Individual variation (3rd International E-BIRD Workshop), Vancouver 17-18 March 2006

Abstracts are at end of meeting schedule (below)

Friday March 17th


09.00-09.45     Ben Sheldon - Evolutionary ecology of individual variation.


09.45-10.30     Tony Williams – The tyranny of the Golden Mean 20 (or more) years on: individual variation in physiological systems.


11.00–12.30    Session 1: Concepts, theory and technical issues


Wolfgang Forstmeier - Determinants of behavioural individuality: a framework for the evolution of proximate mechanisms.


Leonida Fusani - Variability of hormone-dependent traits: the linear correlation fallacy.


Karen Spencer - The role of developmental conditions in shaping individual phenotypes.


Mark Clark, Wendy Reed, and Ellen Ketterson - Individual-based modeling approaches: incorporating variation into population demography.


Julian Christians – QTL approaches and individual variation.


14.00–15.30    Session 2: Individual variation and reproduction


Marcel Eens - Honesty of bird song: endocrine and neural correlates of singing behavior in songbirds.


Marcel E. Visser - Individual variation in laying date in the great tit: genetic variation in reaction norms.


Patrice Bourgault and Don Thomas - Between-population differences in the fitness consequences of individual-based variation in egg investment in Corsican blue tits (Parus caeruleus).


Camilla Hinde, Kate Buchanan, and Rebecca Kilner - What explains individual variation in canary nestling begging intensity?


Claudio Carere, Piet J. Drent, Jaap M. Koolhaas, Ton G.G. Groothuis - Food availability and sibling competition affect the development of personality traits in great tits (Parus major).


16.30-18.00     Session 3: Individual variation and the stress axis


Julio Blas, Gary Bortolotti and Tracy Marchant - Individual variation in adrenocortical response to stress in red-legged partridges.


Wada H., Breuner C.W., Salvante K., Wagner E., Curnillon M. and Williams T.D. - Too stressed to be sexy?: acute stress and its relation to reproductive quality.


Frances Bonier - Physiological mediation of condition-dependent sex ratio manipulation: are corticosteroids the missing link?


Mike Clinchy et al. - Environmental quality, physiological stress and female mating strategies in song sparrows.


Creagh W. Breuner and Rachel S. Sprague - Reduction in CBG capacity during acute stress: using individual variability to explore competing hypotheses.


Saturday March 18th


09.00-09.45     Gregory F. Ball - Individual variation and the endocrine regulation of behavior and physiology from a cellular/molecular perspective.


09.45-10.30     Bart Kempenaers - Individuality in behaviour, hormones and genes


11.00-12.30     Session 4: Individual variation in other systems


Blandine Doligez - Maternal yolk androgens and natal dispersal in passerine birds: insights on between-individual and between-family variation.


Joel McGlothlin - Short-term testosterone increases in dark-eyed juncos: individual variation and relationships with morphology and behavior.


Maud Poisbleu - Hormonal correlates of social dominance status in Anatids.


Anthony J. Porter and Sharon E. Lynn - Individual variation or trapping technique? Trapping initiates stress response in nonbreeding house sparrows.

Kees van Oers  - Avian personalities: genes and environment.


14.00-15.00     Session 5: Individual variation in a life-history context


Kathryn E. Arnold - Does early nutrition affect behavioural responses to novel situations?


Oliver P. Love, Katrina G. Salvante, James Dale and Tony D. Williams - Individual and sex-specific variability of cell-mediated immunity across life-history stages.


David W. Winkler - The ecology and organismal biology of individual variation in Ithaca Tree Swallows.


15.45–18.00    General discussion and synthesis (Ellen Ketterson, Michael Romero)




Evolutionary ecology of individual variation. Ben Sheldon, Edward Grey Institute, Department of Zoology, University of Oxford (


A central aim of evolutionary ecology is to understand why individuals differ. Differences between individuals are the raw material on which natural selection acts to produce adaptations, and understanding the importance of the  various processes that potentially contribute to variation among and between populations is key to understanding (1) why these populations have the characteristics that they do, (2) why populations may differ from one another and (3) how they might change in the future. I will review the conceptual approaches used to understand variation in quantitative characters in wild populations, and illustrate their use with examples from studies of variation in the time of breeding among individual birds obtained from long-term studies of birds. I will discuss the extent to which these approaches can be applied to other traits, and argue that understanding variation in endocrinological mechanisms actually provides the potential for key insights into the reasons for variation at some of these levels of analysis.


The tyranny of the Golden Mean 20 (or more) years on: individual variation in physiological systems. Tony D Williams, Biological Sciences, Simon Fraser University, Burnaby, Canada (


Twenty years ago Al Bennett published a paper in the influential book “New Directions in Ecological Physiology” (1987) arguing that individual variation was an “underutilised resource”. Twenty years on I will describe how well we (physiologists/endocrinologists) have exploited this underutilised resource (or not!) and the extent to which the “tyranny of the Golden Mean” still holds sway. I will then discuss some methodological, experimental and analytical issues relating to use of individual variability. Using examples from the physiological literature I will discuss what we know about repeatability and heritability of physiological traits – as we measure them - and what we know about how individual variability in physiology relates to performance and fitness. A key question throughout the talk will be the extent to which systematic relationships between physiology, performance and fitness that are evident at the interspecies level can also be detected at the inter-individual or intraspecific level. If they can not then what are the implications for our understanding of how selection on individual variability generates inter-specific differences?


