Investigating avian behaviour using opportunistic camera-trap imagery reveals an untapped data source

Understanding the behavioural responses of bird species to their environments is important for effective conservation, especially in captive-management and resource-provisioning programs. Camera traps present a growing opportunity to research bird breeding and foraging behaviour in situ. Remotely triggered cameras are commonly deployed to study mammals and large terrestrial birds. They are rarely used to survey small or arboreal birds due to habitat constraints. However, a wealth of information about small or arboreal birds can be generated opportunistically from camera traps in the course of collecting data on other taxa. Here, we describe and quantify the types of behavioural information that can be so gleaned, based on over 1,700 small-bird images captured as “collateral” during a geographically extensive mammal-focused camera study in Tasmania, Australia in 2018–2020. Postural analysis of images revealed 10 distinct behaviours. Large- and medium-sized terrestrial bird species were most commonly observed (61.6% of behavioural images), but small and arboreal species were also photographed at high rates (18.4% and 29.5% of behavioural images respectively). Investigative activity was the most commonly observed behaviour in small and arboreal species (around half of all images), but feeding, mating and even very rare behaviours like fur plucking, were also captured photographically. This case study reveals the value of opportunistically analysing camera trap images for small or arboreal birds species, especially when they are of conservation interest, even for cases where deliberately targeting them would not be a cost-effective strategy.