Despite many counter measures, the number of collisions between aircrafts and birds (bird-strikes) has increased in the past decades. Annually the strikes cost civil aviation (disregarding military aviation) worldwide over 1 billion Euros. Particularly the multiple collisions during strikes with bird flocks lead to engine failure. Unfortunately, flocks are difficult to control. As a solution, the proposed project aims to develop a method of using robot-falcons, so-called RoboFalcons, to chase away flocks of birds. Exploiting the synergy between RoboFalcon experiments, computer-modeling and observational data, the project will deliver a prototype of an easily steerable RoboFalcon and a protocol for how to drive away flocks of birds.

To obtain a better understanding of the behavior of groups of coordinating animals, such as flocks of birds and schools of fish, models of self-organization have proven very useful. Recently such computational models are being compared in detail to empirical data. These comparisons are confined however to the context of undisturbed groups. Yet, when avoiding attacks by a predator the patterns formed by flocks are most spectacular. Besides, the main reasons why animals group is protection against predation. Therefore it is time to compare models of self-organized flocking to empirical data of flocks under attack. Since 2002 we have contributed to the field of collective motion. After initially developing models of schools of fish and comparing these to empirical data, we started studying flocks of birds. We have developed a model related to flocks of starlings, StarDisplay [1,2,3] and compared it to detailed empirical data. Our model, StarDisplay, includes simplified flying behavior next to the rules for coordination by attraction, alignment and avoidance as used for fish schools. The model StarDisplay shows resemblance to empirical data in many traits, such as (a) shape and orientation of the flock, (b) aspects of turning, such as maintenance of shape during a turn, the change of the orientation of the shape relative to the movement direction and the repositioning of individuals during turns as well as (c) aspects of internal structure, namely as measured by the scale free correlation between the absolute length of the flock (in m) and the correlation length of the deviation of the velocity and speed of individuals from that of the centre of gravity [1,4] and as illustrated by the degree of disorder or diffusion in the group. Recently we have moved our interest to predator interactions with flocks of birds. We have started studying details of the attacks by predators (particularly falcons) on flying birds. We received a grant from NWO, dossier 823.01.017, for a PhD position (January 2014): ?Optimisation of navigation for intercepting prey during aerial hunting by birds?. Here our PhD student Mills is in his first year. For comparing to empirical data we cooperate with Dr. Taylor from the animal flight group of Oxford, UK. At present we need to learn more about the complex patterns of escape of flocks of starlings. First we must get more insight in empirical data of collective evasion of predators by flocks of starlings. For this the visit of Dr. Carere is designed. Subsequently we will use these results to write a proposal on collective evasion to be submitted to NWO. The proposal will be aimed at developing a computational model in order to increase our insight in the processes underlying these collective patterns of escape. References [1] Hemelrijk, C. K. & Hildenbrandt, H. 2012 Interface Focus. 2, 726-737. [2] Hildenbrandt, H., Carere, C. & Hemelrijk, C. K. 2010 Behav Ecol. 21, 1349-1359. [3] Hemelrijk, C. K. & Hildenbrandt, H. 2011 PLoS ONE. 6, e22479. [4] Hemelrijk, C. K. & Hildenbrandt, H. 2014. J. Stat. Phys. 10.1007/s10955-014-1154-0

Determination of offspring sex ratio is a fundamental reproductive decision that is predicted to have a major impact on an individual’s genetic contribution to future generations. We propose to test the key prediction of sex-ratio theory (Trivers-Willard hypothesis), namely that parents should adapt the sex ratio of their offspring to their local conditions; overproducing the sex that yields the highest fitness per unit of investment. Testing this prediction requires accurate quantification of how fitness costs and benefits depend on local conditions. In natural populations this is challenging, since fitness needs to be quantified in terms of reproductive values (RV), the long-term contribution of an individual to the gene pool of the population. We will undertake the first realistic quantitative test of the Trivers-Willard hypothesis in a wild population using the Seychelles warbler Acrocephalus sechellensis, a species that shows extreme variation in offspring sex ratios. To do this we will first develop new theoretical models, specifically tailored to the Seychelles warbler, that predict under what environmental and social circumstances individuals should bias the offspring sex ratio. Then, using lifetime data of all individuals from our long-term study spanning more than 30 years, we will test whether, under varying parental and environmental conditions, adjustments in sex ratios happen accordingly to predictions. Finally we will calculate the realised RVs of sons and daughters. By quantifying RVs, we will, for the first time, be able to fully understand the validity, extent and consequences of adaptive sex ratio modification in a wild vertebrate population.

