Joost M. Tinbergen

Nestling Weight and Survival in Individual Great Tits (Parus major)

(1) The aim of this paper is to estimate the shape of the curve relating first year survival to nestling weight in individual great tits (Parus major) and to study the causality of this relationship. (2) Data were collected in a mainland and an island population. Nestlings were weighed and sexed in the nest when 2 weeks old. A recapture programme provided data for recapture-rate estimates in the winter. Local survival until next breeding season was estimated by capturing the breeding population. Brood-size manipulation experiments were performed in the mainland population in order to manipulate nestling weights. (3) The relation between local recapture rate and nestling weight was described using logistic regression techniques. The descriptive model included positive weight and negative squared weight regression coefficients, if controlled for year, sex and date. Recapture rate approached zero at weights of c. 70% of the adult body weight. The curves for both populations showed an approximately linear part over a rather long range of weights. At high weights, the curve levelled off in the mainland population and curved down in the island population. (4) Survival from weighing till fledging and recapture rate from fledging till winter were related to nestling weight, but recapture rate from winter till breeding was not. (5) The effect of brood-size manipulation on nestling weight and subsequent recapture rate suggests causality of the recapture rate-nestling weight curve. Additional information from a comparison of the association between recapture rate and nestling weight within and between broods leads to the conclusion that weight does play a causal role in this relationship. Recapture rate-nestling weight curves can thus be estimated from non-experimental data.

Foraging Decisions in Starlings (Sturnus vulgaris L.)

Six seasons of field work on the Dutch island Schierminnikoog were devoted tot testing the hypothesis that parent Starlings conform to the principle of caloric maximization in their choice of prey and hunting site as would be predicted by the profitability concept in Royama. ...Zie: Saummary

Experimental evidence for a causal relationship between timing and success of reproduction in the great tit Parus m. major

SUMMARY (1) We investigated experimentally whether timing of reproduction is causally involved in the seasonal decline in reproductive success in the great tit Parus m. major L. This is important because of its implications for the optimization of reproductive decisions of the individual bird. (2) Timing of breeding was manipulated by inducing repeat clutches through removal of the first clutch. The experiment was performed in 1987 in two forests (W and 0) and followed up the year after. It was assumed that parental quality was unaffected by the ex-periment. Reproductive success of the experimental and undisturbed control clutches were compared. For forest 0, reproductive success of the experimental clutches was also compared with the expected reproductive success of first clutches laid at the same time. (3) Clutch size, fledging success and nestling weight in experimental clutches were reduced as compared with controls in forest W but not in forest 0. We conclude that late breeding causes reduced pre-fledging reproductive success in forest W but not in forest 0. (4) Recruitment of fledged young in the breeding population was strongly reduced by the experiment. We conclude that late breeding caused reduced post-fledging reproductive success in both forests. (5) Survival of females was reduced by the experiment in forest 0 relative to controls and this corresponded with the natural seasonal trend. Survival of females in W and of males in both forests was unaffected. In experimental females, clutch size in the next breeding season was reduced by 16 eggs compared with controls. The clutch size of the males was unaffected, as was the following years laying date for both sexes. We conclude that future reproductive success of females, but not of males, is also related to the timing of current reproduction. (6) Possible mechanisms underlying the relationship between date and reproductive success are discussed. It is suggested that differences in pre-fledging reproductive success induced by the experiment are related to food availability. Differences in post-fledging reproductive success are probably caused by competition between early and late young.

Association between DRD4 gene polymorphism and personality variation in great tits: a test across four wild populations

Polymorphisms in the dopamine receptor D4 gene (DRD4) have been related to individual variation in novelty‐seeking or exploratory behaviour in a variety of animals, including humans. Recently, the human DRD4 orthologue was sequenced in a wild bird, the great tit (Parus major) and a single nucleotide polymorphism in exon 3 of this gene (SNP830) was shown to be associated with variation in exploratory behaviour of lab‐raised individuals originating from a single wild population. Here we test the generality of this finding in a large sample of free‐living individuals from four European great tit populations, including the originally sampled population. We demonstrate that the association between SNP830 genotype and exploratory behaviour also exists in free‐living birds from the original population. However, in the other three populations we found only limited evidence for an association: in two populations the association appeared absent; while in one there was a nonsignificant tendency. We could not confirm a previously demonstrated interaction with another DRD4 polymorphism, a 15 bp indel in the promoter region (ID15). As yet unknown differences in genetic or environmental background could explain why the same genetic polymorphism (SNP830) has a substantial effect on exploratory behaviour in one population, explaining 4.5–5.8% of the total variance—a large effect for a single gene influencing a complex behavioural trait—but not in three others. The confirmation of an association between SNP830 genotype and personality‐related behaviour in a wild bird population warrants further research into potential fitness effects of the polymorphism, while also the population differences in the strength of the association deserve further investigation. Another important future challenge is the identification of additional loci influencing avian personality traits in the wild.

