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Within breeding years, male birds vary in their reproductive strategy. While some maintain monogamy with a social partner, others also engage with extrapair partners, while others forgo monogamy altogether in favour of exclusively seeking extrapair paternity. Although theory predicts that extrapair paternity is beneficial to males, which sire extrapair offspring without investing in costly parental care, empirical examples from wild populations are sparse. We used 17 years of data from a closed population of house sparrows, Passer domesticus , with a complete genetic pedigree, to test the hypothesis that extrapair paternity increases male lifetime reproductive success. We compared a mixed strategy of within-pair (or social) and extrapair paternity with total genetic monogamy and total extrapair paternity. We demonstrate that males who combine within-pair and extrapair paternity have increased reproductive success against the other two groups. Our results also suggest that males that exclusively seek extrapair paternity have the lowest lifetime fitness. Overall, we provide an empirical demonstration of the theory, showing that where males can sire extrapair offspring alongside within-pair offspring, extrapair paternity is beneficial to male lifetime fitness. • Within years, male house sparrows invested in social or extrapair offspring, or both. • Within a year, reproductive strategy depended on the environmental context. • Males that had extrapair and social offspring had the highest lifetime fitness. • Floating males, which only had extrapair offspring, had the lowest lifetime fitness. [ABSTRACT FROM AUTHOR]

Foraging animals usually select foods that balance the intake of key nutrients, for example essential amino acids that cannot be synthesized and must be obtained from the diet. However, the ability to gain optimal ratios, proportions and amounts of nutrients may be hampered by a changing environment, competitive conspecifics or species and predators. Here, we used an experimental system in which house sparrows, Passer domesticus , were fed a manipulated diet with different compositions of amino acids (in the experimental diet phenylalanine and tyrosine content was 42% of that in the control diet). Phenylalanine and tyrosine are precursors of coping hormones: dopamine, noradrenaline (norepinephrine) and adrenaline (epinephrine) which are involved mainly in the expression of stress and fear, but also in learning and long-term memory formation. Accordingly, birds fed a diet deficient in these amino acids learned to avoid unpalatable food markedly slower, coped worse with stress in the presence of a novel object and were more aggressive towards other sparrows than control birds. Surprisingly, circulating amounts of the catecholamines in blood plasma were higher in these birds than in sparrows on the control diet. This study provides the first evidence that variation in amino acid composition in the diet is associated with variation in behaviours and hormone levels in birds. We conclude that food, besides its nutritional function, seems to represent one of the modulators of behavioural expression making a balanced diet crucial for survival. • Animals balance the intake of key nutrients such as essential amino acids. • An imbalance of amino acids may result in behavioural changes. • Birds on an imbalanced diet learned slower and were more aggressive and stressed. • Food seems to represent one of the main modulators of behaviour. [ABSTRACT FROM AUTHOR]

Cognitive flexibility may be necessary for animals facing changing conditions and has long been tested by the reversal learning paradigm. However, while this paradigm is typically based on training animals to discriminate between a rewarding and nonrewarding stimulus and then reversing their roles, under natural conditions animals usually face more than one set of two stimuli. Here, we addressed these potential intricacies by studying the reversal learning of house sparrows, Passer domesticus , in a two-set task. Sparrows previously trained as either colour or shape specialists exhibited different reversal dynamics: While colour discrimination was acquired faster than shape discrimination, shape specialists, including those reaching perfect preference of the rewarding shape, reversed faster than colour specialists. The reversal success of shape specialists was also less variable than that of colour specialists. Additionally, despite being slower, during the reversal, colour specialists sampled shapes more than shape specialists sampled colours. These results suggest that (1) when comparing different reversal tests, significant differences in reversal behaviour may be explained by the type of learned stimulus (e.g. shape versus colour) rather than by differences in cognitive flexibility and (2) under realistic conditions of multiple foraging options, preferences that are difficult to reverse (and typically viewed as indicating low cognitive flexibility) may nevertheless facilitate an ecologically flexible shift to novel food types. Finally, our results also demonstrate that a two-set (multiple-cue) experimental design may help to tease apart some of the different processes underlying reversal behaviour and cognitive flexibility. • The results of reversal learning tests differed depending on stimulus type. • Differences were independent of the discrimination level reached before reversal. • Associations that were difficult to reverse induced flexible shift to novel cues. • Reversal scores may not reflect ecological flexibility in multiple-cue environments. • A multiple-cue set-up helps tease apart the subcomponents of the reversal process. [ABSTRACT FROM AUTHOR]