Session 1: Concepts, theory and technical issues


Determinants of behavioural individuality: a framework for the evolution of proximate mechanisms. Wolfgang Forstmeier, Max Planck Institute for Ornithology, Germany (


Quantitative genetic analyses can help us identify the proximate causes underlying lifelong persisting individual differences in behaviour (personality differences). Behavioural polymorphism may result from genetic polymorphism, maternal programming, or from effects of the early rearing environment such as sexual imprinting or niche selection within peer groups. Using the example of lifelong lasting individual differences in sex drive of male zebra finches, which are closely mirrored by plasma testosterone levels, I demonstrate the usefulness of an experimental quantitative genetic approach to identify the key factors in creating individuality. I then ask which proximate mechanism is most likely to evolve under which environmental conditions and under which developmental constraints. I predict that increasing costs of behavioural flexibility, i.e. when specialists out-compete generalists, will favour genetic polymorphism or maternal programming, while decreasing predictability of the social environment will favour sexual imprinting or niche choice during puberty.


Variability of hormone-dependent traits: the linear correlation fallacy. Leonida Fusani, Department of Physiology, University of Siena, Italy (


Most studies on hormones and behaviour focus on the same old question: does the behaviour ‘depend’ on the hormone? The answer is influenced by a number of critical factors, such as the modalities of the hormonal treatment and the type of control used. Nevertheless, methods developed and validated by behavioural endocrinologists in controlled laboratory conditions are often modified for field experiments without analysing the implications these modifications may have for the interpretation of the results. This highlights the necessity of developing new methods to study evolutionary aspects of hormone-behaviour interactions. Here I will discuss some of critical points raised by the current developments in behavioural endocrinology using examples from my own work and from other studies. First, I will show how the meaning of the term ‘hormone-dependent’ changes between experimental contexts and why we need to understand the nature of the relationships between the hormone and the behaviour. Secondly, I will review the problems relative to experiments involving hormonal manipulation, and the pro and contra of different approaches.  Finally, I will discuss the conclusions that can be drawn by these experiments and the theoretical limitations of the currently used approaches.


The role of developmental conditions in shaping individual phenotypes. Karen Spencer, School of Biological Sciences, University of Liverpool, UK, (

The potential influence of environmental conditions experienced during development on adult phenotypes has recently developed as an important research focus. Whilst much empirical work has been directed at the effects of variation in nutrient supply, another important hormonal axis linking early conditions to the adult phenotype is that mediated via environmentally induced stress. Here I report data from experiments where nestling zebra finches (Taeniopygia guttata) were exposed to exogenous corticosterone via oral administration for a 10 or 25 day period. Experimental administration of corticosterone significantly depressed growth rates in both male and female birds. Upon reaching sexual maturity previous exposure to corticosterone also resulted in reduced success in competitions for non-food based resources and reduced sexual signal quality. These results provide evidence that early life conditions are important in shaping adult phenotypes, significantly influencing several fitness-related traits. In addition they provide data on the possible long term origin of individual variation seen in many of these important life history traits.

Individual-based modeling approaches: incorporating variation into population demography. Mark Clark1, Wendy Reed1, and Ellen Ketterson2; 1 North Dakota State University, Fargo, ND, 2 Indiana University, Bloomington, IN (


Understanding physiological and behavioral mechanisms underlying the diversity of observed life-history strategies is challenging because of difficulties in obtaining measures of fitness and in relating fitness to these mechanisms.  One approach is to estimate fitness (population growth rate) by incorporating variation in physiological and behavioral traits among individuals into population models.  We used this approach to evaluate effects of experimentally elevated testosterone on male fitness in dark-eyed juncos and to evaluate the effects of juvenile survival on optimal clutch size in American coots.  This modeling approach provides a way to use information about individuals to evaluate life-histories.


Quantitative trait loci (QTL) approaches to understanding individual variation.  Julian K. Christians, Biological Sciences, Simon Fraser University, Canada (


Phenotypic variation among individuals is caused by both the environment and a potentially large number of genes.  In the past two decades an enormous amount of effort has been directed at detecting quantitative trait loci (QTL) in the hopes of identifying the genes responsible for quantitative variation.  QTL are naturally-occurring regions of the genome that contribute to continuous variation, rather than major mutations that cause serious abnormalities.  Many QTL mapping studies have focused on traits of medical importance in humans and model organisms and on economically-important traits in agricultural species.  However, a small number of studies have also mapped ‘ecologically important’ traits with spectacular success.  Assuming certain genetic resources (a linkage map of many molecular markers) and the ability to perform controlled crosses, it is potentially (relatively) easy to detect QTL.  However, these loci are actually large regions of chromosome that harbour hundreds of genes.  Refining the location of QTL to regions that contain only a few genes, and demonstrating that a particular gene is responsible for the phenotypic effects of a QTL is extremely difficult and expensive, even in model organisms.  Linkage maps have been developed for some avian species, and developing maps for new species will likely become more tractable, but identifying genes responsible for quantitative variation in natural avian populations will remain a daunting task for some time.


