Age-dependent trajectories differ between within-pair and extra-pair paternity success.

Reproductive success is associated with age in many taxa, increasing in early life followed by reproductive senescence. In socially monogamous, but genetically polygamous species, this generates the interesting possibility of differential trajectories of within-pair and extra-pair siring success with age in males. We investigate these relationships simultaneously using within-individual analyses with 13 years of data from an insular house sparrow (Passer domesticus) population. As expected, we found that both within- and extra-pair paternity success increased with age, followed by a senescence-like decline. However, the age trajectories of within- and extra-pair paternity successes differed significantly, with the extra-pair paternity success increasing faster, albeit non-significantly so, in early life, and showing a delayed decline by 1.5 years on average later in life compared to within-pair paternity success. These different trajectories indicate that the two alternative mating tactics should have age-dependent payoffs. Males may partition their reproductive effort between within- and extra-pair matings depending on their current age in order to reap the maximal combined benefit from both strategies. The interplay between these mating strategies and age-specific mortality may explain the variation in rates of extra-pair paternity observed within and between-species. This article is protected by copyright. All rights reserved

Flexibility but no coordination of visits in provisioning riflemen

Parental care strategies occupy a continuum from fixed investments that are consistent across contexts to flexible behaviour that largely depends on external social and environmental cues. Determining the flexibility of care behaviour is important, as it influences the outcome of investment games between multiple individuals caring for the same brood. We investigated the repeatability of provisioning behaviour and the potential for turn taking among breeders and helpers in a cooperatively breeding bird, the rifleman, Acanthisitta chloris. First, we examined whether nest visit rate is an accurate measure of investment by assessing whether carers consistently bring the same size of food, and whether food size is related to nest visit rate. Our results support the use of visit rate as a valid indicator of parental investment. Next, we calculated the repeatability of visit rate and food size to determine whether these behaviours are fixed individual traits or flexible responses to particular contexts. We found that riflemen were flexible in visit rate, supporting responsive models of care over ‘sealed bids’. Finally, we used runs tests to assess whether individual riflemen alternated visits with other carers, indicative of turn taking. We found little evidence of any such coordination of parental provisioning. We conclude that individual flexibility in parental care appears to arise through factors such as breeding status and brood demand, rather than as a real-time response to social partners

Personality and its repercussions in the house sparrow

The fundamental puzzle of personality is why personality – between-individual differences and within-individual consistency of behaviour – exists. Personality has been measured in many taxa and understanding the origins of personality means understanding a common basis to all behaviours. This study uses the isolated Lundy Island house sparrow Passer domesticus system to give a whole-population overview of how personality is formed, maintained, and may influence fitness. House sparrows are globally successful, and might help us to understand the role of personality – inflexible behaviour – in a highly adaptable species. This research uses cross-fostering, where offspring are exchanged between broods, to separate genetic and environmental effects on personality, and first examines whether cross-fostering has inherent biases. We establish that cross-fostering is linked to spatio-temporal breeding heterogeneity, changes to the rearing environment, and, possibly, observer-based sampling bias, influencing individual survival and potentially study outcomes. Thus, we provide practical guidelines for reducing such bias. Second, this thesis investigates how personality traits develop and might link to fitness by measuring three main personality traits. Our results indicate that heritability varied widely among personality traits. No traits were correlated across contexts, implying no cross-context constraint between these traits. Physiological state, in this case nestling mass, was an important factor shaping personality in nestlings. Social broods also shaped nestling personality, though personality was more similar within social broods, which is contrary to theoretical predictions. Lastly, personality was weakly correlated with fitness in females but not in males, and male behaviour might influence female behaviour and reproductive investment. Therefore, the partner can probably modulate the link between fitness and behaviour. This thesis shows that personality can have stable genetic and physiological bases, but social interactions are associated with more similar personalities between interacting individuals. The fitness consequences of personality might be sex specific and moderated by partners