Males that provide parental care may lose opportunities to acquire extrapair mates or secondary social mates. These opportunity costs can be estimated as the product of (1) the degree to which a male's participation in care makes him unready for mating (i.e. represents 'time-out' from the mating pool) and (2) the availability of potential mating partners. One stage of parenting may therefore be more costly than another because it depresses a male's probability of capitalizing on any given mating opportunity, and/or because it occurs when alternative mating opportunities are more abundant. To determine whether male parental care limits extrapair mating in house sparrows, Passer domesticus, we tracked changes in male extrapair mating success across stages of their nesting cycles. We then assessed whether periods of reduced extrapair mating by males coincided with a scarcity of fertilizable females, or whether certain activities placed males in time-out. We found that the number of potential extrapair mates was significantly higher on days when a male's social mate was fertile than during incubation or nestling provisioning; breeding synchrony consequently reduces the realized opportunity costs of male parenting. Nevertheless, males with nestlings to feed suffered greater opportunity costs than might be expected because of their relative inefficiency at obtaining extrapair matings with potentially available females. During the incubation stage, by contrast, the males' probability of extrapair mating per fertile female averaged four times higher. Thus, nestling provisioning apparently places males in a partial time-out, but male incubation does not. Males may be more fully engaged in the extrapair mating pool during incubation because they typically devote little time to this formof care and, when confronted with an increase in the abundance of extrapair mating prospects, they reduce the time they commit to incubation. [ABSTRACT FROM AUTHOR]

Forming foraging groups may help to improve protection from predators, foraging efficiency and exchange of information, but to benefit from these advantages, animals need to maintain group cohesion. Several studies have investigated how social status or behavioural and physiological traits promote leadership and followership in various species, but the potential role of ecological factors in modulating social cohesion of foraging groups has received less attention. We used social network analysis to investigate how a temporary shortage of food affects within-group following behaviour in house sparrow, Passer domesticus, flocks and which individual characteristics influence birds' positions in the following networks. To test this, we observed nine captive house sparrow flocks, composed of 12 individuals each, in three consecutive sessions, in which the food availability was altered. We found that food reduction did not modify the following network structure and that individuals had consistent positions within the flocks, as males and adults were followed more often than females and juveniles, respectively. However, short-term food reduction affected individuals' following behaviour according to their age: adults increased their following rates during food scarcity, whereas the opposite trend was found in juveniles. This pattern also remained after the re-establishment of initial conditions, suggesting that ecological changes can also induce individual-level lasting effects. Our study provides empirical evidence that food reduction does not affect the global social structure of house sparrow flocks but nevertheless individuals respond differently to ecological changes according to their age. [Copyright &y& Elsevier]

Despite rapidly accumulating evidence for the existence of consistent individual differences in suites of correlated behaviours (i.e. ‘animal personalities’), little is known about proximate mechanisms causing such variation. Individual variation in circulating levels of testosterone (T) is often hypothesized to underpin personality traits such as aggressiveness and exploratory behaviour. Here we provide a comprehensive test of this hypothesis. We quantified variation in exploratory behaviour of a novel environment in a captive population of wild-caught male house sparrows, Passer domesticus. We then investigated the relationship between the observed behaviours and circulating levels of T, using two approaches. First, we tested whether measures of exploratory behaviour correlated with (1) point-sampled plasma T levels and (2) T-dependent ornamentation (bill coloration) in 114 males. Neither direct nor indirect estimates of individual variation in T levels were correlated with the assayed behaviours. Second, we experimentally increased plasma T levels of 21 males with T implants, using 21 placebo-implanted males as a control group. Experimentally induced between-individual variation in T levels did not increase the amount of between-individual variation in exploratory behaviour. Our results thus strongly suggest that, in house sparrows, between-individual variation in circulating levels of T cannot serve as a causal explanation for the existence of individual variation in exploratory behaviour. [ABSTRACT FROM AUTHOR]