Session 2: Individual variation and reproduction


Honesty of bird song: endocrine and neural correlates of singing behavior in songbirds. Marcel Eens, University of Antwerp, Department of Biology, Universiteitsplein 1, B-2610 Wilrijk, Belgium (


Song is one of the most studied sexually selected characters. Individual variation in song characteristics has been shown to affect reproductive success through mate choice and male-male competition. A fundamental question regarding the evolution of sexually selected signals is how their honesty is maintained. I will discuss two kinds of potential costs that may limit the expression of song. First, in adult songbirds, the expression of male song appears to be under the regulation of gonadal steroids, primarily testosterone (T). Involvement of circulating T in the regulation of inter-male differences in song performance may possibly contribute to the maintenance of the honesty of male song performance because of the presumed costs that elevated plasma T levels entail (for instance immune costs). While the overall relationship between testosterone and singing is well established, very little is known about how individual variation in plasma testosterone is related to individual variation in song characteristics and results are often conflicting. Based on a meta-analysis of all available intraspecific studies, I show that performance-related song traits such as song rate correlate significantly with T, while this is not the case for other song traits. Second, I will discuss the neural cost of singing which has been highly debated recently. A meta-analytical study provides strong intraspecific evidence for repertoire size and song length being related to the volume of song control nuclei in the brain. The brain space required for having a complex song thus seems to be a key constraint in songbirds. Finally, I will present data that there also exists a large variation in song complexity and activity among female European starlings that appears to give honest information about their quality. I discuss whether similar costs as described above are present in females.


Individual variation in laying date in the great tit: genetic variation in reaction norms. Marcel E. Visser, Netherlands Institute of Ecology (NIOO-KNAW), P.O. Box 40, 6666 ZG Heteren, The Netherlands (


One of the hypotheses to explain variation in avian laying dates is that individuals differ in the way their timing of reproduction is affected by environmental variables. Some individuals may vary their laying date strongly with spring temperatures while others may be relatively insensitive. In other words, there may be within population variation in the reaction norm of laying date versus temperature.  We have shown in a Dutch great tit population that such variation in reaction norm indeed exists, that this variation is heritable and that, due to climate change, there is now selection for a steep reaction norm. We are now following up this finding with experiments in temperature and photoperiod controlled aviaries. We have brought in offspring from early and late pairs. The pairs are now kept under two temperature regimes to measure the onset and speed of gonadal growth and the laying date of these birds to determine how these ‘early’ and ‘late’ great tits differ.


Between-population differences in the fitness consequences of individual-based variation in egg investment in Corsican blue tits (Parus caeruleus). Patrice Bourgault and Don Thomas, Département de Biologie, Université de Sherbrooke, Sherbrooke, Canada, J1K 2R1.


This study focuses on the importance of individual variation in egg quality in free-ranging Corsican blue tits in heterogeneous habitats.  We show that the range of variation in egg size and yolk mass is high (ratio of the smallest to the highest mean yolk mass = 0.75), and that a large part of this variation is explained by inter-individual differences (repeatability > 0.6).  Given the potentially far-reaching consequences of variation in egg size and yolk mass on nestlings’ growth and development, especially for some Corsican populations breeding under harsh environmental conditions, it is surprising to note such a high degree of variability between females. However, few studies have unequivocally demonstrated that egg size affects offspring performance, although it is likely that the disadvantages of small eggs appear only under adverse breeding conditions.  Our study system offers this unique opportunity to compare the fitness consequences (nestlings’ growth pattern, fledging mass and survival) of variation in egg investment between populations facing contrasting habitat features.  One habitat (deciduous oak wood) offers an extremely high spring peak in caterpillar abundance, coupled with low infestation of ectoparasitic blow-fly larvae, which contrasts with the very low caterpillar abundance and high infestation rates of ectoparasites in the evergreen habitat at the time of hatching.  It is very likely that the potential negative effects of egg and yolk size variation on offspring fitness become apparent in this latter habitat.  This study thus aims at determining to what extent selection pressures on egg size may differ according to specific ecological context, and could therefore provide a new insight on the consequences of intra- and inter-individual phenotypic variation in egg quality in heterogeneous habitats.


