Survival is the main concern of all animals which means the ability to find food and stay alive to reproduce successfully. This makes avoiding threats to their life extremely important. Since the organisms that survive are the ones that are reproducing at the greatest rates, species have evolved to possess traits that best allow them to assess and adjust their behaviors to avoid these threats. One such threat is predation, which if not accurately judged in a given situation, can prove fatal. Since predation poses the greatest risk to an organism’s survival, many species have developed ways of determining the level of risk so that they can protect themselves while not expending unnecessary energy and time avoiding an animal that is not a threat. Some animals judge the severity of the threat by visual cues (such as body size, color, beak shape, or eye shape), or species-specific auditory cues made by a predator.
Predatory birds generally perch with their wings back and closed when observing and locating prey, and when they are swooping or diving down to try and capture prey, their wings are outstretched and spread. This spread of their wings increases the size of their body significantly, and indicates they are initiating an attack on possible prey.
In a 2024 study performed on Japanese Tits (Parus minor), Jin et al. (2024), performed an experiment in which they observed the behavior of these birds when faced with one of their common predators, to better understand the factors that influence their assessment of threat level. In this study, two types of taxidermy dummies of the Eurasian sparrowhawk (Accipiter nisus) were used, as well as a dummy of the oriental turtle dove (Streptopelia orientalis) which was used as a control. In one condition, the dummy presented was posed with spread wings, and in the other, the wings of the bird were closed and to the sides of its body. The dummy of the dove with closed wings was also presented in another condition to the tits to compare behavioral responses to that of the sparrowhawks. The researchers predicted that when the sparrowhawk dummy with spread wings was presented to the Japanese tits, they would show more of a fear response since this poses a greater predatory threat to their survival.
The behavioral responses of the tits were quantified by the researchers by recording the hovering, skipping, and observing behaviors which indicate the level of perceived threat these birds perceived.
The results confirmed their hypothesis, since when faced with the hawks that had spread wings, the birds exhibited far more hovering and skipping behaviors, indicating they assessed this posture as far more threatening compared to the hawks that have closed wings, in which they displayed mostly skipping and observation behaviors. When presented with the closed-wing doves, they also showed the same non-threatened behaviors, indicating they can distinguish between predators and non-predators. The researchers also observed distinctly different alarm calls elicited when presented with the sparrowhawks compared to the doves, which provides additional evidence that they can distinguish between these species.
The ability of animals to accurately assess the level of risk of a possible nearby predator, as indicated by the observed alterations in their behaviors, is essential for their survival and fitness as it allows them to protect themselves without expending unnecessary energy to non threatening stimuli. This study supports the assertion that Japanese tits can accurately judge the risk of a bird close-by, and adjust their behavioral response by the posture and therefore threat level of the bird. The results from this study are significant because they help us better understand how certain species have evolved to best alter their behavioral responses to increase their fitness.
References:
E, M., Jin, J., Luo, Y. et al. The Japanese tits evaluate threat level based on the posture of a predator. Sci Rep 14, 22340 (2024). https://doi.org/10.1038/s41598-024-73124-1