When the potential contributions that offspring can make to parental fitness vary, parents benefit by diverting resources towards the offspring offering the highest return on investment. In birds, nestling begging has been hypothesized to allow parental assessment of the relative contribution that each offspring can make to parental fitness. Although begging is often interpreted as a signal of need, studies of nestling morphology, specifically carotenoid-based mouth colours, suggest that these traits signal not the need, but the quality of the nestlings. Here, I manipulated flange colour in a free-living population of house sparrows with experimental paints that did not feature a UV reflectance peak, but otherwise approximated carotenoid-based colours within the range of natural variation. I presented parents with one nestling that appeared to have the carotenoid-rich rictal flanges associated with high condition and one that appeared to have the carotenoid-poor flange colour associated with poor condition. Parents delivered more food items to the nestling that appeared to have carotenoid-rich flanges, a pattern driven by a strong female bias and a similar, but nonsignificant, trend in males. This study shows that parents attend to these visual signals rather than correlated features of nestling physiology associated with carotenoids. Broadly, this result suggests that at least some components of begging are used by parents to bias resource allocation towards their most promising, rather than most needy, offspring. [Copyright &y& Elsevier]

Because parental investment for multiple offspring often proves insufficient, diverse taxa have evolved systems for reducing family size secondarily. We found brood reduction to be common (42% of 1000 nesting cycles) in Oklahoma house sparrows, Passer domesticus, especially when families of four or more nestlings were furnished with less food. Whereas deliveries of large-bodied prey have been shown previously to predict long-term survival of nestlings (to breeding age), smaller prey items appear adequate for short-term survival (to fledging). Parents did not prune deliveries in the aftermath of brood reduction, thereby bestowing a likely food bonus on surviving siblings. Individual male and female parents that were observed for multiple nesting cycles produced similar measures of day 11 offspring mass (including largest chick, smallest chick, and brood mean). By contrast, an index of overall sibling mass inequality was not repeatable. Parents skewed food deliveries towards the larger members of relatively passive day 3 broods, probably influencing early mortality: median age for brood reduction was day 4 posthatching. Patterns of allocation that can be inferred from mass inequities of older chicks (on day 11) also pointed to persistently skewed deliveries; nestlings underweight at that age were more likely to die without fledging. Large broods early in the season tended to have nestlings less equally sized than broods late in the season, whereas small broods showed no such season effect. Brood reduction appears advantageous to parents if surviving offspring thereby increase prefledging mass sufficiently to compensate for the drop in numbers. [Copyright &y& Elsevier]

Kin selection is often important in the evolution of reproductive behaviour, but we know much less about its significance for nonreproductive social groups. We investigated whether relatedness affects social-foraging behaviour in captive house sparrow, Passer domesticus, flocks, where birds may either search for food or exploit flockmates'' food findings by scrounging. In such systems, both increased and decreased frequency of scrounging from relatives can be predicted by kin selection theory, depending on the relative costs and benefits of exploiting close kin. We found that birds used aggressive joining less often and obtained less food by that tactic from their close kin than from unrelated flockmates. In nonaggressive joinings, males also tended to join less often and obtained less food from close kin flockmates than from unrelated birds, whereas an opposite trend was found in females. Close kin males also spent less time feeding together from the same food patch than unrelated males, further suggesting reduced exploitation by male kin. These results suggest that house sparrows are able to recognize their close kin flockmates and reduce aggressive scrounging towards them, and that the sexes may differ in some forms of kin exploitation. [Copyright &y& Elsevier]

Group foragers can use a ‘producer’ tactic which involves searching for food or a ‘scrounger’ tactic which involves joining others who have discovered food. While these alternative behaviours are well documented, it is not clear to what extent an individual''s tendency to forage independently or to follow others is under genetic control or rather is affected by experience. To examine whether hand-reared juveniles can learn to prefer using a producer or a scrounger tactic, we hand-reared house sparrow, Passer domesticus, nestlings that upon fledging were assigned to one of two training groups; the first was expected to enhance joining (scrounging) behaviour and the second to enhance searching (producing) behaviour. In the first group, fledglings were imprinted on a parent model (stuffed female sparrow) that visited locations containing food. In the second group, fledglings were imprinted on a parent model that visited locations containing no food, while food was available in different locations. At the end of a 5-day training phase, all fledglings were released into a shared aviary, and their social foraging tendencies were measured. We found that fledglings from the first group used significantly more joining behaviour than fledglings from the second group, suggesting that an individual whose early experience positively reinforced joining behaviour is more likely to later become a joiner. To our knowledge, this is the first experimental evidence for the effect of learning on the choice between social foraging strategies in the context of the producer–scrounger game. [Copyright &y& Elsevier]