What explains individual variation in canary nestling begging intensity? Camilla Hinde, Kate Buchanan, and Rebecca Kilner (


Previous work on canary eggs has shown that yolk testosterone (T) levels increase with each successive egg in the clutch, and that pre-natal exposure to these maternal hormones affects chick begging levels shortly after hatching. In addition, observations of older chicks found that later hatched nestlings, hatching from later laid eggs, beg more intensely than their older siblings. Our aims in this study were 1) to investigate the influence of nestling T on chick begging intensity and 2) to determine experimentally the extent to which individual variation in nestling begging intensity is determined pre-natally by mothers and post-natally by offspring. We muddled the hatch sequence of eggs in a clutch and measured nestling begging intensity and nestling T levels five and eight days after hatching to test the following predictions. If maternal hormones influence the development of the nestling endocrine system, and so affect begging intensity, we predicted that nestling T levels should be positively correlated with begging intensity after hatching and both should increase with egg number but not hatch rank. However, if nestlings can secondarily adjust T production after hatching in relation to their competitive environment, we predicted that nestling T and begging intensity should increase with hatch rank and may or may not vary with egg number as well. We will discuss individual variation in chick begging and testosterone levels, and the extent to which this is due to parental or environmental effects.


Food availability and sibling competition affect the development of personality traits in great tits (Parus major). Claudio Carere1,4, Piet J. Drent2, Jaap M. Koolhaas3, Ton G.G. Groothuis4; 1 Section of Behavioural Neurosciences, Dipartimento di Biologia cellulare e Neuroscienze, Istituto Superiore di Sanità, Rome; 2 Netherlands Institute of Ecology, Center for Terrestrial Ecology, Heteren, The Netherlands; 3 Department of Animal Physiology, University of Groningen, The Netherlands; 4 Department of Animal Behaviour, University of Groningen, The Netherlands (


Individual animals vary in the way they cope with challenges in their environment, comparable with variation in human personalities. This variation has a substantial genetic basis. Here we show the strength of environmental factors (food availability and sibling competition) in shaping avian personality traits. We manipulated the early rearing condition in two lines (F4) bidirectionally selected for different personalities (fast line: high exploration speed and high aggression; slow line: low exploration speed and low aggression) with a food rationing protocol inducing an impairment in growth rate and an enhancement in levels of offspring solicitation. Growth impairment was more marked in the slow line. In a first experiment each nest contained experimental and control siblings of the same line (within-nests design). Slow chicks became faster than their parents in the exploration tests regardless of the treatment, whereas fast chicks had scores similar to their parents and showed no treatment effect. As a consequence, the line difference in exploration behaviour of the offspring was not apparent in the juvenile phase. Six months later the offspring of the slow line was still relatively fast, but lines differed in exploration, since the fast line became even more fast. Food-rationed birds of the fast line were more aggressive than both controls and their fathers, while treatment did not affect the slow line. In a second experiment, carried out only in the slow line, each nest contained either control or experimental siblings (between-nests design). Now, only the food-rationed chicks became faster in exploration. We suggest that the shift in the controls in the within-nests design was due to enhanced sibling competition, forced by the experimental chick. Indeed, the control chicks in the first experiment begged more persistently and had higher exploration scores than the control chicks in the between-nests design. Environmental factors during ontogeny modulate the expression of phenotypic traits against the background of the reaction norm allowed by the genome even in selected lines of animals resulting in profound and reliable differences in behaviour.


Session 3: Individual variation and the stress axis


Individual variation in adrenocortical response to stress in red-legged partridges. Julio Blas, Gary Bortolotti and Tracy Marchant, Department of Biology, University of Saskatchewan (


We studied intra and inter-individual variation in the adrenocortical response to stress in red-legged partridges (Alectoris rufa). Twenty breeding birds were subjected to a standardized capture, handling and restraint protocol, and the concentration of circulating corticosterone (cort) was determined in blood samples taken at fixed times during the pre-laying and laying periods. Despite handling time having a very significant effect on plasma cort concentration it only explained 47% of the overall variability. A detailed analysis of stress-induced cort levels revealed that neither body condition index nor sex or calendar date affected cort titers. Acute (i.e. stress-induced) levels were lower during laying compared to pre-laying stages, and negatively correlated with the current number of eggs laid at the moment of sampling. Our results support the hypothesis that red-legged partridges down-regulate their adrenocortical response to stress as a function of their current reproductive investment.


Too stressed to be sexy?: acute stress and its relation to reproductive quality. Wada H. 1, Breuner C.W. 1, Salvante K. 2, Wagner E. 2, Curnillon M. 2, and Williams T.D. 2; 1 Integrative Biology, University of Texas at Austin and 2 Biological Sciences, Simon Fraser University (


Individual variation in stress response has been documented in both young and adult vertebrates in numerous studies.  However, there is an ongoing debate about what constitutes a ‘good stress response’.  Exploring the ties between the glucocorticoid secretion and fitness of individuals can help us understand the ‘good stress response’ in an evolutionary sense. Two main questions of this study are 1) does corticosterone response to stress correlate with reproductive quality in adulthood, and 2) is this response fixed during development, or plastic throughout life? Stress series were taken from both sexes of zebra finches (Taeniopygia guttata) at two ages; day 16 (~2 days before fledging) and again at 3 months of age (sexually mature adults), allowing us to determine the plasticity of the stress axis with age. Males were then subjected to courtship trials while females went through mating trials. Different aspects of individual’s reproductive quality (such as song, clutch size etc.) were then related to various parameters of the individual’s stress response. The data suggest a large individual variation in various aspects of stress response. However, it appears that there is no strong correlation between nestling and adult levels of corticosterone, indicating that the reactivity of the stress axis is plastic beyond the nestling period. We are currently analyzing data correlating corticosterone levels and reproductive qualities in these same individuals.


