Biology subjects

Hemelrijk, C. K.

Publications and source records attributed to Hemelrijk, C. K..

5 recordsLinked to original sources

bioRxiv2024

Starling murmurations under predation

Large flocks of European starlings change shape, size, and internal structure continuously and rapidly when hunted by aerial predators. How their diverse patterns of collective escape emerge is still unknown. Here, we disentangle the collective behavior of starlings combining video footage of flocks pursued by a robotic predator and a data-driven 3-dimentional agent-based model. In vivo, we show that flock members often differ in their evasive maneuvers and that several collective patterns arise simultaneously across a flock. In silica, we identify individual-level rules that lead to dynamics of collective motion and escape similar to real starlings. Our results suggest that the mechanisms underlying starling murmurations depend on how fast escape information propagates through the flock, the relative positions of the escaping individuals to the predator, and the previous state of the flock (hysteresis). Our study highlights the importance of investigating fine-scale dynamics and micro-macro feedback when studying self-organized adaptive systems.

animal behavior and cognition↗

bioRxiv2022

Improved deterrence of birds using an artificial predator, the RobotFalcon

Collisions between birds and airplanes, bird strikes, can damage aircrafts, resulting in delays and cancellation of flights, costing the international civil aviation industry more than 1.4 billion U.S. dollars annually. Bird deterrence is therefore crucial, but the effectiveness of all available deterrence methods is limited. For example, live avian predators can be a highly effective deterrent, because potential prey will not habituate to them, but live predators cannot be controlled with sufficient precision. Thus, there is an urgent need for new deterrence methods. To this end we developed the RobotFalcon, a device that we modelled after the peregrine falcon, a cosmopolitan predator that preys on a large range of bird species. Mimicking natural hunting behaviour, we tested the effectiveness of the RobotFalcon to deter flocks of corvids, gulls, starlings and lapwings. We compared its effectiveness with that of a drone, and of conventional methods routinely applied at a military airbase. We show that the RobotFalcon scared away bird flocks from fields immediately, and these fields subsequently remained free of bird flocks for hours. The RobotFalcon outperformed the drone and the best conventional method at the airbase (distress calls). Importantly, there was no evidence that bird flocks habituated to the RobotFalcon. We propose the RobotFalcon to be a practical and ethical solution to drive away bird flocks with all advantages of live predators but without their limitations. HighlightsO_LIWe present and test a new method of deterring of deterring birds, the RobotFalcon. C_LIO_LIThe RobotFalcon chased away flocks fast and prevented early returns. C_LIO_LIThe RobotFalcon outperformed both a drone and convential methods. C_LIO_LINo evidence of habituation to the RobotFalcon was found during the study period. C_LI

animal behavior and cognition↗

bioRxiv2021

Self-organization of collective escape in pigeon flocks

Bird flocks under predation demonstrate complex patterns of collective escape. These patterns may emerge by self-organization from simple interactions among group-members. Computational models have been shown to be valuable for identifying the behavioral rules that may govern these interactions among individuals during collective motion. However, our knowledge of such rules for collective escape is limited by the lack of quantitative data on bird flocks under predation in the field. In the present study, we analyze the first dataset of GPS trajectories of pigeons in airborne flocks attacked by a robotic falcon in order to build a species-specific model of collective escape. We use our model to examine a recently identified distance-dependent pattern of collective behavior that shows an increase in the escape frequency of pigeons when the predator is closer. We first extract from the empirical data the characteristics of pigeon flocks regarding their shape and internal structure (bearing angle and distance to nearest neighbours). Combining these with information on their coordination from the literature, we build an agent-based model tuned to pigeons collective escape. We show that the pattern of increased escape frequency closer to the predator arises without flock-members prioritizing escape when the predator is near. Instead, it emerges through self-organization from an individual rule of predator-avoidance that is independent of predator-prey distance. During this self-organization process, we uncover a role of hysteresis and show that flock members increase their consensus over the escape direction and turn collectively as the predator gets closer. Our results suggest that coordination among flock-members, combined with simple escape rules, reduces the cognitive costs of tracking the predator. Such rules that are independent of predator-prey distance can now be examined in other species. Finally, we emphasize on the important role of computational models in the interpretation of empirical findings of collective behavior. Author summaryBird flocks show fascinating patterns of collective motion, particularly when escaping a predator. Little is however known about their underlying mechanisms. We fill this gap by firstly analyzing GPS data of pigeon flocks under attack by a robotic-predator and secondly, studying their collective escape in a computer simulation. Previous research on pigeons has revealed that flock-members turn away from the predator more the closer the predator gets. Using computer simulations that are based on pigeon-specific characteristics of motion and coordination among individuals, we study what escape rules at the individual level may underlie this distance-dependent pattern. We show that even if individuals do not intend to escape more when the predator is closer, their escape frequency still increases the closer they get to the predator. This happens by self-organization from the coordination among individuals and despite their tendency to turn away from the predator being constant. A key aspect of this process is the increasing consensus among flock members over the escape direction when the predator gets closer.

animal behavior and cognition↗

bioRxiv2019

Conditioning a collective avoidance response in rummy-nose tetra

We develop an experimental method to induce controlled and local perturbations in a group of fish. Using the paradigm of the shuttle box we condition aversive escape reactions in groups of rummy-nose tetra (Hemigrammus rhodostomus) in response to a green light. Our experiments suggest that aversive conditioning can (i) be used successfully in this schooling species, (ii) trigger collective escape reactions and (iii) be transferred from the training set-up to a new environment. These results are discussed in the context of propagation of information among group members in reaction to external stimuli such as perturbations mimicking sudden changes in the environment, e.g. predator attack.

animal behavior and cognition↗

bioRxiv2017

Domino-Like Propagation Of Collective U-Turns In Fish Schools

Moving animal groups such as schools of fish or flocks of birds often undergo sudden collective changes of their travelling direction as a consequence of stochastic fluctuations in heading of the individuals. However, the mechanisms by which these behavioural fluctuations arise at the individual level and propagate within a group are still unclear. In the present study, we combine an experimental and theoretical approach to investigate spontaneous collective U-turns in groups of rummy-nose tetra (Hemigrammus rhodostomus) swimming in a ring-shaped tank. U-turns imply that fish switch their heading between the clockwise and anticlockwise direction. We reconstruct trajectories of individuals moving alone and in groups of different sizes. We show that the group decreases its swimming speed before a collective U-turn. This is in agreement with previous theoretical predictions showing that speed decrease facilitates an amplification of fluctuations in heading in the group, which can trigger U-turns. These collective U-turns are mostly initiated by individuals at the front of the group. Once an individual has initiated a U-turn, the new direction propagates through the group from front to back without amplification or dampening, resembling the dynamics of falling dominoes. The mean time between collective U-turns sharply increases as the size of the group increases. We develop an Ising spin model integrating anisotropic and asymmetrical interactions between fish and their tendency to follow the majority of their neighbours nonlinearly (social conformity). The model quantitatively reproduces key features of the dynamics and the frequency of collective U-turns observed in experiments.

animal behavior and cognition↗