Parental food deliveries are generally assumed to promote offspring fitness in altricial birds, mainly because mass at fledging often predicts recruitment as breeding adults. We studied how such provisioning influences recruitment in house sparrows, Passer domesticus, through both a traditional two-step indirect analysis (via fledging mass) and a single direct analysis. In our study, total parental deliveries predicted neither fledging mass nor recruitment. Instead, delivery of the largest food items (‘e-prey’) predicted both. Offspring recruitment was determined only by personal mass, but from a parental perspective, the number of recruits per brood hinged principally on two factors, brood size and mean nestling mass at fledging. As in other species, recruitment probability declined across the breeding season, even though deliveries of the largest food items increased. Within the natural range of provisioning that parents achieved, the function relating e-prey and recruitment appeared to be accelerating, indicating that parents could rapidly enhance offspring success if bringing more of those items were possible. The failure of adults to do so suggests that the associated foraging costs are likely to be prohibitive, illustrating what has been called a ‘food ESS’ for parental care. [Copyright &y& Elsevier]

High genetic similarity or dissimilarity between parents may result in viability consequences for offspring. However, because female choice of a social mate often reflects access to resources or male parental care, optimal genetic complementarity may be unattainable for social pairs. Thus, extrapair copulations may serve to increase offspring viability by allowing females to obtain sperm from males with more compatible genomes than those of social mates. We investigated whether parental genetic similarity influences offspring viability, including immunocompetence, in house sparrows, Passer domesticus. We also explored whether genetic similarity of social mates predicts the prevalence of young sired through extrapair fertilizations, and whether females enhance offspring viability by engaging in extrapair matings. We used DNA fingerprinting to estimate genetic similarity between social mates, and we assessed offspring viability using two measures of nestling immune response, the phytohaemagglutinin skin test and heterophil:lymphocyte ratios, plus nestling body mass and hatching success. We found no associations between the genetic similarity of parents and offspring immunocompetence, mass or hatching success; however, parental genetic similarity was positively correlated with clutch size. Genetic similarity of social mates also did not predict the frequency of extrapair young. Furthermore, maternal half-siblings within broods of mixed paternity did not differ in immunocompetence. Thus, our results provide no evidence for enhancement of offspring viability as an incentive for female engagement in extrapair copulations. [Copyright &y& Elsevier]

In social animals, dominance rank often influences individuals'' behaviour, but in most cases it is unknown how dominance modulates the effects of other phenotypic traits. We investigated the mutual effects of social dominance and the level of energy reserves on the use of social-foraging strategies in captive flocks of house sparrows, Passer domesticus. We used experimental wind exposure to manipulate overnight energy expenditure of dominant and subordinate individuals. In response to the experimental treatment dominants used scrounging (exploiting others'' food finding) significantly more, whereas for subordinates there was only a moderate and nonsignificant increase in scrounging. Individual variability in the frequency of scrounging was higher in subordinates than in dominants and this difference between the dominance groups was unaffected by the treatment. These results suggest that individuals of different dominance status adopt different strategies: to cope with an energetically challenging situation, dominants behave rather uniformly by increasing further their preference for scrounging, whereas subordinates do not alter their tactic, but may rely on using scrounging opportunistically. [Copyright &y& Elsevier]

