sex differences in means and variances for over 2100 effects (204 studies) from 220 species (covering five broad taxonomic groups) across five personality traits: boldness, aggression, activity, sociality and exploration. We also tested if sexual size dimorphism, a proxy for sex-specific sexual selection, explains variation in the magnitude of sex differences in personality. We found no significant differences in personality between the sexes. In addition, sexual size dimorphism did not explain variation in the magnitude of the observed sex differences in the mean or variance in personality for any taxonomic group. In sum, we find no evidence for widespread sex differences in variability in non-human animal personality.

Are cognition and personality related in budgerigars?

In recent years, researchers have been attempting to relate differences in personality (e.g., boldness, aggressiveness, exploration tendency) to variation in cognition (performances in tasks that require learning, reasoning, attention, or memory, etc.) both theoretically and empirically. However, it is unclear on what basis personality and cognition might be associated with each other. Previous theory suggests a connection between fast–slow personality types and cognitive speed–accuracy tradeoffs. In this study, we tested this hypothesis in budgerigars and found that, in their 1st associative learning, birds with fast personality (less fearful of handling stress) were fast learners in the beginning, while slow personality individuals improved faster, but both types of birds did not differ in accuracy. However, these relationships were context-dependent. No significant relationship was found in subsequent learning tasks (reversal learning and a 2nd associative learning) in the familiar context (task setup and apparatus similar to the 1st associative learning). We then conducted a problem-solving experiment with novel setup and apparatus to test 1 possible explanation that the association between personality and cognition in the 1st associative learning might be caused by noncognitive constraint, such as fearfulness when facing novel task setup and apparatus. We found that fast individuals interacted more with the problem box and solved it, whereas the slow birds were not. We suggest that personalities can influence cognitive performances and trigger a cognitive speed-improvement tradeoff under the novel context. However, there are no consistent cognitive styles that co-varied with different personalities.

Host personality predicts cuckoo egg rejection in Daurian redstarts Phoenicurus auroreus

In species that are subject to brood parasitism, individuals often vary in their responses to parasitic eggs, with some rejecting the eggs while others do not. While some factors, such as host age (breeding experience), the degree of egg matching and the level of perceived risk of brood parasitism have been shown to influence host decisions, much of the variation remains unexplained. The host personality hypothesis suggests that personality traits of the host influence its response to parasitic eggs, but few studies have tested this. We investigated the relationship between two personality traits (exploration and neophobia) and a physiological trait (breathing rate) of the host, and egg-rejection behaviour in a population of Daurian redstarts Phoenicurus auroreus in northeast China. We first show that exploratory behaviour and the response to a novel object are repeatable for individual females and strongly covary, indicating distinct personality types. We then show that fast-exploring and less neophobic hosts were more likely to reject parasitic eggs than slow-exploring and more neophobic hosts. Variation in breathing rate-a measure of the stress-response-did not affect rejection behaviour. Our results demonstrate that host personality, along the bold-shy continuum, predicts the responses to parasitic eggs in Daurian redstarts, with bold hosts being more likely to reject parasitic eggs.

You're Just My Type: Mate Choice and Behavioral Types

Consistent individual differences in behavior [i.e., behavioral types (BTs)], are common across the animal kingdom. Consistency can make behavior an adaptive trait for mate choice decisions. Here, we present a conceptual framework to explain how and why females might evaluate a male's BT before mating. Because BTs are consistent across time or context, a male's BT can be a reliable indicator of his potential to provide direct benefits. Heritable BTs can enable informed mate choice via indirect benefits. Many key issues regarding patterns of mate choice, including sensory biases, context dependence, and assortative mating apply to BT-dependent mate choice. Understanding the relationship between BTs and mate choice may offer insights into patterns of variation and consistency common in behavioral traits.

Stability of a behavioural syndrome vs. plasticity in individual behaviours over the breeding cycle: Ultimate and proximate explanations

Animals often show correlated suites of consistent behavioural traits, i.e., personality or behavioural syndromes. Does this conflict with potential phenotypic plasticity which should be adaptive for animals facing various contexts and situations? This fundamental question has been tested predominantly in studies which were done in non-breeding contexts and under laboratory conditions. Therefore, in the present study we examined the temporal stability of behavioural correlations in a breeding context and under natural conditions. We found that in the great reed warbler (Acrocephalus arundinaceus) females, the intensity of their nest defence formed a behavioural syndrome with two other traits: their aggression during handling (self-defence) and stress responses during handling (breath rate). This syndrome was stable across the nesting cycle: each of the three behavioural traits was highly statistically repeatable between egg and nestling stages and the traits were strongly correlated with each other during both the egg stage and the nestling stage. Despite this consistency (i.e., rank order between stages) the individual behaviours changed their absolute values significantly during the same period. This shows that stable behavioural syndromes might be based on behaviours that are themselves unstable. Thus, syndromes do not inevitably constrain phenotypic plasticity. We suggest that the observed behavioural syndrome is the product of interactions between behavioural and life history trade-offs and that crucial proximate mechanisms for the plasticity and correlations between individual behaviours are hormonally-regulated.

Consistent individual and sex-specific differences in behaviour of common cuckoo chicks: is there a potential impact on host-parasite coevolutionary dynamics?

Research on brood parasitism has focused primarily on specific host anti-parasite behaviours and parasite counter-adaptations, and little is known about other aspects of their behaviours such as consistent behavioural differences between individuals. Therefore, we examined consistency in behaviour of nestlings of common cuckoos (Cuculus canorus) raised by great reed warblers (Acrocephalus arundinaceus). Cuckoo chicks showed high repeatability of both aggressive behaviour and breath rate, and both traits were strongly correlated with each other. This represents the first evidence for consistent differences in behaviour among avian brood parasites. Males were consistently more aggressive and less stressed than females. Nestlings of both sexes that hatched later in the season exhibited higher levels of aggression and lower stress responses than nestlings hatched earlier. This suggests that rearing conditions (e.g., food availability and quality) may modulate stress and aggressive phenotypes of brood parasites. We discuss potential effects of the observed patterns on host-parasite dynamics.

Effect of acute stressor on reproductive behavior differs between urban and rural birds

The life‐history trade‐off between self‐maintenance and reproduction posits that investment in one function decreases investment in the other. Manipulating the costs and benefits of functions involved in a trade‐off may alter this interaction. Here we ask whether investment in self‐maintenance during a stress response alters territorial behavior in wild Dark‐eyed Juncos and whether rural and urban birds, which are known to differ in the magnitude of the stress response (greater in rural), also differ in the degree to which stress reduces territorial behavior. In rural and urban habitats, we measured territorial behavior using song playback, followed by either an acute stressor (capture and collection of a blood sample) or a nonstressful control situation. The following day, we again measured territorial behavior, predicting greater reduction in territorial behavior in individuals exposed to the stressor but a lesser reduction in territorial behavior in the urban as compared to the rural environment. We further assessed individual and population differences in response to stressors by measuring flight initiation distance, breath rate, and corticosterone levels in the blood. The rural population had a higher physiological and behavioral stress response than the urban population, and acute capture stress had a lasting (24 h) negative effect on territorial behavior, but only in the rural habitat. However, individual‐level differences in measures of the stress response did not explain variation in the impact of stress on territorial behavior. Our findings show that stressors can have a negative effect on territorial behavior, but that this effect may differ between populations that vary in their stress ecology.