Family Planning in the Great Tit (Parus major) : Optimal Clutch Size as Integration of Parent and Offspring Fitness

Fitness variations due to natural variation in the size of the first clutch and its laying date were estimated using Fishers reproductive value for both the clutch (Vc) and the parent (Vp) in a population of great tits. In order to test the hypothesis that individual birds maximize their reproductive value by the choice of clutch size, artificial variation in brood size was introduced and the consequences in terms of reproductive value estimated. Maximal Vc, computed on the basis of natural variation in clutch size, occurred at a clutch size of 15.2, and increased slightly with laying date. Vp increased with natural variation in clutch size and decreased with date. The total reproductive value V (= Vc+Vp) was maximal at a clutch size of 15.4, substantially higher than the population mean clutch size (9.2). The components of the reproductive value of the clutch (Vc) that were negatively affected by manipulation were the survival of the nestlings and the recruitment rate. The reproductive value of the parent (Vp) was negatively affected only through the probability of having a second clutch. Maximal Vc computed on basis of artificial variation in clutch size, occurred at a clutch size of 10.0, and also increased with date. Vp decreased with artificial variation in clutch size causing the clutch size maximising reproductive value V to shift to a value of 9.4, very close to the population mean clutch size (9.2). It is concluded that the majority of great tits produces the number of eggs (9-10) that maximizes their individual fitness, even though those individual birds laying 15 eggs have the highest reproductive value in the population. The fact that birds laying very large clutches have the highest reproductive value points in the direction of a selection pressure towards larger clutches. Yet, over the last 30 years clutch sizes have not increased in the study population. This apparent contradiction is discussed. Either no genetic variation in clutch size is involved, or a complex polymorphism exists.

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.

Fitness cost of incubation in great tits (Parus major) is related to clutch size.

Life-history theory predicts that parents produce the number of offspring that maximizes their fitness. In birds, natural selection on parental decisions regarding clutch size may act during egg laying, incubation or nestling phase. To study the fitness consequences of clutch size during the incubation phase, we manipulated the clutch sizes during this phase only in three breeding seasons and measured the fitness consequences on the short and the long term. Clutch enlargement did not affect the offspring fitness of the manipulated first clutches, but fledging probability of the subsequent clutch in the same season was reduced. Parents incubating enlarged first clutches provided adequate care for the offspring of their first clutches during the nestling phase, but paid the price when caring for the offspring of their second clutch. Parents that incubated enlarged first clutches had lower local survival in the 2 years when the population had a relatively high production of second clutches, but not in the third year when there was a very low production of second clutches. During these 2 years, the costs of incubation were strong enough to change positive selection, as established by brood size manipulations in this study population, into stabilizing selection through the negative effect of incubation on parental fitness.

Adaptive density dependence of avian clutch size

In birds, the annual mean clutch size is often negatively correlated with population density. This relationship is at least in part due to adjustment by individuals. We investigated whether this response is adaptive in two ways. First we used an optimality model to predict how optimal clutch size (the clutch size that maximizes the number of breeding birds (recruits and surviving parents) in the next season) varies with density. We parameterized the model using data on fitness consequences of experimental variation in brood size and natural variation in population density in a Great Tit ( Parus major) pop- ulation. Predicted optimal clutch size decreased with density, but the predicted relationship was stronger than the observed relationship. Second, we investigated the relationship be- tween the annual selection differential for clutch size and density. We found no relationship, indicating that there is no selection for a steeper than observed relationship between clutch size and density. This implies that the observed response is adaptive, and that the prediction of the optimality model lacks some important constraints or selection pressures. We further used the optimality model to examine the sensitivity of the optimal clutch size to density at different stages in the reproductive cycle. This analysis suggested that the nestling stage was most important. To the best of our knowledge this is the first study that makes quan- titative predictions of optimal clutch size in relation to population density.

Evolutionary signals of selection on cognition from the great tit genome and methylome

For over 50 years, the great tit (Parus major) has been a model species for research in evolutionary, ecological and behavioural research; in particular, learning and cognition have been intensively studied. Here, to provide further insight into the molecular mechanisms behind these important traits, we de novo assemble a great tit reference genome and whole-genome re-sequence another 29 individuals from across Europe. We show an overrepresentation of genes related to neuronal functions, learning and cognition in regions under positive selection, as well as increased CpG methylation in these regions. In addition, great tit neuronal non-CpG methylation patterns are very similar to those observed in mammals, suggesting a universal role in neuronal epigenetic regulation which can affect learning-, memory- and experience-induced plasticity. The high-quality great tit genome assembly will play an instrumental role in furthering the integration of ecological, evolutionary, behavioural and genomic approaches in this model species.

Experimental evidence for density-dependent reproduction in a cooperatively breeding passerine

Temporal variation in survival, fecundity, and dispersal rates is associated with density-dependent and density-independent processes. Stable natural populations are expected to be regulated by density-dependent factors. However, detecting this by investigating natural variation in density is difficult because density-dependent and independent factors affecting population dynamics may covary. Therefore, experiments are needed to assess the density dependence of demographic rates. In this study, we investigate the effect of density on demographic rates of the Seychelles Warbler (Acrocephalus sechellensis). This species, endemic to a few islands in the Indian Ocean, went through a severe population bottleneck in the middle of the last century, with only approximately 30 individuals left on one small island, but has since recovered. Our monitoring shows that since reaching the islands carrying capacity, population density has remained stable. However, we detected neither density-dependent reproduction nor survival on the basis of natural density variation during this stable period. For conservation reasons, new populations have been established by transferring birds to nearby suitable islands. Using the change of numbers during the process of saturation as a natural experiment, we investigated whether we can detect regulation of numbers via density-dependent survival and reproduction within these new populations. We found that populations were mainly regulated by density-dependent reproduction, and not survival. Variation in density between islands can be explained by food abundance, measured as insect density. Islands with the highest insect densities also had the highest bird densities and the largest breeding groups. Consequently, we suggest that the density-dependent effect on reproduction is caused by competition for food.