Interference ideal free distribution (IFD) models predict animal distributions across resource patches, taking into account the effects of resource density and competitor interference on an individual''s resource intake rate. Assuming that individuals behave to maximize fitness, foragers should aggregate at patches of high resource abundance when interference is weak. However, when interference is strong, foragers should choose to reduce interference by foraging at less crowded patches, even if these patches have lower resource density. Consequently, interference IFD predicts disproportionately high animal densities at rich patches when interference is low and a more uniform distribution among patches when interference is strong. To test this prediction we observed house sparrows, Passer domesticus, at a rich and a poor patch with different seed densities. We manipulated interference by altering the size of the pair of patches: two small patches (high interference) or two large patches (low interference). Birds experienced no interference at large patches where fighting was infrequent and preferred the rich patch where foraging rates increased with bird numbers. In contrast, birds aggressively interfered with each other at small patches, and interference was higher in rich patches than in poor patches. As predicted, birds increased their use of poor patches to minimize interference, resulting in an even distribution of birds across rich and poor patches. Our results show how changes in interference with resource density can make consumer distributions independent of resource distribution, even at moderate interference intensities. Manipulating interference through patch size may provide a unique opportunity to examine the effects of competitive asymmetries on patch use. [Copyright &y& Elsevier]

Traits that influence social interactions (signals) are widely thought to be honest indicators of some underlying quality of their bearer. One hypothesis is that a signal and the bearer''s immunocompetence are linked via a condition-dependent pathway. We tested this idea by measuring the effect of specific dietary components on the development of a melanin-based plumage signal and the production of antibodies in juvenile male house sparrows entering their first moult. We maintained sparrows on one of three artificial diets: high total protein, low total protein, or intermediate protein with the precursors of melanin, phenylalanine and tyrosine (PT), reduced by 50%. Diet did not affect survival or weight gain. Two aspects of male plumage differed between treatments; the white wing bar was significantly smaller in low-protein males, and the black bib feathers had significantly higher reflectance in PT-reduced males. PT reductions had no effect on bib size. PT-reduced birds also produced more antibodies to diphtheria and tetanus antigens than did other subjects. After repeating the experiment using a better control and a different diet formula to compensate for an energy imbalance resulting from reduced PT levels, PT reduction again produced lighter bib feathers, but the effect of diet on antibody production disappeared. We conclude that the amino acid precursors to melanin affect melanin synthesis if scarce in the diet, but in this case, do not affect size, the most conspicuously variable aspect of the signal. We found no evidence of a condition-dependent link between melanin synthesis and immunocompetence. [Copyright &y& Elsevier]

We explored behavioural adjustments made by parent house sparrows, Passer domesticus, when the nutritional condition of their dependent nestlings was improved experimentally. Male parents responded to artificially supplemented broods by increasing food deliveries, whereas female parents continued matching the already high rate of control females. Thus, parental care was not truncated in the face of fortified offspring, but actually escalated (ca. 17% more adult food deliveries overall). Supplemented nestlings showed a nonsignificant tendency to recruit into the adult breeding population more than controls. We propose that one important reason why male parents responded more strongly than their female partners centres on the lower marginal costs for additional male posthatching investment, specifically by demonstrating that increasing paternal investment is likely to confer higher fitness than alternative male activities. [Copyright &y& Elsevier]

Examines the overall behavioral allocation of a flock of house sparrows, Passer domesticus, and the behavior of individual birds in this social context. Use of typical matching law experiment design; Tests for departure from the `habitat matching' theory; Competitive abilities in a patch; Food input ratio; Observed undermatchings; Costs of interactions.

Explores the infanticidal tendencies of replacement male house sparrows and adjustments made in the behavior of the females. Varying stage of the female's reproductive cycle; Ensurance of genetic paternity; Strategic ovulation retardation.

Tests hypotheses about the evolution of monogamy by using observational and experimental evidence collected in a four year study of house sparrows, Passer domesticus, in a Spanish population. In other areas the house sparrow has been cited as regularly polygynous. Hypotheses and predictions; General methods; Results; Discussion.

Reports an experimental study of dominance in differentially food-deprived house sparrows competing for food. Studies in game theory which have dealt with the possible effects of motivational asymmetries on social behavior; Impact of difference in hunger; More.

Reports on an experiment on wild house sparrows, Passer domesticus, and starlings, Sturnus vulgaris, in which distance from protective and obstructive cover had contrasting effects on vigilance as predicted by compensatory logic. Methods; Results.

Discusses the effects of hunger on the dominance in differentially food-deprived house sparrows competing for food. Motivational asymmetries' effects on social behavior; Study of 30 house sparrows in Sweden over a two-month time span; Three series of observations that were performed; Results.