Physiological mediation of condition-dependent sex ratio manipulation: are corticosteroids the missing link? Frances Bonier, Dept. of Zoology, University of Washington.


Females are predicted to manipulate the sex ratio of their offspring when the fitness value of sons and daughters differ. In many systems, daughters, regardless of their condition, are more likely than sons to reproduce, whereas high quality sons can leave many more offspring than daughters but low quality sons may fail to reproduce at all. In systems where this is true, a female that can produce high quality offspring should produce more sons, whereas a female constrained to produce low quality offspring should produce more daughters. Variation in numerous factors, including mate quality, habitat quality, rainfall, dominance status, maternal condition, and maternal hormone levels, is associated with skewed offspring sex ratios. It is unclear, however, what mechanisms underlie sex ratio manipulation and which physiological cues indicate to a mother that she should manipulate her brood's sex ratio. Hormonal signals provide organisms with information about variation in individual and local environmental condition. Measures of baseline levels of corticosteroids correlate with indices of food abundance and quality, habitat quality, weather conditions, dominance status, and individual condition. Here I review experimental and empirical data linking corticosteroids to sex ratio manipulation. Given the coincidence between factors that affect sex ratio and factors that affect baseline corticosteroid levels, it seems plausible that corticosteroids could be the missing mechanistic link between conditions favoring sex ratio manipulation and the manipulation itself. Alternatively, baseline corticosteroid levels may simply be correlated with other indicators of condition and quality that are directly involved in adaptive sex ratio manipulation.


Environmental quality, physiological stress and female mating strategies in song sparrows. Elizabeth A. MacDougall-Shackleton, Michael Clinchy, Liana Zanette, Bryan D. Neff, John C. Wingfield and Rudy Boonstra.


Abstract: Ecological factors such as food availability and predator pressure that affect reproduction and survival likely also affect life-history traits such as mating strategies. We conducted a 2 x 2, manipulative food addition plus natural predator reduction experiment on song sparrows (Melospiza melodia) that demonstrated: interactive food and predator effects on egg production, nest survival and annual reproductive success; as well as food and predator effects on the stress physiology of parents. Here we report the effects on extrapair paternity (EPP). EPP was more frequent the more challenging (less food, more predators) the environment. Correspondingly, females producing extrapair offspring appeared more stressed since they had elevated total plasma corticosterone, significantly higher plasma glucose and elevated plasma free fatty acid levels, and were significantly more anaemic, than females producing only within-pair young. There were no significant physiological differences between males with full paternity and cuckolded males, nor were there significant differences in size or symmetry between extrapair and within-pair nestling brood-mates. Conceivably, females may be using extrapair mating to diversify their offspring and so hedge their bets in challenging circumstances. We suggest our results highlight the importance of understanding both the ecological and physiological context in which EPP occurs.


Reduction in CBG capacity during acute stress: using individual variability to explore competing hypotheses. Creagh W. Breuner and Rachel S. Sprague, Integrative Biology, University of Texas at Austin (


Within studies of acute stress physiology, increase in glucocorticoid secretion is thought to be the primary mediator of tissue response to stress.  Corticosteroid binding globulin may regulate tissue availability of steroid, but has not been considered a dynamic component of the acute stress response.  We examined CBG level over the common 60 minute time-frame of the acute capture and handling protocol, to investigate whether CBG capacity is dynamic or static over short stressors.  We measured CBG response to capture and handling stress in 9 species of birds, representing 5 orders and 9 families.  CBG capacity significantly declined within 30-60 minutes of capture in 5 of the 9 species examined.  This decline may serve to significantly increase the level of corticosterone reaching tissues during acute stress.  In light of these data, we took a strong inference approach in developing multiple, competing hypotheses which may explain the pattern of CBG decline seen across species.  Many of these hypotheses can be tested by looking at patterns of individual variation within a species.  We tested two of the hypotheses, reproductive value and body condition, within the long-lived Laysan Albatross.  The reproductive value hypothesis predicts that individuals with greater reproductive value (younger animals) should be more sensitive to stressors, favoring self-maintenance over reproductive output, and therefore show a greater decline in CBG during stress.  The body condition hypothesis posits that CBG decline will be greater in low condition birds, mobilizing a greater response when the focal animal has less endogenous reserves to deal with the stressor at hand.  The Albatross data provide support for the reproductive value hypothesis, but not the body condition hypothesis.