Understanding the causes of sexual differences in aggression is a major goal in studies of evolution. Although males are widely considered the more aggressive sex, females often accrue substantial fitness benefits through competition. Competitive females frequently gain priority access to limited resources that directly impact reproductive success. Despite such benefits, substantial costs can be associated with the hormones that regulate aggressive behaviour. Females aggression is often mediated by testosterone, and females face substantial costs from this hormone because it interferes with breeding physiology. A tradeoff therefore exists between resource acquisition, and the depression of reproductive output. Although female social behaviour has traditionally been understudied, recent emphasis is focused on the adaptive role of female competition. However, little evidence compares positive and negative selective pressures acting concurrently on a single system, and, as a result, we only have a partial view of the evolutionary pressures acting to mold this core female behaviour. The objective of this proposal is to forge an enduring collaboration with international colleague, Prof. Troy Murphy (Trinity University, USA). My goal is to bring Prof. Murphy to The Netherlands for 4 months to evaluate the evolutionary benefits as well as the costs associated with female aggression using a model bird species, the Blue Tit (Cyanistes caeruleus), a species with which I have worked for many years, and a species where female aggression is mediated by testosterone and female-female competition for nesting sites is remarkably violent. This study system presents an ideal opportunity to study fitness outcomes because the population is large and tractable (approx. 150 nesting pairs utilize nest boxes in our study population) and so manipulative experiments will yield large sample sizes that can detect small but meaningful variations in behaviour and fitness. Our research will involve three main procedures: first, we will increase competition for breeding sites by rendering half of the nest boxes inaccessible. Second, we will capture wild females and implant half of them with testosterone pellets, and implant the other half with empty pellets as a control (following methods previously used in my laboratory). We expect that testosterone implanted females will be more competitively successful. Third, we will assess the costs faced by females by comparing testosterone treatment to various measures reproductive performance and output (e.g., incubation and provisioning behaviour, fledging success). This research will add valuable insights into which components of fitness are affected by aggression, and will provide essential information for interpreting the selective processes underlying the female competitive phenotype. Our results will be highly impactful because they will provide detailed fitness assessment based on experimental manipulation of both competition and hormone levels in females, and our use novel techniques (i.e., increasing population wide competition) and modern technologies (i.e., automated video monitoring) will provide us with a solid integration of proximate and ultimate components of this behaviour. This work will yield multiple high impact journal articles, and because we recognize the importance of public education, there is already a plan to publish this research in a popular science book.

In most primates males are bigger in their body size than females. Consequently, by default males have been assumed to be dominant over all females, with the exception of bonobos (where co-dominance was apparent), squirrel monkeys (with interspecific variation in co-dominance, male dominance, and female dominance; e.g. [2]) and certain lemurs (with clear female dominance). Since 2000 we have investigated the consequences for social structure of the self-reinforcing effects of winning and losing fights, in general [2] and for the dominance relationships between the sexes [3,4]. We have shown, first in a series of computer models that the degree of female dominance over males will depend not only on body size but also on the self-reinforcing effects of winning and losing fights [4]. Here we showed that the degree of dominance by females over males was higher in species with aggression that was fiercer rather than milder and, if aggression was fierce, that female dominance increased with the percentage of males in the group. This happens because a high percentage of males in a group implies that males will be defeated more often by other males and thus some males become low in rank. Particularly over low-ranking males, females may become dominant. We confirmed empirically that female dominance is greater in fiercely aggressive macaques (despotic species) than in mildly aggressive ones (egalitarian species) [4], and that female dominance increased with the percentage of males in the group, not only in primates [4], but also in humans [5]. To obtain a better understanding how general these phenomena are in primates and how they come about, we need empirical data particularly on species where female dominance is observed in varying degrees. This is the case in capuchin monkeys [6,7]. Therefore, we asked Prof. dr. P. Izar to visit us. She will bring empirical data on several groups of capuchins observed under natural conditions in Brazil. These groups differ in sex-ratio of adults. She observed qualitatively that intensity of aggression and female dominance differs between groups and between sites and sub-species. We will together analyze her data with our standard methods. This will result in a scientific paper and a conference talk. Hopefully it will also result in a long-term cooperation in which we learn more about the benefits of dominance over males for female capuchins. It may be beneficial, for instance, for exerting female choice, by rejecting copulation attempts or for forming coalitions against males. Such a study is of great importance for increasing our understanding not only on behavior of capuchins, but also, for emancipatory issues in humans. References [1] S. Boinski, K. Sughrue, L. Selvaggi, R. Quatrone, M. Henry, and S. Cropp, Behaviour 139, 227 (2002). [2] C. K. Hemelrijk, P Roy Soc Lond B Bio 266, 361 (1999). [3] C. K. Hemelrijk, J. Wantia, and M. Daetwyler, Behaviour 140, 1247 (2003). [4] C. K. Hemelrijk, J. Wantia, and K. Isler, PLoS ONE 3, e2678 (2008). [5] K. Stroebe, B. A. Nijstad, and C. K. Hemelrijk, Social Psychological and Personality Science 1-10 (2016). [6] K. Izawa, Primates 21, 443 (1980). [7] M. Verderane, P. Izar, E. Visalberghi, and D. Fragaszy, Behaviour 150, 659 - 689 (2013).