Background: Many animals travel in groups1. There are benefits and consequences to group travel, neither of which will be distributed equally among group members. What determines who obtains the most benefits when travelling in a group? One factor could be your physical positioning within the group, but in turn, what dictates where you are positioned? This cost-benefit can be exacerbated in bird flocks, as the animals are moving through a three-dimensional fluid, and having to make decisions and precise movements at immensely high speeds2. Positioning could result in you being in energetically advantageous or disadvantageous positions1,3,4. Previously it has been demonstrated that (a) dominance hierarchies that persist on the ground do not dictate positioning within a flock, and (b) birds within a flock will stop following a previously known leader if they sense that the individual’s knowledge has been compromised5,6. During flight, therefore, birds must be looking to specific individuals to extract information from. Is it your position within a flock, of the degree of information and knowledge you have that will determine how much other birds look to you for movement information? What are the energetic benefits and consequences of such positioning? How many other birds within the flock can actually see you? How do individuals recognise one another? These are pivotal questions for understanding how flock dynamics function and how the flow of information operates within flocks, yet relatively little is known about these factors.
Methods & techniques: This project will use state-of-the-art biologging technology. GPS loggers (5Hz) will be deployed to track each individual’s positioning within a flock, while accelerometer loggers (300Hz) will monitor every movement of the body, focusing on wingbeat frequency and amplitude as proxies for work rate1,3-6,7. Individual phenotyping will involve behavioural and physiological aspects. Personality testing will include three components typically used to assess individual behavioural traits; boldness/exploration, neophobia and dominance7. The key physiological determinant will be basal metabolic rate (BMR), measured via respirometry. These complimentary approaches will ascertain how behavioural or physiological parameters regulate positioning within a flock, and whether they determine leadership tendencies. Social network analyses for both ground- and flight-based scenarios will be used to ascertain which individuals prefer to be beside which8. The two model species to be used are homing pigeons6,7 (Columba livia) and southern bald ibis1,3 (Geronticus calvus), which typically fly in cluster- and V-formations, respectively, the two flock types being functionally different. Birds will initially be flown in static groups in flocks that live together and comprise all known individuals, over familiar then unfamiliar routes. Degree of following/information flow from one individual to another will be determined from alignment and trajectory derived from the loggers. Birds will then be flown in mixed groups comprising ‘friends’ and ‘strangers’, again over familiar then unfamiliar flight routes. All experiments will then be repeated with a third of the individuals in a flock having their appearance altered via non-toxic paint. The effects of physical alterations to the birds will also be investigated on the ground, with the impact on personality and dominance hierarchies studied
Key hypotheses: (i) individuals who spend more time associating with each other on the ground will choose to fly beside each other during travel, (ii) during familiar flights, birds will look to regular known flock members (‘friends’) to receive information on trajectory and heading, largely ignoring the unfamiliar (‘stranger’) birds, (iii) during unfamiliar flights – from novel release sites – individuals will retrieve information on trajectory and heading equally from familiar and unfamiliar birds due to the lack of knowledge about route in any flock members, (iv) alterations of individual appearance will cause all flock-types and manipulations to respond the same as mixing up familiar and stranger birds, as birds are unable to recognise individuals, and (v) birds flying in scenario (ii) will exhibit lower wingbeat frequencies and amplitudes than those in manipulated flocks, suggesting there is a cost to flying with unfamiliar birds.