Individual variation and the endocrine regulation of behavior and physiology from a cellular/molecular perspective. Gregory F. Ball, Departments of Psychological and Brain Sciences, Neuroscience and Biochemistry and Molecular Biology, Johns Hopkins University, Baltimore, MD 21218 USA (


Scientists investigating cellular and molecular mechanisms of physiology and behavior have tended to avoid trying to explain individual differences.  The goal has rather been to discover general processes that are widely applicable to many species. However, understanding individual variation in many phenomena of interest to avian eco-physiologists will require a consideration of cellular and molecular mechanisms.  For example, changes in plasma concentrations of steroid hormones are important in the activation of social behaviors related to reproduction and aggression.  Attempts to explain individual and even population differences in these behaviors as a function of variation in plasma steroid hormone concentrations have generally failed.  A consideration of cellular variables related to the effectiveness of steroid hormone action such as concentrations of steroid binding proteins as well as the target sensitivity of different brain areas has been useful in some cases. Steroid hormone target sensitivity can be affected variables such as metabolizing enzyme activity, hormone receptor expression as well as receptor co-factor expression.  However, no general theory has emerged that might provide a guide for eco-physiologists when trying to explain individual variability.  Studies of variation in the response to environmental stimuli such as photoperiod have similarly failed to reveal a key set of variables to be considered though there are many candidates that will be discussed.  Two proposals will be made as useful ways to proceed when trying to establish the cellular and molecular basis of individual variation.  One will be to learn from studies of large units of intra-specific variation such as population differences and sex differences to provide ideas about variables that might be important in explaining individual variation.  The second will be to consider the use of molecular genetic approaches such as the identification of single nucleotide and repeat polymorphisms as a promising avenue for avian eco-physiologists to pursue given the molecular genetic tools that have recently become available for use in avian species.


Individuality in behaviour, hormones and genes. Bart Kempenaers – not available


Session 4: Individual variation in other systems


Maternal yolk androgens and natal dispersal in passerine birds: insights on between-individual and between-family variation. Blandine Doligez * and Barbara Tschirren **, * Department of Biometry and Evolutionary Biology, CNRS - University Lyon I, Villeurbanne, France; ** School of Biological, Earth & Environmental Sciences, University of New South Wales, Kensington, Sydney, Australia; (


Dispersal has long been recognized as a key life-history trait for many evolutionary processes in wild populations. However, the proximate mechanisms of dispersal still remain poorly understood. In vertebrate species, similarities in dispersal behaviour commonly observed among family members have recently been advocated to indicate a genetic basis of dispersal. However, these similarity patterns could also originate from common pre- or post-natal parental effects. Recent studies have stressed the potential importance of pre-natal maternal effects in shaping offspring phenotype and behaviour, including dispersal. In oviparous species, androgenic hormones of maternal origin that are deposited into egg yolks have been shown to promote the offspring’s embryonic development and postnatal growth, but also their social status after independence, thus implying long-lasting effects. Females might thus influence their offspring’s dispersal behaviour by modifying the concentration of androgens deposited in egg yolks, as recently suggested in the great tit. We investigated the role of maternal yolk androgens in shaping offspring natal dispersal and its potential for explaining intra-family similarities in dispersal behaviour. The study was conducted in a fragmented population of collared flycatchers and great tits, small hole-nesting passerine birds, breeding in 15 different discrete woodland patches on the island of Gotland, Sweden. In this population, parents and offspring show resemblance in dispersal behaviour. We tested (1) whether dispersing females deposit higher yolk androgens concentration in their eggs, thereby predisposing their offspring to disperse, and (2) whether dispersal behaviour of recruits correlates with yolk androgens concentration of sibling eggs, as predicted if maternal androgens in egg yolk play an important role in determining natal dispersal behaviour. This would suggest that similarity in natal dispersal behaviour between siblings can result from between-clutch differences in egg yolk androgens level. We also investigated the simultaneous effect of other parental traits on yolk androgen deposition, in particular male attractiveness, which has been shown to influence breeding decisions by females in these species (“differential allocation hypothesis”).

Short-term testosterone increases in dark-eyed juncos: individual variation and relationships with morphology and behavior. Joel W. McGlothlin, Indiana University.

Quantifying the extent to which individuals differ from one another is essential for understanding both how selection acts on hormonal mechanisms and how such mechanisms mediate life history trade-offs.  We studied breeding males in a wild population of dark-eyed juncos and measured both baseline levels of testosterone (T) and the magnitude of short-term increases in T above baseline in response to a GnRH challenge.  Over a period of two years, we found that individual differences in response to a challenge were more pronounced (i.e. more repeatable) than were baseline measures.  In addition, we detected seasonal variation in the magnitude of the response, positive co-variation between the response and an attractive plumage trait, and negative co-variation between the response and nestling-feeding behavior.  We suggest that individual variation in sensitivity to a GnRH challenge may predict individual variation in the resolution of the trade-off between mating effort and parental effort.