The function of animal ‘eyespots’: conspicuousness but not eye mimicry is key

Many animals are marked with conspicuous circular features often called ‘eyespots’, which intimidate predators, preventing or halting an attack. It has long been assumed that eyespots work by mimicking the eyes of larger animals, but recent experiments have indicated that conspicuousness and contrast is important in eyespot function, and not eye mimicry. We undertake two further experiments to distinguish between the conspicuousness and mimicry hypotheses, by using artificial prey presented to wild avian predators in the field. In experiment 1, we test if eyespot effectiveness depends on the marking shape (bar or circle) and arrangement (eye-like and non-eye-like positions). We find no difference between shapes or arrangement; all spots were equally effective in scaring birds. In experiment 2, we test if the often yellow and black colors of eyespots mimic the eyes of birds of prey. We find no effect of shape, and no advantage to yellow and black spots over non-eye-like but equally conspicuous colors. The consistent finding is that eyespot function lies in being a conspicuous signal to predators, and not necessarily due to eye mimicry [Current Zoology 55 (5): –2009]

Outline and surface disruption inanimal camouflage

Camouflage is an important strategy in animals to prevent predation. This includes disruptive coloration, where high-contrast markings placed at an animal's edge break up the true body shape. Successful disruption may also involve non-marginal markings found away from the body outline that create ‘false edges’ more salient than the true body form (‘surface disruption’). However, previous work has focused on breaking up the true body outline, not on surface disruption. Furthermore, while high contrast may enhance disruption, it is untested where on the body different contrasts should be placed for maximum effect. We used artificial prey presented to wild avian predators in the field, to determine the effectiveness of surface disruption, and of different luminance contrast placed in different prey locations. Disruptive coloration was no more effective when comprising high luminance contrast per se, but its effectiveness was dramatically increased with high-contrast markings placed away from the body outline, creating effective surface disruption. A model of avian visual edge processing showed that surface disruption does not make object detection more difficult simply by creating false edges away from the true body outline, but its effect may also be based on a different visual mechanism. Our study has implications for whether animals can combine disruptive coloration with other ‘conspicuous’ signalling strategies

Data from: Troubleshooting the potential pitfalls of cross-fostering

1. Cross-fostering is the transfer of offspring between their natal environment and a new social environment. This method allows researchers to disentangle the genetic and interacting environmental effects that influence phenotypes, and is popular in both wild and laboratory studies. Here, we discuss three factors that might bias cross-fostering and influence ecological and evolutionary conclusions if not accommodated. 2. First, cross-fostering tends to be spatially and temporally non-random because heterogeneous breeding conditions can result in clustered breeding attempts. Second, cross-fostering will often change the brood composition because the exchanged broods are unlikely to be precisely matched in age, size, and composition. Third, some methods can introduce bias by using a systematically structured subset of the population, leading to a systematically structured data-set. 3. We use a 12-year case study of wild house sparrows (Passer domesticus) to demonstrate how to identify these biases with statistical modelling and how to adjust the cross-fostering protocol according to the identified biases. 4. In our dataset, cross-fostered nestlings were more likely to survive than non-cross-fostered nestlings, but post-fledging and overall survival were not affected. Survival differed between cross-fostering treatments, partially due to temporally non-random breeding conditions and non-random offspring selection, demonstrating two of the three forms of bias in data from a wild population. 5. In all cases, we suggest using statistical models to examine whether cross-fostering opportunities and offspring fitness are affected by non-random breeding, changes to the brood composition, and biased methodology. We provide guidelines for optimising a cross-fostering design and reducing inherent bias

Models 1,3,4, paired analysis, supplement models, figures - nestling survival and recruitment

Nestling survival and recruitment in relation to morphometrics and demographic data. Data to produce models 1,3,4, and the paired analysis in the main text, models in the supplementary information, and figures in the main text and supplementary information. For a description of the column names, advice on using the data, and units, see the README file