Volume-concentrated searching by an aerial insectivore, the common swift, Apus apus

• Published in: Animal Behaviour
• Main Authors: de Margerie, Emmanuel, Pichot, Cécile, Benhamou, Simon
• Other Authors: Ethologie animale et humaine (EthoS), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Centre d’Ecologie Fonctionnelle et Evolutive (CEFE), Université Paul-Valéry - Montpellier 3 (UPVM)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-École Pratique des Hautes Études (EPHE), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD France-Sud )-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: 3D optical tracking; aerial predation; aero-ecology; flight behaviour; foraging behaviour; movement ecology; [SDV.NEU.SC]Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]/Cognitive Sciences; [SDV.NEU.PC]Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]/Psychology and behavior; [SCCO.NEUR]Cognitive science/Neuroscience; [SDV.BA.ZV]Life Sciences [q-bio]/Animal biology/Vertebrate Zoology; [SDV]Life Sciences [q-bio]; Apus apus
• Online Access: https://univ-rennes.hal.science/hal-01711103; https://doi.org/10.1016/j.anbehav.2017.11.026

International audience How predators search for prey is a cornerstone question in behavioural ecology, which has yet to be investigated for animals foraging in 3D airspace. Do insectivorous birds such as swifts (Apodidae), swallows and martins (Hirundinidae) use similar strategies to those performed by terrestrial predators in 2D, or do they rely on different spatial search strategies because of some properties of the aerial open space? We addressed this question in the common swift, one of the most aerial birds, using a novel 3D optical tracking method. The analysis of fine-scale flight tracks revealed how birds distribute their presence in 3D space while foraging near their breeding colony. Common swifts concentrated the time spent per volume unit by adopting a tortuous path, and, to a much lesser extent, by decreasing their movement speed. By independently observing the birds' posture on tracking images, we were able to identify the occurrence of putative prey captures along flight tracks. We show that swifts' presence was concentrated mainly in the vicinity of prey captures, unveiling a volume-concentrated search (VCS) strategy in this aerial insectivore. This is an extension in 3D of the area-concentrated search classically described in terrestrial 2D space. VCS can (but does not necessarily) take place in thermal updrafts, where small insects can be concentrated in patches. In contrast to terrestrial and aquatic predators that can easily slow down or stop their movement in profitable places, a different speed–cost relationship underlying aerial movement prevents swifts from stopping in prey patches and explains why these birds rely mainly on movement tortuosity to perform intensive search. Our study thus shows how some physical properties of the environment can modulate the way an animal concentrates its search in profitable places.