Hormonal correlates of social dominance status in Anatids. Maud Poisbleau, (


Through case studies on dark-bellied brent geese Branta bernicla bernicla and dabbling ducks, this work focuses on social dominance relationships in  gregarious species such as wintering anatids. I used individual behavioural based-studies, combining results from experiments in captivity and observations in field conditions, to (1) underline inter-individuals differences in hormonal levels during winter and spring periods and to (2) explore the potential use of hormones as indicators of the individual social status.Through their potential roles in aggressiveness, individual responses to environmental changes, or as health indicators, plasmatic levels of  testosterone and corticosterone are good indicators of the individual social status of wintering dabbling ducks. Conversely, there are no obvious direct relationship between hormone levels and individual social dominance in groups of wintering brent geese. The best estimator of the social dominance score of a goose being the size of its family, which is not preserved from one winter to the other, it is nevertheless likely that the role of hormones on the winter social status finds its source in the breeding quarters.


Individual variation or trapping technique? Trapping initiates stress response in nonbreeding house sparrows. Anthony J. Porter and Sharon E. Lynn, The College of Wooster (

Baited traplines are a relatively easy method of capturing and collecting blood samples from large numbers of birds in a short period of time.  However, one potential drawback of this technique is that birds may be left in traps for an unknown period of time prior to sampling.  We assessed the impact of being left in traps for up to 30 minutes on hypothalamo-pituitary-adrenal (HPA) axis activity in non-breeding house sparrows (Passer domesticus).  Traps were baited with seed, and after entering the traps, birds were either removed immediately (controls), or left undisturbed for 15 or 30 min.  Birds appeared to be feeding on seed while in the traps.  Upon removal from the trap, birds were subjected to standardized capture and restraint protocol in which blood samples were collected to be analyzed for corticosterone (CORT) within 3 minutes of removal, and again at 15, 30, 45, and 60 minutes.  Entry into the traps appeared to initiate CORT secretion in all birds.  Sparrows that were left in the traps for 30 minutes had significantly higher baseline CORT than controls, and baseline levels were in fact similar to CORT levels measured after 30 min of restraint in controls.  Similarly, baseline CORT levels in sparrows removed from the trap after 15 minutes were similar to levels after 15 minutes of restraint in controls. We suggest that the length of time birds spend in a trap prior to sampling may represent a significant source of variation in studies assessing HPA activity. At least one other study has investigated this phenomenon in several species, and taken together with the results of our study, suggest that the influence of trapping techniques on CORT secretion may be species and stage specific. 


Avian personalities: genes and environment. Kees van Oers, Netherlands Institute of Ecology (NIOO-KNAW) (


Meetings like this show that there is currently a burst of interest in consistent individual differences in behavioural and physiological traits. These differences cannot be explained anymore by a deviation from optimality only, but they reflect a possible adaptive mechanism. In the great tit we have shown that individual differences are partly inherited and we have identified several environmental factors that alter the phenotypic expression of different genotypes. Thereby several behavioural and physiological traits are phenotypically and genetically correlated within the same context forming so called behavioural syndromes or personalities. We have also shown that genotypes may well be differently expressed in different contexts, which seems in contradiction to standing theories from human personality research. A possible explanation for this might be that the function of the phenotypic expression of different personality genotypes is non-parallel. This interaction between genotype and environment has however not been tested directly. My main project for the next coming years will therefore focus on this genotype by environment interaction. I am thereby interested whether reaction norms of different genotypes indeed cross and if this changes genetic correlations between traits.


Session 5: Individual variation in a life-history context


Does early nutrition affect behavioural responses to novel situations? Kathryn E. Arnold Division of Environmental and Evolutionary Biology, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, UK (


Many animals, including humans, show consistent individual differences in how they respond to novel situations. Exposure to a novel object can, for example, elicit bold exploratory behaviour in some individuals with a continuum of responses through to shy avoidance. In wild birds, there has been a focus on studying the heritability of such behavioural traits. However, studies of mammalian model species have shown that embryonic and neonatal nutritional conditions can have a huge impact on how, as an adult, an individual responds to novel circumstances. In this study we assessed how manipulating amino acid nutrition during the nestling phase of wild blue tits (Parus caeruleus) affected an individual’s responses to novelty as an adult. Within each nest, half the nestlings were hand-fed once per day with an amino acid supplement and the rest with the control treatment. At 14 days, one experimental chick and one control chick per nest, matched for size and sex, were brought into captivity and raised to independence. A novel object was presented to each individual at 38 and 39 days of age. Bolder birds were defined as having both a shorter latency to approach each item and a shorter minimum distance to the object than more shy birds. Within individuals there was a consistent response to the two novel objects. Overall, there was a correlation between the latency and minimum distance to the novel objects. GLMM analyses revealed that females were significantly faster to approach the novel objects and got closer during that time. Heavier birds were found to get closer to the novel objects than lighter individuals, but overall did not have a shorter latency to approach. Neonatal diet was found to affect the relationship between body mass and latency. Among offspring in the control group, lighter offspring were significantly shyer than heavier offspring. Birds that had received an amino acid supplement as nestlings were overall faster to approach the novel objects than controls and their boldness did not vary with body mass. Our results show that neonatal diet produced consistent individual differences in adult behaviour. Thus, variation in early rearing environment provides a non-genetic mechanism for the maintenance of population-level variation in responses to novel situations.


Individual and sex-specific variability of cell-mediated immunity across life-history stages. Oliver P. Love 1, Katrina G. Salvante 1, James Dale 2 and Tony D. Williams 1, 1 Biological Sciences, Simon Fraser University and 2 Max Planck Institute for Ornithology, Starnberg (Seewiesen), Germany (

Organisms must manage physiological systems optimally across life-history stages and under varying environmental conditions to maximize fitness. There has been much recent  integrative research aimed at testing ecological and evolutionary questions involving immunocompetence, with numerous studies focusing on measures of cell-mediated immunity (CMI) in birds. Research to date has focused mainly  on the short-term management of CMI at particular life-history stages. We therefore lack basic information on 1) how CMI is managed over the long-term across life-history stages in relation to varying resources, 2) whether the sexes manage CMI differentially across these stages and 3) whether CMI is repeatable within individuals across these stages. Here, we examined inter-sexual differences in CMI using a within-individual repeated-measures design across the major life-history stages in a captive colony of zebra finches (Taeniopygia guttata). Juveniles sex-specifically managed CMI between fledging and sexual maturity with males demonstrating higher CMI at fledging but similar CMI as females at adulthood. Adult females and males had similar responses during non-breeding and during egg-laying stages on a high-protein diet. However, when females were laying while on a low-protein diet they significantly reduced CMI . In contrast, males did not modulate CMI with limited proteinavailability. CMI of juveniles was not repeatable between either fledging and pre-basic molt or fledging and adulthood. Adult males showed relatively high repeatability between non-breeding and egg-laying stage on both diets. CMI in females was similarly repeatable between non-breeding and egg-laying on the high-protein diet, however in contrast to males repeatability disappeared when females were laying on the protein-poor diet. Optimal immunity theory predicts significant variation across life-history stages as organisms attempt to manage within-stage immune response to maximize lifetime fitness. In support of this, our results clearly indicate that zebra finches manage CMI sex-specifically across life-history stages when faced with variation in environmental quality.


The ecology and organismal biology of individual variation in Ithaca Tree Swallows. David W. Winkler, Dept. of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853 USA (


Most aspects of reproduction and breeding behavior show considerable individual variation in Tree Swallows Tachycineta bicolor nesting near Ithaca, New York. Research on the patterns of reproductive effort in the late 1980’s revealed variation in the date of clutch initiation to be the life history trait most intimately connected to variation in reproductive output. The heritability of lay date appears to be neglible, and repeatability within females is moderate. Tree Swallows in Ithaca rear only one brood per season, and they display the seasonal decline in clutch size characteristic of single-brooded species. A series of experiments and statistical tests indicate that the smaller clutches of later-laying birds are most likely a strategic adjustment rather than the result of a physiological constraint, and Tree Swallows appear to be classic income breeders. In addition to larger clutches, earlier laying females have stronger immune systems, and they have greater acceleration and sharper turning angles in standardized flight performance tests. In an environment in which available food increases throughout the period of clutch initiations, variations in female flight performance may be able to explain why not all females are able to begin laying at the same time. Earlier laying females appear to pay no survival cost for their earlier reproduction and larger reproductive output, and recent work on the biology of aging suggests new biochemical tools for assessing survival chances of individuals, thus creating a strong new connection between organismal biology and life history theory.



Maternal hormones in eggs of the communally breeding smooth-billed ani (Crotophaga ani): effect of group size and egg-laying order. Grégory Schmaltz1, James S. Quinn1, & Stephan J. Schoech2 1Dept. Biology, McMaster University, Hamilton, ON, Canada. 2Dept. Biology, University of Memphis, Memphis, TN, USA (


Avian eggs contain maternal hormones that affect behaviour, growth, immune function, morphology, and survival of chicks. In this study, we measured hormonal concentrations in eggs of smooth-billed anis (Crotophaga ani) to understand the female’s influence on offspring success in this joint-nesting mating system. In anis, females lay eggs either singly or in groups of up to five females. Intense egg-laying competition occurs in multi-female groups with eggs laid early having the highest probabilities of egg loss because of egg tossing and burial. We measured concentrations of testosterone, estradiol, and corticosterone in ani egg yolks. Results suggest that females deposited more testosterone and corticosterone in late-laid eggs Vs early laid eggs. Within multi-females groups, females also deposited more testosterone and corticosterone as group size increased. Females therefore seem to adjust hormonal concentrations in eggs depending on female group size and the probability of a given egg to hatch. We hypothesize that these hormonal depositions may lead to the production of more competitive chicks in multi-female nests which may be beneficial during sibling-sibling competition with unrelated nestmates.


Part 1.2